Calcium handling in porcine coronary endothelial cells by gastrin-17.

In porcine coronary artery endothelial cells (PCAEC), gastrin-17 has recently been found to increase nitric oxide (NO) production by the endothelial NO synthase (eNOS) isoform through cholecystokinin 1/2 (CCK1/2) receptors and the involvement of protein kinase A (PKA), PKC and the ß2-adrenoreceptor-related pathway. As eNOS is the Ca(2)(+)-dependent isoform of the enzyme, we aimed to examine the effects of gastrin-17 on Ca(2)(+) movements. Thus, experiments were performed in Fura-2-acetoxymethyl-ester-loaded PCAEC, where changes of cytosolic Ca(2)(+) ([Ca(2)(+)]c) caused by gastrin-17 were analysed and compared with those of CCK receptors and ß2-adrenoreceptors agonists/antagonists. In addition, some experiments were performed by stimulating cells with gastrin-17 in the presence or absence of cAMP/PKA activator/inhibitor and of phospholipase C (PLC) and Ca(2)(+)-calmodulin dependent protein kinase II (CaMKII) blockers. The results have shown that gastrin-17 can promote a transient increase in [Ca(2)(+)]c mainly originating from an intracellular pool sensitive to thapsigargin and from the extracellular space. In addition, the response of cells to gastrin-17 was increased by the adenylyl cyclase activator and the ß2-adrenoreceptor agonists and affected mainly by the CCK2 receptor agonists/antagonists. Moreover, the effects of gastrin-17 were prevented by ß2-adrenoreceptors and CaMKII blockers and the adenylyl cyclase/PKA and PLC inhibitors. Finally, in PCAEC cultured in Na(+)-free medium or loaded with the plasma membrane Ca(2)(+) pump inhibitor, the gastrin-17-evoked Ca(2)(+) transient was long lasting. In conclusion, this study shows that gastrin-17 affected intracellular Ca(2)(+) homeostasis in PCAEC by both promoting a discharge of an intracellular pool and by interfering with the operation of store-dependent channels through mainly CCK2 receptors and PKA/PLC- and CaMKII-related signalling downstream of ß2-adrenoreceptor stimulation.

Levosimendan induces NO production through p38 MAPK, ERK and Akt in porcine coronary endothelial cells: role for mitochondrial K(ATP) channel.

BACKGROUND AND PURPOSE: Levosimendan acts as a vasodilator through the opening of ATP-sensitive K(+) channels (K(ATP)) channels. Moreover, the coronary vasodilatation caused by levosimendan in anaesthetized pigs has recently been found to be abolished by the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine methyl ester, indicating that nitric oxide (NO) has a role in the vascular effects of levosimendan. However, the intracellular pathway leading to NO production caused by levosimendan has not yet been investigated. Thus, the purpose of the present study was to examine the effects of levosimendan on NO production and to evaluate the intracellular signalling pathway involved. EXPERIMENTAL APPROACH: In porcine coronary endothelial cells (CEC), the release of NO in response to levosimendan was examined in the presence and absence of N(omega)-nitro-L-arginine methyl ester, an adenylyl cyclase inhibitor, K(ATP) channel agonists and antagonists, and inhibitors of intracellular protein kinases. In addition, the role of Akt, ERK, p38 and eNOS was investigated through Western blot analysis. KEY RESULTS: Levosimendan caused a concentration-dependent and K(+)-related increase of NO production. This effect was amplified by the mitochondrial K(ATP) channel agonist, but not by the selective plasma membrane K(ATP) channel agonist. The response of CEC to levosimendan was prevented by the K(ATP) channel blockers, the adenylyl cyclase inhibitor and the Akt, ERK, p38 inhibitors. Western blot analysis showed that phosphorylation of the above kinases lead to eNOS activation. CONCLUSIONS AND IMPLICATIONS: In CEC levosimendan induced eNOS-dependent NO production through Akt, ERK and p38. This intracellular pathway is associated with the opening of mitochondrial K(ATP) channels and involves cAMP.

