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PubMed1981

Pavlovian control of cross-tolerance between pentobarbital and ethanol.

Tolerance to several effects of a number of drugs has been shown to depend on Pavlovian conditioning processes. Experiment I extended the compensatory conditioning model (Siegel 1975) to tolerance to the hypothermic effect of pentobarbital (30 mg/kg). In Experiment I, rats that acquired hypothermic tolerance in one environment did not display tolerance when tested in an environment not previously associated with drug administration. In Experiment II, rats were made tolerant to the hypothermic effect of pentobarbital (30 mg/kg) and tested for cross-tolerance to ethanol (2.5 g/kg). Cross-tolerance was observed, but it was significantly reduced if the test was in an environment different from the one in which tolerance to pentobarbital was originally acquired. Thus, the compensatory conditioning model accounts for at least part of the tolerance and cross-tolerance to the thermic effects of alcohol and pentobarbital. The physiological processes in the CNS underlying tolerance and cross-tolerance for these drugs, therefore, are controlled by associative processes.

Animals↗

PubMed2001

Chronic ethanol exposure results in increased acute functional tolerance in selected lines of HAFT and LAFT mice.

RATIONALE AND OBJECTIVES: Functional (pharmacodynamic) ethanol tolerance can be evidenced within a single session of exposure to ethanol (acute or within-session tolerance), or after repeated ethanol exposures (chronic or between-session tolerance). To investigate whether acute and chronic tolerance to ethanol are inter-related phenomena, the effect of chronic ethanol exposure was evaluated in mice selectively bred for high (HAFT) or low (LAFT) acute functional tolerance to an ataxic effect of ethanol, i.e., loss of balance on a stationary dowel. METHODS: Mice were tested for sensitivity (threshold ethanol concentration for loss of balance on the stationary dowel) and acute functional tolerance to ethanol before and after a regimen of chronic ethanol exposure (twice-daily ethanol injections for 6 days). RESULTS: Chronic ethanol treatment did not alter the threshold for ethanol's ataxic effect (i.e., produced no change in sensitivity). However, this treatment, in a dose-dependent manner, resulted in an increase in the magnitude and rate of development of acute functional tolerance. CONCLUSIONS: This finding supports previous postulates that chronic ethanol tolerance can be characterized by a more rapid acquisition or a greater magnitude of acute (within-session) tolerance. However, the increase in acute tolerance that occurred after chronic ethanol exposure was similar in both selected lines of mice, indicating little or no genetic correlation between acute tolerance and chronic tolerance.

Alcoholic Intoxication↗

PubMed1987

Interference with tolerance induction in vivo by inhibitors of prostaglandin synthesis.

Prostaglandins (PG) have been implicated as modulators of both humoral and cellular immune responses. In order to evaluate a possible role for PG in tolerance, the effect of inhibitors of prostaglandin synthesis on tolerance induction and circumvention has been investigated. Injection of deaggregated human gamma-globulin (DHGG) into A/J mice leads to unresponsiveness to a subsequent challenge with immunogenic aggregated human gamma-globulin (AHGG). Administration of indomethacin (IM) or acetylsalicylic acid (ASA) shortly before and after DHGG injection prevents tolerance induction. PGE2 reverses the tolerance overriding effect provided by IM. IM is not able to overcome unresponsiveness when given 10 and 20 days after tolerance induction, at a time point when both T and B lymphocytes are tolerant. As previously shown, lipopolysaccharide (LPS) both inhibits the induction of tolerance to HGG and circumvents tolerant T helper cells late in tolerance when competent B cells are present. In contrast, IM is unable to circumvent T-helper cell tolerance when given at Day 60 after tolerogen, when B cells (but not T cells) are responsive. Furthermore, LPS acts as an adjuvant, B-cell mitogens, inducer of polyclonal Ig secretion, and primes mice when given with tolerogen, while IM has none of these properties. These results indicate a difference between the effects of IM and LPS on tolerance and a possible role of PG in DHGG-mediated tolerance induction.

Adjuvants, Immunologic↗

PubMed1979

Cross-tolerance between delta9-tetrahydrocannabinol and ethanol: the role of drug disposition.

