Early liver metastases in patients with medullary carcinoma of the thyroid gland

In 13 patients who had been thyroidectomized for medullary carcinoma (MCT), basal and pentagastrin-stimulated immunoreactive calcitonin (iCT) concentrations were measured in a peripheral vein and concomitantly in hepatic veins as well as in the superior and inferior caval veins. The basal concentrations of iCT in serum from the antecubital vein ranged from normal values (less than 0.50 micrograms/1) to grossly elevated (greater than 100 micrograms/1). Intravenous pentagastrin injections (0.5 micrograms/kg) stimulated transiently calcitonin secretion in all patients and peak concentrations occurred in peripheral venous blood and in the inferior caval vein after 3 to 5 minutes. In all patients peak iCT values in the hepatic vein occurred at 1 to 2 minutes and were much higher than in samples taken from other veins. Only three patients showed metastases to liver as judged by conventional clinical and laboratory examinations. Two patients with nonthyroid, malignant disease did not show an increase in serum iCT concentration of hepatic veins. The authors conclude that MCT may spread early to the liver. The presence of liver metastases is an important prognostic factor in patient evaluation and can be demonstrated by measuring iCT in hepatic veins before and during pentagastrin stimulation.

Microinjection and expression of a mouse metallothionein human growth hormone fusion gene in fertilized salmonid eggs

Using a microinjection method (Rokkones et al. 1985) deoxyribonucleic acid was introduced into fertilized salmonid eggs. The survival rate after a 28 day period was 91% for injected eggs in comparison to non-injected controls. A gene construct containing the mouse metallothionein promoter fused to the human growth hormone structural gene was microinjected either as a supercoiled plasmid or as a linear sequence. In Southern blot analysis of both 5 and 73 day old dissected rainbow trout embryos, as well as in 1 year old Atlantic salmon, the mouse metallothionein human growth hormone gene sequence was detected together with the chromosomal DNA when micro-injected as plasmid or as linear DNA. After digestion with Bam HI restriction endonuclease, the human growth hormone gene was excised from the high molecular weight DNA fraction. Transcription into human growth hormone specific RNA, as well as translation and release of human growth hormone immunoreactive protein, could be demonstrated in early embryonic stages.

A 64 kDa protein is a candidate for a thyrotropin-releasing hormone receptor in prolactin-producing rat pituitary tumor cells (GH4C1 cells)

A thyrotropin-releasing hormone (TRH) binding protein of 64 kDa has been identified by covalently crosslinking [3H]TRH to GH4C1 cells by ultraviolet illumination. The crosslinkage of [3H]TRH is UV-dose dependent and is inhibited by an excess of unlabeled TRH. A 64 kDa protein is also detected on immunoblots using an antiserum raised against GH4C1 cell surface epitopes. In a closely related cell line (GH12C1) which does not bind [3H]TRH, the 64 kDa protein cannot be demonstrated by [3H]TRH crosslinking nor by immunoblotting. These findings indicate that the 64 kDa protein is a candidate for a TRH-receptor protein in GH4C1 cells.

Hormone-sensitive adenylate cyclase of prolactin-producing rat pituitary adenoma (GH4C1) cells: molecular organization

