![]() In addition, several studies indicate that cortical secretory activity can be modulated by changes in blood flow. However, neural elements are found in close proximity to cortical vessels, and the cortical vasculature responds to changes in O2 tension and to a number of pharmacological agents. In contrast to medulla, cortical secretory activity is not associated with altered blood flow. However, morphological confirmation of vascular innervation is not available, and effects of released chromaffin cell products on adjacent vessels are also possible. The two responses can be pharmacologically dissociated, suggesting possible direct innervation of adrenal vessels. Both catecholamine secretion and medullary vasodilation are neurally mediated. Coupling of blood flow with secretion is particularly apparent in medulla, where severalfold increases in blood flow occur during catecholamine secretion elicited by hemorrhage, hypoxia, and splanchnic nerve stimulation. ![]() ![]() It is likely that abundant blood flow serves to speed entry of adrenal secretory products into the systemic circulation. ![]() ![]() With the introduction of a radiolabeled microsphere methodology, which permitted independent measurement of blood flow to the two regions, it became apparent that medulla and cortex regulate blood flow independently and that both regions receive levels of blood flow considerably in excess of that required for nutrient delivery. Before 1986, little was known concerning regulation of blood flow to adrenal medulla and cortex. ![]()
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