CHRONIC MATERNAL THIRD TRIMESTER HYPOXIA ON MEDIONINE ENKEPHALIN LEVELS IN PRETERM RABIT BRAINSTEN

Abstract

Acute hypoxia alters the content of the neuropeptide methionine enkephalin (ME) within specific brainstem regions involved in respiratory control. This alteration is both age and region specific (Ped Res 20:655-657, 1986). Since ME is implicated in abnormalities of respiratory control, particularly in the newborn, we examined the effect of chronic hypoxia on ME levels within specific brainstem regions of prenatal animals. 6 pregnant animals were placed in environmental chambers at gestational day E-10. Between days E-14 and E-28, 3 pregnant animals breathed 21% O2 (control) and 3 pregnant animals breathed 14% O2. On E-28 (term = E30-31) the fetuses were delivered by hysterotomy and immediately sacrificed. The brains were removed and sectioned into the colliculi, pons and medulla, and ME measured by RIA. The results are reported as ng ME/mg protein ± SEM and are tabulated below: These data show: 1) In both control and hypoxia exposed fetuses ME is greatest in the medulla, lesser in the pons and lowest in the colliculi and 2) ME is increased within the pons (a regulator of respiratory frequency) of prenatally hypoxia-exposed animals. This tendency (but not significance) is also seen in the medulla of hypoxia-exposed animals. These results offer additional support for a role of ME in abnormalities of respiratory control under basal conditions and a role in the increased susceptibility of the hypoxic preterm infant.