MESENTERIC ARCADE ARTERIES CONTRIBUTE SUBSTANTIALLY TO VASCULAR-RESISTANCE IN CONSCIOUS RATS

This paper describes a new technique for determining the intravascular pressure at the base of mesenteric arcades (arterial diameter less than 200 mum) in conscious, unrestrained, resting rats. using this technique we found that under Brietal anaesthesia, shortly after implanting the catheters, the pressure in the base of the arcades (P(mes)) was 86% of systemic pressure (P(sys)). After recovering from the anaesthetic, 6-8 h later, while P(sys) rose from average 79 to 114.5 mm Hg, P(mes)/P(sys) fell to 69%. By contrast, when anaesthesia was induced, although P(sys) immediately fell by 44%, P(mes)/P(sys) did not change. Acute pharmacological experiments in resting animals showed that the relative contribution of the arcade vessels to the peripheral resistance was variable. When serotonin was injected into the aorta, although P(sys) was unaffected, P(mes)/P(sys) fell from 67 to 27%. Conversely, with noradrenaline, P(sys) rose by 30%, but P(mes)/P(sys) remained unchanged. Angiotensin-II showed a third pattern, where P(sys) increased by 38%, but P(mes)/P(sys) rose transiently to 86%. The data suggest that in the rat mesenteric bed, under conscious conditions, the arcade arteries can contribute substantially to the control of peripheral resistance.