Biomedical subjects

V Gopalakrishnan

Publications and source records attributed to V Gopalakrishnan.

At least 19 recordsLinked to original sources

PubMed2006

Scattering for mixtures of hard spheres: comparison of total scattering intensities with model.

The angular dependence of the intensity of x-rays scattered from binary and ternary hard sphere mixtures is investigated and compared to the predictions of two scattering models. Mixture ratio and total volume fraction dependent effects are investigated for size ratios equal to 0.51 and 0.22. Comparisons of model predictions with experimental results indicate the significant impact of the role of particle size distributions in interpreting the angular dependence of the scattering at wave vectors probing density fluctuations intermediate between the sizes of the particles in the mixture.

Journal Article↗

PubMed2006

Effect of ethanol on human osteosarcoma cell proliferation, differentiation and mineralization.

The habitual consumption of even moderate quantities of alcoholic beverages is clearly associated with reduced bone mass, increased prevalence of skeletal fracture and also it is the major risk factor for the development of secondary osteoporosis. The present in vitro study was designed to determine the dose response effects of ethanol on osteoblast-like human osteosarcoma cells (SaOS-2) proliferation, differentiation, mineralization and cyto-toxicity. SaOS-2 cells were plated in 48 and 6 well culture plates and exposed to different concentrations of ethanol (1, 10, 100, 200 and 300 mM) for 24, 48 and 72 h. At the end of incubation, proliferation of cells was studied using crystal violet Bioassay. The cell lysate was utilized to determine ALP activity and conditioned media were used to measure LDH activity. Histochemical localization of ALP and mineralized nodules were studied from cells treated with ethanol (10 and 100 mM) for 21 days. At higher doses, there was a significant reduction in cell number, whereas at lower doses there were variable effects. In 24 h treatment, the higher doses showed a significant increase in ALP activity, whereas 48 and 72 h treatments showed an opposite trend. Ethanol treatment caused a dose- and time-dependent increase in LDH activity. Ethanol treatment altered the quality of mineralization at 10 mM dose whereas completely inhibited mineralization at 100 mM dose, despite the presence of serum. In conclusion, the toxic effect of ethanol is reflected on cell proliferation, differentiation and mineralization even at low doses and at extended treatment duration.

Alkaline Phosphatase↗

PubMed2006

Effects of glucose and its modulation by insulin and estradiol on BMSC differentiation into osteoblastic lineages.

It is well known that diabetes affects bone in human and animal models, and leads to osteopenia and osteoporosis. Bone-mineral density and other biochemical markers of bone turnover are very much affected in people with diabetes. Reduced bone mass, occurring with increased frequency in diabetes mellitus, has been attributed to poor glycemic control, but the pathogenic mechanisms remain unknown. High concentrations of glucose (hyperglycemia) in diabetics leads to this complication. Very few in vitro studies using bone-cell lines have been carried out to address this problem. In this study, we examined the effects of different doses of glucose concentration (5.5, 16.5, and 49.4 mmol/L), alone, with insulin (0.6 microg/mL), or with 17beta-estradiol (E2) (10 nmol/L), on rat bone-marrow stromal cells (BMSCs) in the presence of an osteogenic medium. BMSC proliferation and alkaline phosphatase (ALP) were studied after 3 and 7 d of culture, respectively; the area stained for collagen and mineralized nodules was studied after 28 d of culture. With high concentrations of glucose, BMSC proliferation, ALP activity, the number of nodules formed, and the area stained for collagen were greatly reduced. Insulin treatment alone was able to increase [3H]-thymidine uptake or ALP activity, whereas both insulin and estradiol were able to increase the number of mineralized nodules and the area stained for collagen and mineralization. In conclusion, this study suggests that insulin and estradiol are able to contain the deleterious effect of high concentrations of glucose on BMSC-derived osteoblast proliferation and function.

Alkaline Phosphatase↗

PubMed2006

Effects of streptozotocin-induced diabetes mellitus on some bone turnover markers in the vertebrae of ovary-intact and ovariectomized adult rats.

