Maternal stress and the neonate's response to hypoxia
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AbstractGlucocorticoids promote cellular differentiation over proliferation. This physiological principle inspired the antenatal exogenous glucocorticoid administration in threatened preterm labor to be a standard in practice, as it significantly reduces the incidence of respiratory distress syndrome, intraventricular hemorrhage, and neonatal mortality. The specific aim of this study was to investigate the neonate's response to hypoxia following exposure to a maternal endogenous glucocorticoid release in response to a psychological stressor, as opposed to exogenous glucocorticoid administration. Hence we postulated there may be differences in corticosterone levels measured in rat dams exposed to a psychological stressor versus controls. We then hypothesized that when exposed to hypoxia, rat pups antentally exposed to a maternal endogenous glucocorticoid release, may respond differently, as compared to controls. We measured the effects on corticosterone levels, in pregnant rat dams on gestational days 17, 18 and 19, following a 30 minute exposure to a simulated open field, and compared these levels to levels obtained from control dams on the same gestational days. Exposure to the open field resulted in significantly increased, non-attenuated, and reproducible corticosterone levels, sustained 120 minutes after exposure to the open field. Thereafter, spontaneously breathing rat pups on day of life 1, 5, and 10, were placed in a temperature controlled metabolic chamber, and were exposed to either sustained or intermittent hypoxia, during which heart rates and respiratory rates were recorded via 12 channel Polygraph and then analyzed. We found no significant differences between rat pups exposed to a maternal psychological stressor versus control rat pups on day of life 1, 5, or 10, to withstand hypoxia; as measured by time to last gasp, or number of successful autoresuscitations. However, the total number of gasps in day of life 1 pups exposed to a maternal psychological stressor was significantly less than controls. These findings provide new information regarding factors that influence the neonate's ability to withstand hypoxia: specifically pertaining to intrauterine exposure to an endogenous neuroendocrine stress response in late pregnancy.
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