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ABSTRACT

In cultured porcine and human thyroid cells, electrophysiological and morphological studies showed that cultivation in the presence of TSH, prostaglandin E₂ (PGE₂) or dibutyryl cyclic AMP (dbcAMP) maintained normal cell polarity with iodine incorporation and organification. Cells cultivated in the absence of these substances had inverted cell polarity and lacked iodide incorporation.

In the presence of TSH, PGE₂ or dbcAMP, the thyroid cells formed follicles with normal cell polarity and the microvilli pointed toward the follicle lumina. Intracellular resting potentials were − 60 mV and the electrical potentials in the follicle lumina were negative at − 20 mV. The transmembrane potential differences (p.d.) between the follicle lumina and the epithelial cells were − 40 mV and those between the epithelial cells and the culture media − 60 mV.

In the absence of TSH, PGE₂ or dbcAMP, the thyroid cells formed 'domes' or hollow spheres with inverted cell polarity and the microvilli pointed toward the culture media. Intracellular resting potentials were − 40 mV, being less negative than those in the presence of TSH, PGE₂ or dbcAMP. The electrical potentials in the 'dome' or hollow sphere cavities were positive at + 19 mV. The transmembrane p.d. between the culture media and the epithelial cells was − 40 mV and that between the epithelial cells and the cavities − 60 mV, indicating that electrophysiologically the cell polarity was inverted in the absence of TSH, PGE₂ or dbcAMP.

No significant differences in electrophysiology and iodine metabolism were observed between normal and Graves' human thyroid cells in culture.

J. Endocr. (1984) 101, 189–196

ABSTRACT

Thyrotrophin (TSH) and prostaglandin E₂ (PGE₂) increased cellular cyclic AMP (cAMP), calmodulin levels and cAMP phosphodiesterase activity in cultured porcine thyroid cells. Dibutyryl cAMP (dbcAMP), a stable analogue of cAMP, increased calmodulin levels and cAMP phosphodiesterase activity. These results indicate that TSH- and PGE₂-stimulated increases in calmodulin are mediated by cAMP. This increased concentration of calmodulin in turn stimulates cAMP phosphodiesterase. Double reciprocal plots of cAMP hydrolysis yielded two apparent Michaelis constants (K _m); the lower in the 1 μmol/l and the higher in the 10 μmol/l range. Thyrotrophin, PGE₂ and dbcAMP increased the values of maximal velocity without changing the K _m values.

J. Endocr. (1988) 117, 109–114

ABSTRACT

12-O-Tetradecanoylphorbol 13-acetate (TPA) is a potent tumour promoter and shows several biological activities of epidermal growth factor (EGF). EGF and TPA stimulated proliferation and inhibited differentiation of porcine thyroid cells in primary culture. They also stimulated [³H]thymidine incorporation and inhibited an early step in thyroid hormone synthesis (iodine organification). The results indicate that EGF and TPA switch the developmental course of porcine thyroid cells from differentiation to proliferation.

J. Endocr. (1987) 113, 485–487

ABSTRACT

Evidence is accumulating that adrenal steroids may be involved in the metabolic effects of cytokines. We evaluated the possible involvement of glucocorticoids in the inhibition of pancreatic insulin secretion by interleukin-1β (IL-1β), one of the cytokines produced by inflammatory cells. In the first group of experiments, adrenalectomized rats showed a significant reduction in basal and glucose (0·5 g/kg, i.v.)-stimulated immunoreactive insulin (IRI) levels after injection of IL-1β (1·0 μg/kg), but intact rats did not. Pretreatment with IL-1β increased plasma glucose levels 2 and 15 min after an i.v. bolus of glucose in adrenalectomized rats. In the second group of experiments, dexamethasone supplement (0·1 mg/kg) given to adrenalectomized rats cancelled the reduction in plasma glucose levels by IL-1β, and rats treated with 1·0 mg dexamethasone/kg showed a significant increase in basal IRI levels and enhanced serum IRI levels after IL-1β injection. However, 1·0 mg deoxycorticosterone/kg given daily for 7 days failed to cancel the effect of IL-1β on the reduction of serum IRI levels, although it attenuated the weight loss after adrenalectomy. The data suggested that withdrawal of glucocorticoids after adrenalectomy potentiates the effect of IL-1β on the reduction of serum IRI levels. Glucocorticoids may have a protective action against the reduction of serum IRI levels by IL-1β.

