Biomedical subjects

K A Dora

Publications and source records attributed to K A Dora.

35 records · Page 2Linked to original sources

PubMed1996

Perfused skeletal muscle contraction and metabolism improved by angiotensin II-mediated vasoconstriction.

In the present study, the effects of angiotensin II (ANG II) on tension development and associated metabolism during twitch and tetanic stimulation via the sciatic nerve of the gastrocnemius-plantaris-soleus muscle group of the perfused rat hindlimb were investigated. Rat hindlimbs were perfused at constant flow with an erythrocyte-containing medium equilibrated with 95% air-5% CO2 at 37 degrees C, and determinations of oxygen and glucose uptake, lactate and glycerol release, and 2-deoxy-D-[1-3H]glucose uptake (Rg') into individual muscles were carried out. ANG II (1 nM) infusion alone caused vasoconstriction with increased oxygen (55%) and glucose (98%) uptake and lactate (37%) and glycerol (64%) release. ANG II infusion during muscle contraction gave less vasoconstriction but increased the tension development during tetanic stimulation by 80% and increased the contraction-induced oxygen uptake and Rg' by plantaris and gastrocnemius red and white muscles. These effects of ANG II may have been due to increased nutritive flow to contracting muscles or to redirection of flow from noncontracting and type I fiber muscles to the type II fiber contracting muscles in the hindlimb. The results indicate that the regulation of flow by the vasculature is an important regulator of muscle contraction and metabolism.

Angiotensin II↗

PubMed1995

Functional and metabolic evidence for two different vanilloid (VN1 and VN2) receptors in perfused rat hindlimb.

Vanilloid spice principles, including capsaicin, stimulate vasoconstriction in the rat hindlimb perfused at constant flow and, depending on dose, either stimulate or inhibit oxygen consumption by this vascular bed. We now present metabolic and functional evidence for two different vanilloid (VN1 and VN2) receptor types. These receptors can be distinguished on the basis of their differing agonist affinity for capsaicin, their different calcium and oxygen dependencies for inducing vasoconstriction, and whether they stimulate, or inhibit, oxygen consumption. The higher affinity vanilloid receptor, VN1 can be distinguished on the basis of initiating vasoconstriction at low doses of capsaicin and simultaneously stimulating oxygen consumption. Its apparent biological function is dependent on the presence of oxygen and external calcium. In contrast, the lower affinity receptor, VN2 induces vasoconstriction associated with inhibition of oxygen consumption. Its vasoconstriction action can occur independently of either external calcium ions, or the presence of oxygen in the perfusate.

Animals↗

PubMed1995

Inhibition of insulin-mediated glucose uptake in rat hindlimb by an alpha-adrenergic vascular effect.

The vasoconstrictor norepinephrine, at high doses, inhibits oxygen uptake (VO2) in the perfused hindlimb, possibly by opening vascular shunts and reducing nutrient access. Thus, in the present study, the effect of norepinephrine on insulin-mediated glucose uptake (IMGU) was assessed. Rat hindlimbs were perfused at constant flow with medium containing 8.3 mM glucose and a tracer amount of 2-deoxy-D-[1-3H]glucose (2-DG) with and without 15 nM insulin, 10 microM norepinephrine (NE), and combinations of the adrenergic blockers propranolol (Prop) and prazosin. Perfusions were also conducted at a lower dose of 1 microM NE where VO2 is stimulated. NE (10 microM) inhibited IMGU > 80%, and this inhibition, when measured by 2-DG uptake, was most pronounced in muscles rich in white fibers. The inhibitory effect of NE on IMGU comprised a beta-adrenergic component also partly evident at lower concentrations of NE (i.e., 1 microM) and an alpha-adrenergic component only evident at 10 microM NE. In contrast to the results for the hindlimb, 10 microM NE plus Prop (alpha-adrenergic combination) had no significant effect on insulin-mediated 2-DG uptake by isolated incubated soleus or extensor digitorum longus muscles. It is concluded that NE, at doses likely to occur at sympathetic vasoconstrictor synapses in muscle, impairs IMGU by a vascular effect to cause shunting and reduce access.

