Effects of colchicine on the morphology and prolactin secretion of rat anterior pituitary cells in monolayer culture

The effects of incubation of rat anterior pituitary cells in monolayer culture with 10^?6 M colchicine have been investigated during timeintervals extending from 1 to 96 hours. Prolactin release, as measured by radioimmunoassay, was rapidly inhibited by colchicine, this inhibition being accompanied by increased cellular prolactin content for up to 24 hours of treatment and followed by decreased values of cellular prolactin concentration at later time-intervals. Immunocytochemical localization showed an increased positive reaction for prolactin up to 24 hours after colchicine treatment, whereas transmission electron microscopy demonstrated, in parallel, an increased number of intracellular prolactin secretory granules during the same interval. Longer periods of treatment (24–96 hours) resulted in the appearance of more lysosomes, autophagic vacuoles and microfilaments in the cells, whereas the number of Golgi elements was decreased. Following four hours of colchicine treatment and at later stages, microtubules could no longer be observed in the sections. Scanning electron microscopic data showed that colchicine treatment induced dramatic changes in the cell surface morphology: at short time intervals (4 and 8 hours), the number of microvilli decreased and the cell surface became folded, whereas, later, “bleb”-like protrusions of variable dimensions partially covered the cell surface and seemed to be released from it. These data show a good correlation between secretory activity of prolactin-producing cells and morphological changes induced by colchicine treatment.     

Effect of acrylonitrile on the rat pituitary: enlargement of Golgi region in prolactin cells, crinophagy in prolactin cells and growth hormone cells

Since it has been shown that acrylonitrile prevents the appearance of spontaneous pituitary adenomas, we have investigated its effect in acute experiments on rat pituitaries by histology, immunocytochemistry, electron microscopy and morphometry; in addition, serum prolactin and growth hormone levels were measured by radioimmunoassay. Electron microscopy of prolactin cells revealed hypertrophy of the Golgi region without significant change in volume densities and diameters of forming and storage granules. In the 24 h group, crinophagy was observed in prolactin cells and growth hormone cells. Corticotrophs, thyrotrophs and gonadotrophs were unaltered. Dilation, congestion and rupture of capillaries, as well as pericapillary and intercellular oedema were evident in the 24 h group. One hour after intravenous acrylonitrile injection, serum prolactin levels were within the normal range, whereas at 24 h, hyperprolactinemia was noted. Serum growth hormone concentrations were unchanged. It can be concluded that acrylonitrile has a complex effect on prolactin cells. Hypertrophy of Golgi complex and hyperprolactinemia may reflect increased prolactin synthesis and release. Since volume densities and diameters of secretory granules in prolactin cells remained unchanged, it appears that newly synthesized prolactin was preferentially released and not the prolactin stored in secretory granules. Crinophagy may be the morphological manifestation of a discrepancy between hormone synthesis and release suggesting increased degradation of unused hormone by lysosomes.     

Effect of acrylonitrile on the rat pituitary: enlargement of Golgi region in prolactin cells,crinophagy in prolactin cells and growth hormone cells.

Since it has been shown that acrylonitrile prevents the appearance of spontaneous pituitary adenomas, we have investigated its effect in acute experiments on rat pituitaries by histology, immunocytochemistry, electron microscopy and morphometry; in addition, serum prolactin and growth hormone levels were measured by radioimmunoassay. Electron microscopy of prolactin cells revealed hypertrophy of the Golgi region without significant change in volume densities and diameters of forming and storage granules. In the 24 h group, crinophagy was observed in prolactin cells and growth hormone cells. Corticotrophs, thyrotrophs and gonadotrophs were unaltered. Dilation, congestion and rupture of capillaries, as well as pericapillary and intercellular oedema were evident in the 24 h group. One hour after intravenous acrylonitrile injection, serum prolactin levels were within the normal range, whereas at 24 h, hyperprolactinemia was noted. Serum growth hormone concentrations were unchanged. It can be concluded that acrylonitrile has a complex effect on prolactin cells. Hypertrophy of Golgi complex and hyperprolactinemia may reflect increased prolactin synthesis and release. Since volume densities and diameters of secretory granules in prolactin cells remained unchanged, it appears that newly synthesized prolactin was preferentially released and not the prolactin stored in secretory granules. Crinophagy may be the morphological manifestation of a discrepancy between hormone synthesis and release suggesting increased degradation of unused hormone by lysosomes.     

Diethylstilbestrol inhibits tumor growth and prolactin production in rat pituitary tumors.

