Activation of pituitary gonadotropic function by an agonist of luteinizing hormone-releasing factor in the puerperium

Circulating inhibin levels in lactating and nonlactating women

OBJECTIVE

To investigate the role of inhibin in the human puerperium, by measuring serum levels of immunoreactive inhibin in both lactating and nonlactating women.

DESIGN

Prospective, comparative, open study.

SETTING

Department of obstetrics and gynecology of a university hospital.

PATIENTS

Fourteen healthy women who delivered at term: seven lactating women and seven nonlactating women treated with the dopamine-agonist CV 205-502.

MAIN OUTCOME MEASURES

Serum immunoreactive inhibin, PRL, FSH, LH, E2, and P.

RESULTS

All women showed a rapid decline of immunoreactive inhibin levels during the first postpartum days. Thereafter the pattern depended on the way of feeding. Nonlactating women, with their rapid return of pituitary and ovarian function, showed increasing immunoreactive inhibin levels to a maximum on day 24 (950 +/- 180 U/L). Lactating women did not show ovarian activity despite high FSH levels, and immunoreactive inhibin stayed on a low level (230 +/- 40 U/L on day 24). There was a significant correlation between immunoreactive inhibin and E2.

CONCLUSIONS

The rapid decline of immunoreactive inhibin (elimination of placental hormone) is followed by an increase in nonlactating women (production by the maturing follicle) and by persistently low levels in lactating women. The lack of adequate levels of immunoreactive inhibin in lactating women may be an explanation of the relatively high FSH levels during lactation.

Priming with gonadotropin-releasing hormone restores gonadotropin secretion during first but not second trimester of pregnancy

This study was designed to determine whether the lack of secretion of endogenous gonadotropin-releasing hormone is the etiology of the hypogonadotropic state of pregnancy. For this purpose, five pregnant women in their first trimester received a single intravenous dose of 150 micrograms of gonadotropin-releasing hormone. Another five women in the first trimester and five women in the second trimester of pregnancy received daily intramuscular injections of 500 micrograms of gonadotropin-releasing hormone for 10 consecutive days. This was followed by a single 150 micrograms gonadotropin-releasing hormone test and then a 24-hour pulsatile infusion of gonadotropin-releasing hormone of 10 micrograms/min/6 min given every hour. Baseline plasma beta-luteinizing hormone and follicle-stimulating hormone were undetectable in all women. Mean +/- SEM plasma beta-human chorionic gonadotropin was significantly higher (p less than 0.001) in the first trimester than in the second trimester, and mean plasma estradiol and prolactin were significantly increased (p less than 0.001 and 0.05, respectively) during the second trimester of pregnancy. After the 10-day treatment with gonadotropin-releasing hormone there was a significant increase (p less than 0.05) in baseline beta-luteinizing hormone and follicle-stimulating hormone only in the first-trimester pregnant women. The single as well as the pulsatile administration of gonadotropin-releasing hormone resulted in a further significant increase in both beta-luteinizing hormone and follicle-stimulating hormone. In contradistinction, women in the second trimester of pregnancy showed a blunted response to the daily and pulsatile administration of gonadotropin-releasing hormone. Since the pituitary secretion of gonadotropin was functionally restored by the administration of exogenous gonadotropin-releasing hormone, possibly there is a lack of secretion of endogenous gonadotropin-releasing hormone during the first trimester of pregnancy. An increased negative feedback produced by increasing levels of plasma estradiol might be the cause of pituitary refractoriness to gonadotropin-releasing hormone during the second trimester of pregnancy.

Postpartum hypogonadotrophinism: evidence for increased opioid inhibition

To investigate a proposed role for endogenous opioids in the inhibition of LH:RH-gonadotrophin release in the postpartum hypogonadotrophic state, LH and FSH responses to naloxone infusion (1.6 mg/h for 2 h) and to a pulse of LHRH (10 micrograms) were measured in five non breast-feeding women. Sequential studies were made at four intervals during the first 25 d postpartum. LH and FSH responses to naloxone were absent on Day 10 postpartum, but significant increments were observed in all studies performed between Days 13-25 postpartum. The relative increments of FSH and LH during naloxone varied as the puerperium progressed; a 3-fold greater release of FSH than LH was found on Day 13 to 15 while the reverse was observed on Day 25. The intermediate days (17-20) yield an equal response. There was a positive linear correlation between the LH and FSH responses to naloxone infusion and to LHRH. These data suggest that the hypogonadotrophinism of the puerperium is due at least in part to increased opioid inhibition of LHRH secretion.

Functional capacity of the gonadotrophs during pregnancy and the puerperium

The nature of secretion of gonadotropin during pregnancy and the puerperium was determined by measuring plasma levels of beta-subunit luteinizing hormone (GnRH) during the first, second, third trimesters of pregnancy, and at 10 days post partum in lactating and nonlactating women. The nonlactating subjects were divided into two groups according to whether hormonal suppression of lactation was used. Baseline and response levels of beta-LH and FSH after GnRH were below the limits of assay sensitivity (less than 0.5 ng/ml and less than 1.5 mlU/ml, respectively) in all pregnant subjects. In contrast, postpartum lactating and nonlactating subjects who received no hormonal treatment for suppression of lactation had a small but significant increase in FSH after GnRH. In lactating women, FSH increased from 1.5 +/- 0.3 mlU/ml to 2.7 +/- 0.3 mlU/ml (p less than 0.05); and in nonlactating subjects, FSH increased from undetectable levels to 2.0 +/- 0.4 mlU/ml (p less than 0.001). Patients who received estrogenic compounds for suppression of lactation had undetectable FSH baselines and no response after GnRH. beta-LH in both lactating and nonlactating women had a variable but not a significant response to one administration of GnRH. In conclusion, our findings indicate that the functional capacity of the gonadotrophs recovered earlier (at 10 days) than previously reported (less than 14 days) after term pregnancy, and the recovery of FSH secretion occurs earlier and is more consistent than the recovery of beta-LH.