The effect of neurohypophyseal hormones on the female reproductive tract of lower vertebrates

Abstract

Experimental evidence concerning the contractile response of the oviduct of nonmammalian tetrapods to neurohypophyseal hormones is reviewed and the conclusion is drawn that the organ in vitro usually responds preferentially to vasotocin. However, there are indications that the discrimination of the oviductal receptors between various neurohypophyseal active peptides and their threshold concentrations vary with the species and the physiological state of the oviduct. The oviducts of teleost and elasmobranch fishes could also be shown to respond to neurohypophyseal extracts in vitro but the results suggest that in the case of the dogfish Scyliorhinus the unidentified oxytocin-like hormone(s) in the animal's pituitary are more active than vasotocin. The doses to which the oviducts of the various vertebrate classes respond in vitro are usually equivalent to only a fraction of the hormone content of the animal's neurohypophysis. In certain species of ovoviviparous teleosts it could be shown that the oviductal muscle extends into the ovary where it divides into an external layer that surrounds the organ, and an internal layer which envelops the follicles. Ovaries of this type were found to give a contractile response to vasotocin in vitro and the sensitivity to the hormone could be shown to increase markedly with the progress of gestation. Experiments in which the pituitary of pregnant fishes was implanted into nonpregnant animals suggest that the increase in the response to vasotocin is mediated by the adenohypophysis. Experiments with implants of estradiol and/or progesterone have, so far, been inconclusive but it was notable that both hormones stimulated “spontaneous” contractile activity of the ovaries of nonpregnant fishes.