FACTORS CONTROLLING STEROID-BIOSYNTHESIS IN THE ZONA GLOMERULOSA OF THE ADRENAL

The biosynthesis of aldosterone in the adrenal zona glomerulosa is influenced by a number of factors of which the main physiological regulator is the octapeptide, angiotensin II (AII). Sodium restriction increases plasma aldosterone, adrenal glomerulosa AII receptors and the activity of enzymes of the early and late aldosterone biosynthetic pathway. The effects of sodium restriction are mimicked by prolonged administration of low doses of AII, and prevented by blockade of AII formation using converting enzyme inhibitors, indicating that the effects of sodium restriction are mediated by AII. However, the adrenal glomerulotrophic actions of AII are impaired in rats on high sodium diet indicating that other factors are modulating the effects of AII in these conditions. A number of factors are known to influence aldosterone secretion, several of which have been shown to preferentially modulate the effect of AII. While the stimulatory effect of AII is potentiated by serotonin or increases in extracellular potassium, it is inhibited by dopamine, somatostatin and atrial natriuretic peptide. Future investigations will be important to understand the relative role of the individual regulators in the physiological control of adrenal sensitivity to AII, and how activation of various intracellular messenger systems results in changes in activity of the enzymes of the aldosterone biosynthetic pathway.