Appearance and disappearance of tubular paracrystalline structures in somatotrophs and lactotrophs during the annual life cycle of the bat (Myotis lucifugus).

The fine structure of the endocrine (granulated) cells of the adenohypophysis of the bat was examined at different periods of the annual life cycle. During the active homeothermic period (early spring until late summer) the endocrine cells were heavily granulated, and evidence of granule release was commonly seen. At this time, but not at other times (hibernation and arousal), prominent paracrystalline structures were numerous and transiently appeared in the cytoplasm of acidophils (apparently both lactotrophs and somatotrophs) but not in the cytoplasm of basophils. These paracrystalline bodies were composed of densely packed, parallel arrays of tubules. The paracrystalline structures in lactotrophs differed in size, shape, and the pattern of arrangement of component tubules from those of somatotrophs. During hibernation no evidence of exocytosis was seen, and secretory granules accumulated in the cytoplasm. Prior to arousal, secretory granules were removed by autophagy.