INHIBITION BY OXYTOCIN OF ENDOTHELIN-1-INDUCED ACTH-SECRETION IN NORMAL MEN

The effect of oxytocin (OT) on the ACTH response to the intravenous ad ministration of Endothelin-1 (ET-1) was investigated in 7 normal men. ET-1 was given alone at a dose of 5.0 ng/kg/min for 15 min plus 2.5 ng /kg/min for 105 min or together with OT (2 I:U. injected plus 4 I.U, i nfused over 2 hours). In addition, control tests with normal saline in stead of drugs were performed. No significant change in ACTH secretion was observed during the control test. In contrast, within 20 min ET-1 induced a significant increase in serum ACTH levels which continued w ith a plateau during infusion. The concomitant administration of OT si gnificantly reduced the ACTH response to ET-1 infusion. During ET-1 an d OT combined treatments, ACTH values were slightly higher, but not si gnificantly different from those observed in the control test. These d ata confirm the stimulating effect of ET-1 on ACTH secretion in normal men; furthermore, our results show that ET-1-induced ACTH rise is sen sitive to OT inhibition, suggesting a possible interaction between ET- 1 and OT in the control of ACTH secretion.