Hormonal activation and inhibition of the GH4Cl1 cell adenylate cyclase complex is delineated. In the presence of the guanyl nucleotide GTP, enzyme activity was enhanced twofold by thyroliberin, sixfold by vasoactive intestinal peptide (VIP), twofold by prostaglandin E2 and twofold by isoproterenol. The diterpene, forskolin, increased, the activity 14-fold. In the presence of high GTP (400 microM) and NaCl (150 mM) concentrations, somatostatin inhibited (ED50 = 0.5 microM) the cyclase activity by 40%. In the presence of 10 microM somatostatin, the ED50 values (5 nM) for thyroliberin- and VIP-stimulated adenylate cyclase activities were shifted to 20 nM. Forskolin-elicited activation was, however, not affected by somatostatin. Cholera-toxin and pertussis-toxin pretreatment of the enzyme brought about some 20-fold and twofold activation, respectively. Inhibition by somatostatin was abolished upon pre-exposure to pertussis toxin. Mild alkylation by N-ethylmaleimide increased basal and hormone-activated adenylate cyclase while somatostatin again failed to express its inhibitory potential. Further alkylation caused a gradual decline and convergence of hormone-modulated cyclase activities towards zero. The N-ethylmaleimide-induced attenuation of thyroliberin-elicited activity was paralleled by a decrease in [3H]thyroliberin binding. Trifluoperazine and an anti-calmodulin serum reduced basal and net thyroliberin-, VIP- and forskolin-enhanced cyclase activities by some 30%, 100%, 70% and 80%, respectively. The Vmax of basal and thyroliberin-stimulated adenylate cyclase was diminished by 65%, leaving the apparent Km values (7.2 mM and 2.6 mM, respectively) for Mg2+ unaltered. Finally, the phorbol ester 12-O-tetra-decanoyl-phorbol 13-acetate (TPA) doubled the activity. This effect was counteracted by the protein kinase C inhibitor, polymyxin B, while thyroliberin-enhanced adenylate cyclase remained unaffected. In summary, we have described an adenylate cyclase with stimulatory (Rs) and inhibitory (Ri) receptors coupled to a calmodulin-sensitive holoenzyme through the Gs and Gi type of GTP-binding proteins. The ratio of the Gs to Gi is high. It appears that the GH4C1 cell adenylate cyclase is also activated by protein kinase C by interference with Gi. Apparently, thyroliberin activates the cyclase both directly through Gs and indirectly via protein kinase C stimulation.

Phorbol esters and thyroliberin have distinct actions regarding stimulation of prolactin secretion and activation of adenylate cyclase in rat pituitary tumour cells (GH4C1 cells)

The phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) enhances the effects of TRH on phase II of prolactin secretion as well as on hormone synthesis at both low and high TPA receptor occupancy. Furthermore TPA, but not the biologically inactive substance 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD), stimulates the particulate bound adenylate cyclase with a time course paralleling that of TRH activation. However, the combined additions of TRH and TPA activate this cyclase in an additive manner while the Gpp(NH)p- and the forskolin-sensitive enzyme are unaffected by TPA addition. Polymyxin B, which inhibits protein kinase C, abolishes activation of adenylate cyclase by TPA without interfering with the stimulatory action of TRH. Also, when phosphatase activity is preferentially inhibited by pretreatment of the cells with sodium vanadate, the TRH-sensitive cyclase is unaltered, while TPA activation is obliterated. Maximal stimulation of adenylate cyclase by cholera toxin pretreatment, obliterated the actions of TRH and TPA. Cells pretreated with pertussis toxin retained their TRH-sensitive cyclase, however, TPA-responsiveness was lost. We therefore suggest that the action of TPA as it relates to activation of adenylate cyclase, is probably mediated via the Gi component of the adenylate cyclase complex, while TRH stimulates the enzyme via the classical pathway involving the stimulatory GTP binding protein (Gs).

Distribution of Thyroliberin (TRH)- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-activated adenylyl cyclase in normal and neoplastic tissue with special reference to the prostate

Tissue specificity of the Thyroliberin (TRH)- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-sensitive adenylyl cyclase has been studied using normal or neoplastic organ samples or cells from the pituitary gland, stomach, prostate, myocardium, liver and bone. It appeared that TRH stimulates the adenylyl cyclase in both normal (basal cells), hyperplastic and adenocarcinomatous prostate as well as in the pituitary and stomach. TPA also stimulated the enzyme from the prostate and other organs/cells, but to a greater extent in neoplastic tissue. Functional links from protein kinase C to adenylyl cyclase and from protein kinase C to tyrosine kinase/oncogene expression have been established. Hence it is believed that TRH, which stimulates the adenylyl cyclase and protein kinase C in the pituitary, may serve as a factor contributing to transformation of prostatic cells or enhanced cell proliferation in prostatic cancer.