GABAA receptors expression pattern in rat brain following low pressure distension of the stomach.

It is known that gastric mechanoreceptor stimuli are widely integrated into neuronal circuits that involve visceral nuclei of hindbrain as well as several central brain areas. GABAergic neurons are widely represented in hindbrain nuclei controlling gastric motor functions, but limited information is available specifically about GABA(A)-responding neurons in brain visceral areas. The present investigation was designed to determine the central sensory neuronal pathways and their GABA(A)-alpha1 and -alpha3 receptor presenting neurons that respond to gastric mechanoreceptor stimulation within the entire rat brain. Low pressure gastric distension was used to deliver physiological mechanical stimuli in anesthetized rats, and different protocols of gastric distension were performed to mimic different stimulation patterns with and without sectioning vagal and/or splanchnic afferent nerves. Mapping of activated neurons was investigated using double colorimetric immunohistochemistry for GABA(A)-alpha1 or -alpha3 subunits and c-Fos. Following stomach distension, neurons expressing GABA(A) receptors with alpha1 or alpha3 subunits were detected. Low frequency gastric distension induced c-Fos expression in nucleus tractus solitarii (NTS) only, whereas in the high frequency gastric distension c-Fos positive nuclei were found in lateral reticular nucleus and in NTS in addition to some forebrain areas. In contrast, during the tonic-rapid gastric distension the neuronal activation was found in hindbrain, midbrain and forebrain areas. Moreover different protocols of gastric stimulation activated diverse patterns of neurons presenting GABA(A)-alpha1 or -alpha3 receptors within responding brain nuclei, which may indicate a probable functional significance of differential expression of GABA(A)-responding neurons. The same protocol of gastric distension performed in vagotomized rats has confirmed the primary role of the vagus in the response of activation of gastric brain areas, whereas neuronal input of splanchnic origins was shown to play an important role in modulating the mechanogastric response of brain areas.

The role of nitric oxide in the peripheral vasoconstriction caused by human placental lactogen in anaesthetized pigs.

Regional intra-arterial infusion of human placental lactogen in anaesthetized pigs has been shown to cause coronary, renal and iliac vasoconstriction by antagonizing the vasodilatory effects of beta2-adrenergic receptors. Since nitric oxide is known to modulate or mediate beta2-adrenergic effects, the present study was planned in the same experimental model to determine the role of nitric oxide in the above vascular responses to human placental lactogen. In eight pigs anaesthetized with sodium pentobarbitone, changes in anterior descending coronary, left renal and left internal iliac blood flow caused by intra-arterial infusion of human placental lactogen at constant heart rate and arterial blood pressure were assessed using electromagnetic flowmeters. Intra-arterial infusion of the human placental lactogen caused decreases in coronary, renal and iliac blood flow which, respectively, averaged 16.7, 8.1 and 12.2% of the baseline values. The role of nitric oxide in this response was studied in the same pigs by repeating the experiments, after measured blood flows had returned to baseline values, following intra-arterial administration of N(omega)-nitro-L-arginine methyl ester (L-NAME). The subsequent intra-arterial infusion of human placental lactogen did not cause any significant changes in measured blood flows, even when performed after reversing the increase in arterial blood pressure and coronary, renal and iliac resistance caused by L-NAME with continuous intravenous infusion of papaverine. These results indicate that the coronary, renal and iliac vasoconstriction caused by human placental lactogen, known to involve antagonism of beta2-adrenergic vasodilatory effects, was mediated by inhibition of nitric oxide release.

Human placental lactogen decreases regional blood flow in anesthetized pigs.

