Adrenal medullary responses to stimulation of the splanchnic nerve in the conscious calf

Abstract

1. Right adrenal medullary and various cardiovascular responses to stimulation of the peripheral end of the right splanchnic nerve have been investigated in conscious calves, 2--5 weeks after birth. 2. The output of both adrenaline and noradrenaline was linearly related to stimulus frequency over the range 2.0--10.0 Hz, 2 1/2 min after stimulation was initiated. Peak outputs of both amines were obtained in response to stimulation at 15.0 Hz. 3. The output of adrenaline invariably exceeded that of noradrenaline, roughly in the proportion 3:2. At all frequencies tested between 7.0 and 40.0 Hz this difference was statistically significant (P less than 0.1). 4. Continuous stimulation at either 4.0 or 10.0 Hz produced a small but significant rise in the output of dopamine-beta-monooxygenase (DBH) activity from the right adrenal gland. Mean maximal outputs were obtained after 10 min; the levels were closely similar at both 4.0 and 10.0 Hz and could not be related to stimulus frequency or to the output of either adrenaline or noradrenaline. 5. The results are discussed in relation to perfusion studies in vitro and experiments in anaesthetized animals. It is concluded that the levels of DBH in adrenal effluent plasma is an unreliable index of catecholamine exocytosis in the conscious calf.