Chronic Maternal Hypoxia

We examined the effect of chronic maternal hypoxia on methionine-enkephalin concentrations in fetal (gestational day E-28) and neonatal (postnatal days 3, 7, 21) brainstem regions. Pregnant rabbits were housed in environmental chambers at gestational day E-10. Between E-14 and E-28 the pregnant rabbits were separated into two groups. Group I were controls (C) and breathed 21% 02/79% N2 and group II, hypoxia (H), breathed 12–14% 02/86–88% N2. Sacrifice occurred at various days depending on the experimental paradigm. On gestational day E-28, the first group of 6 pregnant animals (3 C, 3 H) were delivered by hysterotomy and the pups were immediately sacrificed. On and after gestational day E-28, the remaining 12 pregnant animals breathed room air. These animals delivered spontaneously between 30 and 32 days of gestation. The pups remained with their mothers until sacrifice. On postnatal days 3, 7, or 21, methionine-enkephalin was measured by radioimmunoassay in the colliculi (fetal animals), superior and inferior colliculi (postnatal animals), pons and medulla (both groups). In both normoxia-exposed and hypoxia-exposed animals, methionine-enkephalin was highest in the medulla, intermediate in the pons, and lowest in the colliculi. Chronic maternal hypoxia significantly increased the methionine-enkephalin concentration in the pons of E-28 fetuses (p < 0.02). Levels were increased in the medulla as well but these did not reach significance (p = 0.09). In contrast, chronic maternal hypoxia had no effect on brainstem methionine-enkephalin concentrations at 3 and 7 days postnatally, but did decrease the methionine-enkephalin concentrations in the superior colliculi, pons and medulla (but not the inferior colliculi) at postnatal day 21. These data support the concept that regional differences exist in basal methionine-enkephalin concentrations within the brainstem regions of fetal and neonatal animals, and show that maternal hypoxia has both immediate and long-term effects on brain methionine-enkephalin concentrations. Both fetal and postnatal animals show regional susceptibility to changes in brainstem methionine-enkephalin concentrations after exposure to chronic maternal mid-gestational hypoxia.