NEW CONCEPTS FOR THE ALDOSTERONE AND CORT ISOL REGULATION - ENDOCRINE, PARACRINE, AUTOCRINE AND NEUROCRINE INTERACTIONS

An increasing number of recent investigations reveal that the secretio n of aldosterone by the zona glomerulosa and, to a lesser extent, the secretion of cortisol by the zona fasciculata may in fact be under aut ocrine and paracrine control rather than regulated by peripheral influ ences. These hypotheses are based on (1) the evidence of a local produ ction of angiotensin II by the endogenous renin-angiotensin system, wh ich is expressed in zona glomerulosa cells ; (2) the importance of loc ally-induced stimulation by products of the vascular endothelium ; (3) the demonstration that local innervation stimulates the production of endogenous stimuli which in turn modulate the secretion of aldosteron e and cortisol ; and (4) the presence of chromaffin cells extending in to the cortex via medullary rays, which may account for the fact that many neurotransmitters and peptides of the medulla regulate steroid se cretion. This local regulation may provide an explanation on the one h and for the continued normal secretion of aldosterone in conditions wh ere peripheral stimulation by angiotensin II is altered, but also for the increases observed in aldosterone secretion, even when circulating angiotensin II concentrations remain unchanged.