Adrenergic receptors of adrenal medullary vasculature

The present study evaluates possible effects of adrenal catecholamines, released by splanchnic nerve stimulation, on adrenal medullary blood flow (MQ) and adrenal catecholamine secretion (CS). Twelve pentobarbital-anesthetized mongrel dogs were subjected to three identical splanchnic nerve stimulations (5 V, 20 Hz, for 3 min) at 30-min intervals, and MQ (radiolabeled microsphere technique) and CS (high-performance liquid chromatography) were measured before and during each nerve stimulation. Animals were assigned to one of three groups and administered either saline, pindolol (1 and 4 mg/kg), or prazosin (1 and 4 mg/kg) before the second and third nerve stimulation, respectively. In the saline control group, each nerve stimulation resulted in similar increases in MQ and CS. Pindolol attenuated nerve stimulation-induced increases in MQ and CS by 50%, but had no effect on medullary catecholamine concentration. Prazosin augmented nerve stimulation-induced MQ, CS, and medullary catecholamine concentration by 35%. These data suggest that adrenal adrenergic receptors modulate elicited CS and mediate changes in adrenal medullary vascular tone.