Treatment of rats bearing transplantable MtT/W15 tumors with 10 mg of diethylstilbestrol (DES) for 3 weeks led to inhibition of tumor growth. The inhibition of tumor growth was reversible after removal of the DES. Histologic examination revealed decreased mitotic activity; however, DES did not produce cell necrosis. Concomitantly, the anterior pituitary glands of animals treated with DES became hyperplastic, with an increased number of prolactin (PRL)-producing cells. DES resulted in a decreased number of PRL cells in the tumor and decreased serum PRL/tumor weight, compared with that of control rats. There was also an increase in the number of growth hormone (GH) tumor cells and an increased serum GH/tumor weight. 17 beta-Estradiol had an effect similar to that of DES, while progesterone did not inhibit tumor growth or cause pituitary cell hyperplasia. Ovariectomy resulted in a decrease in the tumor growth rate, compared with that of control animals, suggesting that the MtT/W 15 tumors are relatively dependent on estrogens for optimal growth. These results indicate that DES inhibition of MtT/W 15 tumor growth is an excellent model for study of the mechanism of the inhibition of tumor growth and the modification of GH and PRL expression by the tumor cells.     

Effects of propylthiouracil on growth hormone and prolactin messenger ribonucleic acids in the rat pituitary

The effects of hypothyroidism induced by propylthiouracil (PTU) treatment on growth hormone (GH) and prolactin (PRL) messenger ribonucleic acid (mRNA) levels were analyzed in adult female rat adenohypophyses by in situ hybridization histochemistry and Northern hybridization analyses. Twenty-eight days of PTU treatment produced a significant decrease in GH mRNA levels and a smaller decrease in PRL mRNA determined by both in situ hybridization histochemistry and Northern hybridization analyses. A combined procedure of in situ hybridization histochemistry followed by immunochemistry on the same sections revealed mammosomatotropic cells expressing GH mRNA and PRL protein in the same pituitary cells from all treatment groups. Cells expressing GH mRNA and thyroid-stimulating hormone protein were not detected by this method. Immunochemical staining revealed a decrease in GH cells and an increase in thyroid-stimulating hormone cells in hypothyroid rats. Cells expressing both GH and thyroid-stimulating hormone protein were not detected by immunostaining. These results indicate that hypothyroidism produces significant decreases in GH mRNA and also decreases PRL mRNA and that mammosomatotropic cells can be detected in pituitaries from normal and hypothyroid rats.     

Effects of cations on prolactin and growth hormone secretion by rat adenohypophyses in vitro

1. Explants of rat adenohypophyses were incubated in medium 199, Earle's saline, or modified Earle's saline (K-Earle's) with different calcium, magnesium, sodium and potassium concentrations for 4-6 hr at 37 degrees C in 5% CO(2) in O(2).2. The amount of prolactin and growth hormone in explants and in medium was estimated by disk electrophoresis and densitometry.3. Low calcium inhibited prolactin secretion by 40-60%. Low magnesium and slightly increased (5x) magnesium (4.1 mM) did not influence prolactin secretion in either 1.8 mM or low calcium, but 10 and 20 mM magnesium inhibited secretion by 50 and 70%, respectively. Inhibition of prolactin secretion by high magnesium was reversible.4. Decreasing sodium by 80% had no effect on prolactin secretion, but low sodium inhibited the sustained, although not acute, secretion of this hormone.5. Low potassium did not affect the secretion of either prolactin or growth hormone. Increased potassium (32 or 54 mM) slightly stimulated prolactin secretion by adenohypophyses of males but had no effect on the secretion of this hormone by female glands.6. In 1.8 mM calcium, growth hormone secretion by pituitaries of males and females was markedly stimulated by increased potassium, but it was not appreciably affected by high potasium in low calcium. Increased potassium did not stimulate growth hormone secretion in medium containing low sodium with normal calcium.7. Secretion of prolactin and growth hormone by rat adenohypophyses is dependent upon calcium, but only growth hormone secretion is markedly stimulated by increased potassium. The difference in responsiveness to increased potassium, between the somatotrophs and lactotrophs, may be related to the predominant mode of hypothalamic control of these hormones.     

Immunoelectron microscopy for growth hormone and prolactin in pituitary adenomas

Growth hormone (GH)- and prolactin (Prl)-producing pituitary adenomas were studied with immunoelectron microscopy using protein A-gold complex, and were compared with the normal pituitary gland. GH-producing cells were readily identifiable by numerous, uniformly dense, round secretory granules in both adenomas and normal pituitary gland. In contrast, Prl secretory granules in normal pituitary gland were much larger in size than the scarce, smaller, secretory granules of Prl-producing adenomas. Thus immunoelectron microscopic identification of Prl is more valuable for prolactinoma. With more specific antigens available as tumor markers, immunoelectron microscopy appears to be a powerful tool for tumor diagnosis.     

