Direct recording of postcapillary resistance in cat skeletal muscle: measurement in the presence of humoral stimuli.

A procedure involving the parallel perfusion of deep veins in a cat shank preparation with endogenous blood and a constant volume of dextran solution has been devised. The dextran is supplied to these deep veins via superficial and communicator veins (venae communicantes). With this method it is possible to record dynamic changes in the resistance of the deep veins (postcapillary resistance) in response to intraarterial administration of vasoactive agents into the vascular bed of the shank. Data are presented which indicate that the number of deep veins involved in the changes in venous resistance is equivalent to 67% of the total capacity of the vascular bed of the shank. It is shown that the increase in venous perfusion pressure caused by infusion of noradrenaline into the vascular bed of the shank is essentially equivalent to the increase in mean capillary pressure as determined isovolumetrically. With this new method it is demonstrated for the first time that angiotensin II causes constriction of the deep veins of the shank and that isoproterenol causes dose-dependent dilatatory reactions in the veins within the muscle preparation.