Pituitary gonadotroph adenomas in old Sprague-Dawley rats.

Light microscopic and immunocytologic investigation revealed focal or diffuse pituitary gonadotroph hyperplasia in 3/27 male and 3/39 female Sprague-Dawley rats over 2 years of age. Three male and 2 female rats exhibited proliferation of morphologically abnormal gonadotrophs which were described as nodules, and 4 male and 5 female rats possessed gonadotroph adenomas which contained both immunoreactive beta-LH and beta-FSH. On plastic sections at the ultrastructural level, a further female rat was found to possess focal gonadotroph hyperplasia, 2 male and 2 female rats, gonadotroph nodules and 2 male and 2 female rats gonadotroph adenomas. While extensive gonadotroph and thyrotroph hyperplasia was observed in the nontumorous portion of the 2 pituitaries harboring thyrotroph adenoma, widespread gonadrotroph hyperplasia was noted in only 2 of 13 pituitaries with gonadotroph adenoma. Gonadotroph adenomas appeared to develop from discrete foci of morphologically altered gonadotrophs. These foci probably then progressed to form nodules and subsequently adenomas. Gonadotrophs within the nodules were often similar in morphology to adenomatous gonadotrophs whereas the earlier, smaller lesions were pleomorphic or more commonly trabecular in appearance. Serum LH levels were measured in some animals. As a group, rats displaying changes in gonadotroph morphology had a higher mean serum LH level than those without these changes, however, the values ranging from 23-249 ng/ml were well within the normal serum LH levels reported in aging rats. Gonadotroph adenomas in human patients have only recently been identified with accuracy and are relatively uncommon. As in the case of rats, they do not appear to arise from a pre-existing end organ hypofunction or pre-existing gonadotroph hyperplasia. A suitable animal model, in the form of spontaneously occurring gonadotroph adenomas in aging rats, might be useful in establishing the etiology, biochemical properties and appropriate therapy for these tumors.

Morphologic effects of cysteamine on the rat adenohypophysis.

In pituitary lactotrophs of female Sprague-Dawley rats given cysteamine (300 mg/kg, per os/day) for 7 days, forming granules were increased in number and contained many separate electron-dense structures suggesting crinophagy. Compared to control values, cysteamine treatment caused no change in blood prolactin (PRL) levels, measured by radioimmunoassay (RIA). 17 beta-Estradiol (50 micrograms, sc/day) for 7 days, induced lactotroph hyperplasia and increased blood PRL levels which were unaffected by simultaneous cysteamine administration. The ultrastructural changes did not reflect those due to bromocriptine suppression of secretory activity, and supported the concept that cysteamine altered lactotroph morphology by an unknown mechanism. In pituitary gonadotrophs following cysteamine treatment, increased electron lucency of luminal contents of dilated rough endoplasmic reticulum was noted; however, blood luteinizing hormone (LH) levels did not differ from those of control values. In ovariectomized rats, cysteamine suppressed castration cell formation and reduced blood LH levels, suggesting an interference with the cell's ability to respond to GnRH stimulation. The morphologic effects of cysteamine appeared to be selective to lactotrophs and gonadotrophs, and were not secondary to vascular impairment, as capillary endothelial cells were undamaged.

Some functional and morphological characteristics of an acutely dispersed purified cell suspension of rat lactotrophs prepared with Percoll.

A cell suspension containing more than 90% lactotrophs can be prepared from enzymically dispersed adenohypophyses obtained from male rats pretreated with estradiol. The lactotrophs are separated from the mixed cell population by centrifugation on a discontinuous density gradient prepared from a commercial preparation of colloidal silica (Percoll, Pharmacia). The method allows isopycnic separation of these delicate cells under very mild conditions; normal ionic strength and normal pH were maintained throughout the gradient, centrifugal acceleration did not exceed 1600 X g, and all procedures were done at room temperature. Histological verification that at least 90% of the cells were lactotrophs was done using specific immunoperoxidase staining. The functional capability of the lactotrophs was established by measuring the dose--response to the dopamine agonist bromocriptine and to thyrotropin-releasing hormone (TRH). Bromocriptine decreased spontaneous release in a dose-related way over the concentration range of 10(-10) to 10(-8) M. TRH, which causes an in vivo release of prolactin (PRL) in estrogen-primed rats, produced a dose-related increase in the release of PRL over the concentration range of 3 X 10(-10) to 3 X 10(-8) M after the high spontaneous release had been previously reduced by bromocriptine (3 X 10(-8) M).

