Among the cells of the pituitary generally believed to produce glycoprotein gonadotropin (GTH) five forms were distinguished, based on the amount and the diameter of granules and globules and the appearance of the rough endoplasmic reticulum. In sham-operated trout so-called "globular" cells predominated, whereas after ovariectomy these were replaced by so-called "cisternal" cells, suggesting that both belong to one GTH-cell type. In addition, ovariectomy caused a strong increase in plasma GTH-levels. This indicates that the transition from globular to cisternal cells is accompanied by extrusion of GTH, and thus points to a storage of GTH in the granules and globules. It is argued that one of the five forms has the morphological characteristics of thyrotropic cells and may not produce glycoprotein GTH.

Prolactin cells were identified by means of immunocytochemistry with protein-A gold as a marker on ultrathin sections of the pituitary gland of young (3-4 months), middle-aged (16-19 months), and aged (26-30 months) male Wistar rats. Point-counting volumetry revealed that the prolactin (PRL) cell-volume density in middle-aged rats was significantly increased in comparison to the volume densities in young and aged rats. Within the PRL-cell population, four types of PRL cells were distinguished on the basis of the shape and size of their secretory granules. During aging, dramatic changes occurred in the relative volumes of the four cell types. The volume percentage of cells with round granules (type I, granule diameter 150-250 nm, and type IIA, granule diameter 250-350 nm) increased from +/- 30% in young rats to +/- 90% in old rats. The volume percentage of cells with round and polymorphic granules (type IIB; granule diameter 350-400 nm and type III; granule diameter 500-600 nm) decreased from +/- 70% in young rats to +/- 7% in old rats. Age-related changes in serum PRL levels were not found. It is concluded that although during the life span of the male Wistar rat considerable changes in PRL-cell volume densities and in the ratios of PRL-cell types occur serum, PRL levels remain more or less constant.

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Preembedding visualization of exocytosis by tannic acid treatment and postembedding immunocytochemical identification of cell types were combined to demonstrate the release of secretory products by exocytosis of characterized cell types. Treatment with tannic acid was carried out by perfusion with Ringer containing tannic acid, followed by fixation, dehydration and embedding. For electron microscopical immunocytochemistry protein A-gold was used as marker. In this study, exocytotic release was demonstrated for prolactin by cells in the pars distalis, and for oxytocin by axon terminals in the pars nervosa of the pituitary gland of the rat.

Alcian blue- and periodic acid-Schiff-positive "granular basophils" with electron-dense granules +/- 160 nm in diameter, and weakly developed irregular cisternae of the granular endoplasmic reticulum (GER) are present in the rostral pars distalis (RPD) and the proximal pars distalis (PPD) of immature rainbow trout. They all react with antisalmon alpha beta-gonadotropin. However, only granular basophils in the caudal RPD and the rostro-dorsal PPD, often bordering on and sometimes surrounded by neurophypophysial tissue, react with anti-human beta-TSH. These cells, considered as the source of thyrotropin, show degranulation and dilatation of the GER-cisternae in fish treated with potassium perchlorate. The thyroids of the goitrogen-treated animals had relatively numerous small follicles with a high epithelium. The remaining granular basophils are gonadotrops.