Somatostatin inhibits prolactin secretion by multiple mechanisms involving a site of action distal to increased cyclic adenosine 3',5'-monophosphate and elevated cytosolic Ca2+ in rat lactotrophs

The release of prolactin (PRL) from a clonal cell-line of anterior pituitary cells (GH4C1) was inhibited by somatostatin (SRIH) in a dose-dependent manner (ED50 nM). The inhibition (20% of control levels) was detectable within 50 s and maximal within 90 s. Thyroliberin (TRH) enhancement of PRL secretion was biphasic. SRIH inhibited both phases equally. Ionomycin in combination with the phorbol ester, TPA, mimics the TRH-elicited PRL release, and SRIH partly inhibited this effect. SRIH had no effect on TRH-stimulated formation of inositol trisphosphate, and only small effects on TRH-activated adenylate cyclase. Vasoactive intestinal peptide (VIP) and forskolin stimulated cAMP formation and PRL release potently. SRIH inhibited both effects of VIP and forskolin, and there was a close correlation between the inhibition of PRL secretion and cAMP accumulation. 8-Bromo-cAMP enhanced PRL release, an effect that was also partly reduced by SRIH. The Ca2+ channel activator, BAY-K-8644 and high extracellular K+ increased PRL release, and SRIH caused a partial reduction in the release response to both secretagogues. SRIH lowered [Ca2+]i, and markedly reduced the rise in [Ca2+]i elicited by TRH, VIP and K+. SRIH did not influence the Ca2+ spikes recorded in Na+-free solution, and had no effect on the TRH-induced membrane potential changes. Our results demonstrate that SRIH may inhibit PRL release from GH4C1 cells by (1) inhibiting hormone-sensitive adenylate cyclase, (2) blocking the effect of cAMP and (3) lowering [Ca2+]i. None of these effects is, however, sufficient to explain all the effects of SRIH, suggesting that SRIH also exerts a major action at a step subsequent to cAMP accumulation and [Ca2+]i elevation. Since the GH4C1 cells possess one single class of binding sites, this implies that the same SRIH receptor is coupled to several cellular signalling systems.

Calcium status and calcium-regulating hormones in alcoholics

To elucidate effects of chronic ethanol consumption on clinical chemical parameters reflecting overall calcium homeostasis 34 hospitalized male alcoholics and 35 age-matched controls were studied during the winter season. Serum concentrations of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 were reduced by 28% (p less than 0.01) and 24% (p less than 0.02) among the alcoholics as compared to the controls, respectively. Dietary intake of vitamin D3 did not differ significantly between the groups. The calcium level was below lower limit of reference in nine alcoholics (26%). Serum concentrations of parathyroid hormone and phosphorus were within normal ranges in both groups, and no differences were observed in levels of magnesium, vitamin D-binding protein, calcitonin, or alkaline phosphatase. In conclusion, it is possible that the activities of enzymes crucial in vitamin D3 metabolism may be altered in alcoholics.

A longitudinal study of pre- and postmenopausal changes in calcium metabolism

Longitudinal changes in the serum concentration of calcium, phosphate, alkaline phosphatase, PTH, calcitonin and the renal handling of calcium and phosphate were studied in 19 normal women of the same age before and after the menopause. Significant increase in serum calcium, phosphate and calcitonin and urine calcium/creatinine and TmPO4/GF were shown to precede the premenopause. After cessation of the menstruation, no statistically significant further changes were observed in these variables. Changes in PTH were not observed neither during the premenopausal nor the post-menopausal period. Alkaline phosphatase increased in the postmenopausal period suggesting an increase in bone turn-over.

The mechanism of [3H]dexamethasone uptake into prolactin producing rat pituitary cells (GH3 cells) in culture

Glucocorticosteroids stimulate growth hormone (GH) synthesis and inhibit prolactin (PRL) synthesis and cell growth in cultured GH3 cells, a clonal cell strain derived from a rat pituitary tumour. This model system was used to study the mechanism by which glucocorticosteroids enter target cells. The cellular uptake of [3H]dexamethasone was temperature dependent and was further inhibited by addition of an excess amount of cold dexamethasone. Half maximal uptake was obtained after about 5 min at 37 degrees C. The initial rates of [3H]dexamethasone uptake were a linear function of the extracellular hormone concentration. The uptake of [3H]dexamethasone in intact cells studied at different temperatures resulted in linear Arrhenius plots, with a calculated energy of activation of 91.0 kJ x mole-1 x degree-1. Scatchard analysis of specifically cell bound [3H]dexamethasone at equilibrium (0 degrees C) showed a straight line with a calculated dissociation constant (Kd) of 1.6 x 10(-9) M and a maximal uptake of 180 x 10(-15) mole/mg cell protein. Specific binding of [3H]dexamethasone to cytosol proteins could only be demonstrated at 0 degrees C. These results indicate that [3H]dexamethasone diffuses passively into the cell, and binds to specific receptors in an energy dependent way.

