This project is designed to define the role of mechanisms other than ACTH in the control of adrenal corticosteroid secretion. Plasma ACTH-like bioactivity that increases after hemorrhage in awake dogs will be characterized using gel filtration and high performance liquid chromatography. Bioactive ACTH, measured using a rat adrenocortical cell assay, will be compared to immunoreactive ACTH. Affinity chromatography prior to bioassay will separate ACTH from other ACTH-like factors. To assess the requirement for an increase of ACTH or other pituitary factors, the cortisol secretory response to hemorrhage will be measured in hypophysectomized awake dogs given infusions of ACTH. Control mechanisms for the release of non-ACTH factors will be defined by determining responses to graded hemorrhage, to corticotropin-releasing factor and to steroids. The role of sympathetic neural input on the adrenal response to ACTH will be assessed in anesthetized, hypophysectomized dogs receiving infusions of ACTH by measuring cortisol secretory responses to electrical stimulation of the splanchnic nerve. Direct neural effects on the adrenal cell will be distinguished from effects on adrenal blood flow by monitoring the distribution of flow using non-radioactive microspheres. Episodic cortisol secretion observed under basal conditions will be examined in awake dogs after hypophysectomy. Also, in dogs with bilateral adrenal venous cannula, synchronicity and periodicity of adrenal secretion will be determined using cross-correlation and spectral analysis; effects of unilateral and bilateral adrenal denervation will be examined. To determine how changes in plasma ACTH, in sympathetic neural input and in adrenal blood flow that occur after acoustic startle interact to mediate the cortisol secretory responses, dogs will be exposed to acoustic startle after hypophysectomy or after adrenal denervation. Alteration of the distribution of adrenal blood flow following acoustic startle will be measured. The results of these studies will elucidate the effectiveness of changes in non-ACTH humoral factors, in sympathetic neural input or in adrenal blood flow to influence the cortisol secretory response to ACTH under different physiological conditions. This information, by establishing a more complete view of stimulus-specific modulation of adrenal corticosteroid secretion, will offer a new perspective to the study and treatment of ACTH-independent adrenocortical disease.
