Splanchnicotomy increases adrenal sensitivity to ACTH in nonstressed rats

Awake rats demonstrate an ultradian rhythm in adrenal secretion of corticosterone. Splanchnic denervation in unstressed rats increases the frequency of corticosterone pulses, revealing an inhibitory function of adrenal innervation. In contrast, one day after surgical stress, adrenal. denervation reduces adrenal pulsatility, suggesting a stimulatory function of adrenal innervation. To test whether neural modulation of pulsatile secretion was due to a direct effect of the splanchnic nerve an adrenal sensitivity to adrenocorticotropic hormone (ACTH), rats treated with dexamethasone were administered repetitive pulses of ACTH, and the amplitude of corticosterone responses was determined. Intact or control (C) and splanchnicotomized (SPLNX) rats were tested at 2 or 5 days after surgery. Five days after surgery, adrenal responsiveness in C animals was reduced compared with SPLNX animals. However, no differences were seen 2 days after surgery. To determine whether the reduction in adrenal responsiveness involved a cellular or organ level mechanism, dispersed adrenal cortical, cells isolated from intact or denervated adrenal glands were stimulated with ACTH, and corticosterone secretion was determined. Consistent with in vivo results, denervation increased the responsiveness of adrenal cells obtained 5, but not 1 or 2, days after surgery. These findings support a neurally mediated inhibition of adrenal sensitivity to ACTH in unstressed rats.