Diabetes mellitus and estrogen deficit are known causes of osteopenia in animal models as well as in humans. In the present work, the combined effect of ovariectomy and diabetes was investigated. Diabetes was induced in ovary-intact and ovariectomized female Wistar rats with a single injection (50 mg/kg body weight, i.p.) of streptozotocin. The rats were administered insulin (I) daily or 17-beta estradiol (E2) on alternate days for a period of 35 days and sacrificed. Serum calcium (Ca2+), phosphorus (P), alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), vertebral ALP, collagen, and glycosaminoglycans were estimated. The levels of serum Ca2+ and P increased in diabetic rats, but decreased after I or E2 treatments. Serum ALP and TRAP activity increased in the ovary-intact and ovariectomized diabetic rats. Vertebral ALP activity increased in ovariectomized diabetic rats, but decreased in diabetic rats, which were treated with I or E2. In the vertebrae, TRAP activity was elevated as a result of diabetes, but this was prevented by insulin or estradiol. Diabetes induced a decrease in total collagen in the vertebrae, while I or E2 treatment induced an increase. The levels of chondroitin sulphate and heparan sulphate decreased significantly in the vertebrae of both ovary-intact and ovariectomized diabetic rats, while hyaluronic acid increased. In conclusion, diabetes and ovariectomy each seem to affect the process of matrix formation and mineralization in the bone, and this is aggravated by the combination of diabetes and ovariectomy. The effects of I and E2 were similar, and both hormones reversed the changes brought about by diabetes.

Acid Phosphatase↗

PubMed2005

Clustering and mechanics in dense depletion and thermal gels.

We report on the microstructure and mechanical properties (elastic modulus) of concentrated depletion and thermal gels of octadecyl-coated silica particles for different values of the strength of interaction--polymer concentration for depletion gels and temperature for thermal gels. The depletion gels are composed of dense clusters and voids, while the thermal gels are devoid of clusters. Shear breaks up clusters in depletion gels while it induces clustering in the thermal gels. In both of these gels, the microstructure recovers to the presheared state upon cessation of shear. The recovery of the elastic modulus mimics the microstructure in the sense that the elastic modulus recovers to the presheared sheared state after shearing is stopped. Calculations of the gel boundary by modeling the interactions with an effective one-component square-well model reveals that suspensions with similar ranges of attraction gel at the same volume fraction at a fixed strength of attraction. Calculations of the elastic modulus using the naïve mode coupling theory for depletion gels are in good agreement with experimental measurements provided clustering is taken into account and have the same magnitude as the elastic moduli of thermal gels with similar strengths of attraction. These calculations, in addition to the experimental observations reinforce the point that the microscopic parameter determining the elastic modulus of dense gels and its recovery is the localization length which is only a fraction of the particle diameter and not the structure on the length scale of the particle diameter and larger.

Colloids↗

PubMed2002

Herbal medicines for liver diseases in India.

The use of natural remedies for the treatment of liver diseases has a long history, starting with the Ayurvedhic treatment, and extending to the Chinese, European and other systems of traditional medicines. The 21st century has seen a paradigm shift towards therapeutic evaluation of herbal products in liver diseases by carefully synergizing the strengths of the traditional systems of medicine with that of the modern concept of evidence-based medicinal evaluation, standardization of herbal products and randomized placebo controlled clinical trials to support clinical efficacy. The present review provides the status report on the scientific approaches made to herbal preparations used in Indian systems of medicine for the treatment of liver diseases. In spite of the availability of more than 300 preparations for the treatment of jaundice and chronic liver diseases in Indian systems of medicine using more than 87 Indian medicinal plants, only four terrestrial plants have been scientifically elucidated while adhering to the internationally acceptable scientific protocols. In-depth studies have proved Sylibum marianum to be anti-oxidative, antilipidperoxidative, antifibrotic, anti-inflammatory, immunomodulating and liver regenerative. Glycyrrhiza glabra has been shown to be hepatoprotective and capable of inducing an indigenous interferon. Picrorhiza kurroa is proved to be anti-inflammatory, hepatoprotective and immunomodulatory. Extensive studies on Phyllanthus amarus have confirmed this plant preparation as being anti-viral against hepatitis B and C viruses, hepatoprotective and immunomodulating, as well as possessing anti-inflammatory properties. For the first time in the Indian systems of medicine, a chemo-biological fingerprinting methodology for standardization of P. amarus preparation has been patented.

