The use of radioactive microspheres to compare the effects of hydralazine, guanethidine and SK & F 24260 on the redistribution of cardiac output in anaesthetized rabbits

Regulation of aortic extracellular matrix synthesis via noradrenergic system and angiotensin II in juvenile rats

CONTEXT

Extracellular matrix (ECM) synthesis regulation by sympathetic nervous system (SNS) or angiotensin II (ANG II) was widely reported, but interaction between the two systems on ECM synthesis needs further investigation.

OBJECTIVE

We tested implication of SNS and ANG II on ECM synthesis in juvenile rat aorta.

MATERIALS AND METHODS

Sympathectomy with guanethidine (50 mg/kg, subcutaneous) and blockade of the ANG II AT1 receptors (AT1R) blocker with losartan (20 mg/kg/day in drinking water) were performed alone or in combination in rats. mRNA and protein synthesis of collagen and elastin were examined by Q-RT-PCR and immunoblotting.

RESULTS

Collagen type I and III mRNA were increased respectively by 62 and 43% after sympathectomy and decreased respectively by 31 and 60% after AT1R blockade. Combined treatment increased collagen type III by 36% but not collagen type I. The same tendency of collagen expression was observed at mRNA and protein levels after the three treatments. mRNA and protein level of elastin was decreased respectively by 63 and 39% and increased by 158 and 15% after losartan treatment. Combined treatment abrogates changes induced by single treatments.

DISCUSSION AND CONCLUSION

The two systems act as antagonists on ECM expression in the aorta and combined inhibition of the two systems prevents imbalance of mRNA and protein level of collagen I and elastin induced by single treatment. Combined inhibition of the two systems prevents deposit or excessive reduction of ECM and can more prevent cardiovascular disorders.

Differential control of collagen synthesis by the sympathetic and renin-angiotensin systems in the rat left ventricle

In the present study, we tested the hypothesis of the indirect (via the sympathetic nervous system (SNS)) and direct (via AT1 receptors) contributions of Angiotensin II (Ang II) on the synthesis of collagen types I and III in the left ventricle (LV) in vivo. Sympathectomy and blockade of the Ang II receptor AT1 were performed alone or in combination in normotensive rats. The mRNA and protein synthesis of collagen types I and III were examined by Q-RT-PCR and immunoblotting in the LV. Collagen types I and III mRNA were decreased respectively by 53% and 22% after sympathectomy and only collagen type I mRNA was increased by 52% after AT1 receptor blockade. mRNA was not changed for collagen type I but was decreased by 25% for collagen type III after double treatment. Only collagen protein type III was decreased after sympathectomy by 12%, but collagen proteins were increased respectively for types I and III by 145% and 52% after AT1 receptor blockade and by 45% and 60% after double treatment. Deducted interpretations from our experimental approach suggest that Ang II stimulates indirectly (via SNS) and inhibits directly (via AT1 receptors) the collagen type I at transcriptional and protein levels. For collagen type III, it stimulates indirectly the transcription and inhibited directly the protein level. Therefore, the Ang II regulates collagen synthesis differently through indirect and direct pathways.

Effect of hydralazine on the blood flow in tumors and normal tissues in rats

The effects of hydralazine on the blood flow in various normal tissues and R3230 Ac adenocarcinomas grown in different sites in rats were studied. Tumors were induced in the kidney, liver, and flank (s.c.) by injection of small pieces of tumors. Tumors were also induced in small intestine, cecum, and mesentery by intraperitoneal injection of finely minced tumor tissue. The blood flow and cardiac output were measured by radioactive microsphere method. An intra-arterial injection of hydralazine at 2.5-10.0 mg/kg significantly reduced the blood flow in most normal tissues, whereas it markedly increased the blood flow in muscle. The blood flow in the brain and testes remained unchanged. The blood flow in the tumors varied depending on the tumor site and was markedly smaller than the blood flow in the host normal tissues in which the tumors grew. The blood flow in tumors decreased significantly upon injection of hydralazine except in the tumors grown in the liver, where the blood flow remained unchanged. The hydralazine injection slightly increased cardiac output and markedly decreased blood pressure. It appeared that the decreases in blood flow by hydralazine in the tumors and most normal tissues were caused mainly by diversion of blood to muscle, resulting in a marked increase in the muscle blood flow without a similar concomitant increase in cardiac output. The results obtained in the present study indicate that hydralazine may be useful for improving the efficacy of hyperthermia or for enhancing the toxicity of hypoxic cell specific bioreductive drugs in treating the tumors grown in skeletal muscle. However, the significant decline in blood flow in most normal tissues may pose potential problems in the use of hydralazine to enhance the effect of hyperthermia or bioreductive drugs on tumors grown in normal tissues other than muscle.

