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At least 649 records · Page 36Linked to original sources
PubMed1990

Different muscarinic receptors mediate autoinhibition of acetylcholine release and vagally-induced vasoconstriction in the rat isolated perfused heart.

Experiments were carried out on rat isolated perfused hearts with both vagus nerves attached. The acetylcholine stores were labelled with [14C]-choline. The effects of muscarinic receptor antagonists on the [14C]-overflow and increase in perfusion pressure evoked by vagus nerve stimulation (10 Hz, 4-10 mA) were studied in order to determine the muscarinic receptor type involved in autoinhibition of acetylcholine release and vagally-induced vasoconstriction in the rat heart. Stimulation of the vagus nerves (1200 pulses) caused an increase in [14C]-overflow and in perfusion pressure which was significantly reduced by hexamethonium 500 mumol/l and abolished by tetrodotoxin 0.3 mumol/l or perfusion with Ca2(+)-free solution. The fractional rate of evoked [14C]-overflow per pulse upon stimulation at 10 Hz (720 pulses) was doubled in the presence of the non-selective antagonist atropine (0.01-1 mumol/l) as well as in that of the M2-selective compounds methoctramine (0.1 mumol/l) and AF-DX 116 (0.1-1 mumol/l), but remained unaffected by the M3-selective hexahydrosiladifenidol (0.1 mumol/l). The increase in perfusion pressure upon nerve stimulation was reduced by atropine (0.01 mumol/l) or hexahydrosiladifenidol (0.1 mumol/l) to approximately 50% and increased by about 50% in the presence of AF-DX 116 (0.1 mumol/l). The results show that the autoinhibition of acetylcholine release in the rat heart is mediated by M2 receptors. On the other hand, the increase in perfusion pressure upon vagus nerve stimulation is caused by a different muscarinic receptor, more sensitive to hexahydrosiladifenidol than to M2-selective antagonists.

Acetylcholine↗
PubMed1992

Dependence of oxygen uptake on ambient PO2 in isolated perfused frog skin.

Rates of O2 uptake across isolated perfused skin of bullfrogs (Rana catesbeiana) were measured in relation to blood flow at three levels of ambient O2 tension: normoxia (O2 tension = 152 torr), hypoxia (12% O2, 87 torr) and hyperoxia (42% O2, 306 torr). At bulk perfusion rates ranging from 3.4 to 10.1 microliters.cm-2 x min-1, O2 uptake was positively correlated with hemoglobin delivery rate in both normoxia and hyperoxia, but was independent of delivery rate in hypoxia. Mean O2 uptake in normoxia was 3.8 nmol O2 x cm-2 x min-1 at a delivery rate of 9.8 nmol.cm-2 x min-1 and 6.5 nmol O2 x cm-2 x min-1 at a delivery rate of 28.3 nmol.cm-2 x min-1. At any given bulk perfusion rate, oxygen uptake averaged about 49% lower in hypoxia than in normoxia, decreasing in proportion to the reduction of O2 tension difference between medium and blood. In hyperoxia, O2 uptake did not increase proportionally with the difference in O2 tension between blood and medium, averaging only 50% higher at a 2.4-fold greater O2 tension difference. Cutaneous diffusing capacity for O2 averaged 0.041 nmol O2 x cm-2 x torr-1 x min-1 during the first hour of perfusion in normoxia, and was not affected by reduction of ambient O2 tension. The results indicate that cutaneous O2 uptake in hypoxia is highly diffusion limited, and consequently, increases in cutaneous perfusion can not effectively compensate for reduction of ambient O2 tension. In hyperoxia, O2 uptake may be substantially perfusion limited because of reduced blood O2 capacitance at high O2 saturations.

Animals↗
PubMed1977

The vasoconstrictive effect of dopamine in the isolated, perfused rat kidney after catecholamine depletion.

In the isolated, perfused kidney of untreated and catcholamine-depleted rats (by 6-hydroxydopamine and reserpine), dopamine (DA) caused a dose-dependent increase in vascular resistance which could be prevented by prior blockade of the alpha-adreno-receptors. The DA-induced vasoconstriction thus appears to be due to a direct stimulation of alpha-receptors in the kidney rather than an indirect sympathomimetic effect through release of noradrena-line from local adrenergic nerve terminals. The effectiveness of the chemical sympathectomy accomplished with 6-hydroxydopamine and reserpine was evaluated by chemical; histochemical and electron microscopical methods.

