Cannulation of the utero-ovarian vein in intact ewes: Hormone concentrations and blood gas levels during the oestrous cycle and early pregnancy

A technique for implanting and maintaining catheters in both utero-ovarian veins (UOV) of intact, conscious sheep has been developed. Both UOV catheters remained patent for more than 2 weeks in 72.7% of animals. In non-pregnant ewes, large pulses of PGF(2α) were observed in UOV plasma collected on days 13 to 16 of the cycle (frequency 1.3 ± 0.2/12 h; pulse height range 1.0-26.9 ng/ml). In contrast, on days 13 to 16 of gestation, significantly (P<0.001) fewer pulses of PGF(2α) (frequency 0.42 ± 0.2/12 h) were observed in both UOVs of pregnant ewes, which were significantly (P<0.001) smaller in amplitude (pulse height range 1.4-4.9 ng/ml). The maintenance of the corpus luteum (CL) during early pregnancy may therefore directly result from a decreased uterine PGF(2α) release. During the luteal phase (day 4-12), the PO₂ of UOV blood draining an ovary containing a CL (UOV/CL) was significantly higher than blood in the contralateral UOV (P<0.001). By days 15 and 16 of the cycle, the PO₂ of UOV/CL blood had decreased and was not significantly different to that observed in the contralateral UOV (P>0.1). On day 17, the PO₂ of blood in both UOVs was elevated significantly compared to levels observed on the two preceding and the two following days (P<0.001). We consider that the higher PO₂ in UOV/CL blood resulted from a very high luteal blood flow, and that the decrease on days 15 and 16 of the cycle resulted from a decline in luteal blood flow during luteolysis. The subsequent increase in PO₂ of blood from both UOVs on day 17 was considered to result from an increased uterine blood flow.