Animals↗

PubMed1995

Vascular and endocrine control of muscle metabolism.

Important differences exist between perfused and incubated (or perifused) skeletal muscle preparations with regard to their metabolism and control. A growing body of evidence suggests that the differences may be due to the role played by the vascular system. In the constant-flow perfused rat hindlimb preparation, a group of vasoconstrictors has been identified that enhance muscle metabolism and aerobic contractility. Another group of vasoconstrictors decrease muscle metabolism and aerobic contractility even though perfusate flow remains constant. All effects of both groups of vasoconstrictors are opposed by vasodilators. Because none of the vasoconstrictor effects is evident when isolated muscles are incubated or perifused, involvement of an active vascular system is indicated. Although some hormones may act directly on muscle by purely endocrine effects, a vascular component of their actions is now emerging. Mechanisms to account for vascular control of perfused skeletal muscle metabolism may involve 1) functional vascular shunts where the proportion of flow processed by these is regulated by site-specific vasomodulators, 2) a direct response to a change in the rate of supply of nutrients and removal of products, and 3) a signal substance released by vascular tissue in association with vasoconstriction that interacts with surrounding skeletal muscle cells. Impaired control at the level of the vascular system may have implications for long-term access of nutrients and hormones and therefore the control of skeletal muscle metabolism and contractile performance.

Animals↗

PubMed1994

Resiniferatoxin and piperine: capsaicin-like stimulators of oxygen uptake in the perfused rat hindlimb.

The naturally occurring capsaicin-like molecules, resiniferatoxin (RTX, Euphorbia spp.) and piperine (Piper nigrum), each stimulated oxygen uptake (VO2) in association with increased vascular resistance in a concentration-dependent manner when infused into the perfused rat hindlimb. 5 microM glyceryl trinitrate (GTN, a nitrovasodilator) significantly blocked the oxygen and pressure responses to both RTX and piperine, indicating a close relationship between changes in VO2 and the vasoconstriction. Concentrations greater than those required for maximal VO2 resulted in an inhibition of VO2, although perfusion pressure continued to increase. Time course studies showed that both RTX and piperine at high doses resulted in a tri-phasic response. An initial phase of transient VO2 stimulation was followed by a second phase of inhibition. A third phase involving an often larger but transient stimulation of VO2 followed removal of the agents and continued after the pressure returned to basal. The actions of RTX and piperine were similar to those of other active capsaicin-like molecules tested previously in this system, including capsaicinoids (Capsicum spp.), gingerols (Zingiber officinale), and shogoals (Zingiber officinale). RTX was the most potent, and piperine the least potent of this series. Although receptor involvement has yet to be unequivocally established, the data are consistent with the presence of a functional capsaicin-like (vanilloid) receptor in the vasculature of the rat hindlimb that mediates vasoconstriction and oxygen uptake. These findings may have implications for the future development of thermogenic agents.

Alkaloids↗

PubMed1994

Vasoconstrictor-mediated release of purines and pyrimidines from perfused rat hindlimb, perfused mesenteric arcade and incubated de-endothelialized aorta.

1. Reperfusion of hindlimbs that had previously been exposed to either 10 or 60 min global ischaemia resulted in transient washouts of uracil and uric acid in approximate proportion to the interval of ischaemia. However, changing the interval of sequential angiotensin II infusions from 10 to 60 min did not affect the magnitude of sustained uracil and uric acid release. 2. Perfused rat mesenteric artery arcade released uracil and uric acid and each was further increased approximately 2-fold by exposure to the vasoconstrictor, serotonin (6.7 microM). 3. Incubated de-endothelialized rat aorta also released purines and pyrimidines and this was increased further when subjected to increased work loads. 4. The increased rates of release of purines and pyrimidines from hindlimb, and the simpler vascular preparations of mesenteric arcade and aorta, were in proportion to the relative rates of increase in oxygen consumption under maximum vascular load. 5. It is concluded that the release of purine and pyrimidine nucleosides and their catabolites from perfused rat hindlimb occurring as a consequence of vasoconstriction is not the result of release from previously ischaemic tissue. In addition, release of purines and pyrimidines appears to be a general feature of vascular smooth muscle subjected to high workloads.