Acute challenge doses of delta9-tetrahydrocannabinol (THC), 10.1 mg/kg, administered intragastrically by gavage (IG), or ethanol, 1.24 g/kg, IP, reduced the rotarod performance of female rats by 50%. Daily treatment of the animals with THC, 10.1 mg/kg, IG, or ethanol, 4 g/kg, IG, resulted in tolerance development to the impairing effects of the challenge doses of each drug on rotarod performance. THC-tolerant animals were cross-tolerant to the challenge dose of ethanol, but ethanol-tolerant rats did not show complete cross-tolerance to the challenge dose of THC. THC-tolerant animals initially had higher blood levels of 14C-THC than controls after IG drug administration. Following IV injection, the rates of 14C-THC disappearance were equivalent in the latter groups. 14C-THC disappearance was not altered in ethanol-tolerant animals. The rates of ethanol disappearance were not significantly modified in THC- or ethanol-tolerant animals. In conclusion, THC-tolerant female rats demonstrated cross-tolerance to ethanol as shown previously for males. Furthermore, the development of tolerance and cross-tolerance was not a function of changes in drug disappearance.

Animals↗

PubMed1995

Contingent tolerance to the anticonvulsant effects of carbamazepine: relationship to loss of endogenous adaptive mechanisms.

Contingent tolerance to the anticonvulsant effects of carbamazepine on amygdala kindled seizures develops when the drug is repeatedly given prior to but not after the electrical stimulation. Such tolerance can be reversed by kindling the rats for several days without drug or even by continuing to give the drug but after each seizure has occurred. Contingent tolerance can be slowed by reducing the electrical stimulus intensity and by chronic continuous (as opposed to repeated paired) drug administration. Contingent cross-tolerance has been demonstrated from carbamazepine to PK11195 (a drug active at peripheral-type benzodiazepine receptors) and valproate, but not to clonazepam and diazepam (two drugs active at central-type benzodiazepine receptors) or phenytoin. Endogenous physiological changes occur in conjunction with contingent tolerance, exemplified by the decrease in seizure threshold that returns to normal upon reversal of tolerance. We suggest that contingent tolerance is associated with a loss of seizure-induced adaptations, since many biochemical changes that occur following seizures (or in non-tolerant animals given drug after seizures) are not observed in tolerant animals. These include a loss of seizure-induced up-regulation of GABAA receptors and a loss of increases in mRNA expression for corticotropin-releasing-factor (CRF), thyrotropin-releasing-hormone (TRH), neuropeptide Y (NPY), glucocorticoid receptors and brain-derived neurotrophic factor (BDNF). Thus, several putative seizure-induced anticonvulsant adaptations, such as increases in GABAA receptors and TRH and NPY mRNA fail to occur in tolerant animals. These findings are consistent with the novel observations that, paradoxically, seizures themselves appear to facilitate the anticonvulsant effects of carbamazepine or diazepam on amygdala kindled seizures. That is, animals given a 'vacation' from seizures show a decreased response to these agents, a phenomenon we have called the 'time-off seizure' effect. Thus, seizures are postulated to induce adaptive changes that influence seizure thresholds and potentiate the anticonvulsant effects of exogenously administered drugs such as carbamazepine and diazepam. Taken together, these data suggest that seizures are associated with endogenous adaptations lasting days to weeks and that a selective failure of some of these to occur during contingent drug administration may underlie the development of contingent tolerance. These observations suggest tht endogenous illness-related mechanisms may participate both in the therapeutic responses of some agents and that their failure to occur could relate to loss of drug efficacy via tolerance; these processes may reveal new potential targets for therapeutic intervention.

Adaptation, Physiological↗

PubMed1995

Cytokine gene expression in rejecting and tolerant rat lung allograft models: analysis by RT-PCR.