The effect of hydralazine on blood flow and misonidazole toxicity in human tumour xenografts

The effect of post-irradiation hypoxia induced by 5 or 30 mg/kg hydralazine has been studied in three human tumour xenografts (two rectocolic adenocarcinomas and one melanoma) treated with two doses of misonidazole similar to those used in patients (0.1 and 0.2 mg/g). Only a small sensitization was detected using an in vitro colony assay. These results are in marked contrast to the results obtained with rodent tumours. This difference between human tumour xenografts and rodent tumours might be explained by differences in the reduction of tumour blood flow after hydralazine administration (5 and/or 10 mg/kg). Using the laser Doppler technique, the tumour blood flow reduction was 33% and 25% of the control for NA11 and HRT18 tumours, respectively. In contrast, hydralazine induced a 60-70% reduction in blood flow in the murine SCCVII tumour. Using the fluorescent marker Hoechst 33342, the reduction in perfusion was again more pronounced in the murine tumour as compared to the Na11 and HRT18 xenografts. The differences between human tumour xenografts and rodent tumours are not linked to the mouse strain used (nude versus C3H) nor to a tumour bed effect.

Effects of prostaglandins on esophageal blood flow

The physiologic mediators of blood flow to the esophagus are poorly understood. We have investigated the effects of prostaglandins on esophageal blood flow as they are known to alter blood flow in other organs of the gastrointestinal tract. Esophageal mucosal and muscularis blood flow (Q) were measured in New Zealand white rabbits treated intravenously with the prostaglandin analogs misoprostol (PGE1), 16,16-dmPGE2 (PGE2), and iloprost (PGI2, prostacyclin). Esophageal blood flow was measured three times in each rabbit using the radiolabeled microsphere technique after a 30-min continuous infusion of (1) saline (baseline), (2) a low dose, and (3) a high dose of each agent. Iloprost significantly increased esophageal mucosal (fourfold) and muscularis (twofold) blood flow. The other two PG analogs, misoprostol and 16,16-dmPGE2, had no significant effect on esophageal blood flow. Iloprost also significantly increased blood flow to the other organs of the gastrointestinal tract; however, the response was not as dramatic as in the esophageal mucosa. Prostacyclin may have a physiologic role in blood flow regulation to the esophagus and may be involved in pathophysiologic processes in the esophagus, such as increasing mucosal blood flow in response to injury.

In vivo pharmacological studies with SK&F 94836, a potent inotrope/vasodilator with a sustained duration of action

1. SK&F 94836 (racemate) was studied in vivo for its cardiovascular properties in cats and dogs. 2. In anaesthetized cats and dogs SK&F 94836 administered intravenously caused increases in left ventricular contractility and decreases in peripheral vascular resistance at similar doses, thus demonstrating the compound to be a mixed acting positive inotropic/vasodilator agent. 3. In conscious instrumented dogs SK&F 94836 was active via the oral as well as intravenous route. 4. The inodilator activity of SK&F 94836 in conscious and anaesthetized animals occurred in association with minimal changes in either blood pressure or heart rate. 5. Detailed studies carried out on anaesthetized cats indicated that SK&F 94836 caused a balanced dilatation of both resistance and capacitance blood vessels. 6. Haemodynamic studies in anaesthetized cats indicated that as a consequence of the inotropic/vasodilator actions, SK&F 94836 caused significant increases in cardiac output and stroke volume. 7. Detailed studies in anaesthetized dogs indicated that significant inodilator activity occurred in the absence of an increase in myocardial oxygen consumption. 8. The duration of action of SK&F 94836 was sustained following both i.v. and oral administration. 9. We conclude that SK&F 94836, as an orally active inotropic/vasodilator agent with a sustained duration in vivo, has potential utility in the treatment of congestive heart failure.