Mixed growth hormone cell- prolactin cell pituitary adenoma with acromegaly: α-subunit most growth hormone cells

A 51 -year-old woman with mixed growth hormone (GH) cell-prolactin (PRL) cell pituitary adenoma is presented. She had clinical signs due to hypersecretion of GH and PRL. Resected tissue was studied immunohistochemically and morphologically. The serial sections revealed that GH and α-subunit were co-localized in most cells, while GH and PRL were localized in different cells.     

Inhibition by nimodipine of growth hormone (GH) releasing factor-induced GH secretion from rat anterior pituitary cells.

The involvement of voltage-sensitive Ca2+ channels has been suggested in growth hormone (GH) releasing factor (GRF)-induced GH secretion from somatotrophs. To characterize further the role of L-type Ca2+ channels in GRF-stimulated GH secretion, we examined the effect of nimodipine on GH secretion induced by several secretagogues in perifused dispersed rat anterior pituitary cells. Excess K+ (50 mM)-induced GH secretion was most effectively suppressed by nimodipine among those examined. The ID50 was between 10(-8) and 10(-7) M. One microM nimodipine suppressed 1 nM human GRF (hGRF)-induced GH secretion to 62.1% of the control and 10 microM nimodipine further suppressed it to 33.4% of the control. Dibutyryl cyclic AMP (DBcAMP)-induced GH secretion was less sensitive to inhibition by nimodipine. One mM DBcAMP-induced GH secretion was suppressed to 67.5% of the control by 10 microM nimodipine. Cs+ (20 mM), known to block K+ channels, slightly augmented basal GH secretion, but the same concentration of CS+ caused greater facilitation both in hGRF- and DBcAMP-induced GH secretion. The inhibitory effect of nimodipine was far greater in these CS(+)-augmented responses than that in normal medium. We have previously proposed that hGRF depolarized the somatotrophs in Na(+)-dependent mechanism. This depolarization may elicit the trains of action potentials which involve the activation of L-type Ca2+ channels. Blockade by nimodipine of these L-type Ca2+ channels is time- and voltage-dependent and is maximized by long depolarization. CS+ may prolong the duration of action potentials by blocking the delayed rectifier K+ channels which may provide enough time for nimodipine to block activated L-type Ca2+ channels. These results suggest that L-type Ca2+ channels play a major role in hGRF-induced GH secretion.     

Effect of thyrotrophin releasing hormone on secretion of thyrothrophic hormone and prolactin in a monolayer culture of rat adenohypophysis

Cells of the adenophypophysis in a primary 5–8-day monolayer culture react to addition of thyrotrophin releasing hormone (TRH) by rapid dose-dependent liberation of thyrotrophic hormone (TSH) and prolactin into the culture medium. This effect is independent of the content of serum in the nutrient medium. The thyroid hormone thyroxin blocks the stimulating action of TRH on the secretion of TSH, but not of prolactin. The blocking effect of thyroxin is evidently manifested not on cell membranes, but in the cytoplasm distally to the effect of cyclic AMP, along the pathway of transmission of the hormonal signal.Laboratory of Biological Standardization of Hormones, Institute of Experimental Endocrinology and Hormone Chemistry, Academy of Medical Sciences of the USSR, Moscow. Department of Morphology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest. (Presented by Academician of the Academy of Medical Sciences of the USSR N. A. Yudaev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 2, pp. 215–217, February, 1978.     

The effect of age on the number of pituitary cells immunoreactive to growth hormone and prolactin

The results of a combined immunocytochemical, morphometric, and clinicopathologic analysis of growth-hormone-producing and prolactin-producing pituitary cells in 28 subjects ranging in age from 16 to 90 are reported. There was a significant age-related decline in the number and size of growth-hormone-producing cells, which was most marked in the transition from youth to middle age. There was also a significant age-related decline in the number of pituitary parenchymal cells but not in pituitary weight. Prolactin cells did not show a significant decline in number with age.     

