Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 1997
Publication Date: N/A
Interpretive Summary: Twenty to thirty percent of fetal pigs die prior to birth; of those born, another 10-15% die prior to weaning. The greatest death and sickness rates of the latter neonatal pigs occur with those having small birth weights. Abnormally high amounts of the steroid cortisol have been associated with retardation of fetal development and fetal death in other species. Indeed, ,we have previously shown that lower birth weight pigs have higher blood levels of cortisol. The current study was conducted, therefore, to determine if blood levels of cortisol would also be associated with size in fetal pigs. The results indicate that only as the fetuses near birth (100 days; normal gestation length = 114 days) were there higher blood levels of cortisol in smaller fetuses. At earlier ages (days 50 and 75 of gestation), this relationship was not evident. These data suggest that higher fetal cortisol levels may be one causal factor in slower fetal development and in nlower birth weight, but this relationship is not apparent until near term.
A study was conducted to characterize fetal pituitary-adrenal function during porcine gestation and to relate plasma corticosteroids to fetal size. Fetal arterial cortisol decreased (p=.025) by approximately 30% between d 50 and 75 and then increased (p<.01) by 101% between 75 and 100 d. Concomitantly, fetal arterial ACTH increased fourfold between 50 and 75 d of gestation and 45% (p<.05) between 75 and 100 d. Fetal venous cortisol and ACTH concentrations (measured only on d 75 and 100) were lower (p<.01) than arterial cortisol. The percentage of free cortisol on d 75 and 100 was a constant 24%, whereas CBG-bound cortisol was a constant 60% and albumin- bound cortisol was 16%. Fetal plasma cortisone concentrations were always lower than cortisol concentrations (p<.01), did not differ between arterial and venous plasma (p=.65), decreased 50% between 50 and 75 d (p=.01), and did not change thereafter. Plasma cortisol concentrations in Chinese Meishan fetuses were 30% greater (p<.01) than in white crossbred fetuses o the same age whereas plasma ACTH and cortisone did not differ between the two breeds (p>.31). Analysis of covariance procedures indicated a negative regression (p<.025) of fetal weight (b= -13.1 g/ [ng cortisol/ml]) and fetal length (b= -1.5 mm/ [ng cortisol/ml]) on arterial cortisol in white crossbred fetuses only at d 100 of gestation. In Meishan fetuses, a negative regression (p </- .04) of weight (b= -5.1) and length (b= -1.0) on arterial cortisol existed at d 75. These data provide information concerning prenatal development of the porcine pituitary-adrenal axis, indicate breed differences in such development, and suggest that there is a negative relationship between endogenous cortisol concentrations and fetal development at specific gestational stages.