Effect of oxytocin structural changes on rat renal excretion of Na, K, and water

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Abstract
The common action of oxytocin on the smooth musculature of the uterus and on the renal excretion of sodium, potassium, and water suggests a relationship between the two effects. In order to investigate this possibility, the action of oxytocin treated with chymotrypsin and with sodium thioglycollate on sodium, potassium, and water excretion was studied. These agents greatly reduce the uterotonic activity of the hormone as well as its effect on electrolyte and water excretion in rats. Equivalent uterotonic doses of oxytocin, Val3-oxytocin, and Phe2-Tyr3-oxytocin were assayed on the excretion of electrolytes and water. Excretion of sodium and potassium produced by Val3-oxytocin was less than that produced by oxytocin. Phe2-Tyr3-oxytocin was approximately one-ninth as active as oxytocin in this respect. In studies with low doses of oxytocin it was established that 0.25 mU was necessary to increase sodium excretion while 0.5 mU had to be administered in order to increase potassium as well.