Effects of Various Hormones on the Pituitary-Adrenal Axis
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Most discussions of the mechanisms concerned with regulation of the pituitary-adrenal axis consider only components intrinsic to the system. Current understanding of the essential factors involved may be summarized briefly as follows. Stimulatory and inhibitory inputs from a variety of sources converge on centers in the basal hypothalamus. These signals result in stimulation (or inhibition) of corticotropin releasing factor (CRF) secretion from the median eminence. CRF is transported via the hypothalami co-hypophyseal portal system to the anterior pituitary gland and stimulates adrenocorticotropic hormone (ACTH) secretion; ACTH in turn, stimulates adrenal corticosteroid secretion. Corticosterone, the principle glucocorticoid hormone in the rat, is bound in plasma to corticosterone binding globulin (CBG); however, a fraction remains unbound in equilibrium with the bound portion. The liver clears circulating corticosteroids and metabolizes them, by reduction and conjugation, to inactive compounds which are excreted.
KeywordsReductase Activity Pineal Gland Corticotropin Release Factor Gonadal Hormone Estradiol Replacement
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