The effect of a xanthine derivative, 1-(5' oxohexyl)-3-methyl-7-propylxanthine (HWA 285), on heart performance and regional blood flow in dogs and rabbits

1. The effect of a new xanthine derivate 1-5' oxohexyl-3-methyl-7-propylxanthine (HWA 285) was studied on heart performance in dogs and rabbits and on regional blood flow in rabbits. 2. Heart performance (cardiac output and dP/dt max) in dogs was increased. Cardiac work (calculated as CO x mean BP) was not changed in dogs and did not change or was slightly decreased in rabbits. Heart rate was increased in dogs and unchanged in rabbits. 3. Blood pressure decreased slightly in dogs, and more markedly in rabbits. Total peripheral resistance was decreased in both species. 4. Regional blood flow (studied by use of 15 micrometers labelled microspheres) was increased in the heart, brain and skeletal muscle; the increase was dose-dependent in the range 0.3, 1.0 and 3.0 mg HWA 285 per kg intravenously. The highest dose produced a 2 fold decrease in the peripheral resistance in the brain, a 2.5 fold decrease in the heart and 4 fold decrease in skeletal muscle. 5. The drugs preferentially dilated small (7 to 10 micrometers) rather than larger (12 to 17 micrometers) arterioles; 9 micrometers microspheres were found in the outflowing blood after application of the drug, and the calculated blood flow increases were smaller, or absent, as compared with values obtained with 15 micrometer microspheres.

Haemodynamic effects of hydralazine at rest and during exercise in patients with chronic heart failure

The administration of vasodilator drugs has been shown to have beneficial effects at rest in patients with acute or chronic heart failure. To determine the efficacy of hydralazine during exercise, 10 severely symptomatic patients with chronic left ventricular failure from diffuse coronary disease or cardiomyopathy were studied at rest and during upright exercise on a bicycle ergometer. All patients were already receiving optimal treatment with digitalis and diuretics. At rest treatment with hydralazine resulted in a fall in both mean arterial and pulmonary wedge pressure. There was a 50 per cent reduction in systemic vascular resistance compared with pretreatment measurements and there was an equally impressive increase in stroke volume index. During exertion the changes noted at rest were sustained though occurred to a lesser degree; thus there was a 20 per cent fall in arterial resistance and a 20 per cent rise in stroke volume index compared with control. These findings show that hydralazine administration not only results in a beneficial effect on cardiac function at rest but that this effect is maintained during upright exercise in patients with impaired left ventricular function, thus providing further support for its use in the long-term management of such patients.

Comparison of the acute and chronic hemodynamic effects of captopril and guanethidine in spontaneously hypertensive rats

The present study compared the hemodynamic effects of captopril with those of guanethidine as well as with a combination of these two drugs in conscious male spontaneously hypertensive rats. Acutely, captopril or guanethidine or a combination of the two lowered arterial pressure to similar levels. The reduction in pressure with captopril alone or in combination with guanethidine, was due to a lowering of all organ vascular resistances. Guanethidine alone lowered pressure by reducing cardiac output. Chronically, captopril or guanethidine lowered arterial pressure to similar levels by reducing organ vascular resistances to comparable levels, particularly skeletal muscle, skin and splanchnic organs. Combination of these two drugs had an additive effect on the reduction of arterial pressure and organ vascular resistances. Since, chronically, the addition of guanethidine to captopril therapy enhanced rather than attenuated the hemodynamic changes induced by captopril, these drugs are probably acting by different mechanisms and the mechanisms of action of captopril does not require an intact sympathetic nervous system.

