[Effect of long-term suppression and long-term stimulation of ACTH secretion on the ultrastructure of tanycytes[].

The ultrastructure of the tanycyte ependyma in males of Wistar albino rats (160--180 g of weight) was studied under experimental long-term suppression of ACTH secretion and its long-term stimulation. The former effect was accomplished by daily (for 8 days) intraperitoneal administration of dexamethasone phsophate; the stimulation of ACTH secretion was achieved by bilateral adrenalectomy. The long-term suppression of the hypophyseal adrenocorticotrophic function was followed by the ultrastructural markers of an increased transport and secretory activity in the tanycytes (mainly in beta-tanycytes, i. e. the ependyma lining floor of the third ventricle): the increased amount of microvesicles in the Golgi area and in the vicinity of the particular membranous cavity system (MCS, according to the authors' definition), the appearance of some figures of exocytosis, the elevated amount of lipid inclusions. On the contrary, the long-term stimulation of ACTH secretion was followed by the ultrastructural changes of the opposite character. The data obtained are in agreement with the previously established fact that there is a negative correlation between the tanycyte activity and the hypophyseal adrenocorticotrophic activity. It is supposed that this correlation is regulated by a feedback mechanism and attest to the involvement of tanycytes in the inhibitory control of ACTH secretion. A possible substrate inhibiting ACTH secretion by the tanycytes is discussed.