Advancement of reproductive senescence and changes in the early expression of estrogen, progesterone and µ-opioid receptors induced by neonatal hypoxia in the female rat

Perinatal hypoxia is a frequent birth complication, and although its early consequences on brain development have been well studied, few studies address any long-term effects. Postnatal insults producing small disturbances in endocrine function can have marked and long-lasting effects. In the present work we studied the effects of two types of perinatal brain injury: global hypoxia (H, 6.5% O2 for 50 min) and hypoxia plus ischemia (HI, ligature of the right carotid artery) on female rat reproductive performance and expression of mediobasal hypothalamus-preoptic area (MBH-PO) estrogen, progesterone and µ-opioid receptors at different times after injury, measuring the mRNA (by semiquantitative RT-PCR) and protein (by Western blot). H or HI advanced approximately 3 months after the appearance of blunted preovulatory LH surges and cyclic irregularities (prolonged estrus) characteristic of the early stages of reproductive senescence. 48 h after H or HI we observed decreases in ERβ, µOR and PR (only in the H group) mRNAs and in total ER and µOR proteins, followed by increased PR levels (mRNA and protein) 7 days post-injury and by increased µOR protein and ERβ mRNA in the H group and ERα, ERβ and µOR mRNAs and ER protein in the HI group 30 days post-injury. Thus, an episode of hypoxia suffered during early postnatal life induces premature reproductive senescence on the female rats, accompanied by early changes in some MBH-PO hormone receptors (µOR, ER and PR), whose expression is intimately involved in the regulation of gonadotropin secretion and female sexual cyclicity.