Effect of glucagon on magnesium renal reabsorption in the rat

The recent localization, in the rat, of a glucagon-sensitive adenylate cyclase in these segments where the bulk of calcium and magnesium is reabsorbed suggests an effect of this hormone on calcium and magnesium tubular transport. Renal tubular handling of calcium and magnesium as well as of sodium and phosphate was therefore studied by clearance methods in anesthetized rats, either intact or thyroparathyroidectomized (TPTX), infused with glucagon at a rate of 25 ng.min-1/100 g bw just after a priming dose of 2.5 micrograms. The hormone administration resulted in a significant decrease of absolute and fractional magnesium excretion (from 16.3 +/- 0.7% to 9.7 +/- 1.7% for intact rats and from 20.9 +/- 1.8% to 6.9 +/- 1.0% for TPTX rats), associated with the well-known increase in sodium and phosphate fractional excretion. Moreover, a small and transient decrease of calcium fractional excretion was observed concomitantly with a decrease of plasma calcium concentration. The significant increase in magnesium absolute reabsorption, observed whatever the filtered load and independently of PTH and calcitonin, may be an evidence for a direct tubular effect of glucagon.