Effects of guanethidine on the blood pressure response to splanchnic nerve stimulation in the rat: role of the adrenal medulla.

1. Splanchnic nerve stimulation provokes a larger increase in blood pressure in intact rats than in rats previously demedullated by means of expression of the adrenals in situ and adrenalectomy followed by adrenocortical grafting.2. Rats pretreated with guanethidine showed an attenuated albeit prolonged hypertensive response to splanchnic stimulation. Similar effects were exerted by guanethidine in rats demedullated by expression. In rats demedullated by grafting, smaller doses of guanethidine induced a more substantial depression of the blood pressure response without increasing its duration.3. It is concluded that inhibition of the peripheral sympathetic endings induced by guanethidine was partially compensated by the enhancement of the cardiovascular effects of the mediators released by the adrenal medulla and that demedullation by expression did not completely eliminate chromaffin tissue.