Journal of Endocrinology (1992) 132, 419–423

ABSTRACT

This study set out to elucidate the mechanism by which H₂O₂ generation is regulated in cultured porcine thyroid cells. We monitored continuously the effects of the calcium ionophore A23187 and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on H₂O₂ generation, using homovanillic acid and horseradish peroxidase. A23187 and TPA stimulated H₂O₂ generation. A23187 increased cytoplasmic free calcium and TPA activated protein kinase C. Generation of H₂O₂ is therefore regulated by cytoplasmic free calcium and protein kinase C. Exposure to A23187 or TPA augmented further the stimulation of H₂O₂ generation by TPA or A23187 respectively. Thus A23187 and TPA, by increasing cytoplasmic free calcium and activating protein kinase C respectively, synergistically activate H₂O₂ generation.

Journal of Endocrinology (1989) 120, 503–508

Abstract

Pioglitazone hydrochloride (AD-4833), one of the thiazolidinedione analogs, is a new anti-diabetic agent which improves peripheral insulin resistance in diabetic patients. We determined the direct effect of AD-4833 on insulin secretion in HIT-T 15 cells. The effects of AD-4833 (10⁻⁷ m to 10⁻⁵ m) on insulin secretion were examined in 3 and 7 mm glucose-containing F-12 K media. The addition of 10⁻⁵ m AD-4833 significantly increased insulin secretion in both media, but its stimulatory effect was more potent in the medium containing 7 mm glucose. The addition of 10⁻⁵ m AD-4833 caused an immediate, significant increase in cytosolic free Ca²⁺ concentration ([Ca²⁺]_i). Nifedipine at all concentrations from 10 to 1000 nm significantly attenuated insulin secretion by 10⁻⁵ m AD-4833. In addition, 10⁻⁵ m AD-4833 failed to stimulate insulin secretion in the Ca²⁺-free Kreb's-Ringer bicarbonate buffer. These data indicated that AD-4833 stimulates in vitro insulin secretion in HIT-T 15 cells, perhaps by inducing Ca²⁺ influx.

Journal of Endocrinology (1996) 150, 107–111

Abstract

The decrease in estrogen in menopausal women increases body fat. The present studies were undertaken to investigate the involvement of estrogen in leptin production in vivo. In the first study, expression of ob gene mRNA in white adipose tissue was measured at 2 and 8 weeks after ovariectomy in rats. In the second, serum leptin concentration was measured in total body fat of 87 weight-matched human subjects (29 men, 29 premenopausal and 29 postmenopausal women). In the third, changes in serum leptin concentration with the menstrual cycle were determined, ob gene expression decreased in subcutaneous and retroperitoneal white adipose tissue of ovariectomized rats 8 weeks after the operation, while ovariectomy increased ob gene expression in mesenteric white adipose tissue. Serum leptin concentration was decreased by ovariectomy. Estradiol supplement reversed the effect of ovariectomy on ob gene expression and circulating leptin levels. In humans, serum leptin concentration was higher in premenopausal women than in men, and in postmenopausal women it was lower than in premenopausal women, but still higher than in men. In 13 premenopausal women, serum leptin levels were significantly higher in the luteal phase than in the follicular phase. The present studies strongly indicate that estrogen regulates leptin production in rats and human subjects in vivo. Regional variation in the regulation of ob gene expression by estrogen was found.

Journal of Endocrinology (1997) 154, 285–292

ABSTRACT

The effects of insulin-like growth factor-I (IGF-I) on cytoplasmic pH (pHi) and [³H]thymidine incorporation were studied in primary cultures of porcine thyroid cells. IGF-I alkalinized thyroid cells and stimulated thymidine incorporation in a dose-dependent manner; the effects of IGF-I on alkalinization (the maximal rates of change of cytoplasmic pHi/min ((dpHi/dt)max)) and thymidine incorporation were observed at 2 ng/ml and were maximal at 100 ng/ml, with half-maximal stimulation at approximately 10 ng/ml. The results indicate that Na⁺/H⁺ exchange or cell alkalinization may function as a transmembrane signal transducer in the action of IGF-I on thyroid cell proliferation. Several mitogens and comitogens which activate sodium hydrogen exchange, including epidermal growth factor, platelet-derived growth factor and nerve growth factor, have been listed. Activation with IGF-I has not, however, been presented before. Thus the present study constitutes the first demonstration of IGF-I-stimulated activation of Na⁺/H⁺ exchange or cell alkalinization.

Journal of Endocrinology (1990) 127, 305–309