Adrenergic alpha-Antagonists↗
PubMedDate not supplied

Myocardial damage by ventricular fibrillation in isolated perfused rat hearts, and its underlying mechanisms.

In isolated perfused rat hearts ventricular fibrillation (VF), elicited electrically and persisting further spontaneously, led to an extensive release of creatine kinase (CK). Coronary flow volume and oxygen consumption were increased. In contrast, the CK release was only very small in hearts which were stimulated permanently with rhythmic impulses of 10 Hz, whereas the increase in coronary flow and oxygen consumption was significantly greater. When a relative ischemia was induced by perfusion at a low pressure, the CK release from fibrillating hearts was not greater, but less than at a higher perfusion pressure. It appeared unlikely, therefore, that the CK release from fibrillating hearts was simply due to an oxygen deficiency, although a decrease of ATP and glycogen, and an increase of glucose-6-phosphate and lactate in the myocardium were found. When VF was interrupted by lidocaine, the enzyme leakage was reduced only in the experiments with the higher perfusion pressure. A partial restoration of the myocardial metabolites after 1 h was observed. Findings in maximally ischemic hearts further supported the idea that the enzyme release in fibrillating hearts was not merely due to a lack of oxygen. Complete interruption of the coronary perfusion led to the release of only small CK activities during subsequent coronary reperfusion, whereas the metabolic alterations were more distinct than in fibrillating hearts. Mechanisms responsible for the enzyme release during fibrillation, besides a moderate oxygen deficiency, are discussed.

Adenosine Triphosphate↗
PubMed1987

Bile lipid secretion in isolated perfused rat liver. A model for metabolic studies.

Isolated perfused rat liver was used to study the effects of constant taurocholate perfusion, with or without the addition of phosphatidylcholine unilamellar vesicles, upon both the bile salt-dependent and bile salt-independent secretion of bile. Taurocholate introduction increased bile flow and normalized the bile lipid secretion by restoring the bile salt-dependent secretion. At a flow rate of 30 ml/min, the liver was perfused by a single-pass method. The perfusion medium contained 17.5 microM taurocholate with or without 5.83 microM phosphatidylcholine. In light of a recent quantitative dynamic concept on the interphase partition of lipids, it was calculated that more than 99% of the taurocholate reaches the liver as monomers and/or dimers. It was also deduced that the lipids were secreted in bile as small discoidal lipoprotein structures rather than unilamellar lipoproteic vesicles. During the course of the experiments (2 hr), the excellent criteria of viability of this model make it highly suitable for the investigation of hepatic metabolism. Furthermore, the addition of phosphatidylcholine unilamellar vesicles to the perfusate constitutes a potential vector for various liposoluble molecular species.

Animals↗
PubMed1994

Formoterol and salmeterol are both long acting compared to terbutaline in the isolated perfused and ventilated guinea-pig lung.

An isolated, perfused and ventilated guinea-pig lung was used to compare the duration of effect of the bronchodilating beta 2-adrenoceptor agonists formoterol, salmeterol and terbutaline. Lung conductance was measured real time with the aid of a computer. Bronchoconstriction was induced in the preparation every 10 min by bolus injections of acetylcholine into the pulmonary artery. Lung conductance was reduced by about 70% after acetylcholine. The test compounds or the vehicle was administered for 1 min as aerosols generated from solutions: formoterol (10 mumol/l), salmeterol (100 mumol/l) and terbutaline (1000 mumol/l). This treatment inhibited the response to acetylcholine by 50-60% within the first 10 min for all three test compounds. The onset of action appeared to be slower for salmeterol than for formoterol and terbutaline. The inhibitory effect of terbutaline disappeared completely during the next 20 min of continuous perfusion (single pass), while both formoterol and salmeterol displayed a significant inhibitory effect 40 min after their administration. Formoterol, when inhaled at a higher dose (100 mumol/l), caused a 90% inhibition of the response to acetylcholine. This effect was completely reversed by 0.1 mumol/l propranolol in the perfusion medium. There were in general no major changes in the basal conductance measured between the acetylcholine provocations.

Acetylcholine↗
PubMed1984

Glutathione biosynthesis in the isolated perfused rat lung: utilization of extracellular glutathione.