Analysis of Variance↗

PubMed1994

Characterization of perfused periaortic brown adipose tissue from the rat.

A technique was developed for the perfusion of periaortic brown adipose tissue (BAT) with a view to assessing vascular system involvement in BAT thermogenesis. The procedure involved cannulation of the thoracic aorta and ligation of the intercostal branches and the distal thoracic aorta. Perfusion was conducted in a buffer-filled chamber using constant flow at 37 degrees C. Lactate dehydrogenase leakage was less than 2%/h, and after 30 min of perfusion the energy charge was 0.72 +/- 0.05 (n = 4) and differed little from freshly sampled interscapular BAT (0.71 +/- 0.03 (n = 7)). Periaortic BAT was indistinguishable from interscapular BAT in enzyme content, mitochondrial size, mitochondrial cristae, lipid content, and cell size. Basal oxygen consumption (VO2) was 64.3 +/- 7.4 mumol.h-1.g-1 wet weight, and basal perfusion pressure was 65 +/- 3 mmHg (1 mmHg = 133.3 Pa). Norepinephrine and isoproterenol each increased VO2 of perfused periaortic BAT in a time-dependent and reversible manner. Half-maximal stimulation of VO2 occurred at 12 nM norepinephrine and 8 nM isoproterenol; maximally stimulated tissue had a VO2 of approximately 150 mumol.h-1.g-1 wet weight. Norepinephrine (50 nM) had no consistent effect on perfusion pressure, but the increase in VO2 by this agonist was completely blocked by 10 microM DL-propranolol and unaffected by phentolamine (1-20 microM) or nitroprusside (0.01-1 mM). Increasing the perfusion flow rate increased pressure and had no effect on basal VO2 but increased the VO2 response due to norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1994

Potential defect in the vascular control of nonshivering thermogenesis in the obese Zucker rat hind limb.

Vascular control of nonshivering thermogenesis in the perfused hind limb of obese and lean Zucker rats were compared using two vasoconstrictors, norepinephrine and serotonin. For hind limbs of both phenotypes, norepinephrine infusions resulted in a dose-dependent uninterrupted increase in perfusion pressure and a biphasic change in oxygen uptake (VO2), characterized by a stimulation at low concentrations, and an increasing inhibition at higher concentrations that gradually overcame the stimulation in a dose-dependent manner. At concentrations of norepinephrine greater than 1 microM, the inhibitory effect predominated and gave rise to values for VO2 less than basal. The obese hind limb had a lower basal VO2 and a lower maximal VO2 mediated by norepinephrine than the lean rat, but these differences appeared to relate largely to the lower muscle mass and higher content of fat of the obese hind limb. Serotonin infusions resulted in dose-dependent increase in perfusion pressure and an accompanying decrease in VO2. Pressure changes were identical for the obese and lean hind limbs, but the decrease in VO2 due to serotonin was greater in the hind limbs from the lean rats, and this difference remained when the data were expressed in terms of muscle mass perfused. It is concluded that the relatively lower content of muscle of the obese hind limb accounts for its lower basal and lower maximal norepinephrine-mediated thermogenesis. In addition, an intrinsic defect in obese hind limb muscle response to serotonin is present, which may be indicative of a decrease in the potential for vasoconstrictor-regulated thermogenesis that could have implications for whole-body energy balance by the obese phenotype.

Animals↗

PubMed1994

Aerobic muscle contraction impaired by serotonin-mediated vasoconstriction.

