5 Transport and cholinergic innervation in the bovine oviduct are dysregulated in cystic ovary disease

Abstract

Cystic ovary disease (COD) is one of the most common causes of bovine infertility and affects 7-14% of cows in European herds. The morphological and molecular causes of this disease are largely unknown. Because the oviduct is pivotal to gamete transport, fertilization, and early embryonic development, the aim of this study was to analyse the effects of COD on the function of the oviduct. Oviducts were excised from cows affected by COD (n = 29) as well as from healthy cows in mid diestrus (n = 20) immediately after slaughter. A unique digital live cell imaging system established in our laboratory was used to capture real-time videos of ciliary beat and tubal fluid flow under near in vivo conditions. For ciliary beat frequency, the differences in grayscale of beating cilia were transformed into frequencies using ImageJ (National Institutes for Health) and AutoSignal (SyStat Software Inc.). For particle transport speed (PTS), polystyrene beads were added to the buffer media and were automatically tracked using ImagePro (Media Cybernetics). Additionally, smooth muscle contraction and epithelial ion transport were investigated using organ baths and Ussing chambers. Our results showed that PTS was significantly decreased in oviducts from cows affected by COD as compared with controls (P = 0.01, unpaired t-test). Further, in healthy control cows, PTS was consistently increased in the oviduct ipsilateral to ovulation as compared with the contralateral oviduct (P = 0.03, paired t-test). This was not the case in cows affected by COD (P = 0.47, paired t-test). Reduced PTS in oviducts from cows with COD was not due to changes in ciliary beat frequency. Although smooth muscle contraction was similar in oviducts from healthy and COD cows, the contractile response (mN) to the cholinomimetic drug carbachol (10⁻⁷-10⁻⁴ M) was significantly reduced in COD as compared with the controls (P < 0.0001, nonlinear regression best fit analysis). Active epithelial ion transport, as measured by the change in short circuit current (μA cm⁻²), was stimulated by carbachol. Carbachol-induced active ion transport in the oviducal epithelium of COD cows was significantly decreased as compared with controls (P = 0.03, unpaired t-test of area under the curve). These results suggest, for the first time, that the transport of the gametes and the early embryo might be impaired in COD. Further, inadequate or insufficient cholinergic innervation may result in dysregulated fluid flow, which might be associated with alterations in oviducal metabolism and gamete or embryo nutrition. This knowledge is pivotal to establish novel therapeutic concepts for successful treatment of infertility in individuals affected by COD.