In 22 pigs anesthetized with sodium pentobarbitone, changes in blood flow caused by infusion of human placental lactogen into the left renal, external iliac, and anterior descending coronary arteries were assessed using electromagnetic flowmeters. In 17 pigs, infusion of human placental lactogen whilst keeping the heart rate and arterial pressure constant decreased coronary, renal and iliac flow. In 5 additional pigs, increasing the dose of human placental lactogen produced a dose-related decrease in regional blood flow. The mechanisms of the above response were studied in 15 of the 17 pigs by repeating the experiment of infusion. The human placental lactogen-induced decrease in regional blood flow was not affected by blockade of cholinergic receptors (5 pigs) or of alpha-adrenergic receptors (5 pigs), but it was abolished by blockade of beta2-adrenergic receptors (5 pigs). The present study showed that intra-arterial infusion of human placental lactogen primarily decreased coronary, renal and iliac blood flow. The mechanism of this response was shown to be due to the inhibition of a vasodilatory beta2-adrenergic receptor-mediated effect.

Hemodynamic effect of intracoronary administration of levosimendan in the anesthetized pig.

In this study the hemodynamic effects of intracoronary injection of levosimendan in anesthetized pigs and the mechanisms involved were examined. In 12 anesthetized pigs instrumented for measurement of heart rate (HR), aortic blood pressure (ABP), central venous pressure (CVP), left ventricular end-diastolic blood pressure, left ventricular contractility and relaxation, and mean coronary blood flow (CBF), levosimendan has been injected into the left anterior descending coronary artery at doses corresponding to the ones commonly used in clinics as bolus administration but adapted to the measured CBF. In a further 9 pigs levosimendan has been administered after the blockade of alpha and beta adrenoceptors, muscarinic receptors, and coronary nitric oxide synthase (NOS) to investigate the action mechanism of the drug. The intracoronary bolus administration of doses of levosimendan corresponding to 12 and 24 microg/kg in 10 minutes exerted, respectively, CBF increases of 26.3% and 41.3% of the control values in the absence of changes in the other hemodynamic variables. The blockade of the autonomic nervous system did not prevent the coronary vasodilation, which was, however, abolished by the NOS inhibition. The intracoronary administration of levosimendan exerts positive effects on myocardial blood supply without changes in ABP, HR, CVP, or in myocardial kinetics. The coronary effects of levosimendan are related to NO production.

The pattern of c-Fos immunoreactivity in the hindbrain of the rat following stomach distension.

It has been previously shown that the walls of the stomach contain vagal and splanchnic afferents, connected to low and high threshold (LT and HT) gastric receptors, that convey physiological and noxious information to areas of the hindbrain involved mainly in the control of gastrointestinal function. Because distension of the stomach also reflexly increases the sympathetic drive to the cardiovascular system, the present study was planned to examine the pattern of activation of all nuclei encountered throughout the hindbrain in response to gastric distension. In anaesthetized rats, the stimulus was controlled by employing different transmural pressures and frequencies of distension, and c-Fos immunohistochemistry was used to characterize neuronal activation. Low intensity stimulation induced c-Fos expression in the cranial part of nucleus of solitary tract (NTS), the nucleus ambiguus (NA), the lateral reticular area (LRt) and the ventrolateral medulla (RVL/CVL). At low frequency of stimulation c-Fos positive nuclei (p.n.) were found in NTS only. At high frequency of stimulation an increase in c-Fos immunoreactivity was found. High intensity stimulation induced c-Fos expression in area postrema (AP), the lateral vestibular nucleus (LVe) and the caudal part of the NTS. At low frequency, only the number of c-Fos p.n. was increased. Increasing the frequency of stimulation induced c-Fos expression in further nuclei such as the parabrachial nucleus (PBN), the inferior olive subnuclei (IOn), the oral part of spinal trigeminal nucleus (Sp5O) and locus coeruleus (LC). At higher frequencies c-Fos immunoreactivity decreased in NTS and LRt, disappeared in VLM and increased in NA. Thus stomach distension activated several neuronal excitatory and inhibitory circuits that are involved in the control of gastrointestinal function as well as in cardiovascular, respiratory and pain regulation. The differences in c-Fos immunoreactivity induced by changing the distension patterns suggested interactions between groups of vagal and splanchnic afferents.

