Cyclic GMP, cyclic AMP, glucose at birth, and maturation of rat liver mitochondria

The improvement in mitochondrial functions which normally occurs in newborn rat liver in vivo during the few hours following delivery is inhibited by a glucose injection at birth (Meister, R., Comte, J., Baggetto, L., G., Godinot, C. and Gautheron, D.C. (1983) Biochim. Biophys. Acta 722, 36-42). To test whether this improvement could be correlated to changes in cyclic nucleotides, the levels of cAMP and cGMP have been measured during the 2 h following birth. At birth, a short rise followed by a decrease of cAMP occurs, then a significant increase of cAMP level is observed between 45 min and 2 h. The cAMP level for animals injected at birth with glucose is lower than for control animals at each time studied. The cGMP level is not significantly affected in control animals, while in glucose-treated animals a significant decrease of cGMP is observed in the postnatal 2 h. The present work shows also that the glucose-induced inhibition of mitochondrial maturation is mimicked by injection at birth of either 8-Br-cGMP or nitroprusside. The latter transiently increases intracellular cGMP. In contrast, the glucose-induced inhibition is prevented by the injection at birth of either dbcAMP or alkylxanthines together with glucose (Comte, J., Meister, R., Baggetto, L.G., Godinot, C. and Gautheron, D.C. (1986) Biochem. Pharmacol. 35, 2411-2416). It is concluded that the postnatal improvement of mitochondrial functions is stimulated by cAMP and inhibited by cGMP, and that glucose-induced inhibition of the maturation is at least partly supported by a decrease in cAMP but not correlated to an increase in cGMP.     

Adenosine-induced cyclic AMP increase in pig lymphocytes is not related to adenylate cyclase stimulation.

Adenosine-cyclic AMP relationships have been studied in pig mesenteric lymph node lymphocytes. The early 2--3-fold increase in cyclic AMP accumulation elicited by adenosine and 2-chloroadenosine, an adenosine deaminase-resistant analogue, could not be correlated to similar effects on the adenylate cyclase activity of disrupted cell preparations, but rather to the competitive inhibition of the low Km (0.17 muM) cyclic AMP phosphodiesterase. The existence of adenosine receptors coupled to lymphocyte adenylate cyclase, which had been proposed by several authors, could not be confirmed by this study Adenosine-cyclic AMP relationships do not appear to be involved in concanavalin A stimulation of pig lymphocytes.     

Induction of cyclic AMP phosphodiesterase in Blastocladiella emersonii and its relation to cyclic AMP metabolism.

Extracts of vegetative cells of Blastocladiella emersonii contain 5% or less of the cyclic AMP phosphodiesterase activity in zoospore extracts. This difference in activity could be accounted for entirely by an increase in the differential rate of phosphodiesterase synthesis during sporulation, beginning after a lag period of about 60 min and extending for at least an additional 90 min into the 4-h sporulation process. To examine the relation between enzyme synthesis and cyclic nucleotide metabolicm, we determined the substrate specificity of phosphodiesterase synthesized during sporulation and partially purified from zoospores. Zoospore extracts contain two components, separable by gel filtration chromatography, with cyclic AMP phosphodiesterase activity. The larger component accounts for 20% of the total activity and the smaller component for 80%. Both components show essentially an absolute substrate specificity for cyclic AMP among several cyclic purine and cyclic pyrimidine nucleotides tested. Nevertheless, we found no change in the total cyclic AMP content of sporulating cells before, during, or after enzyme activity increased. We speculate that some other component of cyclic AMP metabolism or function limits the rate of cyclic AMP hydrolysis in sporulating cells.     

Attenuation of epinephrine-induced increase in liver cyclic AMP by endogeneous insulin in vivo.

1. Epinephrine-induced increase in rat liver cyclic AMP in vivo was potentiated when the circulating insulin was suppressed by injection of anti-insulin serum or by induction of diabetes. Consequently, phosphorylase was activated, glycogen synthetase was inactivated and glycogen accumulation induced by glucose load was prevented by epinephrine in the insulin-deficient rats to a much larger extent than in normal rats. 2. Insulin lack was effective in potentiating epinephrine-induced increase in liver and muscule cyclic AMP even after the treatment of rats with theophylline; the potentiation could not be solely accounted for by the inhibition of cyclic AMP phosphodiesterase. Thus, it is likely that insulin lack enhaces epinephrine activation of adenylate cyclase. 3. Unlike epinephrine, glucagon increased liver cyclic AMP to essentially the same extent whether the rat was treated with anti-insulin serum or not. 4. Based on the difference in dose-response curves between normal and insulin-deficient rats, a possibility is discussed that there are two adenylate cylase in the liver with higher and lower affinities for epinephrine and that circulating insulin blocks the high affinity enzyme selectively.     