Bombesin stimulates prolactin secretion from cultured rat pituitary tumour cells (GH4C1) via activation of phospholipase C

Bombesin (BBS) stimulated prolactin (PRL) secretion from monolayer cultures of rat pituitary tumour cells (GH4C1) in a dose-dependent manner with half maximal and maximal effect at 2 nM and 100 nM, respectively. No additional stimulatory effect on PRL secretion was seen when BBS was combined with thyroliberin (TRH) used in concentrations known to give maximal effects, while the effects of BBS and vasoactive intestinal peptide (VIP) were additive. Using a parafusion system, BBS (1 microM) was found to increase PRL secretion within 4 s and the secretion profiles elicited by BBS and TRH (1 microM) were similar. Both BBS and TRH increased inositoltrisphosphate (IP3) as well as inositolbisphosphate (IP2) formation within 2 s. BBS also induced the same biphasic changes in the electrical membrane properties of GH4C1 cells as TRH, and both peptides caused a rapid and sustained increase in intracellular [Ca2+]. These results suggest that BBS stimulates PRL secretion from the GH4C1 cells via a mechanism involving the immediate formation of IP3 thus resembling the action of TRH.

A permissive role for extracellular Ca2+ in regulation of prolactin production by 1,25-dihydroxyvitamin D3 in GH3 pituitary cells

A clonal strain of rat pituitary tumor cells (GH3) that spontaneously synthesizes and secretes prolactin (PRL) and growth hormone (GH) was used as model system to study the mechanism of action of 1,25-(OH)2D3. We have previously demonstrated that these cells possess specific cytosol binding proteins for 1,25-(OH)2D3 (Haug and Gautvik, 1985). When the GH3 cells were incubated in a serum-free, chemically defined medium of low extracellular Ca2+ concentration, 1,25-(OH)2D3 stimulated PRL production in a dose-dependent manner. The stimulation was detectable at 10(-11) M, and the maximum effect (2-fold increase) was observed at 10(-9) M (ED50 = 2 x 10(-11) M). The dose-response curve was bell-shaped, and at 10(-6) M 1,25-(OH)2D3 even suppressed PRL production to about 75% of controls. The stimulatory effect was first seen after 2 days and was maximal after 4 days. On a molar basis 25-OHD3 and 1-OHD3 were at least 100 times less potent than 1,25-(OH)2D3, while 24,25-(OH)2D3 had no effect on PRL production. At an extracellular concentration of Ca2+ as low as 4 x 10(-5) M the stimulatory effect of 1,25-(OH)2D3 was small (1.3-fold). Increasing extracellular Ca2+ to 1.5 x 10(-4) M increased the 1,25-(OH)2D3-induced PRL response to 2.1-fold. In contrast to the biphasic effect of 1,25-(OH)2D3 on PRL production, GH production was decreased to about 60% of controls at 10(-8) M and above. These findings indicate that in serum-free medium the stimulatory effect of 1,25-(OH)2D3 on PRL production is critically dependent on the concentration of extracellular Ca2+.

Effects of trifluoperazine on prolactin release and cyclic AMP formation and degradation in GH4C1 pituitary cells

In GH4C1 cells, the calmodulin antagonist trifluoperazine (TFP) showed a dose-dependent, biphasic effect on the basal release of PRL. An inhibition of PRL release was observed with 15-50 mumol/l TFP, whereas a concentration of 100 mumol/l and above had a stimulatory effect. The increase in basal hormone release evoked by TRH (1 mumol/l) and high extracellular concentration of K+ (50 mmol/l) was eliminated by 30 mumol/l TFP. The stimulatory effect of 100 mumol/l TFP on basal hormone release was not affected by addition of TRH (1 mumol/l) or K+ (50 mmol/l). The Ca2+ antagonists Co2+ (5 mmol/l) and verapamil (100 mumol/l), and the Ca2+ chelator EgTA (4 mmol/l) abolished the stimulatory effect of TRH (1 mumol/l) and of K+ (50 mmol/l) on PRL release, whereas only Co2+ inhibited the stimulation caused by 100 mumol/l TFP. TFP (75 mumol/l) caused a transient increase in the concentration of cellular cAMP. Incubation of intact GH4C1 cells with TFP (75 mumol/l), had an inhibitory effect on both the low and the high affinity form of cAMP phosphodiesterase. Basal as well as TRH-stimulated adenyl cyclase activity were inhibited by TFP, and this effect was counteracted by addition of calmodulin.

