Pulsatile secretion of prolactin and luteinizing hormone and their synchronous relationship during the human menstrual cycle

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Abstract
Recent investigations have demonstrated the pulsatile nature of prolactin (PRL) secretion and the synchronous relationship between PRL and LH pulses in normal and hypogonadal women. The present study was designed to confirm this synchrony and to investigate the characteristics of PRL pulses at different stages of the menstrual cycle. Blood samples were obtained at 10-minute intervals, beginning at 10.00 hours, for a duration of 4-7 hours, from women during the follicular (n = 11), preovulatory (n = 2) and luteal (n = 10) phases. Detectable pulses in plasma PRL concentrations were present in almost all subjects during each phase of the cycle. During the total 121-hour blood sampling throughout the 3 phases, 62 PRL pulses and 74 LH pulses were detected and about 80% of the PRL pulses were observed to coincide with LH pulses. The mean (± SD) pulse frequency of PRL was significantly lower during the luteal phase (0.28 ± 0.17 pulses/hour) than during the follicular (0.64 ± 0.25 pulses/hour) and preovulatory (0.72 ± 0.16 pulses/hour) phases, while the mean pulse amplitude of PRL was significantly greater during the luteal phase (6.8 ± 2.3 ng/ml) than during the follicular (3.6 ± 1.2 ng/ml) and preovulatory (4.1 ± 1.0 ng/ml) phases. These changes in pulse frequency and amplitude were also observed in LH pulses between the follicular and luteal phases, except at the LH surge, when LH pulse amplitude increased markedly, but that of PRL did not alter. Furthermore, a positive linear correlation between the pulse frequency of PRL and LH (r = 0.74, p ± 0.001) was found throughout the 3 phases of the cycle. These results demonstrate that a marked degree of synchrony between PRL and LH pulses is observed during the menstrual cycle and suggest that the frequency and amplitude of PRL pulses vary from the follicular to luteal phases, except at the LH surge, almost in parallel with those of LH pulses.

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