Regional Hemodynamic Variables Research Articles

Systemic and regional haemodynamic responses to isoprenaline in conscious renal hypertensive rabbits.

1. Using the electromagnetic flow probe and the radioactive microsphere technique, systemic and regional haemodynamic variables were measured in conscious normotensive and hypertensive rabbits. The rabbits were made hypertensive by unilateral nephrectomy combined with cellophane-wrapping of the remaining kidney and systemic and regional haemodynamic effects of isoprenaline infusions (0.5 micrograms.kg-1 .min-1) were compared in the two groups of animals. 2. Isoprenaline evoked increases in heart rate and cardiac index while the total peripheral resistance decreased. In the hypertensive rabbits the effects were similar, except for a significantly more pronounced decrease in blood pressure. 3. Isoprenaline increased the fraction of the cardiac output delivered to the heart, skin and fat, at the expense of the fractions to the brain, stomach, small intestine, pancreas, liver and kidney(s) in both normotensive and hypertensive animals. Local peripheral resistance was decreased, most prominently, in the heart, skin, skeletal muscle and fat. 4. In the normotensive rabbits pretreatment with propranolol (4 mg.kg-1 infused in 1 h) effectively blocked the cardiovascular responses following isoprenaline infusion. 4. Since the systemic and regional haemodynamic effects of isoprenaline were not less (if anything, slightly more) in the hypertensive than in the normotensive rabbits, our results provide no evidence for subsensitivity of beta-adrenoceptors as a contributory factor in the development of hypertension in this model.

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.

The effect of ergotamine on tissue blood flow and the arteriovenous shunting of radioactive microspheres in the head.

1 The radioactive microsphere method was used to study the effects of ergotamine (5, 10 and 20 mug/kg, i.v.) on systemic and regional haemodynamic variables in chloralose-urethane anaesthetized cats. The influence of the drug was also studied on the number of 15 mum microspheres escaping entrapment in the head to emerge in the left external jugular vein.2 Ergotamine decreased the heart rate and cardiac output. Since arterial blood pressure remained unchanged, calculated total peripheral resistance increased.3 The regional distribution of cardiac output obtained with 15 mum microspheres agreed well with previous studies in cats where 25 mum spheres were used. The most pronounced difference was that in the present investigation more microspheres, apparently escaping through arteriovenous anastomoses (AVAs), were detected in the lungs than when larger spheres had been used.4 Coronary blood flow decreased, while uterine blood flow was increased by the drug. The microsphere content of the lungs, which receive the spheres not only via bronchial arteries but also via AVAs, was greatly reduced by all doses of ergotamine. Ergotamine did not influence tissue blood flow to other major organs such as the brain, kidneys, skin, liver, skeletal muscle or the gastrointestinal tract.5 In the 16 experiments, 0.46 +/- 0.05 (s.e. mean)% of the total microspheres injected (equivalent to 11.7 +/- 1.4% of microspheres detected in the left-side of the head) appeared within 2 min of microsphere injection into the left external jugular vein. The highest dose of ergotamine significantly reduced the shunting of the microspheres in the head.6 Since 15 mum microspheres are only likely to reach the lungs by passing into the venous circulation through large glomus-type AVAs, we conclude that ergotamine reduces the fraction of microspheres appearing in the lungs by causing strong vasoconstriction in the AVAs in the head.7 In conformity with the closure of head AVAs is the finding that ergotamine reduced the jugular venous Po(2) and O(2) saturation thereby increasing the A-V O(2) saturation difference.8 It is quite possible that decreased A-V shunting may be the prominent mechanism of the antimigraine action of the drug, since sudden opening of AVA's has been implicated in the pathophysiology of migraine-syndrome.