Adenosine-induced cyclic AMP increase in pig lymphocytes is not related to adenylate cyclase stimulation

Adenosine-cyclic AMP relationships have been studied in pig mesenteric lymph node lymphocytes. The early 2–3-fold increase in cyclic AMP accumulation elicited by adenosine and 2-chloroadenosine, an adenosine deaminase-resistant analogue, could not be correlated to similar effects on the adenylate cyclase activity of disrupted cell preparations, but rather to the competitive inhibition of the low K_m (0.17 μM) cyclic AMP phosphodiesterase. The existence of adenosine receptors coupled to lymphocyte adenylate cyclase, which had been proposed by several authors, could not be confirmed by this study. Adenosine-cyclic AMP relationships do not appear to be involved in concanavalin A stimulation of pig lymphocytes.     

Trypsin-induced increase in intracellular cyclic AMP of lymphocytes.

Trypsin increases intracellular levels of cylic AMP (cAMP) in lymphocytes. The trypsin-induced increase in cAMP is blocked by specific trypsin inhibitors and by high concentrations of different proteins. Several proteolytic enzymes from various sources, including other pancreatic proteases, do not cause an increase in cAMP under the same experimental conditions. Immobilized trypsin induced the same increase in cAMP as does free trypsin. The trypsin-induced rise in cAMP is not due to inhibition of cAMP phosphodiesterase, but consistent activation of adenylate cyclase by trypsin could not be demonstrated. The extent of the trypsin-induced increase in intracellular cAMP correlates with the type of the lymphocyte and with the state of maturity attained by the cells. Transformed lymphocytes and nonlymphoid cells do not react at all.     

Trophoblast estrogen synthetase stimulation by dibutyryl cyclic AMP and theophylline: increase in cytochrome P-450 content.

The inclusion of both dibutyryl cyclic AMP and theophylline in the culture medium of human malignant trophoblast cells (JAr line) for 72 hours results in an enhanced estrogen secretion through the increased specific activity of estrogen synthetase (aromatase), a cytochrome P-450 mono-oxygenase enzyme system. The data described here suggest that this increased aromatase activity is due to an increase in the concentration of only one component of the mono-oxygenase system, cytochrome P-450.     

Prostaglandin E1 effects on cyclic AMP and glycogen metabolism in rat liver.

Prostaglandins E₁ or E₂ (PGE₁, PGE₂)¹ stimulated adenylate cyclase(s) from particulate fractions of whole liver homogenates 5- to 6-fold, but caused only slight (1.5- to 2-fold) stimulation of the enzyme from homogeneous hepatocytes. In contrast, glucagon stimulated enzyme from hepatocytes 12- to 15-fold and enzyme from whole liver 8- to 10-fold. Accordingly, most of the total prostaglandin-sensitive adenylate cyclase in cell suspensions was recovered in fractions containing non-parenchymal cells, and most of the total glucagon-sensitive activity was recovered with hepatocytes. PGE₁ did not change adenosine-3′,5′-monophosphate (cyclic AMP) concentrations, or alter cyclic AMP increases caused by glucagon in hepatocytes. Glucagon consistently increased hepatocyte cyclic AMP concentrations and stimulated glycogenolysis by 35 to 40%. PGE₁ did not affect basal or glucagon-stimulated glycogenolysis in the intact cells.     

The stress induced increase of liver phosphorylase A and cyclic AMP in adrenomedullectomized and adrenalectomized rats.

In adult male rats injected with Pentobarbital, 50 mg.kg-1 i.p. and subjected immediately after administration of the anaesthetic to 400 revolutions (lasting of 6 min and 40 s) in rotating Noble-Collip drums the activity of the active form of hepatic phosphorylase was increased at time 0 after injury without respect to previous adrenomedullectomy or adrenalectomy (7 weeks or 10 days before, respectively). Completeness of surgery was checked by plasma catecholamines which were essentially near zero. The level of liver cAMP was increased in intact and adrenomedullectomized animals at time zero. 90 min after injury a recovery of enzyme activity towards basal levels was observed in contrast to cAMP which was increased in all the three groups. A net glycogenolytic response was found in the injured animals irrespective of previous surgery. It is concluded that for the stress induced activation of hepatic phosphorylase the presence of adrenal cortical and medullary tissue is not always indispensable.     

Control of fatty acid synthetase mRNA levels in rat liver by insulin, glucagon, and dibutyl cyclic AMP

The quantity of translatable fatty acid synthetase mRNA in liver of rats subjected to different hormonal states was determined with a rabbit reticulocyte lysate cell-free translation system. Both membrane-free polysomal and total cellular poly (A)-containing RNA were translated. The level of translatable fatty acid synthetase mRNA was 11-fold or more lower in livers of diabetic rats than in similar animals treated with insulin. In contrast, both glucagon and dibutyl cyclic AMP caused a 3-fold reduction over controls in the amount of translatable fatty acid synthetase mRNA in livers of animals refed a fat-free diet for 12 hr. These changes are consistent with the previously reported alterations in the relative rates of fatty acid synthetase synthesis measured in vivo. This suggests that the changes in the amount of fatty acid synthetase that occur in liver in response to the above hormonal changes are primarily due to changes in the amount of mRNA coding for this enzyme.