Prolactin secretion and corpus luteum function in women with luteal phase deficiency

Luteal phase deficiency (LPD) as a clinical infertility problem is considered to have a heterogeneous etiology. Hyperprolactinemia has long been considered a causative factor of LPD. In this context we investigated PRL secretion in 18 women with LPD. All of the subjects were infertile with 2 out of phase (greater than 2 days) endometrial biopsies; 10 of the women also had daily blood samples, this latter subgroup had significantly decreased integrated luteal phase progesterone (P) levels compared to normal women with in-phase biopsies. PRL secretion was investigated as follows: 1) daily blood levels; 2) pulsatile secretion patterns in 3 cycle phase [early follicular (12 h); late follicular (12 h); midluteal (24 h)], 3) LH-PRL coupling, and 4) nocturnal patterns. Results were compared to findings in 36 normal women. The mean daily levels of PRL over the menstrual cycle were not different between the two groups (LPD, 12.1 +/- 1.5; normal, 13.8 +/- 0.8 microgram/L; P = 0.3). There was no correlation between luteal phase integrated P and PRL levels for either group. There was a small difference in the PRL pulse amplitude in the early follicular phase between the LPD and normal women (2.6 +/- 0.3 vs. 5.5 +/- 1.3 micrograms/L; P less than 0.05). There were no significant differences between groups in PRL pulse frequency or mean level during the 12 or 24 h in any cycle phase. There was an equivalent amount of LH-PRL pulse coupling in both groups in all three cycle phases. Diurnal and nocturnal PRL secretion was studied by breaking the 24 h data (midluteal) into day (0700-2300 h) and night (2300-0700) segments. Mean PRL levels were higher at night in both groups (LPD, 15.9 vs. 12.6; normal, 15.4 vs. 9.3 micrograms/L; P less than 0.05), as expected. There were no differences in nocturnal PRL secretory patterns between the two groups. In summary, we have serious reservations whether abnormalities in PRL secretion are a common or integral part of the pathophysiology of LPD. From previous work we know these subtle abnormalities in PRL secretion in LPD are associated with definite abnormalities in gonadotropin secretion. We believe these gonadotropin abnormalities are probably more significant in terms of decreased P secretion.