Gaston R. Zahnd

Somatostatin lowers the cytosolic free Ca2+ concentration in clonal rat pituitary cells (GH3 cells)

Changes in the cytosolic free Ca2+ concentration, [Ca2+]i, have been proposed to mediate the regulation of the secretion of pituitary hormones by hypothalamic peptides. Using an intracellularly trapped fluorescent Ca2+ probe, quin2, [Ca2+]i was monitored in GH3 cells. Somatostatin lowers [Ca2+]i in a dose dependent manner from a prestimulatory level of 120 +/- 4 nM (SEM, n = 13) to 78 +/- 9 nM (n = 5) at 10(-7)M; the effect is half maximal at 2 X 10(-9) M somatostatin. The decrease in [Ca2+]i occurs rapidly after somatostatin addition and a lowered steady state [Ca2+]i is maintained for several minutes. Somatostatin does not inhibit the rapid rise in [Ca2+]i elicited by thyrotropin releasing hormone (TRH) and can still cause a decrease in [Ca2+]i in the presence of TRH (10(-7)M). Concomitantly with its action on [Ca2+]i somatostatin causes hyperpolarization of GH3 cells assessed with the fluorescent probe bis-oxonol. The lowering of [Ca2+]i by somatostatin is however not only due to reduced Ca2+ influx through voltage dependent Ca2+ channels, since it persists in the presence of the channel blocker verapamil. These results suggest that somatostatin may exert its inhibitory action on pituitary hormone secretion by decreasing [Ca2+]i.

Pertussis toxin selectively abolishes hormone induced lowering of cytosolic calcium in GH3 cells

Pertussis toxin Cytosolic Ca2+ Somatostatin Muscarinic cholinergic agonist TRH Pituitary

Plasma Growth Hormone, Insulin, and Glucagon Responses to Arginine Infusion in Children and Adolescents with Idiopathic Short Stature, Isolated Growth Hormone Deficiency, Panhypopituitarism, and Anorexia Nervosa

Extract: The effects of intravenous infusion of arginine (20 g/m2) after an overnight fast on plasma immunoreactive growth hormone (GH), insulin (IRI), and glucagon (IRG), and blood glucose were examined in five groups of children and adolescents: 10 normal individuals, 18 with idiopathic short stature, 6 with isolated growth hormone deficiency, 8 with panhypopituitarism, and 6 with anorexia nervosa. The mean fasting plasma GH concentration was significantly elevated in the group with anorexia nervosa (P < 0.05), and similar to the value for the normal group in all other groups. After arginine infusion, four- to sixfold increases of plasma GH were observed in the normal children, and similar increases were seen in those with idiopathic short stature as well as in those with anorexia nervosa; whereas, in the children with isolated growth hormone deficiency or panhypopituitarism, there was no significant increase in plasma GH. Fasting blood glucose concentrations were significantly lower than normal in subjects with isolated growth hormone deficiency (p < 0.05), panhypopituitarism (P < 0.001), and anorexia nervosa (P < 0.001), whereas fasting plasma IRI and IRG concentrations were similar to the values in the normal group. Plasma IRI increased eightfold at the end of the 30-min arginine infusion in the normal subjects; the increase was slightly but not significantly less in those with idiopathic short stature, and significantly less in those with isolated growth hormone deficiency (P < 0.05), panhypopituitarism (P < 0.001), and anorexia nervosa (P < 0.05). Arginine infusion resulted in two- to threefold increases of plasma IRG in the normal group, and similar increases were observed in all of the other groups tested. These results suggest that whereas pancreatic β cell responsiveness may be deficient in children and adolescents with isolated growth hormone deficiency, panhypopituitarism, or anorexia nervosa, pancreatic α cell responsiveness, to arginine at least, appears to be intact under these conditions.Speculation: Although plasma glucagon responses to arginine infusion were not less in subjects with hypopituitarism or anorexia nervosa than in normal subjects, relative hypoglucagonemia may have existed, since both basal and postarginine infusion plasma glucagon levels were not higher than normal in the presence of significantly lower blood glucose values. Thus, the present study does not exclude a deficient pancreatic α cell response to hypoglycemia. Alternatively, nonavailability of substrates for gluconeogenesis may have a more important influence than hormonal factors in the genesis of the hypoglycemia observed in these states.

Polyphosphoinositide hydrolysis by phospholipase C is accelerated by thyrotropin releasing hormone (TRH) in clonal rat pituitary cells (GH3 cells)

Thyrotropin releasing hormone (TRH) accelerates the turnover of phosphatidylinositol in GH3 cells (‘phospholipid response’). From the analysis of inositol phosphates in the presence of Li+ which inhibits their dephosphorylation, it can be concluded that the hydrolysis of phosphatidylinositol 4,5‐biphosphate, and possibly of phosphatidylinositol 4‐phosphate by phospholipase C is markedly accelerated by TRH. It appears that this reaction initiates the acceleration of phosphatidylinositol turnover. The specificity of hormonally regulated phospholipase C reaction for polyphosphoinositides has important implications for the potential role of the phospholipid response as a mechanism of membrane signal transduction.

