Intrinsic spontaneous activity and β-adrenoceptor-mediated tubal dilatation affect ovum transport in the oviduct of the cow

Abstract

Oviducts of cows were obtained during the proliferative and secretory phases of the oestrous cycle (determined by macroscopic appearance of the ovaries). Consistently higher frequencies of contraction were observed in the isthmus than in the ampulla, whereas no significant difference was observed between longitudinal and circular specimens, or throughout the oestrous cycle. Basal activity was inhibited by removal of extracellular Ca2+ and by verapamil (10-5 M). Addition of Ca2+ restored activity in the first case, but not in the second. Administration of various adrenoceptor agonists and antagonists revealed that the responses of the longitudinal and circular smooth muscles were primarily mediated by β-adrenoceptors (β2>β1), while the α-adrenoceptor-mediated contractions (α2-subtype) were masked by the marked β-adrenergic dominance. The results support the concept that the significance of adrenergic nerves in the cow oviduct may be to produce relaxation rather than contraction; the combined β1- and β2-adrenoceptor-mediated tubal dilatation and the intrinsic spontaneous activity seem to be the main factors affecting ovum/embryo transport throughout the oviduct in cows.