Prolactin cells and plasma prolactin levels in the aging male Wistar rat: an immunocytochemical and biochemical study.

Non-neoplastic pituitary glands of 12 age-groups of 10 male Wistar rats (subpopulation 1) and of 228 rats with age-related disorders (population 2) were studied. For subpopulation 1 a positive correlation was found between body weight, pars distalis volume and total prolactin (PRL)-cell volume. These values increased during the first half of the life span and decreased to values similar to that found in young rats, after the 50% survival age was reached. Age-related changes were found with respect to the distribution of the PRL cells (from homogeneous into non-homogeneous) and to their ultrastructural features (PRL cells with polymorphic granules were substituted by cells with round granules). Pituitary glands of disordered aged rats (subpopulation 2) showed a similar non-homogeneous distribution of PRL cells. Plasma PRL levels of both subpopulations were similar. No age-related increase of plasma PRL level was found in rats with non-neoplastic pituitary glands.

Studies on prolactin-secreting cells in aging rats of different strains. I. Alterations in pituitary histology and serum prolactin levels as related to aging.

Serum PRL levels and histologically tumor-free pituitary glands of 91 aging rats of the BN/BiRij strain, the WAG/Rij strain and their F1 hybrid were studied. In rats with pituitary glands without signs of hyperplasia, serum PRL levels were, in comparison to rats of 15-24 months, increased 25-29-month-old female BN/BiRij rats and showed a decline with further aging. This rise and decline during aging correlated with changes in the PRL cell volume density and in ultrastructural signs of their synthetic activity. Rats with hyperplastic pituitaries showed similar age-related changes in serum PRL levels, but these levels were higher. Concerning the hyperplasia, some strain differences were found. In BN/BiRij rats anti-r-PRL positive hyperplasia, and in WAG/Rij and F1 rats, anti-r-PRL negative and anti-r-PRL positive hyperplasia were present. All foci of hyperplasia were negative for anti-ACTH and anti-h-GH. In male rats no age-related changes of serum PRL levels could be established, although a decline of PRL cell volume density in the oldest rats is indicated. We conclude that the absence of a continuous age-related rise of serum PRL levels in our animals is caused by exclusion of animals with pituitary tumors.

Environmental influences on prolactin cell development in the cyprinodont fish, Cynolebias whitei.

A combined immunocytochemical and morphometric study on the development of the prolactin (PRL) cells of the annual cyprinodont Cynolebias whitei, transferred as newly hatched larvae to water with different salinities and/or Ca2+-concentrations, was carried out. The percentage of the pituitary volume occupied by PRL cells and the affinity of PRL cells for immunocytochemical staining were used as criteria for their activity. Exposure of the larvae for one day to salt water (260 mOsm/kg) led to a significant reduction in the pituitary volume occupied by PRL cells, indicating an osmoregulatory function of PRL shortly after hatching. In fish reared in diluted artificial seawater (70 and 260 mOsm/kg) or Na+-enriched fresh water the development of PRL cells was significantly retarded, but such an effect was not observed in fish placed in Ca2+-enriched fresh water. These experiments show that in C. whitei the development and activity of PRL cells are influenced by changes in environmental osmolarity and not by changes in ambient Ca2+-concentration.

Immunoreactive prolactin in the pituitary gland of cyprinodont fish at the time of hatching.

In the developing pituitary gland of embryos of the annual fish Cynolebias whitei and the medaka, Oryzias latipes, prolactin cells have been identified before hatching by means of a light-microscopic immunocytochemical method with antiserum against ovine prolactin. At the time of hatching, changes in the intensity of the immunoperoxidase staining occur. Histological staining by Cleveland and Wolfe's trichrome shows differentiation of cell types in the adenohypophysis only later in ontogeny. Our results indicate that, in teleosts, differentiated prolactin cells are present before hatching and that prolactin may be involved in the endocrine control of the hatching process.

The pituitary gland of the coelacanth fish Latimeria chalumnae Smith: general structure and adenohypophysial cell types.

The pituitary gland of Latimeria chalumnae is situated rostroventral to the telencephalon. The hollow pituitary stalk is bent forward and is ventrally connected to a saccus-vasculosus-like organ, rostrally to a neurointermediate lobe. The infundibular lumen protrudes far into the neurohypophysial lobules. The elongated principal part (pars cerebralis) of the pars distalis is partly embedded in a dorsal depression of the pars intermedia and caudally invaded by the neurohypophysis. It may be divided into rostral and proximal pars distalis and includes a ramified hypophysial cleft, which continues rostrally as a duct with adjacent islets of pars distalis tissue (parts of a pars buccalis). The adenohypophysis consists of cell cords and follicles. Eight tinctorial cell types can be distinguished: in the rostral islets: large basophils with acidophil globules, in the rostral pars distalis: small basophils, large basophils with amphiphil characters and erythrosin-, orange G-positive acidophils; in the proximal pars distalis: orange G-positive acidophils and small and large basophils, having similar staining properties; in the pars intermedia: one amphiphil cell type.