Intrathecal injection of an oxytocin-receptor antagonist attenuated postnephrectomy natriuresis in the male rat.

We have previously shown that oxytocin (OT) is a major humoral mediator in postnephrectomy natriuresis. As immunoassayable OT has been demonstrated in the spinal cord, the aim of this investigation was to determine whether OT receptors in the spinal cord are also involved in this natriuresis. The experiments were performed on anesthetized male rats. Before acute unilateral nephrectomy, an oxytocin-receptor antagonist was injected intrathecally in the thoracolumbar region in rats. Postnephrectomy natriuresis was attenuated by this injection but not by intrathecal injection of artificial cerebrospinal fluid. Our results suggest that OT receptors within the spinal cord may influence the autonomic nervous regulation of renal function. In an additional experiment, intravenously infused hexamethonium did not prevent the adaptive natriuresis in the remaining kidney. We conclude that OT receptors in the spinal cord are involved in the postnephrectomy natriuresis, possibly as a component in the afferent signal pathway.