UNLABELLED: Cytokine gene expression is a critical component of the lung allograft rejection (AR) response and tolerance development in rat models. In order to determine the specificity of cytokine gene expression for AR and tolerance, we examined cytokine (interleukin-2) (IL-2), (gamma-interferon) (gamma-IFN), IL-4, IL-10 and tumor necrosis factor-alpha (TNF-alpha) and control (cyclophilin) mRNA levels in two models of rat lung allograft rejection by RT-PCR (reverse transcriptase polymerase chain reaction), Southern blotting. The first model (WKY-->F344) develops a mild to moderate lymphocytic infiltrate on days 14-21 post-transplant (stage II-III AR), which spontaneously resolves by day 35 post-transplant with subsequent development of allograft tolerance (grafts surviving without evidence of AR for > 140 days). Conversely, F344-->WKY develops a similar lymphocytic infiltrate by day 14 post-transplant, but by day 21 post-transplant the graft shows severe AR (stage III-IV) and has haemorrhagic infarction with alveolar haemorrhage. METHODS: RNA was extracted from allografts removed on days 3, 7, 14, 21, 35 and 42 post-transplant. Five animals for each group (WKY-->F344) and F344-->WKY) were examined at each time point, except that no animals in the F344-->WKY were examined on day 42. cDNA was synthesized from total extracted RNA and primers specific for rat TNF-alpha, rat IL-2, rat gamma-IFN, rat IL-4, rat-IL-10 and rat cyclophilin were used for gene-specific amplification. (TNF-alpha, gamma-IFN, IL-10, 20 cycles; IL-2, IL-4, 30 cycles; cyclophilin, 20 cycles). The cycles numbers chosen for comparison were found to be optimal during preliminary experiments and occurred during the exponential phase of amplification. PCR products were electrophoresed on a polyacrylamide gel and silver-stained. Gels were subsequently electrotransferred to nylon membranes which were probed with murine cDNAs specific for IL-2, gamma-IFN IL-4, IL-10 and TNF-gamma. RESULTS: Cyclophilin gene expression was similar for both models at all time points tested; this also served as an internal standard for RT-PCR. In the WKY-->F344 tolerance model, TNF-alpha mRNA levels were not detectable on days 3 and 7 post-transplant, were at very low levels on day 14 and were undetectable on day 21 post-transplant. In marked contrast, the F344-->WKY rejection model showed TNF-alpha mRNA present on day 3 which increased markedly on day 7 and peaked on day 14 post-transplant. TNF-alpha mRNA levels decreased on days 21 and 35 post-transplant, a time when the lung was undergoing AR. The pattern of IL-2 and gamma-IFN mRNA expression was similar to that for TNF-alpha. However, IL-2 mRNA was clearly detectable in the WKY-->F344 tolerance model on day 7 and gamma-IFN was not present until day 14 post-transplant. The F344-->WKY rejection model showed very high levels of IL-2 and gamma-IFN on day 3 which peaked on day 14. The ratio of IL-2/IL-10 in the F344-->WKY rejection model was more than 5 times that seen in the WKY-->F344 tolerance model on day 3 (p < 0.0005). The ratio of IL-2/IL-4 was higher (1.5 times) in the F344-->WKY rejection model than in the WKY-->F344 tolerance model (p < 0.007) on day 3. On day 14 post-transplant, the IL-2/IL-10 ratio in the F344-->WKY rejection model was three times that of the tolerance model (p < 0.0015). The IL-2/IL-4 ratio was 3.5 times greater in the WKY-->F344 tolerance model than in the rejectin model (p < 0.003). This was due to equal expression of IL-2 and IL-4 in the rejection model, but poor IL-4 expression in the tolerance model. CONCLUSIONS: 1) The WKY-->F344 tolerance model develops mild to moderate lymphocytic infiltrates on day 14 which is associated with low level IL-2, gamma-IFN and TNF-alpha gene expression. IL-10 and IL-4 are present at day 3; however, by day 14, IL-10 is the predominantly expressed Th2 cytokine and IL-4 is not expressed. The infiltrates ultimately resolve and the animals develop a functional tolerance to their grafts.4

Animals↗

PubMed2005

Vitamin E deficiency accelerates nitrate tolerance via a decrease in cardiac P450 expression and increased oxidative stress.

Organic nitrates, such as nitroglycerin (NTG), have been used to relieve the symptoms of angina pectoris. However, their biochemical mechanisms of action, particularly in relation to the development of tolerance, are incompletely defined. It has been reported that supplemental antioxidants such as vitamin E attenuate the development of nitrate tolerance. Therefore, we examined the role of vitamin E in the regulation of nitrate tolerance. Continuous NTG infusion induced nitrate tolerance in rats after 48 h, and vitamin E concentrations decreased in a time-dependent manner in tissues and plasma. Vitamin E supplementation (0.5 g/kg diet) maintained higher concentrations of vitamin E during NTG infusion. The onset and extent of the tolerance, estimated by the decrease in blood pressure following NTG bolus injection during the infusion of NTG, were accentuated in the vitamin E-deficient group. Vitamin E supplementation inhibited nitrate tolerance 48 h after NTG infusion. Cardiac P450 expression (CYP1A2) assessed by immunoblotting, markedly decreased 48 h after NTG administration in control rats. The supplementation of vitamin E significantly attenuated the decrease in P450. Treatment of NTG enhanced vascular superoxide production (L-012 chemiluminescence, DHE fluorescence). The peak of lipid peroxidation and free radical generation in the heart was reached before tolerance developed. In contrast, vitamin E-deficient hearts had lower P450 expression and higher free radical generation than control hearts. To evaluate other vitamin E-inhibitable mechanisms of nitrate tolerance, we studied the NO-cGMP pathway. NTG markedly reduced the vasodilator-stimulated phosphoprotein (VASP) serine 239 phosphorylation (specific substrate of cGMP-activated protein kinase I; cGK-I) in tolerant hearts. Vitamin E inhibited the depletion of pVASP. In conclusion, because continuous NTG infusion causes vitamin E depletion as well as nitrate tolerance, vitamin E deficiency may further accelerate nitrate tolerance via an increase in oxidative stress, the reduced bioconversion because of decreased P450 expression, and impairment of the NO/cGMP pathway in tolerant heart tissues.

