Effect of thyroliberin on the concentration of adenosine 3':5'-phosphate and on the activity of adenosine 3':5'-phosphate-dependent protein kinase in prolactin-producing cells in culture

1. The effects of thyroliberin were studied in cultured rat pituitary-tumour cells that synthesize and secrete prolactin (the GH4C1 cell strain). 2. Prolactin and cyclic AMP were measured by radioimmunological methods, and a cyclic AMP-dependent protein kinase was characterized by using histone as substrate. 3. Prolactin release was studied after 5-60min of treatment, and synthesis after 48h of treatment with thyroliberin. One-half maximum stimulation of release and synthesis were observed at 0.25 and at 4nM respectively. 4. Cyclic AMP was temporarily increased in cell suspensions after treatment with thyroliberin, and one-half maximum stimulation was observed at 25nM. 5. Dibutyryl cyclic AMP increased prolactin release and synthesis, one-half maximum effects being obtained at 20 micronM. 6. A cyclic AMP-dependent protein kinase, which was one-half maximally stimulated at 30 nM-cyclic AMP, was demonstrated. 7. An increase in the activity ratio (-cyclic AMP/+cyclic AMP) of the cyclic AMP-dependent protein kinase was observed after treatment with thyroliberin. Total protein kinase activity in the presence of cyclic AMP was unaltered. The time-course of enzyme activation was similar to that of cyclic AMP formation and corresponded to the time when prolactin release was first observed. 8. It is concluded that thyroliberin induces cyclic AMP formation, resulting in the activation of a cyclic AMP-dependent protein kinase.

Effects of sex steroids on prolactin secreting rat pituitary cells in culture

A clonal strain of rat pituitary tumor cells (GH3) was used to study the effects of different sex steroids on the production of prolactin (PRL). Hormone production was measured by radioimmunoassay and expressed as the amount of hormone which accumulated in the medium of monolayer cultures during 24 h. The stimulatory effect of 17beta-estradiol (10(-11)M-10(-6)M) on PRL production was significant after 4 days and the maximum effect (300% of control cultures) was observed at 10(-8)M after 10 days of treatment. After removal of added 17beta-estradiol, the production of PRL returned to control levels in 5 days. Progesterone (10(-11)M-10(-6)M) caused a dose-related decrease in PRL production reaching 60% of control values at 10(-6)M. Testerone (10(-6)M) stimulated the production of PRL (130% of controls), whereas 5alpha-dihydrotestosterone (10(-6)M) had a small effect (107% of controls) which was not always reproducible. None of the sex steroids affected cell growth. Progesterone (10(-6)M) inhibited the stimulatory effect of 17beta-estradiol (10(-8)M) on PRL production. The effect of 17beta-estradiol (10(-8)M) and thyrotropin releasing hormone (TRH) (3 X 10(-7) M) was addititive, while no additional stimulatory effect was observed when 17beta-estradiol (10(-8)M) was combined with testosterone (10(-6)M). If the properties of the GH3 cells are analogous to those of normal lactotropes, the sex steroids may alter PRL production at the pituitary level, an influence that may be further modulated by TRH.

Medullary carcinoma of the thyroid in Norway. Clinical course and endocrinological aspects

A study of the clinical, biochemical and histological findings of 57 patients with medullary thyroid carcinoma (MCT) in Norway, is presented. The diagnosis was established by light and electron microscopy and by measurements of immunoreactive calcitonin (iCT) in serum. The major factor influencing the prognosis was the extension of the disease at presentation. None of the 24 patients with tumour confined to the thyroid gland have died of the disease, and serum iCT was normal in 15 patients. Of 19 patients with regional lymph node metastes only 11 are alive 1 to 14 years after treatment, and of these 9 had increased serum iCt. 14 patients technically inoperable and/or with distant metastases, 12 have died of MCT, 1 are alive with elevated serum iCT. Of 14 patients with raised serum iCT, 8 have no clinical recurrence of the disease from 1 to 15 years after the operation. MCT-associated diseases were found in 8 patients, chronic thyroiditis in 10. Serum iCT was measured in 249 relatives of 42 patients, and abnormal elevations were found in 11 members of 6 families.