Vasoconstriction mediated by serotonin (5-HT) inhibits muscle metabolism in resting constant-flow-perfused rat hindlimb and may do so by vascular shunting. In the present study, the effects of 5-HT on tension development and contraction-induced oxygen uptake by the sciatic nerve-stimulated gastrocnemius-plantaris-soleus muscle group of the perfused rat hindlimb and tension development by electrically stimulated isolated incubated soleus and extensor digitorum longus muscles were examined. In both erythrocyte and erythrocyte-free perfusions, 0.25 microM 5-HT increased perfusion pressure and markedly decreased contraction-induced tension, oxygen uptake, and lactate release. The release of metabolic vasodilators from exercising skeletal muscle did not appear to affect 5-HT-mediated vasoconstriction; rather, vascular resistance increased during the period of muscle contraction. In contrast, vasoconstriction during muscle contraction mediated by alpha-adrenoceptor stimulation did not impair tension and was partially overcome by metabolic vasodilators. In addition, contraction of isolated incubated soleus and extensor digitorum longus muscles was not affected by 5-HT addition to the incubation medium. We conclude that 5-HT impairs contractility of working muscle during the aerobic phase by limiting oxygen delivery through redistributing perfusate flow. The results are consistent with a vasoconstrictor action of 5-HT on larger vessels, perhaps at feed arteries external to the working muscle. When constricted by 5-HT, these vessels are apparently insensitive to metabolic vasodilatation.

Aerobiosis↗

PubMed1993

Serotonin-mediated acute insulin resistance in the perfused rat hindlimb but not in incubated muscle: a role for the vascular system.

We have recently shown that the vasoconstrictor serotonin (5-HT) inhibits oxygen uptake in perfused hindlimb possibly due to vascular shunting. Thus in the present study the effect of 5-HT on insulin-mediated glucose uptake was assessed. Rat hindlimbs were perfused at constant flow with medium containing 8.3 mM glucose and a tracer amount of 2-deoxy-D-[1-3]glucose (2DG) with and without 10 microM 5-HT, 15 nM insulin and a combination of the two. 5-HT inhibited insulin-mediated stimulation of glucose uptake by 30.4% when added after insulin and 34.4% when added before insulin. In addition, 5-HT inhibited insulin-mediated 2DG uptake by perfused muscles with inhibition ranging from 32% (soleus) to 80% (extensor digitorum longus). The effects of 5-HT on insulin-mediated glucose uptake were partially reversed by vasodilation with carbachol. In contrast to the results for the hindlimb, 10 microM 5-HT had no significant effect on either basal glucose uptake or the stimulation of glucose uptake mediated by 15 nM insulin by isolated incubated soleus or extensor digitorum longus muscles. It is concluded that 5-HT impairs insulin-mediated glucose uptake in the perfused rat hindlimb that may derive from vascular shunting not apparent when muscles are incubated with 5-HT in vitro. These findings may have implications for the link between hypertension and diabetes.

Animals↗

PubMed1993

Role of extracellular UTP in the release of uracil from vasoconstricted hindlimb.

The source and function of elevated uracil release during vasoconstriction in the perfused rat hindlimb was investigated. The possibility that uracil release derived from the breakdown of released vasoactive uridine 5'-triphosphate (UTP) was examined. Exogenous UTP was found to be a potent vasodilator in the perfused rat hindlimb, opposing norepinephrine and angiotensin-induced increases in vasoconstriction and oxygen consumption. UTP was rapidly catabolized by the hindlimb to uridine 5'-monophosphate (UMP), uridine, and uracil, which were all devoid of vasoactivity. UTP was similarly catabolized by incubated rat aorta. Degradation of exogenous UTP by perfused hindlimb or aorta was inhibited by alpha, beta-methylene-adenosine 5'-diphosphate (AMP-CP), an inhibitor of ectonucleotidases. However, AMP-CP did not decrease uracil and uridine output by the hindlimb during angiotensin-mediated vasoconstriction and increased oxygen consumption. In particular, simultaneous infusion of AMP-CP with angiotensin did not increase efflux of UMP. Although exogenous UTP is a potent vasodilator in the perfused rat hindlimb, it appears not to be released intact during vasoconstriction. Hence, extracellular UTP is unlikely to be the precursor of the uracil release.

Adenosine Diphosphate↗

PubMed1992

A close association between vasoconstrictor-mediated uracil and lactate release by the perfused rat hindlimb.

