Distribution of lactotroph subpopulations in different regions of the rat pituitary

Live staining and isolation of specific hormone-producing cells from rat anterior pituitary by cytochemistry with lectins and cholera toxin B subunit

Anterior pituitary glands contain five types of hormone-producing cells. Distinguishing and isolating specific types of living cells are essential for studying their function. Although many such attempts have been made, the results have been disappointing. In the present study, we labeled specific types of living hormone-producing cells by using potential differences in sugar chains on the cell surfaces. Cytochemical analysis with lectins and cholera toxin B subunit revealed that PNA, S-WGA, and cholera toxin B subunit recognized sugar chains specific to prolactin cells, ACTH cells, and GH cells, respectively, and that UEA-I recognized most of prolactin cells and GH cells. Next, fluorescence-activated cell sorting was used to isolate GH cells labeled by fluoresceinated cholera toxin B. The purity of the GH cell fraction estimated by immunocytochemistry and quantitative real-time PCR for cell type-specific genes was more than 98%, which was higher than that reported in earlier studies, including those using transgenic animals. We conclude that cytochemistry with lectins and cholera toxin B subunit is a straightforward, acceptable method of isolating specific types of anterior pituitary cells and that the cells isolated by this method can serve as useful materials in the study of anterior pituitary cells.

Hydropic degeneration of the anterior pituitary gland (adenohypophysis) in uremic rats

We observed hydropic degeneration of the anterior pituitary in rats made uremic by nephrotoxic chemicals, especially when the uremic rats were given a pure carbohydrate diet beforehand. The hydropic degeneration caused loss of nuclear and cytoplasmic content of many or most anterior pituitary cells. It was readily visible in paraffin sections by light microscopy. It was exaggerated when water was injected after the nephrotoxin and it was greatly reduced if saline was injected after the nephrotoxin. Low serum sodium levels in affected rats and the response to saline injection suggested that the mechanism for development of hydropic degeneration of the anterior pituitary gland involved hyponatremia. Depletion of total body sodium probably accounts for the enhancement of hydropic degeneration by the pure carbohydrate diet. Morphologic lesions of the anterior pituitary related to hyponatremia and uremia have not been described previously.

Effect of estradiol and FBS on PRL cells, GH cells, and PRL/GH cells in primary cultures of pituitary cells from prenatal rats

The effects of estradiol (E2) treatment on prolactin (PRL) cells, GH cells, and PRL/GH cells in immature pituitary cells were determined using primary cultures from prenatal rats and immunocytochemistry with fluorescent antibodies. Anterior pituitaries obtained from fetuses on day 22 of pregnancy were monodispersed and cultured in chemically defined medium or medium containing 10% fetal bovine serum (FBS). After pre-incubation for 24 hr, E2 (final concentrations were 0 M, 10(-8) M, 10(-7) M, and 10(-6) M) was added into each medium. After 72 hr of incubation, cells were subjected to immunocytochemistry. E2 stimulated the increase of PRL cells in a dose-dependent manner, and the PRL cell percentage cultured with FBS in all groups was significantly higher than that cultured in chemically-defined medium. PRL/GH cells also responded to E2 in the same manner as PRL cells. E2 was not effective in proliferating GH cells, and GH cell percentage significantly decreased with the addition of FBS into the medium. These results suggest that E2 is dose-dependently capable of increasing immature PRL cells and/or PRL/GH cells in vitro. Moreover, there is a factor(s) in FBS that regulates the increase of these cells.

Ovarian steroids modulate responsiveness to dopamine and expression of G-proteins in lactotropes

The effects of chronic ovarian steroid treatment on the secretory activity of individual lactotropes and the mechanisms modulating their responsiveness to dopamine (DA) were studied. Female rats were ovariectomized (OVX) and implanted with Silastic capsules containing progesterone (P4), 17beta), 17beta-estradiol (E2) or both E2 (E2+P4). Ten days after surgery, anterior pituitaries were enzymatically dispersed and the reverse hemolytic plaque assay (RHPA) was performed to assess the release of prolactin (PRL) from individual lactotropes. RHPA was combined with immunocytochemistry (ICC) for PRL, Galphas or Gialpha3/Galphao proteins. E2 treatment alone or in combination with P4 increased the percentage of immunoreactive lactotropes among anterior pituitary cells. Incidence of active (plaque-forming) lactotropes, however, was increased both in P4-, and E2-treated rats and E2+P4 treatment increased it even further. While P4 treatment did not affect the frequency distribution of lactotropes, both E2 and E2+P4 treatments increased the large plaque-forming lactotrope population. This increase was reflected by the significantly greater mean plaque areas of lactotropes from E2- and E2+P4-treated rats compared to OVX or P4-treated animals. The responsiveness of lactotropes to DA from P4-treated rats did not differ from that of OVX rats: thus challenge with 1 microM DA inhibited the release of PRL, while 100 pM DA had no effect. E2 and E2+P4 treatments, however, profoundly changed the lactotrope's responsiveness: challenge with 1 microM DA had no effect and 100 pM DA resulted in moderate stimulation of PRL release in E2+P4 rats. Double-label ICC revealed that ovarian steroid treatments did not affect the expression of Galphas in lactotropes. The incidence of Gialpha3/Galphao-immunoreactive lactotropes, however, decreased after E2 treatment, alone or in combination with P4. Although expression of Galphas was similar in all plaque-forming cells regardless of plaque size, lactotropes expressing Gialpha3/Galphao were more likely to form small plaques in all treatment groups. These data suggest: (1) ovarian steroid treatment recruits quiescent lactotropes to release PRL; (2) E2 treatment alone or in combination with P4 increases the amount of PRL rleased by individual lactotropes; (3) E2-induced alterations in the frequency distribution and lactotrope responsiveness to DA may be due in part to a decreased expression of Gialpha3/Galphao.

Possible involvement of folliculo-stellate cells in the differentiation of muscle fibers during monolayer culture of pituitary cells

A major objective of the present study was to examine the possibility that non-granular folliculo-stellate (FS) cells in the rat anterior pituitary are involved in the myogenesis that occurs during pituitary cell culture. Enzymatically dissociated anterior pituitary cells were fractionated by use of the Percoll gradient method. The proportion of FS cells was 5.8% on average before cell fractionation. After employing the Percoll gradient procedure, FS cells were enriched to a ratio of 12.2%. Three of five cell fractions were separately cultured, and the incidence of striated muscle fibers was quantitatively investigated. There was a good correlation between the numbers of muscle fibers and the proportions of FS cells in the fractions obtained from the Percoll gradient. These results suggest that FS cells are the cells that transform into striated muscles in pituitary monolayer cultures.