Depression by local cooling of 3H-norepinephrine release evoked by nerve stimulation in cutaneous veins

Experiments were performed to investigate whether local cooling facilitates adrenergic neurotransmission in the cutaneous vein of the dog. Helical strips of saphenous veins were incubated with 3H-norepinephrine and mounted for isometric tension recording and superfusion. The superfusate was collected for measurement of total radioactivity or for chromatographic analysis. Electrical stimulation (2Hz) caused contraction and augmented the efflux of 3H-norepinephrine and metabolites. Cooling (from 37 to 28 degrees C) imposed during electrical stimulation caused a further increase in tension, but decreased the amount of 3H-norepinephrine and metabolites overflowing into the superfusate. These experiments demonstrate that the potentiating effect of cooling on the response of cutaneous veins to sympathetic nerve stimulation is not associated with facilitation of adrenergic neurotransmission. It is probably due to an altered sensitivity of the vascular smooth muscle to the transmitter.