1. Angiotensin II (5 nM) increased perfusion pressure, O2 uptake and the release of lactate, uracil and uric acid from the perfused rat hindlimb. The release of all three substances was greatest 5 min after commencement of angiotensin II infusion and then decreased over the next 20 min to reach a plateau value that was approx. 2.5-fold basal values. Following removal of angiotensin, pressure, O2 uptake as well as lactate, uracil and uric acid release each returned to pre-infusion (basal) values. 2. Cyanide (1 mM) when added during angiotensin II (5 nM) infusion blocked the pressor effect and completely inhibited all O2 uptake. Cyanide (1 mM) also inhibited the angiotensin-induced increase in uric acid, uracil and lactate release, but the effects differed. Whereas uric acid release remained inhibited throughout the cyanide infusion, uracil and lactate release were only temporarily interrupted and a secondary release of both ensued. 3. Nitroprusside (0.5 mM) when added during angiotensin II (5 nM) infusion blocked pressure and O2 uptake. Lactate and uracil release were partly blocked and returned to pre-infusion (basal) values. However uric acid release was totally blocked and no release occurred when nitroprusside was present with angiotensin II. 4. Combined data showed a significant correlation (r = 0.831; P less than 0.001) between effluent lactate and effluent uracil. 5. It is concluded that lactate and uracil release which increase markedly during vasoconstriction of the hindlimb reflect an association between glycolysis and uracil nucleotide turnover within the same tissue, possibly vascular smooth muscle.

Angiotensin II↗

PubMed1992

Serotonin and norepinephrine vasoconstriction in rat hindlimb have different oxygen requirements.

Serotonin (5-HT) and norepinephrine (NE) are potent vasoconstrictors in the non-erythrocyte constant-flow perfused hindlimb at 25 degrees C. Because 5-HT inhibits and NE stimulates oxygen uptake, these agonists may exert control at different sites in the vasculature that have different metabolic requirements. In this study, it was found that hypoxia, cyanide, or azide had no significant effect on 5-HT-mediated vasoconstriction; however, in the presence of cyanide and absence of glucose, vasoconstriction was transient. NE-mediated vasoconstriction displayed two prazosin-sensitive components. At low concentrations (less than 50 nM), NE-mediated vasoconstriction was totally blocked by hypoxia, cyanide, or azide. At concentrations of NE significantly greater than 50 nM, oxygen-independent vasoconstriction was observed. In conclusion, NE and 5-HT sites are biochemically distinguishable, with 5-HT sites probably located on larger vessels and supportable by anaerobic metabolism and oxygen-dependent NE sites probably located on smaller arteries or arterioles. Supraphysiological concentrations of NE may interact with a subgroup of vascular alpha 1-adrenoceptors on larger vessels giving results similar to 5-HT, thus highlighting problems with high levels of NE in the perfused rat hindlimb.

Animals↗

PubMed1992

Vasoconstrictor-mediated release of lactate from the perfused rat hindlimb.

The effects of different vasomodulators on lactate release by the constant-flow-perfused rat hindlimb were examined and compared with that by perfused mesenteric artery, incubated preparations of aortas, soleus and epitrochlearis muscles, and perifused soleus muscles. Infusion of vasopressin (0.5 nM), angiotensin II (5 nM), norepinephrine (50 nM), and methoxamine (10 microM) into the hindlimbs of 180- to 200-g rats increased the perfusion pressure by 112-167% from 30.4 +/- 0.8 mmHg, O2 consumption by 26-68% from 6.4 +/- 0.2 mumol.g-1 x h-1, and lactate efflux by 148-380% from 5.41 +/- 0.25 mumol.g-1 x h-1. Hindlimbs of 100- to 120-g rats responded similarly to angiotensin II. Isoproterenol (1 microM) had no effect on O2 uptake or perfusion pressure but increased lactate release by 118%. Nitroprusside (0.5 mM) markedly inhibited the vasoconstrictor-mediated increases in lactate release, perfusion pressure, and O2 consumption by the hindlimb but had no effect on isoproterenol-mediated lactate efflux. Serotonin (6.7 microM) increased lactate release from the perfused mesenteric artery by 120% from 5.48 mol.g-1 x h-1. Lactate release by incubated aorta was increased by angiotensin II (50 nM), isoproterenol (1 microM), and mechanical stretch. The increase mediated by angiotensin II was blocked by glycerol trinitrate (2.2 microM), which had no effect on lactate release by isoproterenol. Neither angiotensin II (5 nM) nor vasopressin (0.5 nM) increased lactate release from incubated soleus and epitrochlearis muscles; however, lactate release was increased by isoproterenol, and this increase was unaffected by glycerol trinitrate (2.2 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Pungent principles of ginger (Zingiber officinale) are thermogenic in the perfused rat hindlimb.

