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 PGF2 alpha 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 less than 0.001) fewer pulses of PGF2 alpha (frequency 0.42 +/- 0.2/12 h) were observed in both UOVs of pregnant ewes, which were significantly (P less than 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 PGF2 alpha 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 less than 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 greater than 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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)