Abstract
To examine whether oxygen (O2) and nitric oxide (NO) are temporally associated with the acute changes in luteal function during luteolysis, we determined the real-time changes in the circulating concentrations of progesterone (P4) and nitrite/nitrate (the stable metabolites of NO) and the partial pressure of oxygen (pO2) during prostaglandin F2α (PGF2α)-induced luteolysis in cattle. Catheters for frequent blood sample collection were inserted into the ovarian vein (OV), jugular vein (JV) and aorta abdominalis (AA) in 12 cows on Day 9 of the oestrous cycle (oestrus = Day 0). On Day 10, the cows were randomly divided into two groups and treated with a luteolytic dose of a PGF2α analogue or saline solution (control). Blood samples were collected at -2, -1, 0, 0.25, 0.5, 0.75, 1 and 2 h and then at 2-h intervals until 12 h after treatment (0 h). Injection of a PGF2α induced a significant decrease in the concentrations of P4 in OV plasma within 2 h. The decrease in P4 concentrations was preceded by an increase in the NO concentrations in the blood collected from OV, JV and AA. Basal pO2 was significantly higher in OV blood than in JV blood (P<0.05). PGF2α injection increased pO2 in OV blood between 0.5 and 2 h. These results demonstrate that PGF2α induced an acute increase in pO2 and NO in the ovarian circulation and suggest that O2 and NO are involved in the early events of CL regression, including inhibition of P4 secretion and output, in cattle.
