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Biomedical subjects

I Mills

Publications and source records attributed to I Mills.

49 records · Page 3Linked to original sources
PubMed1985

Pertussis toxin reversal of the antilipolytic action of insulin in rat adipocytes in the presence of forskolin does not involve cyclic AMP.

Insulin inhibition of lipolysis in the presence of forskolin was reversed by a four hour exposure of adipocytes to pertussis toxin. In contrast, the antilipolytic action of insulin against lipolysis due to theophylline was unaffected by pertussis toxin as was the ability of insulin to lower cyclic AMP in the presence of either forskolin or theophylline. The stimulation of adenylate cyclase by norepinephrine in crude plasma membranes obtained from rat adipocytes was inhibited by N6-(Phenylisopropyl)adenosine (PIA) and abolished by pretreating rat adipocytes with pertussis toxin. The stimulation of glucose metabolism by insulin was not altered by pertussis toxin pretreatment of rat adipocytes. These findings suggest that pertussis toxin selectively abolishes the antilipolytic effect of insulin in the presence of forskolin through a cyclic AMP independent mechanism.

Adenosine Deaminase↗
PubMed1985

A comparison of the mechanisms of alpha-adrenergic inhibition of thyrotropin-stimulated adenosine 3',5'-monophosphate in cat, rat, mouse, hamster, beef, and pig tissues with the stimulatory effect of epinephrine on beef thyroid iodination: evidence for multiple, species-specific adrenergic mechanisms.

Epinephrine was shown to inhibit TSH-stimulated cAMP formation in cat and pig thyroid slices and isolated rat and hamster thyroid lobes. In contrast, no such inhibitory action could be demonstrated in sheep or beef thyroid slices or mouse thyroid-trachea preparations. The inhibitory effect of epinephrine on TSH-stimulated cAMP formation in pig thyroid slices was blocked by 10 microM yohimbine, but not by 10 microM prazosin, suggestive of mediation through an alpha 2-catecholamine receptor mechanism. In cat thyroid slices, the inhibitory effect of epinephrine was blocked by both yohimbine and prazosin, suggestive of a mixed alpha-adrenoceptor mechanism. Meclofenamate and indomethacin attenuated the epinephrine response in cat, but not pig, thyroid slices, but other prostaglandin inhibitors were ineffective. Beef thyroid slices responded to epinephrine with an increase in iodide organification that is mediated through an alpha-adrenergic mechanism not blocked by propranolol. This stimulatory effect of epinephrine was abolished by both 10 microM prazosin and 10 microM yohimbine. In contrast to the inhibitory effect of the catecholamines on TSH-stimulated cAMP formation in cats, the stimulatory response of beef iodide organification to epinephrine was not modified by meclofenamate, indomethacin, or verapamil. These findings suggest that the receptor mechanisms mediating the inhibitory effect of catecholamines on cat thyroid and the stimulatory effect of catecholamines in beef thyroid slices may well be mediated by separate and as yet undefined receptor mechanisms. In contrast, the inhibitory effect of epinephrine on TSH-stimulated cAMP formation in pigs is most likely mediated through an alpha 2-adrenoceptor mechanism. These findings further document the multiplicity of catecholamine actions on thyroid function as well as the diversity observed among various species.

Adenosine Monophosphate↗
PubMed1984

Activation of lipolysis and cyclic AMP accumulation in rabbit adipocytes by isoproterenol in the presence of forskolin or pertussis toxin.

Adipocytes from rabbits are relatively insensitive to catecholamines or forskolin. However, the combination of catecholamines plus forskolin increased cyclic AMP accumulation and lipolysis much more than either agent alone. Pertussis toxin treatment also restored sensitivity to catecholamines. No defect in activation by catecholamines of adenylate cyclase was seen in isolated membranes incubated in the presence of GTP. Rabbit adipocytes appear to have an excess of the inhibitory guanine nucleotide binding protein (Ni). However, in plasma membranes this protein appeared to be relatively inactive as there was an activation of adenylate cyclase activity by catecholamines in the presence of GTP. These data suggest that in intact rabbit adipocytes catecholamines and forskolin are ineffective as stimulators of adenylate cyclase due to an excess of inhibitory guanine nucleotide binding proteins.