Animals↗

PubMed2026

Acyloxyacyl Hydrolase-Mediated Lipopolysaccharide Inactivation Limits Macrophage Endotoxin Tolerance and Promotes Inflammation and Fibrosis in Metabolic Dysfunction-Associated Steatohepatitis.

BACKGROUND & AIMS: Metabolic dysfunction-associated steatohepatitis, a chronic liver disease, is characterized by persistent low-grade inflammation, partially driven by gut-derived lipopolysaccharide. Although repeated lipopolysaccharide exposure can induce endotoxin tolerance in innate immune cells, its role in chronic liver diseases remains unclear. Acyloxyacyl hydrolase is an endogenous enzyme that inactivates lipopolysaccharide, potentially modulating this process. We aimed to investigate how acyloxyacyl hydrolase regulates endotoxin tolerance in Kupffer cells and how this affects hepatic inflammation and fibrosis during metabolic dysfunction-associated steatohepatitis progression. METHODS: Acyloxyacyl hydrolase-deficient mice and wild-type controls were subjected to multiple dietary metabolic dysfunction-associated steatohepatitis models. Inflammatory responses, fibrosis, and transcriptomic changes in liver tissues and isolated Kupffer cells were analyzed. Endotoxin tolerance was modulated through β-glucan administration or lipopolysaccharide preconditioning. Lipopolysaccharide bioactivity was assessed using Toll-like receptor 4-reporter cell assays. RESULTS: Lipopolysaccharide-preconditioned Kupffer cells exhibited reduced proinflammatory cytokine production and transcriptional suppression of inflammatory pathways, indicating tolerance. Despite slight elevation of plasma lipopolysaccharide levels in metabolic dysfunction-associated steatohepatitis, upregulation of hepatic acyloxyacyl hydrolase positively correlated with disease severity, suggesting enhanced lipopolysaccharide inactivation but impaired establishment of tolerance. In contrast, acyloxyacyl hydrolase-deficient Kupffer cells displayed reinforced endotoxin tolerance, leading to diminished hepatic inflammation and fibrosis. Reversal of tolerance using β-glucan reactivated inflammatory and fibrogenic responses in acyloxyacyl hydrolase-deficient mice, whereas tolerance induction by low-dose lipopolysaccharide preconditioning mitigated metabolic dysfunction-associated steatohepatitis pathology, supporting the protective role of macrophage tolerance in chronic liver injury. CONCLUSIONS: Endotoxin tolerance in Kupffer cells represents a protective mechanism against chronic liver inflammation and fibrosis. Acyloxyacyl hydrolase regulates this state by limiting bioactive lipopolysaccharide, thereby modulating the establishment of endotoxin tolerance and downstream inflammatory and fibrotic responses. Enhancing macrophage tolerance by utilizing lipopolysaccharide may offer a novel therapeutic avenue to control the progression of metabolic dysfunction-associated steatohepatitis.

AOAH↗

PubMed2006

Morphine analgesic tolerance in 129P3/J and 129S6/SvEv mice.