Basal and thyroliberin-stimulated prolactin synthesis in single-cell cultures and in populations of rat pituitary cells

1. Newly synthesized prolactin was obtained from cultures of rat pituitary tumour cells (GH4C1 cells) after incubation with [35S]methionine. 2. Radioactive synthesized and secreted prolactin was quantified by an immunoprecipitation method by using disc-gel electrophoresis of the dissolved immunoprecipitate in the presence of sodium dodecyl sulphate. By using a microanalytical modification, hormone synthesis and secretion could also be studied in single-cell cultures. This technique was combined with a cytoimmunofluorescence method in which rhodamine-conjugated antibodies were used for studying intracellular prolactin. 3. The presence of radioactive synthesized and secreted prolactin was demonstrated in nine out of 13 single-cell cultures. Cell cultures containing 10 cells or more and clonal populations originating from one cell always secreted radioactive prolactin. 4. Thyroliberin treatment (2 muM) for 24h increased the extracellular accumulation of radioactive prolactin in five out of seven single-cell cultures and always in populations of cells. 5. The number of cells showing prolactin specific fluorescence increased from 20 to 50% and the intensity of this fluorescence became greater after thyroliberin treatment. 6. Studies of [35S]prolactin secretion from single cells and immunochemical detection of intracellular prolactin showed that some cells in an unsynchronized population did not secret radioactive prolactin or show prolactin specific fluorescence. 7. The quantitative effect of thyroliberin as studied in single-cell cultures suggested that the main if not the only effect was to increase prolactin synthesis in cells already producing hormone.

Radioimmunoassay of human calcitonin in serum and tissue from healthy individuals and patients with medullary carcinoma of the thyroid gland

A specific radioimmunological method for measurement of immunoreactive calcitonin (iCT) in human serum and tissue is decribed. Of healthy individuals of both sexes, 85% had measurable iCT in serum (mean, 0.23 ng/ml). Of 29 patients who had received treatment for medullary carcinoma of the thyroid gland (MCT), 19 had increased serum iCT (0.60 ng/ml to 205 ng/ml). Elevated serum iCT was also found preoperatively in 2 MCT patients. Eleven of the patients with abnormal elevations of serum iCT were alive 4 to 13 years after the operation. Concentration of iCT in extracts from MCT varied from 0.5 to 540 ng/ml wet weight. The diagnostic value of this method and its importance for pre- and post-operative evaluation of these patients are improved by the use of selective venous catheterization in basal state and during stimulation of CT secretion.

Medullary carcinoma of the thyroid. Diagnostic problems

Light microscopy is usually considered sufficient for the diagnosis of medullary carcinoma of the thyroid (MCT). As stromal amyloid is not always present and the tumor may exhibit great variation in growth pattern, light microscopy alone, however, may lead to misinterpretations. Of 1670 thyroid carcinomas registered durging a 15-year period in Norway, 42 were originally interpreted as MCT. The slides were reviewed and the diagnosis maintained in 33 cases only. Twenty-four additional cases were found by reviewing histopathologic slides from neoplasms originally registered as other types of thyroid tumors. Of 57 cases of MCT, stromal amyloid was demonstrated in 43. Calcitonin measurements and electron microscopy, even on formalin-fixed material, were valuable aids in establishing the correct diagnosis, though none of these methods are unequivocal. Different aspects of the problems concerning the diagnosis of MCT are discussed through the detailed presentation of five patients.

Radioimmunoassay of rat prolactin and its use in measuring prolactin production by cultured pituitary cells

A sensitive and specific radioimmunoassay has been developed for rat prolactin (rPRL), employing the double antibody solid phase technique for the separation of free and antibody-bound [125I]rPRL. The anti-serum was raised in rabbits and showed no cross-reaction with rat growth hormone (rGH), follicle stimulating hormone (rFSH), luteinizing hormone (rLH) and thyrotrophin (rTSH). The immunosorbent (sheep anti-rabbit IgG bound to cellulose) showed a surprisingly high binding of [125I]rPRL, but not of the other iodinated anterior pituitary hormones. Addition of serum to the incubation mixtures prevented the binding between [125I]rPRL and the immunosorbent. Three different clonal strains of pituitary cells have been examined for production of rPRL, rLH and rTSH, both in the basal state as well as after treatment with thyrotrophin releasing hormone (TRH) and gonadotrophin releasing hormone (LH/FSH-RH). Monolayer cultures of two of the cell strains produced and secreted rPRL spontaneously, and they showed a 2-fold increase in rPRL production after treatment with TRH (3-10(-7) mol/1). The third cell strain did not produce rPRL spontaneously, or after treatment with TRH. None of these cell strains could be stimulated to produce rTSH by treatment with TRH. Treatment of the same three cell strains with LH/FSH-RH (1.2-10(-6) mol/1) failed to induce production of rLH, and there were no changes in production of rPRL. Prostaglandins E1 and E2 (3-10(-8) mol/1) and oestradiol-17beta (10(-7)-10(-10) mol/1), however, stimulated the production of rPRL. The effects of TRH and prostaglandins E1 and E2 were observed within 24 h of treatment, while the first effect of oestradiol-17beta was seen after 3 days. These results suggest that the stimulatory effect of oestradiol-17beta on rPRL production differs from that of TRH and prostaglandins.

