REGULATION OF RENIN RELEASE BY CALCIUM AND AMMONIUM-IONS IN NORMAL MAN

The effect of infusing CaCl2, magnesium sulfate, sodium lactate and NH4Cl on renin secretion was compared to equimolar infusions of hypotonic and normal saline in Na-deplete normal subjects. Infusion of 75 meq of NH4Cl for 60 min in 6 normal, Na-deplete subjects suppressed plasma renin activity significantly (P < 0.01) from 4.4 .+-. 0.8 to 2.1 .+-. 0.2 ng/ml per h, an effect comparable to that produced by normal saline. Sodium lactate (75 meq Na/h) also significantly reduced renin levels at 20-30 min (P. < 0.01). Infusion of 1/3 normal saline (25 meq Na/h for 2 h) significantly reduced (P < 0.01) plasma renin activity (from control levels of 5.2 .+-. 0.8 to 3.1 .+-. 0.6 ng/ml per h at 90 min). Comparable infusions of 50 meq of magnesium sulfate over 2 h had no effect on renin release (4.6 .+-. 0.8 to 4.6 .+-. 0.9 ng/ml per h at 2 h), while infusion of CaCl2 produced an intermediate reduction (5.2 .+-. 1.2 to 3.7 .+-. 0.8 ng/ml per h at 2 h (P < 0.05). The observed effects of the H and Ca ions on suppressing renin release may be secondary to their known actions on renal Na excretion. Since the infusions of Ca and H ions both result in an increased delivery of Na to the distal segment of the nephron, the results may reflect the regulation of renin by the macula densa, a sensitive intrarenal sensor of renal tubular Na.