Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/1997
Publication Date: N/A
Interpretive Summary: During porcine gestation, embryonic and fetal deaths can be as high as 20-30%. Understanding the causes of this mortality would greatly assist in increasing pig litter size. The adrenal steroid cortisol increases in fetal blood near term and is responsible for final maturational changes in numerous organs in pigs. Abnormally high fetal cortisol concentrations in other species cause fetal death; near term in pigs, higher fetal cortisol levels are associated with smaller fetal size. Hence, this steroid can have both positive and negative effects on fetal development. The current study was conducted to determine if cortisol content of the uterine environment changes during early pig embryonic development. It was found that the adrenal steroids cortisol and aldosterone both increase within the uterus between days 10 and 15 of pregnancy. Further, a protein that binds readily with cortisol and inactivates it while bound, corticosteroid binding globulin, was also found to increase within the uterus at the same time. However, its levels were considerably lower and, hence, over 90% of the uterine cortisol would be in the free or biologically active form. Thus, both cortisol and aldosterone are present in the uterine environment during early pig pregnancy and could influence early embryonic development. Conversely, abnormal levels of these steroids might be associated with embryonic mortality.
Technical Abstract: Studies were conducted to determine if the corticosteroids cortisol and aldosterone and corticosteroid-binding globulin (CBG) were present in the porcine early-embryonic environment. Cortisol was measured in uterine flushings from white crossbred gilts at Days 7, 10, 13, and 16 of the estrous cycle and pregnancy. Total content of cortisol increased (p<.01) between Days 13 and 16, and immunoassayable CBG (iCBG) increased (p<.01) between Days 10 and 13, in both cyclic and pregnant gilts. In a separate study with Chinese Meishan gilts, total cortisol and aldosterone content of uterine flushings increased (p<.02) between Days 10 and 15 of the estrous cycle and pregnancy. In another study with white crossbred gilts, CBG-like binding activity in uterine flushings was low at Day 10, then increased over 100-fold at Day 15 (p<.01). However, levels of CBG-like binding activity on Day 15 were 100-fold less than iCBG measured in the previous study and could bind less than 4% of the uterine luminal cortisol. Differences between iCBG and CBG binding might be due to the ability of the antibody to CBG to recognize either biologically inactive CBG or structurally similar molecules. CBG-like binding activity was also present in the endometrial cytosol of white crossbred gilts. Concentrations (fmol/mg protein) of endometrial CBG-like activity decreased (p = .03) between Days 10 and 15 of the estrous cycle and pregnancy, did not differ with reproductive status, and on Day 15 were comparable to concentrations in uterine flushings but threefold less (p<.01) than those in the serum. These studies indicate that corticosteroids are present primarily in the free form within the porcine uterine lumen and could influence early porcine conceptus development.