During fasting in guinea pigs a marked drop of ammonia excretion parallel to a drop in titratable alkalinity was observed. Feeding of cabbage increased ammonia excretion in excess of the titratable alkalinity. In acute studies in guinea pigs and rabbits after administration of saline, bicarbonate or hydrochloric acid, a depression of ammonia excretion was consistently observed whenever the urinary pH was close to neutrality, while in acid as well as in alkaline urines an increase in ammonia excretion occurred. When the urine flow was very low (<0.02 ml/min. in the guinea pig or <0.1 ml/ min. in the rabbit) excretion of ammonia appeared to be ‘flow-limited.’ If the ‘critical flow’ were exceeded, ammonia excretion was ‘production-limited.’

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The simultaneous renal clearances of rubidium and potassium were studied during the infusion of solutions of rubidium chloride into intact anesthetized dogs. The effects of prior loading with potassium were studied, as were also the responses to acute administration of acetazoleamide and meralluride. It was observed that the clearance of rubidium was usually slightly less than that of potassium and tended under most circumstances to vary in parallel with it. During infusion of RbCl the clearance of rubidium was usually less than the glomerular filtration rate and was independent of plasma level when the latter was varied from 1.0 to 5.0 mEq/l. However, net secretion of rubidium, as well as of potassium, could be demonstrated during periods of reduced filtration rate following administration of acetazoleamide. In the present experiments there was no evidence of interionic competition, but this possibility has not been critically tested. It is concluded that rubidium and potassium are probably handled by similar, if not identical, tubular mechanisms. The secretion of rubidium appears to be slower than that of potassium.

No abstract