We have investigated the cellular mechanisms underlying the catecholamine response of the fetal sheep adrenal to hypoxia before and after the development of adrenal innervation. Adrenals were collected before (80-100 days gestation: n = 7) and after (135-146 days gestation: n = 10) development of innervation and retrogradely perfused with oxygenated Krebs bicarbonate buffer in vitro via the renal vein. Adrenal hypoxia was induced by perfusion with hypoxic Krebs buffer (pO2 = 46.7 +/- 2.4 mm Hg) for 30 min periods in the presence and absence of hexamethonium (500 microM), Ca2+ (2.5 mM), nifedipine (1 microM) and KCl (10 mM). Hypoxia stimulated an increase (P < 0.001) in the output of noradrenaline at 80-100 days (3 min pre hypoxia, 0.18 +/- 0.07 nmol/3 min; 20 min hypoxia, 0.74 +/- 0.22 nmol/3 min) and at 135-146 days (3 min pre hypoxia, 0.53 +/- 0.20 nmol/3 min; 20 min hypoxia, 1.71 +/- 0.85 nmol/3 min). Adrenaline output was also higher (P < 0.001) than basal values (80-100 days, 0.11 +/- 0.06 nmol/3 min; 135-146 days, 0.53 +/- 0.15 nmol/3 min) after 20 min hypoxia (0.41 +/- 0.20 nmol/3 min and 1.35 +/- 0.56 nmol/3 min respectively). The catecholamine responses to hypoxia were abolished by removal of Ca2+ from the adrenal perfusate. There was a reduction (P < 0.05) in the catecholamine secretory response to hypoxia in the presence of nifedipine. Noradrenaline output decreased from 4.33 +/- 0.84 nmol/30 min to 0.16 +/- 0.49 nmol/30 min and adrenaline output decreased from 3.16 +/- 1.66 nmol/30 min to -0.01 +/- 0.24 nmol/30 min in the presence of nifedipine. The fetal adrenal secretes catecholamines by a direct or non-neurogenic mechanism in response to hypoxia. This secretory response is dependent on the activation of voltage sensitive Ca2+ channels in the chromaffin cell membrane.