We examined the time trend effects of approaching parturition on fetal and maternal concentrations of cortisol, corticosterone, 11-desoxycorticosterone and aldosterone in eight chronically catheterized pregnant sheep preparations. Fetal plasma cortisol describes a continuously incrementing, straight log-linear function from at least 18 days prior to delivery. Fetal plasma corticosterone describes a time trend effect similar to that of fetal plasma cortisol. Fetal plasma 11-desoxycorticosterone shows no overall time trend effect except for a terminal rise beginning at approximately delivery - 2 days. Maternal plasma cortisol, corticosterone, and 11-desoxycorticosterone concentrations show no overall time trend effects except for similar terminal rises beginning at approximately delivery - 3 days. Both fetal and maternal plasma aldosterone concentrations show wide random fluctuations with no discernible time trend effects. Concentrations of fetal and maternal 11-desoxycorticosterone and aldosterone respectively do not correlate with one another (P > 0.05) or with cortisol and corticosterone (P > 0.10) and must therefore be regulated through different control mechanisms. Maternal cortisol, corticosterone, 11-desoxycorticosterone and aldosterone concentrations bear no apparent relationship over time to their fetal counterparts with the approach of parturition.
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