Adenosine Deaminase↗
PubMed1984

Metabolic effects of beta, alpha 1, and alpha 2 adrenoceptor activation on brown adipocytes isolated from the perirenal adipose tissue of fetal lambs.

Brown adipocytes can be readily isolated by collagenase digestion of perirenal adipose tissue from fetal lambs. In isolated cells the addition of phenylephrine in the presence of alprenolol (to specifically stimulate alpha adrenoceptors) resulted in an increase in de novo synthesis of phosphatidylinositol and phosphatidic acid. The stimulatory effects were preferentially inhibited by prazosin while yohimbine had little effect, indicating that the adrenoceptors were alpha 1 in character. Isoproterenol stimulated cyclic adenosine monophosphate (AMP) accumulation and lipolysis as well as respiration. Forskolin also mimicked the effects of beta adrenergic stimulation. Clonidine, a specific alpha 2 adrenergic agonist, inhibited lipolysis and cyclic AMP accumulation. Insulin inhibited cyclic AMP accumulation and stimulated glucose metabolism in the adipocytes. The present studies indicate that beta, alpha 1, and alpha 2 adrenergic as well as insulin responses can be detected in ovine perirenal adipocytes.

Adipose Tissue, Brown↗
PubMed1984

Thyroid-catecholamine interactions in isolated rat brown adipocytes.

The effects of hyperthyroidism and hypothyroidism on the metabolism of adipocytes isolated from rat brown adipose tissue were as follows: The yield of brown adipocytes was 65% less in the hypothyroid as compared to the control rats. No change in cell recovery was observed in the hyperthyroid group as compared to controls but there was a 65% increase in cell volume. The stimulation of respiration by isoproterenol and forskolin was markedly greater in cells from hyperthyroid as compared to euthyroid rats. In the adipocytes from hypothyroid rats, respiration and lipolysis were reduced but there was no defect in stimulation of adenylate cyclase by forskolin or isoproterenol as compared to euthyroid controls. The effects of different thyroid states on respiration did not correlate with changes in adenosine 3':5'-cyclic phosphate (cyclic AMP) or lipolysis. Phenylephrine in the presence of alprenolol or octanoate were as potent stimulators of respiration as 10 mumol/L isoproterenol in adipocytes from hypothyroid rats. In cells from hyperthyroid rats phenylephrine was twice, octanoate three times, and isoproterenol 16 times more effective in stimulating respiration than in cells from hypothyroid rats. These data indicate that thyroid status regulates beta-catecholamine and forskolin stimulation of respiration in brown adipocytes.

Adenylyl Cyclases↗
PubMed1984

Forskolin inhibition of glucose metabolism in rat adipocytes independent of adenosine 3',5'-monophosphate accumulation and lipolysis.

Addition of forskolin (1 microM) to rat adipocytes incubated with insulin and 0.2 mM glucose inhibited glucose metabolism in the absence of any significant stimulation of either cAMP accumulation or lipolysis. The action of forskolin was in contrast to that of isoproterenol, since forskolin inhibited [1-14C]glucose conversion to total lipid, whereas isoproterenol had the opposite effect. Elevation of the medium glucose concentration to 10 mM reversed the inhibitory effects of forskolin on glucose metabolism. The ability of forskolin to inhibit glucose metabolism was observed whether glucose was labeled in the 1 or the 6 position. The results of the present study suggest that forskolin affects glucose metabolism independently of adenylate cyclase activation.

Adipose Tissue↗
PubMed1983

Pertussis toxin reverses Gpp(NH)p inhibition of basal and forskolin activated adipocyte adenylate cyclase.