The effects of insulin on mesenteric blood flow in anaesthetized pigs.

Infusion of insulin in anaesthetized pigs has been shown to cause an increase in renal blood flow and a decrease in coronary blood flow, which were the net result of a vasoconstriction involving sympathetic alpha-adrenoceptor-mediated mechanisms and of a local vasodilatation involving the endothelial release of nitric oxide. In the present study, the effect of insulin on superior mesenteric blood flow was examined in pentobarbitone-anaesthetized pigs at constant heart rate, aortic blood pressure, left ventricular contractility and blood levels of glucose and potassium. In 10 pigs, infusion of 0.004 IU kg(-1) min(-1) of insulin increased mesenteric flow. In five of these pigs, intravenous phentolamine enhanced the increase in mesenteric flow elicited by insulin, a response which was abolished by the subsequent injection of N(omega)-nitro-L-arginine methyl ester (L-NAME) into the mesenteric artery. In the remaining five pigs, infusion of insulin after intramesenteric injection of L-NAME caused a decrease in mesenteric flow. This response was abolished by the subsequent intravenous administration of phentolamine. The present study showed that infusion of insulin in anaesthetized pigs primarily caused a mesenteric vasodilatation, which was the net result of two opposite effects, namely a predominant vasodilatation mediated by the endothelial release of nitric oxide and a sympathetic vasoconstrictor mechanism mediated by alpha-adrenoceptors.

The effect of dehydroepiandrosterone on regional blood flow in prepubertal anaesthetized pigs.

Dehydroepiandrosterone has been implicated in vascular disease and its associated insulin resistance and hypertension, though little is known about its vascular effects. We have recently shown in prepubertal anaesthetized pigs that intravenous infusion of dehydroepiandrosterone caused coronary vasoconstriction through the inhibition of a vasodilatory beta-adrenergic receptor-mediated effect related to the release of nitric oxide. The present study was designed to investigate the effect of dehydroepiandrosterone on mesenteric, renal and iliac vascular beds. In prepubertal pigs of both sexes anaesthetized with sodium pentobarbitone, changes in superior mesenteric, left renal and left external iliac blood flow caused by intravenous infusion of dehydroepiandrosterone were assessed using electromagnetic flowmeters. Changes in heart rate and arterial blood pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 22 pigs, infusion of 1 mg h(-1) of dehydroepiandrosterone decreased mesenteric, renal and iliac blood flow. In a further 10 pigs, dose-response curves were obtained by graded increases in the infused dose of hormone between 0.03 and 4 mg h(-1). The mechanisms of the above response were studied in the 22 pigs by repeating the experiment after haemodynamic variables had returned to the control values observed before infusion. Blockade of alpha-adrenoceptors with intravenous phentolamine (five pigs) did not affect the dehydroepiandrosterone-induced mesenteric, renal and iliac vasoconstriction. This response was abolished by blockade of beta(2)-adrenoceptors with intravenous butoxamine (five pigs) and by blockade of mesenteric, renal and iliac nitric oxide synthase with intra-arterial administration of N(omega)-nitro-L-arginine methyl ester (seven pigs), even after reversing the increase in local vascular resistance caused by the two blocking agents with intravenous infusion of papaverine. In five pigs, the increase in measured blood flow caused by intravenous infusion of isoproterenol (isoprenaline) was significantly reduced by infusion of dehydroepiandrosterone. The present study showed that intravenous infusion of dehydroepiandrosterone primarily caused mesenteric, renal and iliac vasoconstriction. The mechanisms of this response were shown to be due to the inhibition of a vasodilatory beta(2)-adrenergic receptor-mediated effect, which possibly involved the release of nitric oxide.

Activation of the renin-angiotensin system contributes to the peripheral vasoconstriction reflexly caused by stomach distension in anaesthetized pigs.

