Natriuretic Effect of α-MSH in the Water-Loaded Rat 1

Summary

α-MSH in doses of 50 and 90 μg showed a significant natriuretic effect when injected intraperitoneally into trained water-loaded rats. This effect did not appear with the administration of either α-MSH inactivated with pepsin or the diluent alone. No changes were observed in [K⁺] or excretion with any of the doses used. Oxytocin in doses of 100 mU showed not only a natriuretic effect but also increased the K⁺ excretion when compared with the preinjection urine sample. α-MSH increased significantly the urine output but only in the sample after the injection of all three doses used, while 25 mU of oxytocin produced an antidiuretic effect in the first two 20-min urine samples after its administration.