Morphine analgesic tolerance is heritable in both humans and rodents, with some individuals and strains exhibiting little and others exhibiting robust tolerance. 129S6/SvEv and 129P3/J mice reportedly do not demonstrate tolerance to morphine analgesia. Using our laboratory's standard morphine tolerance regimen and a between-subjects design, tolerance developed in the hot plate and tail withdrawal assays as indicated by a change in analgesic efficacy following a morphine challenge dose. Furthermore, the non-competitive NMDA receptor antagonist MK-801 (dizocilipine) blocked morphine tolerance in 129S6/SvEv and CD-1 mice in the hot plate assay. As previously reported, when a within-subjects design and cumulative dosing was employed, no tolerance was observed in the 129P3/J strain. However, using the same morphine regimen and a between-subjects design, comparable tolerance developed between 129P3/J and C57BL/6J strains following a single challenge dose of morphine. Spontaneous hyperalgesia was observed in the tail withdrawal assay following chronic morphine in C57BL/6J, but not 129P3/J mice. Additionally, morphine-tolerant C57BL/6J mice, but not 129P3/J mice, exhibited a large increase in the frequency of tail flicks during the first second following the baseline nociceptive response which may facilitate detection of the response during the tolerant state. We conclude that the method of tolerance assessment affects the ability to detect tolerance and thus may affect the degree and pattern of heritability of this trait and this could have implications for gene mapping studies.

Analgesics, Opioid↗

PubMed2001

Tolerance induction across Mls and minor histocompatibility complex by inhibiting activation of T helper type 1 in early period.

We have previously succeeded in inducing persistent donor-specific tolerance across Mls plus multiple minor histocompatibility barriers by portal venous (p.v.) injection of donor spleen or bone marrow cells plus cyclophosphamide (CY) treatment. Microchimerism was established in the lymph-hemopoietic organs of the tolerant recipients. However, the mechanisms, particularly the roles of CY in the tolerance induction, have not been clarified. We examined the tolerance induction using other anti-mitotic agents and evaluated the in vitro proliferative responses and cytokine expression of T cells from the recipients after stimulation with donor alloantigens. The administration of not only CY but also mitomycin C (MMC) and cytosin arabinoside (Ara C) elicited a prolongation of skin graft survival. CY induced tolerance when it was administered 2 days after the p.v. injection, but not immediately or 4 days after the p.v. injection. T cells collected from the tolerant recipients showed no proliferative responses as a result of stimulation with donor alloantigens whereas the responses of T cells from non-tolerant recipients were significantly enhanced. Interferon-gamma (IFNgamma) was extensively expressed in the non-tolerant T cells from 24 to 48 h after the stimulation with donor alloantigens. In contrast, the expression of IFNgamma was observed in the tolerant T cells from 72 h after the stimulation. Also, the tolerant T cells showed the expression of interleukin-10 (IL-10) and transforming growth factor-beta 1 (TGF-beta1) from 72 h after the stimulation whereas the non-tolerant T cells did not. These data suggest that CY, when administered 2 days after the p.v. injection, induces persistent tolerance by inhibiting T helper type 1 (Th1) activity in the early period but not the Th1 activity in the later periods.

Animals↗

PubMedDate not supplied

Characterization of the Phenomenon of rapid tolerance to ethanol.

Motor impairment (tilt-plane) and hypothermia tests were used to further characterize the phenomenon of rapid tolerance to ethanol. Five experiments were carried out to clarify the relationship between rapid and chronic tolerance. The first experiment demonstrated that the extent of tolerance on day 2 produced by the single dose of 4 g/kg alcohol on day 1 was similar to that resulting from two divided doses, administered 2 h apart. In the second experiment, a linear relationship between treatment dose and rapid tolerance development was demonstrated in that higher day 1 treatment doses resulted in greater rapid tolerance development. In the third, a parallel dose-response relationship, similar to that known for chronic tolerance, was observed for rapid tolerance. In the fourth experiment, we compared the development of rapid tolerance under three different conditions: (a) in groups of rats that were not subjected to testing at all (no testing); on day 1, (b) in groups of rats that were not tested on the apparatus but handled at all test times on day 1 (dummy testing); and (c) in groups of rats that were tested at all test times on day 1 (testing or intoxicated group). No testing on day 1 failed to produce rapid tolerance to ethanol whereas testing and dummy testing of animals on day 1 after pretreatment with ethanol-produced rapid tolerance to ethanol on day 2. In the last experiment, immediate posttrial administration of ketamine was found not to block rapid tolerance development. These findings provide additional support for similarities between the mechanisms of rapid and chronic tolerance.

Animals↗

PubMed1997

Reversal of tolerance to the antitransit effects of morphine during acute intestinal inflammation in mice.

