|dc.description.abstract||1. Observations were made on conscious dogs of the effect of oxytocin and of arginine-vand lysine-vasopressins on the rate of urine flow, on the excretion rate of sodium and potassium, and on the clearance rate of diodone and creatinine Both during water-diuresis and at a low rate of urine flow. Vasopressins were used in antidiuretic doses and oxytocin in doses 20 to 25 times greater than the antidiuretic dose of lysine-vasopressin.
2. When injected intravenously at the height diuresis, 2 mU of arginine-vasopressin produced the maximum anti-diuretic while 7 mU of lysine-vasopressin were needed to obtain an equivalent anti-diuretic. The antidiuretic action of arginine-vasopressin lasted longer than that of lysine-vasopressin.
3. Both arginine-vasopressin and lysine-vasopressin, when given as single injections in antidiuretic doses, produced a dear increase in Na excretion during water-diuresis; while lysino-vasopreasin produced also an increase In K excretion, arginine-vasopressin had little or no effect on it. Given as an Intravenous infusion during water-diuresis, lysine-vasopressin greatly increased the excretion both Na K. At a low
rate of urine flow, given as a single injection or as an infusion, either vasopressin had little effect
on the excretion of Na or K.
4. Oxytocin, given as a single intravenous injection, had little effect on the excretion of Na or K during water-diuresis. But at a low rate of urine flow, oxytocin produced a marked increase in the excretion of Na which was maintained for 30-40 mnutes; its effect on K excretion was gather negligible.
5. Simultaneous administration of oxytocin and arginine-vasopressin and of oxytocin and
lysine-vasopressin, given as single injections during water-diuresis, produced a greater increase in Na excretion than that following either vasopressin alone; a clear increase in K excretion was observed following the injection of oxytocin together with either vasopressin. At a low rate of urine flow, the effect of the simultaneous administration of oxytocin and either vasopressin on Na excretion was less than that following oxytocin alone; the effect on K excretion was not significant.
6. Measurements of diodone and creatinine clearances showed that during water-diuresis single inyravenous
injection of 150 nU Oxytocin (7-8 nU/Eg) was followed by a period when the clearance of diodone increased by 50-80 per cent and that of creatinine by 25-50 per cent. Arginine-vasopressin, given in antidiuretic doses (2 mU) together with 150 mU oxytocin, almost completely prevented the expected action of oxytocin on diodone clearance; but lysine-vasopressin in antidiuretic doses (7 mU) had only a slight effect. However, a bigger dose (10.5 mU) of lysine-vasopressin could prevent the expected action of oxytocin (150 mU) on diodone clearance. Either vasopressin had. only a slight effect on creatinine clearance.
7. The results were discussed; and a comparison between the activities of arginine-and lysine-vasopressins has been drawn with respect to their effect on urine flow, on Na and K excretion, and on the clearances of diodone and creatinine. The varying differences in the potencies of the two vasopressins observed suggest that the chemical processes involved in the biological activities of the two substances are not probably identical.||en