Humans↗

PubMed2002

Typhoid fever in Kuala Lumpur and a comparative evaluation of two commercial diagnostic kits for the detection of antibodies to Salmonella typhi.

The aim of this study was to compare two commercial kits, theTyphidot and the PanBio ELISA with the present Widal test. Demographic data for all serodiagnosed cases for the years 1991-1998 were collected. From this data, 144 were selected as samples for comparative evaluation of the commercial kits. Fifty sera were culture positive for Salmonella typhi, 50 were culture negative but clinically diagnosed as typhoid fever and Widal positive and 44 were serodiagnosed as enteric of which 21 were culture positive for other Salmonella species, 20 were serodiagnosed for other febrile illnesses and three sera culture positive for other species of enterobacteriaceae. The specificity, sensitivity and efficiency of the tests were calculated with the positive culture for S. typhi as the gold standard. Sensitivity, specificity and efficiency of test for Typhidot and Typhidot M kits were 98%, 76.6% and 84.0% and PanBio ELISA were 78%, 80% and 79.9%. The two commercial kits evaluated were found to be less time consuming and easier to perform than Widal. The Typhidot M seems to be a practical alternative in the field and in small hospitals with lesser facilities.

Agglutination Tests↗

PubMed2001

Redundant control of rereplication in fission yeast.

The initiation of DNA replication at replication origins in eukaryotic cells is tightly controlled to ensure that the genome is duplicated only once each cell cycle. We present evidence that in fission yeast, independent regulation of two essential components of the initiation complex, Cdc18 and Cdt1, contributes to the prevention of reinitiation of DNA replication. Cdc18 is negatively controlled by cyclin-dependent kinase (CDK) phosphorylation, but low level expression of a mutant form of Cdc18 lacking CDK phosphorylation sites (Cdc18(CDK)) is not sufficient to induce rereplication. Similar to Cdc18, Cdt1 is expressed periodically in the cell cycle, accumulating in the nucleus in G(1) and declining in G(2). When Cdt1 is expressed constitutively from an ectopic promoter, it accumulates in the nucleus throughout the cell cycle but does not promote reinitiation. However, constitutive expression of Cdt1, together with Cdc18(CDK), is sufficient to induce extra rounds of DNA replication in the absence of mitosis. Significantly greater levels of rereplication can be induced by coexpression of Cdc18(CDK) and a Cdt1 mutant lacking a conserved C-terminal motif. In contrast, uncontrolled DNA replication does not occur when either mutant protein is expressed in the absence of the other. Constitutive expression of wild-type or mutant Cdt1 also leads to an increase in the levels of Cdc18(CDK), possibly as a result of increased protein stability. Our data are consistent with the hypothesis that control of rereplication depends on a redundant mechanism in which negative regulation of Cdt1 functions in parallel with the negative regulation of Cdc18.

Cell Cycle Proteins↗

PubMed2001

Role of endothelin and vasopressin in DOCA-salt hypertension.