Effects of selective histamine H3-receptor ligands on prolactin and growth hormone secretion in the rat

The effects of intracarotid (i.a.) administration of the histamine (HA) H₃-receptor agonist (R)--methyl-histamine (MeHA) and of the H₃-antagonist thioperamide, (THIO) on basal or morphine (M)-induced prolactin (PRL) and growth hormone (GH) secretion were studied in male rats. M was administered 3 h after the H₃-drugs. Neither THIO (2.5 mg/kg) nor MeHA (10 mg/kg) changed basal PRL levels and only THIO enhanced the PRL-releasing effect of M (6 mg/kg). Basal GH secretion was not modified by THIO. MeHA slightly increased GH secretion. THIO significantly decreased M-stimulated GH secretion (1 mg/kg, i.a.) and MeHA slightly increased it. These results, in agreement with previous evidence obtained after central HA administration, indicate that endogenous brain HA facilitates PRL and inhibits GH secretion.     

Hormonal secretion by adult pituitary cells in culture

Cells isolated from 24 autopsied adult human pituitary glands by enzymatic dissociation and Percoll density gradient methods were maintained in culture for up to 10 months. Using rabbit antisera specific for individual pituitary hormones and immunoperoxidase staining, we found a large number of cultured pituitary cells to react positively to growth hormone, prolactin, adrenocorticotropin, follicle-stimulating hormone, luteinizing hormone, and thyrotropin immunoreactions. Electron microscopic examination of cultured pituitary cells demonstrated the occurrence of secretory granules in cytoplasm characteristic of in vivo human pituitary cells. The hormone secretion in culture by these pituitary cells was confirmed by the detection of prolactin, thyrotropin, and follicle-stimulating hormone in the culture medium by radioimmunoassay.     

In vitro pituitary prolactin, growth hormone and follicle stimulating hormone secretion during sexual maturation of female rats primed with melatonin

The influence of in vivo melatonin administration on in vitro pituitary follicle stimulating hormone (FSH), growth hormone (GH) and prolactin secretion, as well as the possible influence of dopamine (DA) were evaluated in prepubertal (31-day-old), pubertal (33-day-old) and adult female rats at diestrus phase of the sexual cycle. The in vitro pituitary hormone secretions were evaluated at basal rate for the first hour of incubation only, in Krebs Ringer phosphate (KRP) (I1) and after a second hour of incubation with KRP (I2) or with KRP+DA (I2 plus DA). I1PRL secretion was significantly higher in 33-day-old control and melatonin treated (MEL) rats as compared to I2 periods. However, in 31-day-old rats I1 secretion was higher than in the I2 or I2+DA periods, in MEL rats. In vitro GH secretion was significantly higher at I1 than during I2 periods in the control 31- and 33-day-old groups, but not in MEL rats. The only significant effect of DA was the elevation of GH in prepubertal MEL rats. In vitro FSH release was increased by melatonin in 31- and 33-day-old female rats. No differences in PRL, GH and FSH secretion were found in adult rats. In conclusion, the results show that melatonin effects upon in vitro pituitary gland activity are reproductive-stage-dependent modifying the secretory capacity of the lactotrop, gonadotrop and somatotrop during prepubertal and pubertal ages but not in adult rats studied at a quiescent phase of the sexual cycle.     

The effects of estrogens on tumor growth and on prolactin and growth hormone mRNA expression in rat pituitary tissues.

Estrogens inhibit tumor growth and modify PRL and GH expression in the MtT/W15 transplantable rat pituitary tumor. The effects of estradiol (E2) and diethylstilbestrol (DES) on PRL and GH mRNA levels were investigated. Estrogens increased GH mRNA levels and decreased PRL mRNA levels as detected by in situ hybridization and Northern blot hybridization with oligonucleotide probes, while inhibiting tumor growth. Similar changes in immunoreactive GH and PRL were seen in the tumor cells. The pituitary glands of tumor-bearing rats treated with estrogen for 3 weeks were increased in weight with a concurrent increase in pituitary PRL mRNA when analyzed by dot blot hybridization. These results indicate that estrogens have an inhibitory effect on the growth of the MtT/W15 tumor and increase GH protein and mRNA levels, while causing PRL protein and mRNA levels to decrease. The pituitaries of tumor-bearing rats concomitantly undergo PRL cell hyperplasia with an increase in PRL mRNA. These results also demonstrate a paradoxical effect of estrogens on different pituitary tissues.     

Alterations in stomach ghrelin production and in ghrelin-induced growth hormone secretion in the aged rat

Ghrelin is a recently discovered stomach hormone that stimulates growth hormone (GH) secretion, food intake, adiposity, and growth. In this report, we present new and previously published data from our laboratory showing that stomach ghrelin production and secretion are increased, and that GH release in response to exogenous ghrelin is enhanced in the aged rat. Together, these data suggest that the aging associated decline in GH secretion is not due to a reduction in stomach ghrelin secretion or a stimulatory action on GH release.