REACTIVITY OF THE ISOLATED-PERFUSED RAT TAIL VASCULAR BED

Isolated segments of the perfused rat tail artery display a high basal tone when compared to other isolated arteries such as the mesenteric and are suitable for the assay of vasopressor agents. However, the per fusion of this artery in the entire tail has not yet been used for fun ctional studies. The main purpose of the present study was to identify some aspects of the vascular reactivity of the rat tail vascular bed and validate this method to measure vascular reactivity. The tail seve red from the body was perfused with Krebs solution containing differen t Ca2+ concentrations at different flow rates. Rats were anesthetized with sodium pentobarbital (65 mg/kg) and heparinized (500 U). The tail artery was dissected near the tail insertion, cannulated and perfused with Krebs solution plus 30 mu M EDTA at 36 degrees C and 2.5 ml/min and the procedures were started after equilibration of the perfusion p ressure. In the first group a dose-response curve to phenylephrine (PE ) (0.5, 1, 2 and 5 mu g, bolus injection) was obtained at different fl ow rates (1.5, 2.5 and 3.5 ml/min). The mean perfusion pressure increa sed with flow as well as PE vasopressor responses. In a second group t he flow was changed(1.5, 2, 2.5, 3 and 3.5 mi/min) at different Ca2+ c oncentrations (0.62, 1.25, 2.5 and 3.75 mM) in the Krebs solution. Inc reasing Ca2+ concentrations did not alter the flow-pressure relationsh ip. In the third group a similar protocol was performed but the rat ta il vascular bed was perfused with Krebs solution containing PE(0.1 mu g/ml). There was an enhancement of the effect of PE with increasing ex ternal Ca2+ and flow. PE vasopressor responses increased after endothe lial damage with air and CHAPS, suggesting an endothelial modulation o f the tone of the rat tail vascular bed. These experiments validate th e perfusion of the rat tail vascular bed as a method to investigate va scular reactivity.