Uterine adrenergic and cholinesterase-positive nerves and myometrial catecholamine concentrations during pregnancy in sheep

Uterine adrenergic and cholinesterase (AChE)-positive innervation of the sheep uterus during anestrus and at 4 stages of pregnancy were examined by histochemical methods. In addition, uterine and cervical myometrium concentrations of norepinephrine (NE) and dopamine (DA) were determined using high-performance liquid chromatography. During anestrus, adrenergic and AChE-positive nerve fibers in the uterine myometrium and endometrium were primarily associated with the vasculature. Innervation of myometrial smooth muscle was almost exclusively by adrenergic fibers. In the endometrium, fibers of both types were observed closely associated with endometrial glands, and adrenergic fibers were observed in the connective tissue beneath the luminal epithelium. Density of uterine innervation decreased by day 65 of pregnancy with an additional decrease by day 105. Myometrial NE concentrations were higher in the cervix than the uterus. Uterine NE concentrations generally were not affected by pregnancy. Although cervical NE per gram of tissue decreased during pregnancy, this effect of pregnancy was not detected when NE was expressed per microgram of DNA. Myometrial DA concentrations were higher in uterine segments than in the cervix. DA concentrations decreased during pregnancy in all tissues except the posterior uterine segment. The DA to NE ratio in the uterus was greater than that for the cervix and was not generally affected by the stage of pregnancy. These results demonstrate that cholinergic and adrenergic nerves supply the sheep uterus. Decreasing fiber density during pregnancy suggests that a majority of the innervation to the sheep uterus is supplied by 'short' nerve fibers whose activity is regulated by steroids of pregnancy. The possible role of DA as a neurotransmitter in the sheep uterus is discussed.