Crude extracts of both fresh and dry ginger induced the perfused rat hindlimb to consume oxygen in association with increases in perfusion pressure and lactate production. The principles responsible for these observations, the gingerols and shogaols, were isolated and tested for relative thermogenic activity. The gingerol homologues possessed greater molar potency than their shogaol counterparts. (6)-Gingerol was the most potent principle isolated, causing a mean maximal increase in oxygen consumption of 1.4 +/- 0.1 mumol/g/h (21%), an increase in lactate efflux of 4.7 +/- 0.6 mumol/g/h (87%) with a perfusion pressure increase of 7.7 +/- 0.7 mmHg (30%). Increases in alkyl chain length within each homologous series led to decreased molar potency. Specific nitro-vasodilation using glyceryl trinitrate demonstrated that thermogenesis was at least partly associated with vasoconstriction. Concurrent infusion of alpha or beta antagonists showed that neither adrenergic receptors nor secondary catecholamine release were responsible for the observed effects. Increasing doses of the ginger principles ultimately led to inhibition of steady state oxygen consumption, although perfusion pressure continued to increase. Removal of high ginger principle doses was followed by apparent increases in oxygen uptake unaccompanied by elevated perfusion pressure. As a consequence, the effective concentration ranges of the ginger principles were relatively narrow. The cause of high dose effects is as yet undetermined but may have been due in part to disruption of mitochondrial function.

Animals↗

PubMed1991

The apparent absence of serotonin-mediated vascular thermogenesis in perfused rat hindlimb may result from vascular shunting.

Vasoconstriction by norepinephrine, angiotensin II and vasopressin in the constant-flow perfused rat hindlimb is associated with increased oxygen uptake and has given rise to the concept of vascular thermogenesis. In the present study serotonin (5-hydroxytryptamine, 5HT) was found to inhibit oxygen uptake by up to 40% in a dose dependent manner whilst inducing vasoconstriction in this model, whereas norepinephrine increased oxygen consumption by up to 100% during vasoconstriction. This contrasted with the perfused isolated rat mesenteric artery arcade in which serotonin stimulated oxygen uptake by up to 130% in association with vasoconstriction in a dose dependent manner similar to the previously described norepinephrine induced vascular thermogenesis in this arterial preparation. In both perfusion systems, changes in pressure and oxygen uptake mediated by serotonin were completely blocked by ketanserin. These results and evidence from dye washout studies suggest that serotonin-mediated vascular thermogenesis, if it occurs in the constant-flow hindlimb, is masked by vascular shunting.

Animals↗

PubMedDate not supplied

Evidence for a differential cellular distribution of inward rectifier K channels in the rat isolated mesenteric artery.

The distribution of functionally active, inwardly rectifying K (K(IR)) channels was investigated in the rat small mesenteric artery using both freshly isolated smooth muscle and endothelial cells and small arterial segments. In Ca(2+)-free solution, endothelial cells displayed a K(IR) current with a maximum amplitude of 190 +/- 16 pA at -150 mV and sensitivity to block with 30 microM Ba(2+) (n = 7). In smooth muscle cells, outward K current was activated at around -47 +/- 3 mV, but there was no evidence of K(IR) current (n = 6). Furthermore, raising extracellular [K(+)] to either 60 or 140 mM, or applying the alpha(1)-adrenoceptor agonist phenylephrine (PE; 30 microM), failed to reveal an inwardly rectifying current in the smooth muscle cells, although PE did stimulate an iberiotoxin-sensitive outward K current (n = 4). Exogenous K(+) (10.8-16.8 mM) both relaxed and repolarized endothelium-denuded segments of the mesenteric artery contracted with PE. These effects were depressed by 100 microM ouabain but unaffected by either 30 microM BaCl(2) or 3 microM glibenclamide. These data suggest that functional, inwardly rectifying Ba(2+)-sensitive channels are restricted to the endothelial cell layer in the rat small mesenteric artery.

Animals↗