Conversion of Cortisone to Cortisol and Prostaglandin F_2α Production by the Reproductive Tract of Cows at the Late Luteal Stage In Vivo

Contents: Previous in vitro studies demonstrated that bovine endometrium has the capacity to convert inactive cortisone to biologically active cortisol (Cr) and that Cr inhibits cytokine-stimulated prostaglandin F_2α (PGF) production. This study was carried out to test the hypothesis that bovine reproductive tract has the capacity to convert cortisone to Cr in vivo and to evaluate the effects of intravaginal application of exogenous cortisone on uterine PGF secretion during the late luteal stage. The temporal relationships between PGF and Cr levels in uterine plasma were also determined. Catheters were inserted into jugular vein (JV), uterine vein (UV), vena cava caudalis (VCC) and aorta abdominalis (AA) of six cows on Day 15 of the oestrous cycle (ovulation=Day 0) for frequent blood collection. On Day 16, the cows were divided randomly into two groups and infused intravaginally with vaseline gel (10ml; control; n=3) or cortisone dissolved in vaseline gel (100mg; n=3). Blood samples were collected at -2, -1, -0.5, 0, 0.5, 1, 1.5, 2, 3, 4, 5 and 6h after treatments (0h). Intravaginal application of cortisone increased plasma concentrations of Cr between 0.5 and 1.5h in UV, at 0.5h in VCC, at 1h in JV and at 1.5h in AA. The plasma concentrations of PGF in UV and of PGF metabolite in JV were greater at 0.5 and 1h in the cortisone-treated animals than in control animals. The levels of PGF in UV blood plasma decreased after Cr reached its highest levels. The overall findings suggest that the female reproductive tract has the capacity to convert cortisone to Cr in vivo. Based on the temporal changes of PGF and Cr levels in the uterine plasma, a biphasic response in PGF secretion was found to be associated to the Cr increase induced by the cortisone treatment at the late luteal stage in non-pregnant cows.