1. The relative roles of endothelin (ET) and vasopressin (AVP) in the regulation of blood pressure (BP), cardiac output (CO) and total peripheral resistance (TPR) were investigated in the early stages (24 - 31 days) of development of hypertension in the conscious deoxycorticosterone acetate (DOCA)-salt hypertensive rat model. 2. BP was recorded with radiotelemetry devices and CO with ultrasonic transit-time probes. TPR was calculated from the BP and CO recordings. The contributions of endogenous ET and AVP were studied by infusing [d(CH(2))(5)(1),O-Me_Tyr(2),Arg(8)]-vasopressin, a V(1)-receptor antagonist, and bosentan, a mixed ET(A)/ET(B) receptor antagonist (Study 1). Vascular responsiveness was estimated from the changes in TPR evoked by i.v. infusions of ET-1 and AVP (Study 2). 3. In study 1, infusion of bosentan reduced TPR and BP dramatically in DOCA-salt hypertensive rats but not in SHAM control rats, and this effect was greater when the AVP system had been blocked. In contrast, the V(1) receptor antagonist alone failed to change TPR and BP in DOCA-salt hypertensive rats. However, subsequent infusion of the V(1) receptor antagonist during the plateau phase of the response in bosentan pretreated DOCA-salt hypertensive rats led to significant decreases in both BP and TPR. 4. In study 2, TPR and BP responses to ET-1, but not AVP, were greater in DOCA-salt rats than in control rats. CO responses to ET-1 or AVP were similar in the two groups. 5. The results suggest that both ET and AVP play a role in the maintenance of TPR and BP; when one system is blocked the other compensates. However, the magnitude of the contribution to the hypertensive state appears greater for ET than for AVP. Enhanced vascular responses to ET appear to contribute to this greater role.

Animals↗

PubMed2001

Cysteinyl leukotrienes mediate enhanced vasoconstriction to angiotensin II but not endothelin-1 in SHR.

We assessed whether cysteinyl leukotrienes mediate the vasoconstrictor responses to angiotensin II and endothelin-1 in the mesenteric vascular bed of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) perfused ex vivo at a constant flow rate of 5 ml/min with Krebs buffer. Maximal perfusion pressure response (E(max)) but not EC(50) values to angiotensin II (P < 0.001) and endothelin-1 (P < 0.01) were significantly higher in the SHR, whereas the responses to potassium chloride remained unchanged. Inclusion of the selective 5-lipoxygenase inhibitor AA-861 or the cysteinyl leukotriene receptor antagonist MK-571 significantly reduced the vasoconstrictor responses to angiotensin II but not to endothelin-1 and potassium chloride. The reduction in E(max) to angiotensin II was more pronounced in SHR (P < 0.001) than in WKY (P < 0.05) rats. Cysteinyl leukotrienes LTC(4)-, LTD(4)-, and LTE(4) (1 microM)-evoked vasoconstrictor responses were significantly higher in SHR (P < 0.05), whereas LTB(4) failed to evoke any response in either strain. These data suggest that 5-lipoxygenase metabolites, particularly cysteinyl leukotrienes, contribute to the exaggerated vasoconstrictor responses to angiotensin II but not to endothelin-1.

Angiotensin II↗

PubMed2001

Endothelin antagonist reduces hemodynamic responses to vasopressin in DOCA-salt hypertension.

The contribution of endothelin to the changes in blood pressure, cardiac output, and total peripheral resistance evoked by arginine vasopressin and angiotensin II was investigated in deoxycorticosterone acetate (DOCA)-salt hypertensive rats by infusing the peptides intravenously before and after pretreatment with the endothelin receptor antagonist bosentan. Blood pressure was recorded with radiotelemetry devices and cardiac output was recorded with ultrasonic transit time flow probes in conscious unrestrained animals. The dose-related decreases in cardiac output induced by vasopressin and angiotensin II were unaffected by bosentan. In contrast, the dose-related increases in total peripheral resistance evoked by vasopressin were blunted in both DOCA-salt hypertensive and sham normotensive rats, but this effect of bosentan was greater in the DOCA-salt hypertensive group. In contrast with vasopressin, bosentan failed to change hemodynamic responses to angiotensin II. The exaggerated vascular responsiveness (total peripheral resistance) of the DOCA-salt hypertensive group to vasopressin was largely abolished by bosentan. These results suggest that endothelin contributes to the hemodynamic effects of vasopressin but not angiotensin II in the DOCA-salt model of hypertension.