Gastric distension in anaesthetized pigs reflexly elicits peripheral vasoconstriction and an increase in plasma renin activity (PRA), with vagal afferent and sympathetic efferent limbs. The aim of the present study was to quantify the contribution of the renin-angiotensin system to the peripheral vasoconstriction. In pigs anaesthetized with alpha-chloralose, changes in anterior descending coronary, superior mesenteric and left external iliac blood flow caused by stomach distension before and after blockade of angiotensin II receptors with losartan were assessed using electromagnetic flowmeters. Gastric distension for periods of 30 min was performed by injecting 0.8 l warm Ringer solution into balloons positioned within the viscus. Changes in heart rate and renal blood flow were prevented by atrial pacing and injection of phentolamine into the renal arteries, and changes in regional perfusion pressure and in baroreceptor activity were minimized by aortic constriction and denervation of the carotid sinuses. PRA was assessed by radioimmunoassay of angiotensin I. Before blockade of angiotensin II receptors by administration of losartan, stomach distension decreased coronary blood flow by 14.2 % in six pigs and mesenteric and iliac blood flow by 11 % and 17.3 %, respectively, in another six pigs. After administration of losartan, these decreases were significantly reduced to 7.4 %, 6.8 % and 8.7 %, respectively. The above responses were abolished by bilateral section of the subdiaphragmatic vagal nerves. These results show that the peripheral vasoconstriction reflexly caused by stomach distension was significantly contributed to by the concomitant activation of the renin-angiotensin system.

The effect of dehydroepiandrosterone on coronary blood flow in prepubertal anaesthetized pigs.

Extensive research suspecting an association between plasma levels of dehydroepiandrosterone and the risk of coronary heart disease has not been conclusive. The present study was designed to investigate the effect of dehydroepiandrosterone on the coronary circulation and to determine the mechanisms involved. In prepubertal pigs of both sexes anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary flow caused by intravenous infusion of dehydroepiandrosterone were assessed using an electromagnetic flowmeter. Changes in heart rate and arterial pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 20 pigs, infusion of 1 mg h-1 of dehydroepiandrosterone caused a decrease in coronary flow without affecting left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In a further eight pigs, a dose-response curve was obtained by graded increases in the infused dose of hormone between 0.03 and 4 mg h-1. The mechanisms of the above response were studied in the 20 pigs by repeating the experiment after haemodynamic variables had returned to the control values observed before infusion. Blockade of muscarinic cholinoceptors with intravenous atropine (five pigs) and of alpha-adrenoceptors with intravenous phentolamine (five pigs) did not affect the dehydroepiandrosterone-induced coronary vasoconstriction. This response was abolished by blockade of beta-adrenoceptors with intravenous propranolol (five pigs) and of coronary nitric oxide synthase with intracoronary injection of Nomega-nitro-L-arginine methyl ester (five pigs) even after reversing the increase in arterial pressure and coronary vascular resistance caused by the two blocking agents with intravenous infusion of papaverine. The present study showed that intravenous infusion of dehydroepiandrosterone primarily caused coronary vasoconstriction. The mechanisms of this response were shown to involve the inhibition of a vasodilatory beta-adrenergic receptor-mediated effect related to the release of nitric oxide.

The effect of testosterone on regional blood flow in prepubertal anaesthetized pigs.

