PORCINE FETAL AND MATERNAL ADRENOCORTICOTROPIC HORMONE AND CORTICOSTEROID CONCENTRATIONS DURING GESTATION AND THEIR RELATION TO FETAL SIZE

A study was conducted to characterize fetal plasma ACTH and corticoste roid concentrations during porcine gestation and to relate plasma cort icosteroids to fetal size. Samples were taken in white crossbred pigs at 50, 75, and 100 days of gestation and in Chinese Meishan pigs at Da y 75. Fetuses developed in either ''crowded'' or ''roomy'' uterine env ironments after maternal uterine ligation, and all fluid samples were obtained during surgery. Fetal arterial cortisol decreased by 30% betw een Days 50 and 75 and then increased by 101% between 75 and 100 days. Concomitantly, fetal arterial ACTH increased 4-fold between 50 and 75 days of gestation and 45% between 75 and 100 days. Fetal venous corti sol and ACTH (measured only on Days 75 and 100) concentrations were lo wer than arterial concentrations. Both amniotic and allantoic fluid co rtisol concentrations paralleled those of arterial cortisol but were a t least 4-fold less. The percentage of free cortisol on Days 75 and 10 0 was a constant 24%, whereas cortisol bound to corticosteroid-binding globulin was a constant 60% and albumin-bound cortisol was 16%. White crossbred fetal arterial cortisone concentrations were always lower t han cortisol concentrations, did not differ between arterial and venou s plasma, decreased 50% between 50 and 75 days, and did not change the reafter. Plasma cortisol concentrations in Chinese Meishan fetuses wer e 30% greater than in white crossbred fetuses of the same age, but pla sma ACTH and cortisone did not differ between breeds. Analysis of cova riance indicated a negative regression of fetal weight and fetal lengt h on arterial cortisol in white crossbred fetuses only at Day 100, and at Day 75 in Meishan fetuses. Under the specific conditions of this e xperimental model, these data demonstrate prenatal developmental chang es in plasma ACTH and corticosteroids, indicate breed differences in s uch development, and suggest that a negative relationship exists betwe en endogenous cortisol concentrations and fetal size at specific gesta tional ages.