NONCHOLINERGIC NERVOUS CONTROL OF CATECHOLAMINE SECRETION FROM PERFUSED BOVINE ADRENAL-GLANDS

1. Field stimulation of adrenal nerves was used to study nervous contr ol of adrenal catecholamine secretion in isolated, retrogradely perfus ed, bovine adrenal glands. 2. Secretion of both adrenaline and noradre naline was maximal at 10 Hz. Secretion at 2 Hz was < 10 % of maximum. Stimulating with trains of pulses at ten times the average frequency f or 1 s out of every 10 s gave 2-fold greater secretion at 2 Hz average frequency, similar release at 5 Hz, and only half the secretion at 10 Hz, compared to continuous stimulation at the average frequency. 3. A t 10 Hz, adrenaline and noradrenaline secretion was virtually abolishe d by tetrodotoxin (1 mum), but was only reduced by 75 % by prolonged p erfusion with a combination of mecamylamine (5 mum) and atropine (l mu m). Mecamylamine and atropine completely abolished the secretory respo nse to 2 Hz stimulation. Tetrodotoxin had no significant effect on sec retion induced by perfusing glands with nicotine (5 mum), while mecamy lamine abolished this response. Mecamylamine and atropine had no effec t on secretion induced by K+ depolarization. 4. The secretion of adren aline and noradrenaline induced by 10 Hz stimulation was not inhibited by naloxone at either 1 or 30 mum. 5. The results suggest that bovine adrenal chromaffin cells, like those in the rat, receive a significan t non-cholinergic secretomotor innervation. In contrast to the rat, ho wever, the non-cholinergic component in the bovine adrenal is negligib le at low-frequency nerve stimulation and substantial at higher freque ncies, and is not antagonized by naloxone. The identity of the non-cho linergic transmitter remains to be determined.