Renal actions of dihydroergocristine and of phentolamine in anaesthetized cats.

1. Comparison has been made of the effects of dihydroergocristine (DCS) and phentolamine mesylate (phentolamine) on cardiac and respiratory rates, systemic arterial pressure, renal clearances of creatinine (C(Cr)) and of p-amino-hippuric acid (C(PAH)) and on the secretion of Na and K, in cats under chloralose anaesthesia.2. Phentolamine antagonized vasomotor tone and the pressor effect of circulating noradrenaline to comparable extent. The extent of reduction in urine flow, C(Cr), C(PAH) and Na excretion correlated with the fall in mean arterial pressure. Innervated and denervated kidneys responded similarly. Cardiac and respiratory rates rose slightly as arterial pressure fell.3. DCS, 10 to 20 mug/kg per min, did not reduce vasomotor tone, markedly reduced the pressor effect of exogenous noradrenaline, caused bradycardia and respiratory slowing but had little or no effect on renal function.4. DCS, 30 to 40 mug/kg per min, lowered mean arterial pressure by 15-25 mm Hg, decreased C(PAH) but not C(Cr), so raising the filtration fraction and caused a small reduction in urine flow and in Na excretion. Innervated and acutely denervated kidneys responded similarly.5. DCS, 30 to 40 mug/kg per min, raised mean arterial pressure, decreased C(PAH), urine flow and Na excretion but did not alter C(Cr) in animals pretreated with full alpha-adrenergic blocking doses of phentolamine.6. DCS, 30 to 40 mug/kg per min, increased the rate of secretion of sympathetic amines from the adrenal medulla and increased the concentration of renin in renal venous blood.7. Isolated kidneys perfused at constant pressure from pump-oxygenator circuits and in saline diuresis responded to DCS (15-17 mug/120 ml. blood) by diuresis and natriuresis and by a rise in the rate of secretion of renin. Higher concentrations of DCS (125-250 mug/120 ml.) were without effect on renal function and did not influence renin secretion.8. The renal effects of full alpha-adrenergic blocking doses of DCS and of phentolamine were comparable, in the whole animal.9. The evidence indicates that the release of noradrenaline by DCS 30-40 mug/kg per min from nerve terminals supplying the juxtaglomerular apparatus may have caused the enhancement of renin secretion.