Angiotensin II↗

PubMed2001

Insulin-induced biphasic responses in rat mesenteric vascular bed: role of endothelin.

The vasodilatory capacity of insulin has been widely reported, yet some investigators have not noted this effect. Because insulin has been shown to enhance endothelin release, we speculated that endothelin could be attenuating insulin-evoked vasodilation. We examined the effect of ex vivo insulin perfusion on vascular resistance by using the Sprague-Dawley rat mesenteric vascular bed. In methoxamine-preconstricted preparations, insulin (3.0 pmol/L to 10 nmol/L) evoked a concentration-dependent decrease in perfusion pressure (PP) with a maximal response of 42.0+/-9.2%, whereas continuous exposure to 10 nmol/L insulin induced a 51.8+/-3.5% relaxation. Further exposure to 10 nmol/L insulin resulted in the generation of endothelin and a subsequent loss of the vasodilatory response. Indomethacin had no effect on vascular responses. The vasodilatory response was significantly inhibited by nitric oxide synthase inhibition (20.5+/-4.2%; P<0.01) and calcium-activated potassium channel blockade (28.5+/-3.7%; P<0.05). Endothelial denudation attenuated the vasodilatory component (20.3+/-7.1%; P<0.01) and altered the biphasic pattern of the response. The decline in insulin-evoked vasodilation was significantly prevented by an endothelin-A antagonist (BQ123), an endothelin-B antagonist (BQ788), and nonselective endothelin blockade with both BQ123 and BQ788. These results demonstrate that the endothelium is intimately involved in regulating the vascular response to insulin. Insulin promotes the release of nitric oxide and endothelium-derived hyperpolarizing factor. During sustained exposure to higher concentrations, this vasodilatory effect is countered by the pathological generation of endothelin. Endothelin receptor blockade facilitates the maintenance of vasodilation despite high insulin concentrations.

Animals↗

PubMed2001

Attenuated agonist evoked vasoconstrictor responses in the perfused mesenteric vascular bed of streptozotocin diabetic rats.

We compared agonist-evoked responses in the perfused mesenteric vascular bed (MVB) of streptozotocin (STZ) diabetic Sprague-Dawley rats 2 and 14 weeks after induction of diabetes. Endothelin-1 (ET-1)-, methoxamine (MTX)-, and KCl-evoked vasoconstrictor responses were unchanged in 2-week-old diabetic rats. In contrast, both the sensitivity (P < 0.01) and the maximal vasoconstrictor responses (P < 0.05) to ET-1 were attenuated in 14-week-old diabetic rats, whereas endothelin plasma levels were increased (P < 0.05). Although no differences were observed in responses to KCl in either the 2- or 14-week-old diabetic groups, MTX-evoked maximal responses were attenuated in the 14-week-old group (P < 0.01). Changes in agonist-evoked responses in the 14-week-old diabetic group were unaffected by the protein kinase C (PKC) inhibitor, staurosporine, the phospholipase C (PLC) inhibitor, U73122, the calcium channel blocker, nifedipine, the calcium pump inhibitor, cyclopiazonic acid (CPA), or by endothelial denudation. Sodium fluoride (NaF), an activator of guanosine triphosphate binding proteins (G proteins) normalized the responses in the 14-week-old diabetic group. These data suggest that advanced stages of STZ are associated with alterations in G protein receptor coupling and/or activity leading to the attenuation of responses to vasoconstrictor agonists.

Animals↗

PubMed2000

Vanadate-evoked relaxation of the perfused rat mesenteric vascular bed.

