Adrenergic responses in canine cutaneous vasculature during acute hemorrhagic hypotension

The purpose of this study was to determine the effect of acute hemorrhage on vascular responses to sympathetic nerve stimulation and norepinephrine. The experiments were carried out with sodium pentobarbital anesthesia. The preparation employed was the dog's hindpaw perfused at constant blood flow. Changes in vascular resistance in the paw were indicated by changes in perfusion pressure. Changes in perfusion pressure elicited by sympathetic nerve stimulation and intra-arterially administered norepinephrine were determined before and after hemorrhage of 15 ml/kg in normal and acutely nephrectomized animals. The response to sympathetic stimulation was increased by about 50% in normal but not in nephrectomized dogs, whereas the response to a low dose of norepinephrine (0.5-1 mug) was not significantly changed in either group of animals. In additional experiments in which the plasma renin level was measured, the potentiation of responses to sympathetic stimulation and a high dose of norepinephrine (2 mug) occurred at the time that the renin level was increased by hemorrhage. These results indicate that the level of circulating angiotensin attained after hemorrhage may facilitate vasoconstrictor responses to adrenergic stimuli.