Pregnancy recognition in cattle: effects of conceptus products on uterine prostaglandin production

In cattle, continued progesterone (P4) production by the corpus luteum (CL) is required if pregnancy is to persist. Identification of putative conceptus-derived signals and evaluation of their biological roles relative to CL maintenance during early pregnancy were goals of this research endeavor. Using various chromatography systems, bovine conceptuses (days 19 to 23) exhibited extensive metabolism of tritiated P4 (90-98%), in vitro. A majority of conceptus metabolites were 5β-reduced pregnanes. A major conceptus metabolite was 5β-pregnan-3α-ol-20-one (5β-P). Conversely, endometrial explant cultures metabolized 40 to 50% of P4 substrate to primarily 5α-reduced steroid products. An in vivo test system to evaluate uterine PGF/sub 2α/ production capacity was characterized in experiment two. Exogenous estradiol-17β (E2; 3 mg I.V.) stimulated uterine blood flow, and PGF/sub 2α/ production and metabolism. In experiment three, CL function, interestrous interval, and spontaneous uterine PGF/sub 2α/ production were evaluated in cyclic cows following intrauterine administration of 5β-P, conceptus secretory proteins (CSP) or homologous serum proteins (Control). Results support a role for CSP in suppression of uterine PGF/sub 2α/ production during early pregnancy in cattle