The Journal of endocrinology
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Although arginine-vasopressin (AVP) is reported to produce greater ACTH biosynthetic and secretary responses than does corticotropin-releasing hormone (CRH) in sheep anterior pituitary cells, neither factor appears to increase pro-opiomelanocortin (POMC) mRNA levels, as does CRH in the cells of some other species. Since only a fraction of cells that express POMC mRNA may be able to respond to AVP, the aim of this study was to further delineate the regulation of POMC mRNA in ovine anterior pituitary corticotrophs, as a whole and in functional subpopulations of corticotrophs. We measured the effects of AVP, CRH or activation of protein kinase C by phorbol myristate acetate (PMA) in cultured cells. ⋯ AVP (55 +/- 8 ng/well) and PMA (120 +/- 17 ng/ well), but not CRH, increased ACTH secretion; POMC mRNA was not significantly elevated by any of the treatments. Taken together, these data provide further support for the notion of dissociation between secretion of ACTH and expression of POMC mRNA, and demonstrate that AVP increases steady-state POMC mRNA levels in ovine anterior pituitary cells. The data are also consistent with the concept that complex interactions, possibly including those between cells, influence ACTH secretion and steady-state POMC mRNA levels.
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This study was designed to investigate postprandial responses to a mixed meal in simulated shift work conditions. Nine normal healthy subjects (six males and three females) were studied on two occasions at the same clock time (1330 h) after consuming test meals, first in their normal environment and secondly after a 9 h phase advance (body clock time 2230 h). Plasma glucose, insulin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), triacylglycerol (TAG) and non-esterified fatty acids (NEFAs) were determined at intervals for 6 h after each test meal. ⋯ Plasma postprandial NEFA levels fell during the first 3 h both before and after the phase shift. Their rate of return to basal levels was significantly delayed after the phase shift compared with before. This study demonstrates that a simulated phase shift can significantly alter pancreatic B-cell responses and postprandial glucose and lipid metabolism.
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Previous reports demonstrated that prolactin receptors (PRL-R) are widely expressed on cells of the immune system. We analyzed a possible regulation of PRL-R expression on human mononucleated blood cells by prolactin (PRL) itself. PRL-R expression was analyzed by immunofluorescence on T and B lymphocytes and monocytes from peripheral blood mononucleated cells (PBMC) of patients with hyperprolactinemia or acromegaly compared with sex- and age-matched control subjects. ⋯ No correlation was reported between PRL-R expression and circulating PRL levels. The percentage of PRL-R+ cells on B or T lymphocytes and monocytes as well as the capacity of PBMC to proliferate in response to T cell mitogens were not significantly different in bromocriptine-treated compared with untreated patients. These findings suggest that factors other than pituitary PRL play the major role in regulating PRL-R expression on cells of the immune system.
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Comparative Study
Changes of calmodulin concentration and cyclic 3',5'-nucleotide phosphodiesterase activities in cardiac muscle of hyper- and hypothyroid rats.
To investigate the effect of thyroid hormone on cardiac muscle dysfunction in hyper- and hypothyroid states, we evaluated cyclic 3',5'-nucleotide metabolism by measuring cyclic 3',5'-nucleotide phosphodiesterase activity and calmodulin concentrations in the cardiac muscles of hyper- and hypothyroid rats. Cyclic AMP (cAMP) concentration was significantly high in the cardiac muscle of hyperthyroid rats and low in that from hypothyroid rats compared with control rats. Cyclic AMP and cyclic GMP phosphodiesterase activities were significantly decreased in the soluble fraction of cardiac muscle from hyperthyroid rats and markedly increased in this fraction in hypothyroid rats compared with normal animals. ⋯ It was concluded from these findings that low cAMP-phosphodiesterase activity might, in part, bring about the high concentration of cAMP. Calmodulin was significantly high in the cardiac muscle of hyperthyroid rats and the reverse was the case in hypothyroid rats compared with normal rats. The implication is that, in hyper- and hypothyroid states, these changes may play an important role in cardiac function via their effect on cyclic nucleotide and Ca2+ metabolism.