Effect of an OT antagonist on the control of the midcycle LH surge in women

Abstract

P>Objective Data in women regarding the role of OT in LH secretion during the LH surge are conflicting. As in previous studies blood samples for LH measurements were taken infrequently, we re-examined this matter in women with a fully characterized midcycle LH surge. Design Normal women were studied over two cycles. When the dominant follicle reached a diameter of either 16-17 mm (Group 1) or 18-19 mm (Group 2), the women were infused intravenously for 3 h with normal saline (cycle-1) or atosiban (cycle-2). Patients Fifteen women (10 in group 1 and 5 in group 2) aged 23-35 years. Measurements Blood samples were obtained every 6 h to characterize the midcycle LH surge. Results The time interval (mean +/- SEM) from the start of the infusion to the onset of the LH surge in the two cycles was 46 center dot 8 +/- 4 center dot 8 and 45 center dot 6 +/- 9 center dot 6 h in group 1 and 6 center dot 0 +/- 2 center dot 4 and 7 center dot 5 +/- 2 center dot 8 h, respectively, in group 2. LH values during the LH surge were similar in the two cycles except in group 1 at the point of 30 h at which LH value in cycle-2 (41 center dot 2 +/- 4 center dot 6 mIU/ml) was significantly lower than in cycle-1 (52 center dot 8 +/- 3 center dot 4 mIU/ml, P < 0 center dot 05). Nevertheless, in each group, the area under the curve for LH was similar in the two cycles. Conclusions Antagonism of endogenous OT action by atosiban does not alter the LH profile during a fully characterized midcycle LH surge, suggesting that OT is not a major regulator of LH secretion in women.