The isolated perfused rat lung catalyzed the biosynthesis of GSH when the sulfur amino acids cysteine or N-acetylcysteine, but not methionine, were supplied in the perfusion medium. The lung also had the capacity to utilize extracellular GSH for this purpose. Replenishment of intracellular GSH in perfused lungs from diethylmaleate-treated rats was pronounced even at 25 microM GSH in the perfusion medium. The utilization of extracellular GSH is probably primarily through extracellular break-down and resynthesis rather than direct uptake as indicated by the inhibitory effect of the gamma-glutamylcysteine synthetase inhibitor, buthionine sulfoximine and the gamma-glutamyl transferase inhibitor, anthglutin. The results indicate that the lung in addition to the kidney may utilize circulating plasma GSH.

Acetylcysteine↗
PubMed1990

Cutaneous toxicity of 2-chloroethyl methyl sulfide in isolated perfused porcine skin.

Previous research has shown the isolated perfused porcine skin flap (IPPSF) to be a novel in vitro experimental model for investigating xenobiotic percutaneous absorption. In this study, the IPPSF was used to biochemically and morphologically assess the dermatotoxicity of 2-chloroethyl methyl sulfide (CEMS), a monofunctional analog of the vesicant, sulfur mustard. IPPSFs were perfused in a recirculating perfusion system and were treated with 97% CEMS (n = 4) or served as controls (n = 4). Additional IPPSFs were perfused in a nonrecirculating perfusion system and were treated with CEMS (n = 4) or were controls (n = 4). After dosing, each IPPSF was perfused for 8 hr. Cumulative glucose utilization (GU) and lactate production/glucose utilization ratio (L/GU ratio) were used as viability parameters. The average rate of GU for CEMS was significantly lower than control (p less than 0.05) in the recirculating and nonrecirculating IPPSFs. The L/GU ratio for CEMS was not significantly different (p greater than 0.05) from control for either perfusion system. CEMS resulted in a marked increase in vascular resistance versus control in both perfusion systems. Gross vesicles and bullae formation occurred in six of the CEMS-treated IPPSFs. Light microscopy revealed subepidermal vesicle formation above the basement membrane and extensive basal cell pyknosis in all IPPSFs treated with CEMS. No macroscopic or microscopic lesions were noted in the control flaps. Transmission electron microscopy revealed separation between the lamina lucida and the lamina densa of the basal lamina, with intracellular vacuolization and mitochondrial swelling occurring in the stratum basale and stratum spinosum cells of IPPSFs treated with CEMS. These lesions are similar to those described after human exposure to sulfur mustard. Full characterization of the morphological and biochemical changes seen after topical exposure of the IPPSF to vesicants may shed light on the pathogenesis of cutaneous toxicity of these compounds in vivo and serve as a relevant model to assess protective strategies against vesicant exposure.

Animals↗
PubMed1990

Calcitonin gene-related peptide stimulates adrenocortical function in the isolated perfused rat adrenal gland in situ.

Using the isolated perfused in situ rat adrenal preparation, we have shown a direct stimulatory action of calcitonin gene-related peptide on aldosterone secretion. The threshold dose for this action was 1 pmol, given as a bolus in 200 ul. CGRP also caused vasodilation in the adrenal gland, reflected in increased perfusate flow, and also stimulated corticosterone secretion, with a threshold of 0.1 pmol. Addition of CGRP to incubations of collagenase-dispersed adrenocortical cells had no effect on steroidogenesis. These results support the contention that CGRP, which have been identified in nerve terminals in the zona glomerulosa of the rat adrenal cortex, may have a role in the control of steroid secretion.

Adrenal Cortex↗
PubMed1987

Method for stimulating the adrenergic system of an isolated perfused rat heart.

A method is presented whereby isolated perfused rat hearts can be rapidly prepared for the stimulation of chronotropic activity by electrical pulses or exogenous noradrenaline. The mediation of the response by sympathetic nerves is demonstrated through modulation of the response by compounds with established pharmacological actions. Propranolol inhibits the increase in heart rate to both electrical stimulation and exogenous noradrenaline, whereas bretylium inhibits only electrically induced increases. Chronic pretreatment with 6-hydroxydopamine decreases the response to electrical stimulation but increases that to exogenous noradrenaline.

Amphetamine↗
PubMed1982

Effects of caerulein and bombesin on insulin and glucagon secretion from the isolated, perfused rat pancreas.

