[The ACTH of the pituitary pars intermedia]

The present investigation suggests that the intermediate lobe contains corticotrophic cells that are morphologically similar to those of the adenohypophysis. It can also be concluded that the ACTH molecules extracted from the intermediate lobe do not differ from those from the adenohypophysis. The immunocytochemical studies confirm the presence of ACTH in the intermediate lobes of all species studied so far, and stimulate the question of the mechanism of ACTH synthesis at this level. The interrelationships between different peptides of the intermediate lobe, including LPH, ACTH, CLIP and MSH, require further investigations. The intermediate lobe synthesizes and releases ACTH in vitro. This release can be stimulated by crude extracts of the median eminence or of cerebral cortex, and does not seem to be controlled by the CRF. Although ACTH of the intermediate lobe intervenes in vivo in the response to a neurogenic stress, one may not assume that the intermediate lobe alone plays an important role in the maintenance of the adrenal cortex, as the adrenals are similarly affected by hypophysectomy or pars distalis removal.