RESUMEN
Lead (Pb) can delay sexual maturation; however, the mechanism and critical time of insult are not clearly defined. Therefore, we assessed maternal Pb levels during low-level gestational and/or lactational exposure, as well as blood and tissue Pb in developing fetuses in relation to the subsequent detrimental effects of Pb on puberty-related hormones and the onset of female puberty. Adult Fisher 344 female rats were gavaged daily with either a 1-ml solution of PbAc containing 12 mg/ml Pb or an equal volume of sodium acetate (NaCl), for the controls, from 30 days prior to breeding until their pups were weaned at 21 days. By cross-fostering at the time of birth, the pups were either exposed to PbAc or NaAc during gestation only, lactation only, or during both gestation and lactation. Pb delayed the timing of puberty and this delay was associated with suppressed serum levels of insulin-like growth factor-1 (IGF-1), luteinizing hormone (LH), and estradiol (E(2)). Liver IGF-1 mRNA was not affected, suggesting that Pb altered translation and/or secretion of IGF-1. We reported previously that peripherally derived IGF-1 acts at the hypothalamic level to facilitate LH release at puberty; hence, we suggest that the action of Pb in decreasing circulating IGF-1 contributes to the delayed puberty. The detrimental effects occurred regardless of the developmental time of exposure, although gestational exposure appeared more sensitive to the effects of Pb. Also, the effects noted were with blood Pb levels less than previously reported and these levels are relevant to human health concerns.