Effect of histamine on uterine vasculature in rats

The effects of histamine infusions on the rat uterine vasculature have been studied using the radioactive microsphere technique. Histamine produced a marked uterine vasodilatation which could be partly mimicked by infusion of either the H1-receptor agonist, 2-(2-aminoethyl)pyridine, or the H2-receptor agonist, 4-methyl-histamine. Histamine-induced uterine vasodilatation could only be reduced significantly by administration of a combination of the H1- and H2-receptor antagonists mepyramine and metiamide but not by either antagonist given alone. It was concluded that histamine-induced vasodilatation in the rat uterus is mediated by both H1- and H2-receptors.

MIC-II - a program for the determination of cardiac output, arterio-venous shunt and regional blood flow using the radioactive microsphere method

MIC-II is a versatile BASIC computer program designed to calculate the cardiac output, the arterio-venous shunt and the regional blood flow from data obtained by the radioactive microsphere method. The samples are measured in a gammaspectrometer with a multichannel pulse height analyzer and the data are recorded on tape. Up to 10 different nuclides may be used simultaneously, including tracers which are not bound to microspheres. The nuclides may have overlapping energy spectra. The analysis of the energy spectra is performed according to the matrix method. Standard samples, each containing one pure nuclide, are measured to obtained the overlap matrix. The unkown amounts of the nuclides in the samples are obtained by solving a system of simultaneous linear equations. Up to 100 organ samples may be taken in one experiment. Up to 10 different organ maps, containing a text label for each organ specimen, may be created, edited, modified and stored on tape for convenient identification of input and output. Numerous validity checks for imput and output make MIC-II easy to use, even for non-computer trained personel.

The influence of methysergide on 5-hydroxytryptamine-induced changes in regional distribution of blood flow

Systemic and regional haemodynamic variables were measured at the baseline and after saline or 5-HT infusions (5 microgram kg-1 min-1, i.v.) or methysergide injections (0.5 mg kg-1, i.v.). Cardiac output and its complete distribution were measured by the radioactive microsphere (15 micrometer diam) technique. Although 5-HT did not change the systemic variables, methysergide caused a moderate increase in systolic and mean blood pressure and heart rate. 5-HT caused a substantial increase in gastric and a moderate increase in cerebral and myocardial blood flow at the expense of that to the lungs (arteriovenous shunt + bronchial flows), kidneys and skin. While methysergide was able to reduce the vascular responses to 5-HT in stomach, skin, kidneys, heart, lungs and brain, the drug itself, like 5-HT, decreased the number of microspheres reaching the lungs. Since a large number of 15 micron microspheres can escape through the arteriovenous anastomoses to lodge in the lungs it seems likely that both 5-HT and methysergide can reduce the 'non-nutrient' flow through these anastomoses.

Regional and systemic haemodynamic changes evoked by 5-hydroxytryptamine in awake and anaesthetized rabbits

The radioactive microsphere method has been used to study the effects of the infusions of 5-hydroxytryptamine (5-HT) on cardiac output and its distribution in both pentobarbital-anaesthetized and conscious rabbits. Doses of 5 and 10 microgram kg-1 min-1 caused progressive decreases in diastolic pressure and total peripheral resistance in the anaesthetized rabbits but not in conscious ones. There was no significant effect on systolic pressure, cardiac output or heart rate. However, in spite of minimal systemic changes, in both groups 5-HT evoked increases in blood flow to the brain, heart and stomach at the expense of the kidneys, skin, liver (hepatic artery) and lungs (bronchial artery plus arteriovenous anastomotic flow). The 10 microgram kg-1 min-1 dose at 5-HT also increased blood flow and decreased resistance in the extracerebral tissues of the head. The significance of these findings in relation to the possible role of 5-HT in the migraine syndrome has been discussed.