1. The aim of investigation was to establish and compare the reversibility of tolerance to the antitransit effects of morphine by three different procedures: (a) acute inflammation of the gut, (b) lorglumide a cholecystokininA (CCKA) receptor antagonist, or (c) MK-801, an N-methyl-D-aspartate (NMDA) receptor ion channel blocker. The type of interaction between morphine and lorglumide or MK-801 on the inhibition of gastrointestinal transit (GIT) in naive animals was also evaluated. 2. Male Swiss CD-1 mice were implanted with 75 mg of morphine base or placebo pellets. Gastrointestinal transit was assessed with a charcoal meal and results expressed as % inhibition of GIT. Inflammation was induced by the intragastric (p.o.) administration of croton oil (CO), while controls received castor oil (CA) or saline (SS). Morphine was administered by subcutaneous (s.c.) or intracerebroventricular (i.c.v.) injection, to naive and tolerant animals treated with CO, CA or SS. Dose-response curves for s.c. morphine were also performed in naive and tolerant mice receiving 5.2 or 7.4 nmol (s.c.) lorglumide or MK-801, respectively. 3. The ED50 values for inhibition of GIT by s.c. morphine were: 45.9 +/- 2.7 and 250.1 +/- 3.1 nmol in naive and tolerant animals, respectively, demonstrating a five fold decrease in the potency of morphine. In naive animals, inflammation (CO) decreased the ED50 of morphine three times (14.4 +/- 2.2 nmol). However, no tolerance to s.c. morphine (ED50 16.4 +/- 2.6 nmol) was manifested during intestinal inflammation. After i.c.v. administration, a similar degree of tolerance to morphine was observed (4.8 fold decrease in potency). Intestinal inflammation had no effect on the ED50 values of i.c.v. morphine in naive and tolerant animals, showing that reversal of tolerance is related to local mechanism/s. Mean values for intestinal pH were 6.9 +/- 0.04 and 6.2 +/- 0.04 in SS and CO treated mice, respectively. In addition, morphine was 74 times more potent by the i.c.v. than by the s.c. route (naive-SS). 4. Morphine and lorglumide interacted synergistically in naive animals; in addition, the administration of lorglumide reversed tolerance to s.c. morphine. No interaction (additivity) was observed in naive animals when morphine and MK-801 were administered in combination. However, the drug completely reversed tolerance to the antitransit effects of morphine. 5. The present investigation shows that acute inflammation of the gut reverses tolerance to the antitransit effects of s.c. morphine by a peripheral mechanism. Qualitatively similar results were obtained after the administration of lorglumide or MK-801. Our results suggest that a local decrease in pH could play an important role during inflammation, while antagonism of endogenous compensatory systems would explain the reversal of tolerance induced by lorglumide or MK-801.

Acute Disease↗

PubMed1999

Involvement of phospholipid signal transduction pathways in morphine tolerance in mice.

1. Opioid tolerance involves an alteration in the activity of intracellular kinases such as cyclic AMP-dependent protein kinase (PKA). Drugs that inhibit PKA reverse morphine antinociceptive tolerance. The hypothesis was tested that phospholipid pathways are also altered in morphine tolerance. Inhibitors of the phosphatidylinositol and phosphatidylcholine pathways were injected i.c.v. in an attempt to acutely reverse morphine antinociceptive tolerance. 2. Seventy-two hours after implantation of placebo or 75 mg morphine pellets, mice injected i.c.v. with inhibitor drug were challenged with morphine s.c. for generation of dose-response curves in the tail-flick test. Placebo pellet-implanted mice received doses of inhibitor drug having no effect on morphine's potency, in order to test for tolerance reversal in morphine pellet-implanted mice. Injection of the phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH3 significantly reversed tolerance, indicating a potential role for inositol 1,4,5-trisphosphate (IP3) and protein kinase C (PKC) in tolerance. Alternatively, phosphatidylcholine-specific phospholipase C increases the production of diacylglycerol and activation of PKC, without concomitant production of IP3. D609, an inhibitor of phosphatidylserine-specific phospholipase C, also reversed tolerance. Heparin is an IP3 receptor antagonist. Injection of low molecular weight heparin also reversed tolerance. PKC was also examined with three structurally dissimilar inhibitors. Bisindolylmaleimide I, Go-7874, and sangivamycin significantly reversed tolerance. 3. Chronic opioid exposure leads to changes in phospholipid metabolism that have a direct role in maintaining a state of tolerance. Evidence is accumulating that opioid tolerance disrupts the homeostatic balance of several important signal transduction pathways.

Analgesia↗

PubMed1977

Recirculating, suppressor T cells in transplantation tolerance.

