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

An increasing number of recent investigations reveal that the secretion of aldosterone by the zona glomerulosa and, to a lesser extent, the secretion of cortisol by the zona fasciculata may in fact be under autocrine and paracrine control rather than regulated by peripheral influences. These hypotheses are based on (1) the evidence of a local production of angiotensin II by the endogenous renin-angiotensin system, which is expressed in zona glomerulosa cells ; (2) the importance of locally-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 aldosterone and cortisol ; and (4) the presence of chromaffin cells extending into the cortex via medullary rays, which may account for the fact that many neurotransmitters and peptides of the medulla regulate steroid secretion. This local regulation may provide an explanation on the one hand for the continued normal secretion of aldosterone in conditions where peripheral stimulation by angiotensin II is altered, but also for the increases observed in aldosterone secretion, even when circulating angiotensin II concentrations remain unchanged.