Sodium orthovanadate (SOV) can contract smooth muscle; however, little is known about its effect on the vascular endothelium. We compared the vasorelaxant effects of acetylcholine (ACh) and SOV in the preconstricted, isolated perfused mesenteric vascular bed (MVB) of Sprague-Dawley rats. The maximal relaxation response evoked by SOV (40-45%) was lower than ACh (92-94%) but the IC50 values were similar. At concentrations > 1 mM, SOV elevated the basal tone. Endothelial denudation resulted in a substantial reduction of relaxation responses to both agents, whereas either nitric oxide synthase (NOS) inhibitors or high KCl partially reduced the responses. A combination of NOS inhibitors along with either a calcium-activated potassium channel (KCa) blocker, tetrabutylammonium (TBA), or high KCI inhibited the responses to a similar extent as endothelium denudation. Neither clotrimazole nor TBA attenuated ACh responses; however, maximal responses to SOV in the presence of TBA or clotrimazole were reduced. Indomethacin had no effect on responses to either agonists. These results indicate that like ACh, SOV-mediated vasorelaxation of the MVB involves recruitment of both endothelial derived hyperpolarizing factor (EDHF) and endothelial derived nitric oxide (NO) and not vasodilator eicosanoids. As the relaxation to SOV was dose-dependent at a low concentration range, it is likely that vanadate is involved in the regulation of total peripheral resistance.

Acetylcholine↗

PubMed2000

Altered paracrine effect of endothelin in blood vessels of the hyperinsulinemic, insulin resistant obese Zucker rat.

OBJECTIVE: Earlier, we reported that high insulin incubation in vitro leads to increased ETA receptor expression in cultured rat aortic smooth muscle cells (Diabetes 1998, 47: 934-944). Our later observation of enhanced endothelin-1 evoked vasoconstriction in aorta from the hyperinsulinemic obese Zucker rat indicated that this interaction might also be relevant in vivo. To further examine the relationship between insulinemia and endothelin, we characterized endothelin receptor expression and endothelin-1 peptide levels in vascular tissues and plasma from young and old obese Zucker rats. METHODS: 12 and 40-week-old Zucker obese and lean rats were used. Plasma endothelin-1 levels and endothelin-1 peptide content in the mesenteric artery and in the thoracic aorta were examined by radioimmunoassay. Messenger RNA levels of endothelin-1 peptide and ETA and ETB receptors were examined in the aortic and mesenteric vessels using RT-PCR. RESULTS: Obese rats from both age groups had significantly higher plasma levels of insulin (4-10 fold), total cholesterol (2-3 fold), triglycerides (10-fold), and glucose (approximately 1.5 fold) than their lean counterparts. There was a trend toward worsening lipoproteinemia and glycemia, but improved insulinemia with age in the obese rats. In association with these changes, obese rats exhibited attenuated endothelin-1 peptide and preproET-1 mRNA levels, but conversely elevated ETA and ETB receptor mRNA levels in both aortic and mesenteric vessels. CONCLUSION: These data suggest that vascular tissue from the metabolically dysregulated obese Zucker rat exhibits attenuated endothelin-1 peptide production and elevated endothelin receptor levels. Since elevated insulin levels have been linked to increased endothelin receptor expression, it is plausible that hyperinsulinemia upregulates endothelin receptors contributing to elevated vasoconstrictor responses to endothelin-1 in this model of obesity and hypertension.

Animals↗

PubMed2000

Effect of losartan on angiotensin II-mediated endothelin and prostanoid excretion in humans.