This work was undertaken to study the effects of testosterone on the coronary, mesenteric, renal and iliac circulations and to determine the mechanisms of action involved. In prepubertal pigs of both sexes anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary, superior mesenteric, left renal and left external iliac blood flow caused by intra-arterial infusion of testosterone were assessed using electromagnetic flowmeters. Changes in heart rate and arterial blood pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 12 pigs, intra-arterial infusion of testosterone for 5 min to achieve a stable intra-arterial concentration of 1 microg l(-1) increased coronary, mesenteric, renal and iliac blood flow without affecting the maximum rate of change of left ventricular systolic pressure (left ventricular dP/dt(max)) and filling pressures of the heart. In a further five pigs, a concentration-response curve was obtained by graded increases in the intra-arterial concentration of the hormone between 0.125 and 8 microg l(-1). The mechanisms of these responses were studied in the 12 pigs by repeating the experiment after haemodynamic variables had returned to the control values before infusions. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the responses caused by intra-arterial infusion of testosterone performed to achieve a stable intra-arterial concentration of 1 microg l(-1). In the same pigs and in the remaining six pigs, the increases in coronary, mesenteric, renal and iliac blood flow caused by intra-arterial infusion of testosterone performed to achieve a stable intra-arterial concentration of 1 microg l(-1) were prevented by intra-arterial injection of N(omega)-nitro-L-arginine methyl ester. The present study shows that intra-arterial infusion of testosterone dilated coronary, mesenteric, renal and iliac circulations. The mechanism of this response involved the release of nitric oxide.

Effects of insulin on coronary blood flow in anesthetized pigs.

Insulin can influence the vasculature by a sympathetically mediated vasoconstriction and a vasodilatation; the latter effect predominates in the renal circulation of anesthetized pigs. We determined the effect of intravenous infusion of insulin on coronary blood flow in pentobarbitone-anesthetized pigs at constant heart rate, arterial pressure and blood levels of glucose and potassium. In 6 pigs, infusion of 0.004 IU kg(-1) min(-1) of insulin decreased coronary flow despite increasing left ventricular dP dT(max)(-1); when the latter was abolished by propranolol, the coronary flow response was augmented. The mechanisms of this response were examined in 22 pigs given propranolol. Phentolamine changed coronary flow response to an increase (6 pigs) and this was abolished by intracoronary injection of N(omega)-nitro-L-arginine methyl ester (L-NAME; 5 pigs). L-NAME augmented coronary flow response (6 pigs) and this was abolished by phentolamine (5 pigs). In 18 pigs given propranolol, three incremental doses of insulin caused graded coronary flow decreases whether L-NAME was given (6 pigs) or not (6 pigs) beforehand, and caused graded coronary flow increases after phentolamine (6 pigs). Thus insulin caused a coronary vasoconstriction mediated by sympathetic alpha-adrenergic effects and a vasodilatation related to the release of nitric oxide. The net effect was a coronary vasoconstriction.

Effect of progesterone on peripheral blood flow in prepubertal female anesthetized pigs.

This study was undertaken to determine the effects of progesterone on the peripheral circulation. In prepubertal female pigs anesthetized with sodium pentobarbitone, changes in the superior mesenteric, left renal and left external iliac flow caused by intravenous infusion of progesterone were assessed using electromagnetic flow meters. Changes in heart rate and arterial blood pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 20 pigs, infusion of 1 mg/kg of progesterone increased mesenteric, renal and iliac flow. In a further 4 pigs, the vasodilatory effects of the hormone were enhanced by graded increases in the dose between 1, 2 and 3 mg/kg. The mechanisms of these responses were studied in the 20 pigs by repeating the experiment after hemodynamic variables had returned to the control values before infusion. In 5 pigs, blockade of adrenergic receptors with propranolol and phentolamine did not affect the responses elicited by progesterone. The increases in mesenteric, renal and iliac flow to progesterone were prevented, respectively, by the injection of N(omega)-nitro-L-arginine methyl ester into the mesenteric (5 pigs), the renal (5 pigs) or the iliac artery (5 pigs). The present study shows that intravenous infusion of progesterone dilated mesenteric, renal and iliac circulations. The mechanism of this response involved the release of nitric oxide.

The role of activation of the renin-angiotensin system on the reflex regional vasoconstriction caused by distension of the uterus in anaesthetized pigs.

