The effect of amiloride during infusion of oxytocin in male sprague-dawley rats: a study of a possible intrarenal target site for oxytocin.

A possible natriuretic mechanism of action of oxytocin was investigated in male Sprague-Dawley rats. The effects of an intravenous bolus injection of amiloride on urine volume, potassium and sodium excretion, and osmolality were measured with and without an intravenous infusion of oxytocin in saline. Control values were obtained during the infusion of saline. Amiloride administered during an oxytocin infusion increased sodium excretion from 0.1 +/- 0.0 to 16.6 +/- 2.1 micromol/min. In animals treated with amiloride only, the sodium excretion was 4.5 +/- 0.8 micromol/min. The administration of oxytocin only resulted in a sodium excretion of 1.2 +/- 0.3 micromol/min. After the administration of oxytocin, amiloride increased urinary flow from 4.3 +/- 0.6 microl/min to 48.8 +/- 6.1 microl/min. In animals treated with amiloride only, the flow after the bolus dose was 17.7 +/- 1.8 microl/min. The administration of oxytocin only resulted in a flow of 8.5 +/- 1.6 microl/min. The amiloride-caused change in potassium excretion was not inhibited by oxytocin. In summary, the effects of amiloride were not inhibited by the actions of oxytocin. Amiloride administrated after reaching a near steady-state effect of oxytocin was found to give rise to an effect far greater than that after the administration of oxytocin or amiloride alone. It is concluded that the intrarenal natriuretic mechanisms of oxytocin do not emanate from the amiloride-sensitive sodium channels.