Binding and degradation of vasoactive intestinal peptide in prolactin-producing cultured rat pituitary tumour cells (GH4C1)

Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion from cultured rat pituitary cells (GH cells) (Bjøro et al. 1984). This study demonstrates the presence of specific receptors for 125I-VIP on the GH4C1 cells. Specific binding was rapid and biphasic giving a transient plateau lasting from 7 to 30 min. Thereafter specific binding declined to about one-third after 90 min. This coincided with enhanced degradation of 125I-VIP. The degradation was mainly cell-mediated and only partly receptor dependent. Trichloroacetic acid precipitation and absorption chromatography indicated that the degradation products were either 125I- and/or small labelled peptide fragments. Bioassay, RIA and rebinding studies also demonstrated degradation of VIP. Pretreatment of GH4C1 cells with trypsin decreased the rate of degradation of 125I-VIP, but also reduced the amount of specific binding. Scatchard analysis of binding data indicated the existence of two independent classes of receptors, one with Kd = 2.2 nM and Bmax = 15 fmol per 10(6) cells and another with Kd = 180 nM and Bmax = 550 fmol per 10(6) cells. The IC50 for VIP, PHI and secretin were 4, 5 and 500 nM, respectively. We conclude that the high affinity receptor is the most probable mediator of VIP on PRL secretion. The effect of VIP and PHI on PRL secretion in GH4C1 cells is mediated through one common receptor.

Effects of calmodulin antagonists on hormone release and cyclic AMP levels in GH3 pituitary cells

In GH3 cells the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-napthalene sulphonamide hydrochloride (W-7) showed a dose-dependent, biphasic effect on the release of growth hormone (GH) and prolactin (PRL). Hormone release was inhibited with 15-30 microM trifluoperazine and with 30-80 microM W-7, while stimulation was observed with 50-100 microM trifluoperazine and with 150 microM W-7. Trifluoperazine (greater than or equal to 30 microM) and W-7 (greater than or equal to 80 microM) increased the concentration of cellular cyclic AMP. Sulphoxides of trifluoperazine and chlorpromazine (less than or equal to 150 microM were without effect on hormone release and cellular cyclic AMP. Hydrolysis of cyclic AMP by GH3 cytosol was reduced after incubation of intact GH3 cells with trifluoperazine (15-60 microM). When trifluoperazine was incubated with cytosol, both the high and low affinity forms of cyclic AMP phosphodiesterase were inhibited competitively with calculated Ki of 4.5 and 56 microM, respectively. Stimulation of cyclic AMP phosphodiesterase caused by endogenous calmodulin was blocked by trifluoperazine. Particulate bound adenylyl cyclase activity was inhibited by trifluoperazine, and this effect was counteracted by endogenous calmodulin.

Effects of metabolic inhibitors on hormone release, cyclic AMP levels, and oxygen consumption in rat pituitary cells in culture

