Oviductal progesterone concentration and its spatial distribution in cyclic and early pregnant cows

Changes and local distribution of oviductal progesterone (P(4)) concentration during the estrous cycle and early pregnancy in cows were investigated. Intact reproductive tracts were collected from 16 Holstein cows at an abattoir. Samples were classified in to 4 stages (follicular, postovulatory, luteal and early pregnant,< 20 d) based on visual observation of corpus luteum (CL), uterine characteristics and luteal P(4) concentrations. Oviducts were separated from the uterus at the utero-tubal junction and divided into 4 parts: fimbriae, proximal, medial and distal parts. Luteal tissue samples were also collected. Progesterone levels in oviductal and luteal tissues were determined by radioimmunoassay (RIA). Comparatively higher (P < 0.001) P(4) levels were found in stages with a functioning CL ( luteal phase and early pregnancy) than in those with a regressing CL (follicular phase and post ovulation). The oviduct ipsilateral to the CL bearing ovary during the luteal phase and early pregnancy showed higher ( P < 0.001) P(4) concentrations than the contralateral side. Such a difference was not observed during the follicular phase or post ovulation. The ipsilateral oviduct to the functioning CL at early pregnancy showed higher (P <0.05) P(4) levels than at the luteal phase, while no significant difference in luteal P(4) levels between these 2 stages was observed. Neither were any differences in P(4) concentration within the oviduct observed during any phase of the estrous cycle or during early pregnancy. A positive relationship between luteal and oviductal P(4) concentrations was noted. In conclusion, changes in P(4) levels in the oviduct depend on the location and functional stage of the CL. Localized levels of P(4) in the oviduct may be due to local delivery of P(4) from the CL.