An adoptive transfer system was used to examine the capacity of cellular inocula from rats fully tolerant of Ag-B antigens to transfer tolerance to irradiated recipients. Permanent tolerance in these irradiated recipients involved specific suppression of the regenerating immune response. Cells obtained from tissues rich in recirculating lymphocytes were the most effective suppressors. Highly purified inocula of T cells from tolerant donors were potent suppressors in irradiated hosts, but were not capable of direct suppression of peripheral antigen-sensitive T cells.. The role of the thymus in maintaining the complement of recirculating suppressor T cells in tolerant animals was examined after adult thymectomy. Thymectomized tolerant rats did not reject their tolerated grafts, and the longevity of the suppression in tolerant rats was confirmed by showing that adoptive transfer of cells from thymectomized tolerant donors was effective in suppressing irradiated recipients up to 180 days after thymectomy. Cellular inocula from these donors appeared to lose their suppressor function marginally faster than they lost effector function (as measured by their capacity to mediate rejection of third party control grafts). Thymectomy made tolerant rats more vulnerable to the termination of tolerance by challenge with normal cells. Transplantation tolerance is maintained in adult rats by long-lived rapidly recirculating suppressor T cells. The target for the suppressor action of these cells is probably the precursor of alloantigen-sensitive lymphocytes, and the effect of suppression may be deletion or inactivation of the relevant clone of these cells.

Animals↗

PubMed1984

IgE class-restricted tolerance induced by neonatal administration of soluble or cell-bound IgE. Cellular mechanisms.

Certain aspects of the phenomenon of IgE class-restricted tolerance induced in mice by neonatal treatment with monoclonal IgE, either in soluble form or coupled to syngeneic spleen cells, were examined. The present studies document that this tolerance results from exposure to IgE molecules, irrespective of their antigen specificity, and the resulting effects are polyclonal in nature since IgE responses directed against antigenic determinants unrelated to the tolerance-inducing IgE molecules are affected. Moreover, such findings indicate that the molecular subregion(s) responsible for inducing IgE class-restricted tolerance resides in the epsilon heavy chain constant region domain(s) of IgE. When soluble IgE is employed, tolerance induction results from neonatal treatment with doses as low as 2.5 micrograms per injection per mouse; cell-bound IgE is considerably more potent, in terms of total dose required, since tolerance results from treatment with as few as 1 X 10(6) cells per injection (per mouse), equivalent to an absolute quantity of 0.2 ng of IgE per injection. This long-term class-specific tolerance appears to be a unique feature of the IgE antibody system, since treatment of mice with monoclonal antibodies of the IgA, IgG1, or IgG2b isotypes, either in soluble or cell-bound form, does not perturb antibody responses of their corresponding isotypes or in the IgE class. By analyzing the lymphoid cells of IgE-tolerant mice after they reached adulthood, the following observations were made: (a) lymphoid cells from such tolerant mice fail to develop FcR epsilon + cells upon in vitro stimulation with IgE, as is characteristically observed with lymphoid cells from nontolerant mice; and (b) mice rendered tolerant by neonatal treatment with soluble IgE possess IgE class-restricted suppressor T cells, demonstrable in adoptive transfer experiments, whereas no such suppressor cells are evident in mice in which cell-bound IgE was used for neonatal treatment. The latter observations could mean that two different mechanisms underlie the IgE class-restricted tolerance, or both mechanisms operate coordinately to varying degrees depending upon which regimen is used for tolerance induction, as discussed herein.

Animals↗

PubMed1999

Cytokines in the induction and circumvention of peripheral tolerance.

Injection of deaggregated (monomeric) human gamma globulin (DHGG) into mice induces a state of immunological tolerance to subsequent challenge with immunogenic forms of HGG. Tolerance was shown to be induced in both the Th1 and Th2 CD4+ subsets. These mice fail to demonstrate antibody production, T cell proliferation, cytokine release, or T cell helper function. On the other hand, simultaneous injection of lipopolysaccharide (LPS) as well as interleukin-1 (IL-1) was capable of interfering with the induction of tolerance to DHGG. The purpose of the present study is to extend these investigations to determination of the cellular mechanisms responsible for the interference of tolerance induction in both CD4+ T cell subsets. It was demonstrated that LPS and IL-1 have differential effects on the induction of tolerance in the CD4+ subsets. As evidenced by immunoglobulin G (IgG) subclass, T helper cell function, and lymphokine secretion, coinjection of LPS with tolerogen interfered with the induction of tolerance in both subsets, whereas IL-1 interfered with the induction of tolerance exclusively in the Th1 subset. LPS and IL-1 had differential effects on the interference of the induction of tolerance in LPS-resistant mice where IL-1, but not LPS, was effective. In contrast to IL-1, IL-12 injected along with DHGG failed to interfere with the induction of tolerance in either Th1 or Th2 cells. Previous studies that demonstrated tolerance in the DHGG models induced in both the Th1 and Th2 subsets was further suggested by the demonstrations in the present study that dose-response curves for the induction of tolerance are identical in both subsets. The above findings taken together are compatible with the suggestion that tolerance induction results from the lack of cytokine production, which then prevents the expansion of Th1 and Th2 subsets following activation of the CD4+ precursor T cell. Furthermore, they support the general opinion that the expansion of these two subsets involve different cytokine pathways and that LPS and IL-1 most likely act through different cell receptors.

