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Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology and Infertility (J.A.M.K., L.A.S., C.M.G.T., R.R.), and Department of Medical Statistics (G.B.), St. Radboud University Hospital Nijmegen, The Netherlands
Address correspondence and requests for reprints to: Rune Rolland, M.D., Ph.D., Department of Obstetrics and Gynecology, University of Nijmegen, P.O.Box 9101, 6500 HB Nijmegen, The Netherlands.
To investigate the mechanisms responsible for the postpartum suppression of reproductive function, LH and PRL levels were determined at 10-min intervals for 8 h in 10 lactating women, in 10 nonlactating women treated with bromocriptine, and in 5 nonpuerperal women. The lactating women were studied on postpartum day 7 (n = 5) or between days 28 and 35 (n = 5). All nonlactating women were studied on day 7. Five of them were treated with the opioid antagonist naltrexone to evaluate the role of endogenous opioids. By using a specific LH assay which does not cross-react with hCG, we were able to measure pulsatile LH secretion in the early puerperium for the first time.
On day 7, LH levels were below the detection limit in both lactating and nonlactating women, hence no pulses could be detected. Chronic opioid blockade in bromocriptine-treated non-lactating women did not result in increased LH levels. Pulsatile LH secretion was present between days 28 and 35 of lactation, although pulse amplitude (P < C.05) and mean LH level (P < 0.05) were lower than in nonpuerperal women. Mean LH in lactating women was negatively correlated with mean PRL (–0.87, P < 0.05). Deconvolution analysis of the PRL responses to suckling revealed that PRL was secreted in distinct bursts, separated by intervals of secretory quiescence. Mean duration of PRL bursts was 40 ± 4 min ar d the maximum secretory rate was reached around the end of suckling.
We conclude that pulsatile LH secretion is completely suppressed during early lactation and partially suppressed during late lactation. Because the duration of suckling was similar, the relatively strong suppression during the early puerperium must be due to additional inhibitory factors. It has been suggested that endogenous opioids are involved in this process, but our results in puerperal women do rot support this hypothesis.
Received June 27, 1990.
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