The relationship between serum levels of prolactin and growth hormone in the early postnatal period

BACKGROUND: In the neonatal period, the pituitary hormones including prolactin (PRL) and human growth hormone (hGH) are secreted in high amounts due to immature feedback mechanisms. As both hormones are secreted in part by the same somatomammotrophic cells, we investigated their relationship in newborns with respect to sex, gestational week, method of delivery, and anthropometric data. METHODS: The serum levels of PRL and hGH were measured in blood drawn from 225 newborns. The newborn data were extracted from medical records. RESULTS: A positive correlation was found between log-transformations of PRL and hGH (r = 0.17; P = 0.01; n = 225), with a stronger correlation in newborns whose blood samples were taken more than 2 days after birth (r = 0.42; P < 0.001; n = 130). Log-transformations of the PRL/hGH ratio demonstrated a positive correlation with the gestational week (r = 0.39; P < 0.001; n = 200). Multiple regression analysis showed that 15% of the variance in the logarithm of this ratio is attributed to the gestational week. CONCLUSION: In newborns, serum PRL and hGH levels show a positive correlation that can be explained by common regulatory factors or a drift phenomenon. A higher gestational week is associated with a higher PRL/hGH ratio. Further studies are needed to look for possible confounders and to determine the PRL-hGH relationship in different conditions.