Inhibition of basal adenylate cyclase by GTP or guanyl-5'-yl imidodiphosphate was abolished in membranes isolated from rat adipocytes previously incubated with pertussis toxin. Forskolin (0.1 microM) stimulated adenylate cyclase about 4-fold and inhibition of cyclase by GTP or guanyl-5'-yl imidodiphosphate was also abolished by pertussis toxin treatment of rat adipocytes. Forskolin (1 microM) increased adenylate cyclase activity at least ten-fold and the inhibitory effect of GppNHp was reduced but not abolished by pertussis toxin. In rabbit adipocytes, pertussis toxin reversed the inhibition of adenylate cyclase activity by GppNHp to the same extent as that by GTP in the presence of 1 microM forskolin. The present results indicate that pertussis toxin can reverse the inhibition of adipocyte adenylate cyclase by nonhydrolyzable GTP analogs as well as that by GTP.

Adenylate Cyclase Toxin↗
PubMed1983

Effects of pertussis toxin treatment on the metabolism of rat adipocytes.

The protein toxin present in Bordetella pertussis vaccine blocks the inhibition of adenylate cyclase by prostaglandins and adenosine which may be secondary to ADP-ribosylation of an inhibitory guanine nucleotide-binding protein. The stimulatory effects of alpha 1-catecholamine agonists on 32P uptake into phosphatidic acid and phosphatidylinositol in isolated rat adipocytes were virtually abolished by pertussis toxin treatment. In contrast, the stimulatory effects of insulin were increased in adipocytes after pertussis toxin treatment. Pertussis toxin treatment did not alter insulin stimulation of glucose oxidation and actually increased glucose conversion to lipid. Basal lipolysis was elevated in adipocytes by pertussis toxin treatment but not basal cyclic AMP. However, the increases in cyclic AMP and lipolysis due to low concentrations of catecholamines and forskolin were markedly potentiated by pertussis toxin treatment. The inhibitory effects of adenosine on cyclic AMP stimulation due to catecholamines were abolished by pertussis toxin. These data indicate that pertussis toxin selectively interferes with inhibition of cyclic AMP accumulation in rat adipocytes by adenosine, potentiates the increases in cyclic AMP due to catecholamines, increases the stimulatory effects of insulin on adipocyte metabolism, and interferes with alpha 1-catecholamine stimulation of phosphatidylinositol turnover.

Adenylate Cyclase Toxin↗
PubMed1982

Forskolin as an activator of cyclic AMP accumulation and lipolysis in rat adipocytes.

Forskolin increased cyclic AMP accumulation in isolated adipocytes and markedly potentiated the elevation of cyclic AMP due to isoproterenol. In adipocyte membranes, forskolin stimulated adenylate cyclase activity at concentrations of 0.1 microM or greater. Forskolin did not affect the EC50 for activation of adenylate cyclase but did increase the maximal effect of isoproterenol. Neither the soluble nor particulate low-Km cyclic AMP phosphodiesterase activity was affected by forskolin. Low concentrations of forskolin (0.1-1.0 microM), which significantly elevated cyclic AMP levels, did not increase lipolysis, whereas similar increases in cyclic AMP levels due to isoproterenol elevated lipolysis. Forskolin did not inhibit the activation of triacylglycerol lipase by cyclic AMP-dependent protein kinase or the subsequent hydrolysis of triacylglycerol. Higher concentrations of forskolin (10-100 microM) did increase lipolysis. Both the increased cyclic AMP production and lipolysis due to forskolin were inhibited by the antilipolytic agents insulin and N6-(phenylisopropyl)adenosine. Hypothyroidism reduced the ability of forskolin to stimulate cyclic AMP production and lipolysis. These results indicate that forskolin increases cyclic AMP production in adipocytes through an activation of adenylate cyclase. Lipolysis is activated by forskolin but at higher concentrations of total cyclic AMP than for catecholamines.

3',5'-Cyclic-AMP Phosphodiesterases↗