Serial Prolactin and Thyrotropin Responses to Thyrotropin-Releasing Hormone throughout Normal Human Pregnancy

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Abstract
To determine whether or not the pituitary responsiveness to TRH [thyrotropin-releasing hormone] changes in pregnancy, 9 healthy pregnant women were given serially 200 .mu.g TRH i.v. between 9-15, 26-29 and 35-38 gestational wk as well as 3-5 days postpartum. Serum PRL [prolactin] and TSH [thyrotropin] were measured before, and 20 and 60 min after TRH administration. Serum 17.beta.-estradiol (E2) and progesterone (P) were measured before and 60 min after TRH. The mean (and SD) basal PRL concentration in the nonpregnant state was 7.6 .+-. 4.9 ng/ml; mean values were significantly higher during pregnancy and postpartum (35.9 .+-. 16.0 ng/ml in the 1st trimester, 176.6 .+-. 33.7 ng/ml in the 2nd trimester, 210.0 .+-. 25.3 ng/ml in the 3rd trimester and 197.3 .+-. 65.6 ng/ml in the postpartum period). Basal serum TSH levels ranged from 3.6-14.2 .mu.U[units]/ml in pregnancy. The mean value was not significantly different from that in the nonpregnant control subjects. The mean serum PRL and TSH responses to TRH were similar in the different trimesters and in the puerperium, and were relatively smaller than the nonpregnant response. There is no increase in secretory reserve of the pituitary occurring with advancing gestational age. Baseline serum PRL displayed a significant correlation with the levels of E2 and P, while the baseline TSH or the PRL and TSH responses to TRH did not correlate with the sex steroid levels. E2 and P concentrations were unaffected by TRH itself or by the transient hyperprolactinemia induced by TRH.