Nucleotidase activity in regenerating liver and in clonal strains of hepatoma and pituitary cells in culture

A nucleotidase of the combined 3'- and 5'-type (nucleotide phosphohydrolase, E.C.3.1.3.31) was present in the cytosol of regenerating rat liver cells, and of rat hepatoma and pituitary cells in culture. The enzyme activity per milligram of cell protein was very similar in regenerating liver and in three of the different cell types. The hepatoma cell strain which showed the slowest growth rate had a three-fold higher basal enzyme activity. After the first days of regenerative growth in rat liver and during early plateau phase of cell growth, there was a 50-120% increase in specific enzyme activity. In the hepatoma cells, the enzyme activities were also compared to the cellular content and synthesis of RNA and DNA. The increase in enzyme activity occurred concomitantly with a reduced incorporation of 3H-thymidine into DNA. The possible physiological role of this nucleotidase in nucleic acid and nucleotide metabolism is discussed.

A possible role of cyclic AMP in mediating the effects of thyrotropin-releasing hormone on prolactin release and on prolactin and growth hormone synthesis in pituitary cells in culture

Thyrotropin-releasing hormone (TRH) has 3 effects on clonal strains of rat pituitary cells in culture (GH-cells). Two long-term effects of TRH on GH-cells, which are measurable after 3 h or longer, have been previously reported; these are an increase in prolactin synthesis and a decrease in growth hormone production. We report here that TRH also stimulates the rapid release of stored intracellular prolactin. We have investigated the role of cyclic AMP as a possible mediator of the effects of TRH on GH-cells. Cyclic AMP concentrations are higher in cells treated with TRH compared with paired controls; a maximum difference of greater than 150% of control values is detected at 15 min if the incubation is performed in serum-free medium in the presence of 1 mM theophylline. The concentration of TRH required to give half-maximum increases in both prolactin release and cyclic AMP accumulation is 0.3 nM; half-maximal increases in prolactin synthesis occur at 3 nM TRH. Exogenous cyclic AMP (1 mM) causes only a slight increase in prolactin release; 8-bromo-cyclic AMP and 8-methylthio-cyclic AMP (1 mM) do not cause significant release. Phosphodiesterase inhibitors (0.3 mM theophylline, 0.03 mM isobutyl-methylxanthine) increase prolactin release but their effects on hormone synthesis are more complicated. Isobutylmethylxanthine, 8-bromo-cyclic AMP and 8-methylthio-cyclic AMP (0.4 MM) increase prolactin synthesis, but do not significantly affect growth hormone synthesis. Theophylline increases the synthesis of both hormones. Dibutyryl cyclic AMP (0.5 mM or more) increases prolactin release and both growth hormone and prolactin synthesis, but equivalent amounts of sodium butyrate have the same effects. We conclude that in GH-cells under carefully defined experimental conditions: 1) TRH causes an increase in intracellular cyclic AMP concentrations; 2) the increase in endogenous cyclic AMP and the effects of phosphodiesterase inhibitors are consistent with a model with cyclic AMP as a mediator of the effects of TRH on prolactin release; however, they do not prove this model, because the interpretation of these results depends on assumptions which may not all be valid; and 3) none of the analogs of cyclic AMP or the phosphodiesterase inhibitors tested mimic the decrease in growth hormone production caused by TRH.

Stimulation of prolactin synthesis and of adenosine 3':5'-cyclic phosphate formation by prostaglandins and thyroliberin in cultured rat pituitary cells