The metabolic inhibitors antimycin A (2 mumol/l), dinitrophenol (0.5 mmol/l), and iodoacetate (6 mmol/l) were tested for their effects on hormone release, cAMP levels, and oxygen consumption in clonal strains of rat pituitary cells (GH3 cells). Basal release of growth hormone (GH) and prolactin (PRL) was reduced by all three inhibitors, and thyrotropin-releasing hormone (TRH) (1 mumol/l) and K+ (50 mmol/l) stimulated hormone release were blocked. Trifluoperazine, a calmodulin antagonist, inhibited basal GH and PRL release at concentrations up to 30 mumol/l and stimulated above 50 mumol/l. The stimulatory effect of 80 mumol/l trifluoperazine on basal hormone release was eliminated by antimycin A, dinitrophenol, and iodoacetate, whereas the inhibitory effect of antimycin A, dinitrophenol and iodoacetate on basal hormone was not affected by 30 mumol/l trifluoperazine. None of the inhibitors had any effect on the level of cellular cAMP (i.e. intracellular plus extracellular). Oxygen consumption of GH3 cells was blocked by antimycin A, reduced by 25% by iodoacetate and increased by about 100% by dinitrophenol. In contrast, hormone secretion stimulated by TRH and K+ was not accompanied by any measurable alteration in oxygen consumption. Trifluoperazine (greater than or equal to 80 mumol/l) reduced the basal oxygen consumption and blocked the stimulatory effect of dinitrophenol on oxygen consumption. In conclusion, inhibition of the energy generation of GH and PRL-producing cells severely affects the action of secretagogues, although stimulated hormone secretion may not be accompanied by any measurable increase in oxygen consumption. The cellular energy supporting hormone secretion is mostly generated via oxidative phosphorylation.

Vasoactive intestinal peptide and peptide with N-terminal histidine and C-terminal isoleucine increase prolactin secretion in cultured rat pituitary cells (GH4C1) via a cAMP-dependent mechanism which involves transient elevation of intracellular Ca2+

Vasoactive intestinal peptide (VIP) and peptide (P) with N-terminal histidine and C-terminal isoleucine (PHI) stimulated prolactin (PRL) secretion from GH4C1 cells equipotent with ED50 values of 30-50 nM. In a parafusion system optimized to give high time resolution both VIP and PHI increased PRL secretion with a delay of about 60 s and subsequent to the activation of the adenylate cyclase. Thyroliberin (TRH) increased PRL secretion within 4 s. The dose-response curves for VIP- and PHI-stimulated cAMP accumulation were superimposable on those for PRL secretion. At submaximal concentrations the effects of VIP and PHI on both cAMP accumulation and PRL secretion were additive, whereas the effects were not additive at concentrations giving maximal effects. VIP and PHI increased [Ca2+]i measured by quin-2 in a different way than TRH, without inducing changes in the electrophysiological membrane properties of the GH4C1 cells. We conclude that both VIP and PHI stimulate PRL secretion via a cAMP-dependent process involving an increase in [Ca2+]i.

On the involvement of cyclic AMP and extracellular Ca2+ in the regulation of hormone release from rat pituitary tumour (GH3) cells in culture

Thyroliberin (TRH), dibutyryl cyclic AMP (db-cAMP), and 3-isobutyl-1-methylxanthine (MIX) had a stimulatory effect on prolactin (PRL) and growth hormone (GH) release from GH3 cells. Half-maximal and maximal effects were observed for TRH at 2.5 nM and 10 nM; for db-cAMP at 0.6 mM and 5 mM, respectively. MIX (0.1 mM-1 mM) induced a dose-dependent accumulation of cellular cyclic AMP, while the hormone release was already maximally stimulated at 0.1 mM MIX. The maximal effects on hormone release of TRH and db-cAMP, but not of TRH and MIX, were additive. The Ca2+ channel blockers Co2+ (5 mM) and verapamil (100 microM) and the Ca2+ chelator EGTA (4 mM) abolished the stimulatory effect of TRH (1 microM) on hormone release. Co2+ and verapamil, but not EGTA, inhibited the stimulatory effect of db-cAMP (5 mM) on hormone release. The inhibitory effects of Co2+ and verapamil on GH release were counteracted by the combination of TRH and db-cAMP. For PRL release Co2+, but not verapamil, was able to inhibit the combined action of TRH and db-cAMP. Co2+, verapamil, and EGTA eliminated the stimulatory effect of MIX (1 mM) on PRL release while only Co2+ and EGTA affected the GH release. Hormone release in the presence of MIX plus verapamil or EGTA, but not Co2+, was increased by TRH. The calmodulin antagonist trifluoperazine (TFP) at 30 microM inhibited basal hormone release and hormone release stimulated by TRH (1 microM), db-cAMP (5 mM), and MIX (1 mM). The Ca2+ ionophore A23187 (5 microM) had a stimulatory effect on basal hormone release which was abolished by 30 microM TFP.

