Absent prolactin (PRL) response to thyrotropin releasing hormone (TRH) and somatostatin (SRIF) in at term fetus

To study the effect of thyrotropin-releasing hormone (TRH) and somatostatin (SRIF) on prolactin (PRL) secretion in at term human fetus these peptides have been administered to at term pregnant women during labor. Evidence has been reported that TRH and SRIF cross the placental barrier and affect the secretion of pituitary hormones. 400 μg TRH were administered to 37 pregnant women. As control 11 women received saline. In cord blood (CB) of neonates whose mothers received TRH CB PRL concentration was not different from those treated with saline, with values ranging between 192 ± 18 and 342 ± 48 ng/ml. 500 μg cyclic SRIF diluted in saline was infused over a period of 30 min in 55 women. Control subjects were infused with saline. At birth CB PRL concentration in SRIF treated neonates ranged between 266 ± 32 and 327 ± 48 ng/ml. In neonates whose mothers were treated with saline, CB PRL was 305 ± 31 ng/ml. This value was not significantly different from that in SRI F-treated groups. Our findings suggest that in at term human fetus TRH does not stimulate PRL secretion probably because fetal pituitary secretes PRL at maximal releasing activity. Furthermore SRIF administration does not have any effect on fetal PRL secretion as consistently observed in adults.