The ovine pars tuberalis: a naturally occurring source of partially purified gonadotropes which secrete luteinizing hormone in vitro.

The pars tuberalis and pars distalis are constant subdivisions of the vertebrate adenohypophysis. Unlike the pars distalis, however, direct evidence of an endocrine function for the pars tuberalis is lacking. The present immunocytochemical study shows the ovine pars tuberalis to be unique in that 1) its only immunoreactive hormone-containing cell type is the gonadotrope; and 2) the vast majority of pars tuberalis cells contain no identifiable pituitary hormones. In vitro superfusion studies demonstrate that the ovine pars tuberalis is capable of baseline and GnRH-stimulated gonadotropin secretion which, on a per mg basis, is qualitatively and quantitatively similar to the secretory capacity of the pars distalis.