Caerulein nd bombesin, peptides first isolated from amphibian skin, act upon the mammalian gastrointestinal tract. To determine if these peptides influence mammalian endocrine pancreatic function, we tested their effects on the isolated, perfused rat pancreas. In these experiments, we examined effects of constant infusions of either caerulein (10(-11) M through 10(-8) M) or bombesin (10(11) M through 3.0 . 10(-7) M) which were superimposed upon glucose. Secretory studies consisted of a 20-min basal period (60 mg/dl glucose), then a 15-min infusion of glucose (150 mg/dl). Effects of the peptides (10(-9) M) upon the response to post-glucose arginine (168 mg/dl), confusion with glucose (60 mg/dl) for 15 min. were also studied. Neither peptide had any effect on basal insulin secretion. However, both peptides had distinct effects on insulin responses to the stimuli. Both caerulein and bombesin produced enhancement of glucose-induced insulin secretion, increasing total insulin secretion in a dose-dependent manner. Only caerulein enhanced arginine-induced insulin secretion. These peptides had no effect upon arginine-induced glucagon secretion.

Animals↗
PubMed1985

Effects of gentamicin on renal function in isolated perfused kidneys from male and female rats.

The isolated perfused rat kidney was used to determine whether sex differences in gentamicin nephrotoxicity are related to intrinsic differences in renal response to gentamicin. Acute exposure to gentamicin decreased fractional reabsorption of water and electrolytes without changes in glomerular filtration rate in both sexes. Gentamicin decreased the tubular reabsorption of lysozyme but not glomerular permeability to lysozyme. No sex differences in renal responses were observed following in vitro exposures to gentamicin, suggesting that sex differences in susceptibility to gentamicin in vivo may be attributable to extrarenal factors, such as pharmacokinetics.

Absorption↗
PubMed1997

Rationale for different approaches to combined melphalan and hyperthermia in regional isolated perfusion.

The addition of hyperthermia (HT) to regional isolated perfusion (RIP) with Melphalan theoretically has two advantages. Firstly, heat can selectively kill cells in poorly vascularised areas that are usually not reached by the drug. Secondly, in vitro data have revealed that the effect of Melphalan is enhanced at temperatures 39-45 degrees C. However, for the simultaneous application of Melphalan and HT, as it is given in most institutes, both normal and tumour tissues within the volume are treated with both modalities. It is unclear whether--for the same heat dose--the cytotoxicity of Melphalan is enhanced more in tumour tissue than in normal tissues. As the applied dose of Melphalan in RIP is selected on maximum acceptable toxicity, any enhancement of toxicity is undesired. Indeed, Melphalan application at temperatures > 41 degrees C has resulted in unacceptable toxicity. In most institutes, the hyperthermia dose is reduced in comparison to application as a single-modality treatment, to allow simultaneous combination without unacceptable toxicity. In this review, the rationale for two different approaches is summarised which may make it possible to improve the benefit from the theoretical advantage of the use of HT in RIP. It is meant to stimulate discussion as a possible first step in the design of new treatment protocols.

Animals↗
PubMed1980

Degradation of [3H]chondroitin 4-sulphate and re-utilization of the [3H]hexosamine component by the isolated perfused rat liver.

Radiolabelled chondroitin 4-sulphate was isolated after incubation of rat rib cartilage with N-acetyl-D-[6-3H]galactosamine. After proteolytic digestion of the tissue with either papain or trypsin the released [3H]chondroitin 4-sulphate was added to an isolated perfused rat liver system. Analysis of perfusate after several hours perfusion showed that radiolabelled amino sugars were secreted by the liver in a low-molecular-weight form and as components of glycoproteins.

Acetylgalactosamine↗
PubMed1997

Endothelin-induced vasoconstriction in isolated perfused liver preparations from normal and cirrhotic rats.

Isolated, perfused rat liver preparations (IPRL), obtained from rats with carbon tetrachloride-induced cirrhosis and normal controls, were used to investigate responses to the vasoactive peptide endothelin-1 (ET-1). The mean perfusion resistance (R) of cirrhotic IPRL was significantly greater than that of controls (2.63 +/- 0.24 vs 1.54 +/- 0.14 mmHg/mL per min per g; P < 0.01). Both control and cirrhotic IPRL demonstrated a concentration-related increase in resistance (delta R) in response to ET-1, with a minimum effective concentration of approximately 3 x 10(-11) mol/L. The EC50 (-log of the 50% effective concentration) was not significantly different between cirrhotic and control IPRL (8.48 +/- 0.19 and 8.79 +/- 0.11, respectively); however, the maximum response to ET-1 was significantly greater in cirrhotic preparations (R: 10.4 +/- 2.2 vs 4.4 +/- 0.5 mmHg/mL per min per g, P < 0.01; DR, 7.8 +/- 2.1 vs 2.8 +/- 0.4 mmHg/mL per min per g, P < 0.01). Following maximal stimulation by ET-1, the mean portal-hepatic venous pressure gradient at a physiological flow rate of 1 mL/min per g was approximately 90% greater across cirrhotic IPRL than that across normal IPRL (11.2 +/- 2.0 vs 5.9 +/- 0.9 mmHg, respectively; P < 0.05). These results support the hypothesis that endogenously released ET-1 has a significant influence on the portal vascular resistance of cirrhotic liver in vivo and has an important role in the pathogenesis of portal hypertension.