Angiotensin II (Ang II) stimulates renal prostanoid and vascular endothelin-1 (ET-1) release. Most known Ang II effects are mediated by AT1 receptors. Our aim was to determine whether AT1 receptor activation mediates Ang II-evoked renal prostanoid and ET-1 release. Eleven healthy men were randomized in a crossover, double-blind fashion to receive 100 mg/day of losartan or matching placebo, for 8 days. Blood and urine were sampled before and after a 2-h infusion of Ang II at a rate previously determined to increase mean arterial pressure (MAP) by 25 to 30 mm Hg in each subject. After a 14-day washout, subjects received the alternate treatment. Pretreatment with losartan had little effect on baseline MAP, but increased plasma renin activity, and virtually eliminated the pressor response to Ang II infusion. Angiotensin II significantly increased prostanoid excretion after placebo; the prostanoid response to Ang II was even greater after losartan. Plasma ET-1 was not altered by Ang II infusion, with or without losartan. In contrast, urine ET-1 excretion rate decreased to 40% of baseline after Ang II but not after losartan pretreatment; losartan alone had no effect. We conclude that Ang II decreases renal ET-1 synthesis and release through the AT1 receptor. In contrast, Angiotensin II-mediated renal prostanoid synthesis does not require activation of AT1 receptors. These findings indicate that AT1 receptor antagonists could provide renal protection through indirect mechanisms.

Adult↗

PubMed2000

Intelligent aids for parallel experiment planning and macromolecular crystallization.

This paper presents a framework called Parallel Experiment Planning (PEP) that is based on an abstraction of how experiments are performed in the domain of macromolecular crystallization. The goal in this domain is to obtain a good quality crystal of a protein or other macromolecule that can be X-ray diffracted to determine three-dimensional structure. This domain presents problems encountered in real-world situations, such as a parallel and dynamic environment, insufficient resources and expensive tasks. The PEP framework comprises of two types of components: (1) an information management system for keeping track of sets of experiments, resources and costs; and (2) knowledge-based methods for providing intelligent assistance to decision-making. The significance of the developed PEP framework is three-fold--(a) the framework can be used for PEP even without one of its major intelligent aids that simulates experiments, simply by collecting real experimental data; (b) the framework with a simulator can provide intelligent assistance for experiment design by utilizing existing domain theories; and (c) the framework can help provide strategic assessment of different types of parallel experimentation plans that involve different tradeoffs.

Animals↗

PubMed2000

Radiotelemetric monitoring of blood pressure and mesenteric arterial bed responsiveness in rats with streptozotocin-induced diabetes.

We investigated the changes in arterial blood pressure (BP) and of mesenteric arterial bed (MAB) responsiveness that accompany streptozotocin (STZ)-induced diabetes. BP was recorded by radiotelemetry in conscious animals before and during a 4-week period following induction of the diabetic state with STZ. At the end of this period, the MAB was isolated and perfused under constant flow conditions: perfusion pressure (PP, mmHg) was taken as an index of arteriolar tone. BP was lower (P < 0.05) in STZ-treated diabetic rats (82.9+/-5.0 mmHg) than in vehicle-treated rats (108.9+/-6.3 mmHg). Basal perfusion pressure of the MAB was lower in STZ-treated rats than in control rats and inhibition of nitric oxide (NO) synthesis with N(G)-nitro-L-arginine-methyl-ester and N(G)-nitro-L-arginine (100 microM each) failed to change this relationship. Increases in PP of MAB to phenylephrine (Phe), norepinephrine (NE), and potassium chloride (KCl) were reduced in STZ-treated rats compared with control rats. Inhibition of NO synthesis reduced responses to Phe, NE, and KCL in both STZ and control rats. The reduced responsiveness of STZ rats to Phe, NE, and KCl persisted after inhibition of NO synthesis. Acetylcholine (ACh) evoked relaxation of the MAB in a dose-dependent fashion. Maximal responses to ACh, but not sodium nitroprusside, were lower in STZ rats than in vehicle treated rats. Inhibition of NO synthesis reduced responses to ACh in both STZ and control rats. The reduced responsiveness of STZ rats to ACh persisted after inhibition of NO synthesis. The data demonstrate that STZ-induced diabetes is associated with a fall in blood pressure when pressure is recorded with radiotelemetry. The fall in blood pressure may be related to a non-specific decrease in responsiveness to vasoconstrictor stimuli mediated at least in part by NO-independent mechanisms. A decrease in responsiveness to endothelial dependent vasodilator mechanisms appeared insufficient to restore responsiveness to vasoconstrictor stimuli.

Acetylcholine↗