Effects of standard oral glucose loading on the renin-angiotensin-aldosterone system and its relationship to circulating insulin.

Abstract

The effects of a standard oral glucose load (100 g) on plasma glucose, insulin, potassium, renin and aldosterone levels were investigated in 10 supine normal subjects (Group A). Responses of plasma glucose, insulin, potassium and aldosterone to glucose ingestion were evaluated further in 16 seated normal or borderline hypertensive subjects (Group B), studied in the untreated state as well as following renin-aldosterone activation by diuretic pre-treatment. In both groups, the increase in plasma glucose and insulin following glucose ingestion was accompanied by an acute decrease (p<0.01) in plasma potassium and aldosterone levels, which in Group A was associated with an increase (p<0.02) in plasma renin activity. In all subjects analyzed together, significant (p<0.005) correlations were noted between plasma aldosterone and potassium levels and between glucose-induced changes in these factors. In Group A, there were significant (p<0.001) correlations between glucose-induced changes in plasma aldosterone and renin values and between absolute aldosterone and renin levels in the glucose-loaded state. Plasma aldosterone or renin levels following glucose-load were unrelated to glucose or insulin values. These findings indicate that an oral standard glucose load causes acutely marked aldosterone suppression and mild but distinct renin stimulation. The glucose-induced inhibition of aldosterone secretion appears to depend on insulin-mediated changes in potassium metabolism and may be partly counteracted by concomitant renin activation.