Animals↗
PubMed1993

Influence of pH on the uptake and pharmacodynamics of quinidine in the isolated perfused rat heart.

Using the single-pass isolated perfused rat heart preparation we examined the effect of perfusate pH (pH 7.05, 7.46, 7.71, 7.92) on quinidine output concentration (C(out)) and delta QT. Eight hearts were perfused at 2.5 ml/min. with quinidine (20 microM) for 35 min. followed by a 35-40 min. washout period with drug-free perfusate. This procedure was repeated four times in each preparation with the pH sequence varied and the same pH used in the first and last phases. Increasing pH slowed the rate of equilibration of C(out), the equilibration rate constant (k) decreasing from 0.273 min.-1 at pH 7.05 to 0.095 min.-1 at pH 7.92. A modified Kety-Renkin-Crone equation was fitted to the C(out) versus time data for each pH. The estimated volume of distribution (V) increased significantly with pH from 11.5 +/- 1.1 to 32.5 +/- 2.9 ml/g, but the permeability surface product did not change with pH (mean 17.7 ml/min./g). There was a linear relationship between V and calculated un-ionised quinidine C(out), with an intercept of 5.70 ml/g corresponding to the V of ionised drug. This indicates that ionised and un-ionised drug readily enter the heart and that the slower equilibration with pH is due to the increased V which results from increased partitioning of un-ionised quinidine into myocardial tissue. Perfusion pH did not directly affect baseline QT interval, but the rate of attainment of maximum delta QT decreased with increasing perfusate pH. Plots of delta QT versus calculated coronary output quinidine concentration did not change with pH, showing that this drug effect was due to both ionised and un-ionised moieties. This study shows that myocardial permeability and pharmacodynamic effect (delta QT) of quinidine are not influenced by perfusion pH over the range 7.0 to 7.9, although rate of equilibration of both C(out) and effect vary with pH.

Animals↗
PubMed1996

The disposition of morphine and morphine-3-glucuronide in the isolated perfused rat liver: effects of altered perfusate flow rate.

The rat single-pass isolated perfused liver preparation was used to study the effects of altered perfusate flow rate on the hepatic disposition of morphine and its polar metabolite morphine-3-glucuronide (M3G). Using a balanced, cross-over design, livers of female Sprague-Dawley rats (n = 6) were perfused at 15 and 30 mL min-1 with erythrocyte- and protein-free perfusion medium containing a constant concentration of morphine (2.7 microM). After reaching steady-state, inflow and outflow perfusate and bile samples were collected and morphine and M3G were measured by HPLC. Doubling of perfusate flow rate was associated with a significant increase (P < 0.05) in the availability of morphine (mean +/- s.d. of 0.19 +/- 0.06 at 15 mL min-1 and 0.29 +/- 0.08 at 30 mL min-1). The magnitude of the change in morphine availability was consistent with the predictions of the well-stirred model of hepatic elimination. The fate of hepatically generated M3G was assessed by the biliary extraction ratio of M3G; alterations in perfusate flow rate had no significant effect on this ratio (mean +/- s.d. of 0.49 +/- 0.14 at a perfusate flow rate of 15 mL min-1 and 0.47 +/- 0.22 at 30 mL min-1). A physiologically-based mathematical model, in which the vascular and intracellular spaces of the liver were represented by two well-mixed compartments, was utilized to derive an equation for the biliary extraction ratio of M3G. According to the model, the value of this extraction ratio will become insensitive to changes in perfusate flow rate when the permeability for M3G of the membrane separating the intracellular and vascular compartments is low compared with perfusate flow rate. Hence, the experimental results are consistent with the concept that the hepatic sinusoidal membrane represents a diffusional barrier to M3G.

Animals↗