Autonomic regulation of cutaneous vascular resistance in the bullfrog Rana catesbeiana.

To gain a better understanding of the regulation of cutaneous blood flow in the bullfrog, the vascular innervation, vasoactivity and adrenoceptor types of the cutaneous vasculature were investigated using a pump-perfused skin preparation. Stimulation of cranial nerve I, the vagal ganglion, sympathetic ganglion 1 and sometimes sympathetic ganglion 2 caused cutaneous vascular resistance (CVR) to increase. Stimulation of cranial nerve IX and spinal nerves 1 and 2 had no effect on CVR. The response to stimulation of sympathetic ganglion 1 was antagonized by phentolamine but not by atropine. Phentolamine, atropine and alpha,beta-methylene ATP had no effect on the response to vagal stimulation. Both epinephrine (EPI) and norepinephrine (NE) increased CVR, with EPI being more potent than NE. The minimum concentrations of EPI and NE required for a significant change in CVR were much higher than plasma catecholamine levels reported for resting bullfrogs. Phentolamine antagonized, but propranolol had no effect on, the responses to the catecholamines. Isoproterenol caused small decreases in CVR which were abolished by propranolol. Acetylcholine was a weak vasodilator. The results indicate that the cutaneous vasculature has two types of vasomotor nerves: sympathetic nerves that are probably adrenergic, and other nerves that are non-adrenergic/non-cholinergic and which do not use ATP as a transmitter. Although catecholamines are vasoactive, the sensitivity of the cutaneous vasculature to EPI and NE is probably too low to allow a direct regulatory role of these hormones on CVR. There is no evidence for cholinergic regulation of CVR. Both alpha- and beta-adrenoceptors are present in the cutaneous vasculature. alpha-Adrenoceptors mediate the constrictor responses to sympathetic nerve stimulation and catecholamine administration. It is unlikely that beta-adrenoceptors play a significant role in regulating CVR.