Seasonal changes in the cytomorphology of hypophyseal ACTH cells in relation to the reproduction cycle of the female of the frog Rana tigerina (Daud.)

Abstract

The hypophyseal ACTH (basophil type 3 or B3), cells of R. tigerina display seasonal changes in cytomorphology (nuclear, cytoplasm and cell area), staining intensity and cytoplasmic granulation. The cytoplasmic granules are fine and stain blackish purple with McConaill's lead haematoxylin, with Herlant's AB and the PAS and OG techniques they stain brownish red. The tinctorial response of their cytoplasm is PAS- and OG-positive and AB-negative. The B3 cells are low columnar or cuboidal in form and are smaller than the gonadotrophs (B2 cells). Towards the rostral border of the pars distalis they are larger and are associated with blood vessels, whereas in the caudal region they are smaller. Seasonal changes in the granulation and degranulation of the ACTH cells are also more prominent in the rostral region of the pars distalis than in the caudal region. During April, May and June a marked increase occurs in ACTH cell size and the number of cytoplasmic secretory granules, concurrently with events like vitellogenesis, lipid depletion from the fat bodies and breeding activity. During the post-breeding regression phase (and especially from August to November), the B3 cells decrease markedly in size and become devoid of secretory granules; their recovery begins slowly from December onwards. The findings suggest that the secretory activity of the ACTH cells in the frog undergoes seasonal changes which possibly influence vitellogenesis, lipolysis of the fat bodies and breeding activity.