Animals↗

PubMed1998

Insulin resistance is a common denominator of post-transplant diabetes mellitus and impaired glucose tolerance in renal transplant recipients.

BACKGROUND: Post-transplant diabetes mellitus is a known complication of steroid therapy in renal transplant recipients. Both insulin resistance and insulin deficiency have been shown to be necessary for development of post-transplant diabetes mellitus. It is not known whether recipients with impaired glucose tolerance have similar degree of insulin resistance or deficient insulin response as recipients with post-transplant diabetes mellitus. METHOD: To address this question, we used an oral glucose tolerance test to categorize 46 renal transplant recipients on triple immunosuppressive medication to groups with normal glucose tolerance, impaired glucose tolerance or post-transplant diabetes mellitus. Insulin sensitivity was measured using a hyperinsulinaemic euglycaemic clamp. Insulin response was calculated from the increase in serum insulin concentration during the oral glucose tolerance test. RESULTS: Twenty-five were categorized to normal glucose tolerance, 15 to impaired glucose tolerance and six to post-transplant diabetes mellitus. There were no statistically significant differences between the groups regarding prednisolone dose, azathioprine dose, use of beta-blocker, age, gender, weight, waist-hip ratio, body mass index, donor source, smoking habits, or first-degree relatives with histories of diabetes mellitus. The impaired glucose tolerance and post-transplant diabetes mellitus groups showed a significant reduction in insulin-stimulated glucose disposal rate (mg/kg.min) compared to the normal glucose tolerance group (4.6 +/- 1.6 and 3.4 +/- 1.3 respectively vs 7.1 +/- 2.4, P < 0.05). The insulin response (picomol/l) was not different between the normal glucose tolerance and impaired glucose tolerance groups but was significantly reduced in the post-transplant diabetes mellitus group (448 +/- 310 and 450 +/- 291 respectively vs 170 +/- 128, P < 0.05). CONCLUSION: Insulin resistance is a common denominator of post-transplant diabetes mellitus and impaired glucose tolerance in renal transplant recipients.

Adult↗

PubMed2002

Glucose tolerance and cardiovascular risk in young adult African Americans.

BACKGROUND: Patients with type 2 diabetes have higher rates of cardiovascular events. Among African Americans, there is a higher prevalence of both cardiovascular disease and type 2 diabetes. Few studies have examined longitudinally the change in glucose tolerance in younger adult African Americans. METHODS: To examine the longitudinal relationship of glucose tolerance with other cardiovascular risk factors, 30 African American men and women aged 20 to 43 years were examined twice at an interval of 4 to 5 years. Cardiovascular risk factors, glucose tolerance, and insulin sensitivity (determined from euglycemic hyperinsulinemic clamp procedure) were assessed at each examination. Known diabetics were excluded from initial enrollment. The relationship of glucose tolerance status (normal, impaired, or diabetic glucose tolerance) to body mass index, blood pressure, cholesterol, and insulin sensitivity were further investigated. RESULTS: Initial oral glucose tolerance test identified 24 of 130 (18.5%) subjects with impaired glucose tolerance and 2 of 130 (1.5%) subjects with diabetes. Of the remaining 104 subjects with normal glucose tolerance, subsequent 5-year examination detected 31 (29.8%) with impaired glucose tolerance and 5 (4.8%) with diabetes. Those who later developed diabetes had higher mean systolic blood pressure (133 versus 121, P = 0.037) at exam 1. By exam 2, those with abnormal glucose tolerance had worse cardiovascular risk profiles and increased insulin resistance (P < 0.001). CONCLUSION: Conversion to abnormal glucose tolerance is relatively frequent in young adult African Americans. Deterioration in glucose tolerance may be preceded by higher systolic blood pressure and is accompanied by worsening of other cardiovascular risk factors and insulin resistance.

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