The effects of urea and hydrochlorothiazide on the renal functions of rat and domestic fowl.

1. Rats and domestic fowls were given by stomach tube water, urea and hydrochlorothiazide, alone or in combination, in the following amounts: water, 5 ml./100 g; urea, 4 ml. of 1.5% solution + 1 ml. water/100 g; hydrochlorothiazide, 4 ml. of 1.5% urea solution + 1 ml. containing 0.1 mg hydrochlorothiazide/100 g.2. The onset of water diuresis was faster in the fowl than in the rat. It was accompanied by a lower rate of excretion of osmotically active solutes in the former than in the latter. The rate of excretion of creatinine in rats was fourfold that in birds.3. After urea administration, the amount of urea excreted by the fowl was about one fifth that excreted by the rats. While urea produced in rats an osmotic diuresis, with enhanced excretion of osmotically active solutes, in birds it had little effect on either urine flow or solutes excretion.4. Administration of hydrochlorothiazide in rats produced a moderate antidiuresis accompanied by a marked increased excretion of Na and K; in birds, a small increase in the excretion of Na and K but no effect on the urine flow.5. The differences observed between rats and birds can be attributed to the poor development of filtration rate and the absence of a well developed counter-current system in the fowl.