Assessment of the coronary vasodilator action of SK&F 24260 in the dog

1. The effects of SK&F 24260 administered intravenously or intraduodenally on the coronary outflow, coronary arteriovenous oxygen difference (A-V O2), myocardial oxygen consumption (MVO2), systemic blood pressure, heart rate and atrioventricular (AV) conduction time were examined in open-chest dogs. 2. SK&F 24260 in doses of 0.3-10 microgram/kg, i.v., caused a dose-dependent increase in coronary sinus outflow, but the increase was smaller with 30 microgram/kg, i.v., than with 10 microgram/kg, i.v. 3. SK&F 24260 (0.3-30 microgram/kg, i.v.) decreased A-V O2 and MVO2 in a dose-dependent manner. 4. SK&F 24260 (0.3-30 microgram/kg, i.v.) decreased systemic blood pressure and heart rate, and increased AV conduction time. 5. Intraduodenal administration of SK&F 24260 (1 mg/kg) produced almost the same effects on coronary sinus outflow, A-V O2, MVO2, systemic blood pressure, heart rate and AV conduction time as did the intravenous administration of the compound (10 microgram/kg). 6. The property of SK&F 24260 to increase the coronary blood flow and to moderately decrease MVO2, systemic blood pressure and heart rate indicates that this agent is a potential antianginal drug.

Tissue blood flow and distribution of cardiac output in cats: changes caused by intravenous infusions of histamine and histamine receptor agonists

1 The effects of infusions of histamine on blood pressure, cardiac output, heart rate, total peripheral resistance, stroke volume and tissue blood flow have been determined in anaesthetized cats using radio-active microspheres to measure cardiac output and tissue blood flow.2 Histamine caused dose-dependent falls in blood pressure and total peripheral resistance over the dose-range 1 x 10(-8) to 3.3 x 10(-7) mol kg(-1) min(-1). Histamine had no effect on cardiac output, heart rate or stroke volume.3 Histamine caused vasodilatation in the heart and stomach, with increased blood flow through these organs, and in the small and large intestine where blood flow was maintained despite the falls in arterial blood pressure. Blood flow to the brain, kidneys, liver, adrenal glands, skeletal muscle, spleen and skin was reduced when arterial blood pressure fell. Vascular resistance increased in the skin and spleen, presumably due to reflex vasoconstriction when blood pressure fell.4 The selective H(1)-receptor agonist 2-(2-aminoethyl)pyridine lowered blood pressure and decreased total peripheral resistance but did not change cardiac output, heart rate or stroke volume. 2-(2-Aminoethyl)pyridine caused vasodilatation in the heart, small and large intestine and kidneys. Vascular resistance was increased in the spleen and skin.5 The selective H(2)-receptor agonist 4-methylhistamine also lowered blood pressure and decreased total peripheral resistance but did not change cardiac output, heart rate or stroke volume. 4-Methylhistamine caused vasodilatation in the heart, stomach, small and large intestines and skeletal muscle. Vascular resistance was increased in the skin.

Flux studies in perfused amphibian intestine [proceedings]

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Inflammation and the vascular changes due to thermal injury in rat hind paws

The vascular changes due to thermal injury have been determined in rat hind paws. In anaesthetized rats one hind paw has been injured by immersion in water for 30 seconds; temperature range 49-65 degrees C. Changes in blood flow, blood content and albumin content have been determined and compared with values from uninjured rats. The swelling caused by thermal injury was temperature-dependent, the higher temperatures caused the larger swellings. There were also temperature-dependent increases in blood flow to the injured paw and albumin content of the injured paw. Changes in blood content only occurred at the highest temperatures. Swelling, increased blood flow and albumin content could be detected within 1 minute of injury. The swelling and albumin content of the tissue then continued to increase gradually. The increase in blood flow was greatest 1 minute after injury and then stabilized at a flow some 4-5 times higher than normal paw flow. The method described can be used to measure vascular changes due to other inflammatory stimuli and could be applied to measure changes in other discreet areas.