Distension of the uterus in anaesthetized pigs has been shown to cause a reflex regional vasoconstriction and an increase in plasma renin activity (PRA) through efferent sympathetic mechanisms which respectively involved alpha- and beta-adrenergic receptors. The present study was undertaken to determine the possible contribution of the activation of the renin-angiotensin system (RAS) to the observed regional vasoconstrictive responses to uterus distension. In pigs anaesthetized with alpha-chloralose, blood flow in the left circumflex or anterior descending coronary, superior mesenteric, left renal and left external iliac arteries was assessed using electromagnetic flowmeters. Distension of the uterus for periods of 30 min was performed by injecting 20 ml of warm Ringer solution into balloons positioned within the viscus before and after blockade of angiotensin II receptors with losartan. Changes in heart rate and renal blood flows were respectively prevented by atrial pacing and injection of phentolamine into the renal arteries. Changes in baroreceptors activity and in regional perfusion pressure were minimized by section of cervical vagus nerves and denervation of carotid sinuses and by an aortic constriction. PRA was assessed during the last minute of distension by radioimmunoassay of angiotensin 1. Before blockade of angiotensin II receptors, in six pigs, distension of the uterus decreased coronary blood flow by 19%, and in other six pigs, decreased mesenteric and iliac blood flows by 13.1% and 29.4% in the absence of changes in arterial perfusion pressure. After losartan, these decreases were significantly reduced to 11.7%, 8.2% and 18%. These results showed that the activation of the RAS significantly contributed to the alpha-adrenergic receptor-mediated regional vasoconstrictive responses reflexly elicited by distension of the uterus.

Mechanisms of the renal vasodilation caused by insulin in anesthetized pigs.

The present study was planned to determine the mechanisms involved in the renal vasodilation caused by insulin. Changes in flow caused by the intravenous infusion of 0.004 IU/kg/min of insulin at constant heart rate, aortic blood pressure, left ventricular contractility and blood levels of glucose and potassium in the left renal artery were assessed using an electromagnetic flowmeter. In ten pigs, infusion of insulin caused an increase in renal blood flow which averaged 12.8% of the control values. After hemodynamic variables had returned to control values, insulin infusion was repeated in five pigs following blockade of alpha-adrenergic receptors with injection of phentolamine into the renal artery and in the other five pigs following blockade of nitric oxide formation with injection in the same artery of Nomega-nitro-L-arginine methyl ester (L-NAME). After blockade of alpha-adrenergic receptors, insulin infusion caused an increase in renal blood flow which averaged 18.1% of the control values, being significantly enhanced with respect to the increase previously obtained in the same pigs. On the contrary, after blockade of nitric oxide formation insulin infusion caused a decrease in renal blood flow which averaged 6.5% of the control values. These responses were respectively abolished by the subsequent injection into the renal artery of L-NAME and phentolamine. The present study showed that the renal vasodilation caused by insulin in the anesthetized pig was the result of two opposite effects which involved a predominant vasodilation mediated by the release of nitric oxide from the endothelium and a sympathetic vasoconstrictor mechanism mediated by alpha-adrenergic receptors.

The effect of progesterone on coronary blood flow in anaesthesized pigs.

The present study was designed to investigate the effect of progesterone on the coronary circulation and to determine the mechanisms involved. In pigs anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary blood flow caused by intravenous infusion of progesterone at constant heart rate and arterial blood pressure were assessed using an electromagnetic flowmeter. In 14 pigs, infusion of 1 mg h(-1) of progesterone caused an increase in coronary blood flow without affecting left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In a further four pigs, this vasodilatory coronary effect was enhanced by graded increases in the dose of the hormone of between 1, 2 and 3 mg h(-1). The mechanisms of the above response were studied in the 14 pigs by repeating the experiment after haemodynamic variables had returned to the control values observed before infusion. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the coronary vasodilatation caused by progesterone. In the remaining eight pigs, this response was abolished by intracoronary injection of N(omega)-nitro-L-arginine methyl ester (L-NAME) even when performed after reversing the increase in arterial blood pressure and coronary vascular resistance caused by L-NAME with continuous intravenous infusion of papaverine. The present study showed that intravenous infusion of progesterone primarily caused coronary vasodilatation. The mechanism of this response was shown to involve the endothelial release of nitric oxide.