Improved diagnosis of primary hyperparathyroidism by defining the inverse relationship between serum immunoreactive parathyroid hormone and calcium

Serum concentrations of immunoreactive parathyroid hormone (iPTH) measured with a mid-region specific radioimmunoassay and total calcium were correlated in 300 healthy subjects and 158 patients with surgically verified primary hyperparathyroidism (HPT). All the healthy individuals could be separated from the patients by a monoexponential declining curve in which iPTH at concentrations of 0.60 micrograms/l and 0.33 micrograms/l corresponded to calcium concentrations of 2.20 mmol/l and 2.60 mmol/l, respectively. In 22 patients more than one sample was analysed and serum iPTH and calcium were inversely correlated. In contrast, three patients with parathyroid carcinoma showed no reciprocal fluctuations between serum iPTH and calcium. Of 75 patients with hypercalcaemia due to malignant diseases (metastatic mammary carcinoma, bronchial carcinoma, renal carcinoma, myelomatosis), 62 had a normal iPTH/calcium relationship. Two patients with myelomatosis had a temporary elevation of serum iPTH and calcium due to renal impairment. One patient with bronchial carcinoma probably had ectopic production of iPTH. The remaining 10 patients (six mammary carcinomas and four bronchial carcinomas) were found in the pathological iPTH/calcium range. In conclusion, we have demonstrated that an inverse relationship exists between serum iPTH and calcium in patients with non-malignant, primary HPT. Evaluation of iPTH and calcium in the same serum sample gave a correct diagnosis in more than 90% of patients with primary HPT.

Novel prolactin related mRNAs in rat pituitary cells

From cytoplasm of rat pituitary GH4C1 tumour cells, anti prolactin anti-serum precipitates a polypeptide with apparent molecular weight of 75.000 in addition to prolactin. In vitro translation of size fractionated RNA shows that a 82.000 molecular weight PRL-like polypeptide is encoded by a mRNA larger than the 1 kb prolactin mRNA. Northern blot analysis shows that a rat prolactin cDNA probe hybridize to a 3.2 kb RNA and a 1.5 kb RNA in addition to the 1 kb PRL mRNA. The 82.000 molecular weight translation product and the 3.2 kb mRNA is also detected in rat anterior pituitary cytoplasm. We conclude that at least one high molecular weight mRNA which code for a prolactin-like polypeptide, is present in normal rat anterior pituitary gland and in GH4C1 cells.

On the functional relationship between 45Ca2+ release and prolactin secretion in cultured rat pituitary tumour (GH3) cells

We have evaluated the role of cellular Ca2+ transport associated with stimulus-secretion coupling in prolactin (PRL) producing rat pituitary adenoma cells (GH3 cells). The action of different substances, known to modify PRL secretion, on release of 45Ca2+ from preloaded cells were examined. Surface-bound 45Ca2+ was removed by pretreatment with trypsin in EDTA buffer. During the first 6 min, basal efflux of 45Ca2+ occurred at a constant rate (0.24 min-1) at 37 degrees C. Addition of TRH (5 X 10(-7) M) resulted in an immediate enhancement of 45Ca2+ release representing about 20% of the remaining cellular 45Ca2+. In the same experiments PRL secretion increased by 45%. The EDTA in the external medium reduced the basal rate of 45Ca2+ release by 60%, but did not apparently affect the TRH-stimulated release. Somatostatin (10(-6) M) and verapamil (5 X 10(-5) M) inhibited both basal and TRH-stimulated PRL secretion, whereas high extracellular concentration of K+ (5 X 10(-2) M) had a stimulatory effect. However, neither of these treatments changed cellular 45Ca2+ release. Interference with energy-dependent Ca2+ transport by using metabolic inhibitors (iodoacetate, 6 X 10(-3) M; and antimycin, 2 X 10(-6) M) or by replacing Na+ in the medium by choline or by lowering the incubation temperature from 37 to 25 degrees C, had no effect on TRH-stimulated 45Ca2+ release although basal and TRH-stimulated PRL secretion were reduced. Thus, TRH apparently releases 45Ca2+ from calcium binding sites in the cell membrane.