1. The effects of prostaglandins E2 and F2alpha on prolactin synthesis were examined in a clonal strain of rat pituitary tumour cells, and compared with those of thyroliberin. 2. The prostaglandins and thyroliberin gave a dose-related and time-dependent stimulation of prolactin synthesis. The maximal effects (about twofold increases) were observed after 54h of treatment with 25nM-prostaglandin E2 and 2.5nM-prostaglandin F2alpha. A similar stimulation of prolactin synthesis was observed after 250nM-thyroliberin. The combined treatment with prostaglandins and thyroliberin did not increase prolactin synthesis over and above that obtained with each compound alone. 3. After removal of prostaglandins E2 and F2alpha there was a complete reversal of prolactin synthesis to pre-stimulation values 18h later (t1/2less than or equal to 9h). The rapid reversible effect of prostaglandins was in contrast with that of thyroliberin, where prolactin synthesis returned to control values with a t1/2 of about 42 h. 4. Prostaglandin E2 (5mum) and thyroliberin (5mum) increased cellular concentrations of cyclic AMP eight- and four-fold respectively. Maximal effects were observed after 2-5min of incubation. The increases in cyclic AMP were biphasic; normal values were obtained 60 min after the start of incubation with prostaglandin E2 or thyroliberin. 5. The dose/response curve showed that prostaglandin E2 caused maximal increase of cyclic AMP at 50nM. Concentrations of prostagland in E2 that caused half-maximal stimulation of cyclic AMP accumulation and of prolactin synthesis were 4 and 5nM respectively. 6. Combined treatment with prostaglandin E2 and thyroliberin in concentrations that separately caused maximal cyclic AMP increases did not result in a further increase in this cyclic nucleotide. 7. These results are consistent with a role of cyclic AMP in mediating the effects or prostaglandins and thyroliberin on prolactin synthesis. However, if cyclic AMP is involved as a common intracellular mediator of prolactin synthesis, it cannot alone explain all the effects of prostaglandins and thyroliberin in this cell system.

Rat submandibular gland kallikreins: purification and cellular localization

1 Four submandibular gland kallikreins (E.C.3.4.21.8) were isolated by chromatography on DEAE-Sephadex A-50 and hydroxyapatite, followed by gel filtration and electrofocusing. The pI values were 3.87, 3.96, 4.07 and 4.16, and a common molecular weight of 34,000 was found. 2 The kallikreins were localized by direct immunofluorescence with an antibody to rat urinary kallikrein, to the granular tubules, striated duct cells and some main duct cells in the submandibular gland, and to striated duct cells in the sublingual gland. Kallikrein was not found in acini and stroma. 3 Several non-kallikrein esterases present in the submandibular gland reacted with the antibody to rat urinary kallikrein. The antibody was made monospecific for kallikrein by absorption with the crossreacting esterases. 4 We suggest that kallikrein is produced in striated duct cells. Granular tubules, which are differentiated from striated duct cells, have preserved the ability to produce kallikrein. These cells also store large quantities of kallikrein.

Effects of prostaglandins on prolactin and growth hormone synthesis and secretion in cultured rat pituitary cells

The effects of prostaglandins E1, E2, F1alpha, and F2alpha on prolactin and growth hormone synthesis and secretion were studied in cultured rat pituitary cells. Total extracellular accumulation of prolactin was measured by radioimmunoassay. When hormone synthesis was studied, the cells were cultured in the presence of [3H]leucine for the last hour of each treatment period. The intra- and extracellular radioactive hormones were determined in the same microsample by a specific and quantitative immunoprecipitation method, employing polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The results show that all prostaglandins stimulated the extracellular accumulation of prolactin at 3-30 nM. Prostaglandin E1 was more effective in stimulating extracellular accumulation of prolactin than prostaglandin E2 and the F compounds. Prostaglandin F2alpha at 3 nM doubled the rate of prolactin synthesis, but had no effect on growth hormone or total cell protein synthesis after 24 h of treatment. The first effect of prostaglandin F2alpha was observed after 5 h of incubation, and the time-course of effect on prolactin synthesis was similar to that of thyrotropin-releasing hormone.

Measurements of prolactin and growth hormone synthesis and secretion by rat pituitary cells in culture

A specific and sensitive immunoprecipitation method for measurements of biosynthesized radioactive prolactin and growth hormone is described. Antisera to rat prolactin and growth hormone were developed in the rabbit and monkey, respectively. The specificity of the immune sera was assessed by polyacylamide gel electrophoresis of the dissolved immunoprecipitates. The two antisera showed cross-reactions with the nonhomologous hormone of less than 1%. Separation of tritium-labelled prolactin and growth hormone by immunoprecipitation, followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate was shown to be 95-57% complete. When both hormones were measured in the same microsample by sequential immunoprecipitation, the reaction was 97% complete for determination of intra- and extracellular prolactin and extracellular growth hormone, but 85% complete for determination of intracellular growth hormone. This method has been used to characterize the basal synthesis and secretion of prolactin and growth hormone in three different but related, pituitary cell strains. Radioactive prolactin and growth hormone was obtained from monolayer cultures when the cells were grown in the presence of [3H]L-leucine. The rate of prolactin synthesis and extracellular accumulation was higher than that of growth hormone in a cell strain which produced both hormones. In these cells prolactin synthesis represents 1-5%, and growth hormone 0.1-0.6% of total protein synthesis.