Monitoring Receptor Mediated Regulation of Cytosolic Calcium in Single Pituitary Cells by Dual Excitation Microfluorimetry

Receptor-mediated alterations in the cytosolic free calcium concentration, [Ca2+]i are monitored with the intracellular fluorescent calcium probe fura 2 by dual excitation microfluorimetry. The calcium dependence on the excitation spectrum of fura 2 allows us to choose two wavelengths, lambda 1 and lambda 2, at which an increase in [Ca2+]i causes either a rise or a fall in fluorescence; the ratio of fluorescence at lambda 1 and lambda 2 (R = F lambda 1/F lambda 2) is a measure of [Ca2+]i. It appears essential for such measurements that the alteration between the two excitation wavelengths is done rapidly, to allow us to distinguish between effects on [Ca2+]i and other effects on fluorescence. In addition, specific problems relating to the calibration of fura 2 measurements, such as its relative insensitivity at basal [Ca2+]i, the role of intracellular viscosity on fura 2 fluorescence, and the difficulties encountered in establishing calibration constants have to be appreciated. In spite of these potential drawbacks, it appears that monitoring receptor-mediated [Ca2+]i regulation in single cells will prove essential for the further comprehension of stimulus-secretion coupling in pituitary and probably many other cell types.

Contributions of Physiology to the Understanding of Diabetes

Thoughts on the regulation of adenylyl cyclase systems by hormone-sensitive G-proteins: a tribute to Albert E. Renold intercellular communication and insulin secretion expression of the insulin gene and its regulation implications of the Glucokinase sensor paradigm for pancreatic beta-cell function how Ca2 and other signaling pathways control the exocytosis of insulin in the beta-cell. cell biology of insulin action on glucose transport: looking back. Insulin-like growth factor: endocrine and autocrine/paracrine implications and relations to diabetes mellitus. On the pathogenesis of insulin-dependent diabetes mellitus in man: a paradigm on transition. (part contents)

Peptides of the neurointermediary lobe of rat pituitary stimulate GH secretion in vitro

alpha-MSH and other fragments of ACTH are potent stimulators of GH release in vivo. The action of such peptides and of extracts of the neurointermediary lobe (NIL) of rat pituitary, a source of endogenous MSH-related peptides, on GH release was investigated in vitro. Peptides with the core sequence of alpha-MSH stimulate GH secretion by primary cultures of rat anterior pituitary cells; however, both the absolute and the relative potencies of these peptides exclude the involvement of melanotropic receptors comparable in specificity to the extrapituitary receptors for these hormones. Extracts of the NIL of rat pituitary stimulate GH release in vitro and the bulk of the releasing activity can be attributed to one (or several) factors with an apparent mass of approx. 10 000 M.W. that can be partially purified by HPLC. The active principle appears to be distinct from both beta-LPH and the human pancreatic GHRF. Thus, while rat NIL contains GH-releasing activity that can be demonstrated in vitro, a direct link to the potent action of MSH-related peptides on GH release in vivo cannot be established, and the action of these peptides in vivo must therefore rely on mechanisms which are not expressed in the in vitro system.

Usefulness of serum lipid determination in diabetic practice

SummaryIn order to evaluate the importance of measuring serum lipids in the current care of diabetics, blood triglycerides were measured in 155 diabetics and 59 controls. Comparison with a chemical method confirmed the usefulness of the nephelometric method for the diagnosis and control of hyperlipemia in current practice. The importance of measuring serum lipids was confirmed by a close correlation between lipemia and cardiovascular complications such as coronary insufficiency, high blood pressure, and peripheral arterial insufficiency. It appeared also that glycemia and cholesterol are not sufficient to assess the biological pattern and prognosis of diabetes. Thus, lipemia is an essential parameter in the evaluation of any diabetic because of its value regarding prognosis and control of therapy.

Alanine, insulin and glucose levels in newborns

Plasma alanine (PA), immunoreactive insulin (IRI) and blood glucose (BG) levels were measured in newborns (NB) before any feeding and between 5 and 72 hours of life, 3 hours after glucose administration. At 4 hours of life, in 26 NB (birthweight (BW) : 2,620 to 4,060 g), BG was 52 ± 2 mg/100 ml (mean ± S.E.), PA 447 ± 19 μM, and IRI 3.5 ± 0.4 μU/ml. In 5 premature NB (BW : 1,600 to 2,450 g), BG was 45 ± 11, PA 318 ± 52 (p < 0.05, significantly different from normal NB), IRI 3 .1 ± 0 .5. In 9 small for gestational age (SFGA) NB, (BW : 1,530 to 2,490g), BG was 45 ± 5, PA 384 ± 12 (p < 0.01), IRI 3 ± 0.4. A significant correlation was observed in all NB between PA and BW (r : 0.390, p < 0.05) but not between the other parameters. After glucose administration (31 normal NB and 10 SFGA), BG and IRI were similar, PA was significantly lower in SFGA (250 ± 32 μM) than in normal NB (424 ± 19, p < 0.005). A similar correlation was observed between PA and BW (r : 0.386, p < 0.05). The data suggest that PA may be dependent upon the muscle mass.

The Application of HPLC Methodology for the Analysis of Receptor Mediated Changes in Phosphoinositide Metabolism

HPLC methodology has found wide application in analytical problems in biochemistry. To study the metabolism of phosphatidylinositol and its regulation by receptor mediated events, HPLC could be a valuable technique. It has been recently demonstrated that a variety of hormones and neurotransmittors act to stimulate hydrolysis of phosphoinositides by a phospholipase C. To monitor this reaction, we have analysed the formation of radiolabelled inositol phosphates from phosphoinositides. The present paper describes a rapid HPLC procedure, to separate inositol phosphates from myo-inositol, which could be used in pharmacological studies of receptors linked to phosphoinositide hydrolysis. The potential of the application of HPLC to the analysis of the phospholipids involved is discussed.