Hydroxycholecalciferols modulate parathyroid hormone and calcitonin sensitive adenylyl cyclase in bone and kidney of rats. A possible physiological role for 24,25-dihydroxy vitamin D3

In particulate fractions from rat bone cells, but not from kidney, 24,25-(OH)2 D3 inhibits in a dose dependent manner (1 nM and above) the parathyroid hormone (PTH)-activated adenylyl cyclase. In contrast, 24,25-(OH)2D3 enhances the calcitonin (CT) stimulated cyclase in bone, but attenuates the CT-induced cyclase response in kidney. In supranormal concentrations 1,25-(OH)2D3 is also able to reduce the PTH-stimulated adenylyl cyclase in bone. In comparison, neither vitamin D3 metabolite interferes with stimulation of adenylyl cyclase from pituitary cell membranes by thyroliberin (TRH) or vasoactive intestinal polypeptide (VIP). These findings may have important therapeutical consequences in preventing excessive PTH action and bone demineralization.

Electrophysiological properties of calcitonin-secreting cells derived from human medullary thyroid carcinoma

Primary cultures of human medullary thyroid carcinoma tissue were prepared from lymph node metastases in two patients. The parenchymal, cultured cells displayed positive immunocytochemical staining for CT, and the cells also released the hormone into the culture medium. The membrane potential and resistance of the CT-producing cells were 50.1 +/- 8.9 mV and 634 +/- 154 M omega (mean +/- SD, n = 46). TTX sensitive action potentials with maximum rate of rise up to 51 V s-1 were evoked by current injection in Na+-containing solution, whereas TTX insensitive action potentials with maximum rate of rise up to 9 V s-1 were generated in Na+-free solution. These action potentials were reversibly blocked by D-600. We conclude that the action potentials of the human MTC cells have both a Na+ and a Ca2+ component. Ejection of CA2+-free solution close to the cells caused membrane hyperpolarization associated with decreased membrane resistance. The reversal potential of this response was -66.2 +/- 10.9 mV (n = 10), indicating that a permeability increase to Cl- and/or K+ may be involved. We suggest that elevated plasma Ca2+ concentration in vivo may cause increased excitability due to membrane depolarization and resistance increase, thus leading to enhanced Ca2+ influx and hormone secretion.

Bone changes after castration in rats. A model for osteoporosis

Bone changes 6-12 weeks after castration have been studied in 25 female and 27 male middle-aged rats. Castrated female rats gained more weight than their controls, but had decreased bone density and calcium and hydroxyproline content per cm3 bone volume of tibia. Castrated male rats did not differ from controls regarding body weight and the bone parameters. No influence of castration on the mechanical strength of the femora could be detected in either sex. At 2 weeks after castration, the circulating levels of immunoreactive calcitonin (iCT) were decreased in female rats compared to controls. In contrast, iCT was increased both in castrated male and female rats 10 weeks later. We conclude that castration of 6-month-old female rats causes osteoporosis, and therefore represents a promising experimental model for studying postmenopausal bone loss.

Effects of bromocriptine on prolactin release, electrical membrane properties and transmembrane Ca2+ fluxes in cultured rat pituitary adenoma cells

The effects of the dopamine (DA) agonist bromocriptine on prolactin (Prl) release, electrical membrane properties and transmembrane Ca2+ fluxes have been studied in a clonal strain of rat pituitary adenoma cells (GH3). These cells generate Ca2+ dependent action potentials, and produce and secrete spontaneously both Prl and growth hormone. Prl release stimulated by thyroliberin (TRH) and elevated extracellular K+ concentration was completely blocked by bromocriptine, whereas the basal release was only moderately affected. The TRH and K+ evoked Prl release were half maximally inhibited by bromocriptine at 5-10 and 10-50 microM, respectively. The normal biphasic membrane response to TRH and the depolarizing effect of elevated K+ concentration were not altered by bromocriptine, whereas the Ca2+- spikes in Na+-free solution were suppressed by the drug. We therefore suggest that bromocriptine blocks the voltage sensitive Ca2+-channels of GH3 cell. In agreement with this notion, bromocriptine also suppressed the basal and TRH induced 45Ca2+ efflux from preloaded cells. We conclude that the inhibitory effect of bromocriptine on the voltage dependent Ca2+- channels is an important mechanism responsible for suppression of Prl release.