Bromocriptine suppression of dispersed pituitary lactotrophs from estrogen-pretreated rats: a quantitative electron microscopic study.

Dispersed rat lactotrophs were treated with bromocriptine (10(-10) M) for either 30 min or 3 h to investigate its effect on cell morphology using light and electron microscopy and ultrastructural morphometry. After 30 min, lactotrophs treated with bromocriptine exhibited an increase in storage granule size (p less than 0.05). Crinophagy was also evident and a significant increase in lysosome volume density was observed (p less than 0.001). However, no significant change in prolactin content in the media was detected until 3 h of incubation in bromocriptine (p less than 0.05). At this time a nonsignificant decrease in Golgi region volume density was also observed.

Scanning electron microscopy of rat neurointermediate lobe cells in culture.

Enzymatically dispersed cells of the rat pars nervosa -- pars intermedia (NI) were observed by scanning electron microscopy after 1, 2 and 4 days in culture. The cells attached to the plate slowly, requiring about 3--4 days for the majority to adhere. The epithelial cells became attached singly and in clumps and branched chains, often over a bed of fibroblast-like cells. After the first day in culture, few surface features were evident on the NI cells, but by day 2, the surfaces showed a small number of blebs. In 4-day cultures, the cells revealed extensive areas with blebs and microvilli, and a few structures resembling cilia were observed. The adrenocorticotrophic hormone content of the cells after 4 days in culture was similar to that found in fresh tissue.

Effects of various secretagogues upon 42K and 22NA uptake during in vitro hormone release from the rat adenohypophysis.

1. The in vitro uptake of (22)Na and (42)K was measured simultaneously in rat adenohypophyses during hormone release produced by several secretagogues and during inhibition of hormone release in Ca-free media.2. Intracellular adenohypophysial [Na(+)] and [K(+)] changed only slightly when the uptake changed. This would indicate that relative permeability changes were the primary effect of the treatments.3. The uptake of (42)K was increased by elevated external [K(+)], but was unaffected by the presence or absence of Ca(2+). Acid extracts of hypothalamus-stalk-median eminence or cerebellum also increased the (42)K uptake.4. The uptake of (22)Na or (24)Na was decreased by elevated [K(+)]. Uptake was increased in Ca-free Krebs-Ringer bicarbonate; but was unaltered when [K(+)] was concurrently increased.5. Neither purified growth hormone releasing hormone, synthetic lysine-vasopressin, dibutyryl cyclic AMP nor theophylline had an effect on the uptake of either K(+) or Na(+).6. The rapid uptake of (22)Na and its smaller volume of distribution compared to absolute measurements of intracellular [Na(+)] suggest that the plasma membrane of adenohypophysial cells is relatively impermeable to Na(+).7. We conclude that changes in the uptake of Na(+) and K(+) associated with hormone release are incidental to the release process.8. Hormone release produced by elevated external [K(+)] is most likely due to a non-specific increase in permeability of the cell membranes, facilitating Ca(2+) entry into the cytoplasm.9. The results suggest that the low resting transmembrane potentials of adenohypophysial cells may be due to their conjoint relatively high permeability to both K(+) and Ca(2+), rather than K(+) and Na(+).

Adenohypophysial transmembrane potentials: polarity reversal by elevated external potassium ion concentration.

Incubation of rat adenohypophyses in potassium ion of sufficient concentration to provoke the release of several of the adenohypophysial trophic hormones produces a reversed, positive transmembrane potential in more than half the cells. This finding is consistent with a process of "stimulus-secretion coupling" in which hypothalamic releasing factors act by selective depolarization of their "target" cells. The positive potentials may be due to a prolonged preferential permeability to calcium ions triggered by an initial depolarization of the cell membrane to a threshold value by increased external potassium ion.

Potassium, corticosterone, and adrenocorticotropic hormone release in vitro.

Incubation of rat adenohypophyses in a high concentration of potassium increases adrenocorticotropic hormone release. This increased release is suppressed by the addition of corticosterone to the incubating medium. Our findings are consistent with a process of "stimulus-secretion coupling" proposed for other glands and suggest that corticosterone may operate directly on the adenohypophysial cell membrane to inhibit releasing mechanisms.