Influence of potassium, sodium, calcium, perfusion pressure, and isoprenaline on renin release induced by high concentrations of magnesium.

1. These studies were conducted on isolated, perfused rat kidneys to determine the mechanism through which high concentrations of extracellular Mg (20mM) stimulated renin release. 2. Raising K concentrations in the perfusion fluid from 5 to 50 mM, and raising renal perfusion pressure from 100 to 150 mmHg inhibited the renin release induced by 20 mM-Mg. The response was reversible. 3. Renin release induced by low renal perfusion pressure (50 mmHg) or isoprenaline (2.43 microM) was unaffected by 20 mM-Mg. However, this release was augmented when 5 mM-Ca was added in conjunction with 20 mM-Mg. 4. In medium containing 20 mM-Mg, lowering Na concentration from 145 to 100 mM augmented the renin release induced by low perfusion pressure and isoprenaline. Further lowering Na to 25 mM had no additional effect. 5. It is concluded that 20 mM-Mg activates renin release by a mechanism which involves hyperpolarization of the juxtaglomerular cell membrane and an associated decrease in cytoplasmic Ca. Such a mechanism might be coupled to a Mg-Na exchange pump.