ABSTRACT IBN-9728132 PI = ENGELAND, William C. Secretion of steroid hormones by the adrenal cortex is required to maintain whole body homeostasis; that is, the ability to maintain blood pressure and volume, carbohydrate, protein and fat metabolism and immune and nervous system function within normal limits is dependent on adrenocortical hormones. The primary goal of the project is to understand the role of adrenal innervation in the control of steroid secretion. The hypothesis to be tested is that under non- stress conditions when reduced steroid secretion is required, neural activity is inhibitory, whereas during stress conditions when elevated steroid secretion is necessary, neural activity is excitatory. The capacity for innervation to produce both inhibitory and excitatory effects suggests that neural input must be encoded differentially; encoding could be dependent on the neurotransmitter released or on the target affected. Experiments are designed: (1) to define the neurotransmitters that modulate non-stress and stress- induced secretion of adrenal corticosteroids and (2) to elucidate the adrenal site of neurotransmitter action. Rats will undergo immunological, surgical, or pharmacological sympathectomies to remove selectively adrenal neurotransmitter systems. The effect of adrenal denervation on non-stress steroid secretion will be assessed using in vivo adrenal microdialysis, a technique developed to measure adrenal secretion in awake animals. It is proposed that circadian variation in non-stress steroidogenesis which is reflected by differences in episodic secretion is regulated in part by the inhibitory effects of innervation. Episodic corticosterone secretion will be assessed by time series analysis and diurnal variations in adrenal sensitivity to ACTH will be determined. It is proposed that adrenal neural elements interact positively with ACTH to mediate acute stress-induced increases in steroid secretio n. Neural input could act directly at the adrenal cell to affect steroidogenesis or act indirectly by changing adrenal blood flow. Experiments will assess the interaction between stress and ACTH and characterize the neurotransmitter system(s) mediating facilitatory control. Experiments will also measure adrenal blood flow during stress using fluorescent microspheres and define the neurotransmitters that mediate stress-induced changes. Neurotransmitter-specific innervation will be monitored using immunofluorescence histochemistry and quantitated by radioimmunoassay. Effects on specific steroidogenic enzymes will be assessed by measuring gene expression using in situ hybridization and RNAse protection assay, by measuring enzyme content using western analysis and by quantifying enzyme activity in adrenal cells. Results of these experiments should delineate the role of autonomic nerves as an extra-ACTH mechanism in the control of adrenal corticosteroid secretion and define the neurotransmitter systems involved. Understanding the nature of the this unique neural-endocrine interaction will provide a new perspective on physiological regulation of corticosteroid secretion.
