A typology of the gnathostome adenohypophysis with some emphasis on its gonadotropic function.

Recent publications show that the average gnathostome adenohypophysis consists of four parts and contains six morphological cell types. Histophysiological and immunocytochemical data prove the secretion of one or two gonadotropins by one type of basophils that in numerous species in characterized by the presence of large globules besides secretory vesicles. The existence of a second type of gonadotropin secreting cells remains doubtful. Thyrotropin is produced by a separate type of basophilic cells, prolactin by erythrosinophils of the rostral pars distalis, and somatotropin by orangeophils of the proximal pars distalis. At rostral and caudal places of contact with the neurohypophysis, cells are concentrated that may be lead-haematoxylin-positive, and produce a protein consisting of peptides with hormonal and opiate activities. Among the hormones secreted by these cells, situated in the pars distalis and the pars intermedia, are corticotropin and melanotropin respectively. The factors that cause the differentiation of the primordium of the adenohypophysis are almost entirely unknown.