The effects of atrial natriuretic peptide and glucagon on proximal glomerulo-tubular balance in anaesthetized rats.

1. The renal actions of ANP (average dose 30 ng kg-1 min-1 and glucagon (50 ng kg-1 min-1) were compared using fractional lithium reabsorption as the index of proximal reabsorption in groups of seven rats. Doses were chosen to cause similar increases in glomerular filtration rate (GFR). Time controls were included. 2. Glucagon raised GFR 32% and absolute proximal reabsorption (APR) 26% producing 81% effective proximal glomerulo-tubular balance (GTB) which was not significantly different from the 100% expected for perfect GTB. ANP raised GFR 33% and APR 10% indicating only 30% effective GTB (P less than 0.01). This was a significantly different effect from glucagon (P less than 0.005). 3. Sodium output increased 10-fold with ANP and 3-fold with glucagon. Filtration fraction increased 33% (P less than 0.04) above the pre-treatment value with ANP but was unchanged with glucagon. Plasma renin concentration was suppressed similarly by each hormone (46 and 36%, P less than 0.05, compared with pre-treatment values). 4. Despite a change in peritubular physical factors favouring reabsorption, there was almost complete attenuation of the increase expected in APR with the ANP-induced increase in GFR. In contrast, a similar change in GFR with glucagon resulted in an almost parallel increase in APR demonstrating maintenance of proximal GTB. 5. It is concluded that in the anaesthetized rat, ANP but not glucagon profoundly inhibits the increase in proximal reabsorption that normally follows an increase in filtered load. Such an action would contribute to the more potent natriuretic activity of ANP compared with glucagon.