Local mechanical effects and humoral factors evoke degeneration of guinea pig uterine innervation.

Small porcelain pellets were inserted into one of the uterine horns of virgin guinea pigs. Mating caused pregnancies only in contralateral, non-pellet-containing uterine horns. The number and morphology of uterine nerve structures was studied immunohistochemically. In pellet-surrounding tissues of virgin animals the number of nerves was reduced and remaining nerve structures displayed signs of degeneration. This nerve reduction was further advanced in early to mid-pregnancy when almost no nerve structures could be detected. Myometrial strips were transplanted to the anterior eye chamber and became reinnervated by adrenergic nerves. The pattern and structure of the adrenergic reinnervation did not differ between strips taken from virgin animals, untreated or following chemical sympathectomy, or taken from primiparous animals following pregnancy induced sympathectomy. The adrenergic reinnervation of transplants from virgin animals was not affected by pregnancy of the recipient animal. It is suggested that the uterine innervation can be influenced by local, mechanically-induced effects, which during pregnancy co-operate with conceptus-related humoral factors to cause an almost total uterine nerve degeneration. The ability of uterine adrenergic reinnervation is probably not significantly influenced by local environmental tissue factor(s), but is related rather to extent of nerve damage.