Histological and histochemical studies on the rat pituitary pars intermedia.

Inspite of the recent progress in the endocrinology of the anterior pituitary, a specific part of the adenohypophysis which is in a close contact with the neurohypophysis, i.e., the pars intermedia, has been left in a state of incomplete understanding both in morphology and physiology. For example, early reports by ITANO (1936) and BAILLIF (1938) dealing with the rat pars intermedia, indicated morphologically the secretory activity of this tissue, but no physiological correlation with its fine structure could be established. A fact that the probable secretion from the pars intermedia might stimulate the melanophores of the frog skin was well known, but it is still doubted whether the control on the pigment metabolism by the intermedia hormone might occur in mammalia also. On the other hand, an extraordinary intimate contact between the neural lobe and the pars intermedia may suggest a close relationship between the neurosecretory activity of the hypothalamo-neurohypophyseal system and the probable functions of the pars intermedia. We have reported several findings with the use of electron microscope on the ultrastructure of the rat intermedia cells and their morphological interrelation to the neural lobe (KUROSUMI et al. 1962). Simultaneous observations with the light microscope have revealed certain interesting facts concerning the histology and histochemistry of this tissue which have not been reported hitherto. Combining the light and electron microscopical findings, the result of the present observations may help to some extent to clarify the functional activities of the mammalian pars intermedia.