A B S T R A C T The synthesis and release of human prolactin (hPRL) in the human fetus was assessed by radioimmunoassay analysis of the content and concentration of hPRL in 82 pituitary glands and the concentration of serum hPRL in 47 fetuses of gestational age 68 days to term. Fetal hPRL exhibited parallelism with the reference standard (Lewis 203-1). hPRL was detected by 68 days of gestation (10 wk), the earliest fetal pituitary gland studied; 8 out of 33 pituitaries had a prolactin (PRL) content above 2.0 ng between 10-15 wk gestation. The mean content of PRL in the pituitary gland increased sharply from 14.8±4.6 ng at 15-19 wk to 405±142 ng at 20-24 wk and 542±204 ng at 25-29 wk gestation. By term, the mean content was 2,039± 459 (range 493-3,689) and the mean concentration 15.9±2.4 ng/mg (range 7-20). There was a significant positive correlation (P < 0.001) between the hPRL and human growth hormone (hGH) content of fetal pituitary glands; at term the hPRL/hGH ratio was 1/290. The concentration of serum hPRL between 12 and 24 wk ranged from 2.9 to 67 ng/ml, mean 19.5±2.5 ng/ml (n = 41); by 26 wk fetal serum hPRL increased sharply and attained levels of 300-500 ng/ml in late gestation. At delivery, the mean plasma concentration of hPRL was 167±+14.2 ng/ml in 36 umbilical venous specimens and 111.8±12.3 ng/ml in the matched maternal venous specimens. No correlation between serum hPRL and the pituitary content or concentration of hPRL was demonstrable in 12 matched fetal specimens.In five anencephalic infants, umbilical venous hPRL levels were between 65 and 283 ng/ml. In two anencephalic infants, thyrotropin releasing factor (TRF) (200 Ag IV) evoked a rise in serum hPRL in one patient from 43 to 156 ng/ml at 30 min, and in the other from 65 to Dr. Aubert is recipient of a grant from the Swiss National Fund for Scientific Research.

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