Chlorpropamide and tolbutamide inhibition of adenosine 3'5' cyclic monophosphate phosphodiesterase

These sulfonylurea agents inhibit the cyclic AMP phosphodiesterase, and thereby could increase the steady state level of cyclic AMP in various tissues, depending upon the tissue concentrations achieved after oral or parental administration.     

Regulation of Sertoli cell cyclic adenosine 3':5' monophosphate phosphodiesterase activity by follicle stimulating hormone and dibutyrl cyclic AMP

Total phosphodiesterase activity was measured in Sertoli cell culture after exposure to isobutyl-methyl-xanthine, dibutyryl cyclic AMP and FSH. After 24 hr of incubation both FSH and dibutyryl cAMP caused a significant increase in total phosphodiesterase activity of Sertoli cell homogenates (control: 66 ± 16 pmoles/min/mg protein; FSH: 291 ± 25 pmoles/min/mg protein; dibutyryl cAMP: 630 ± 70 pmoles/min/mg protein). FSH stimulation was potentiated by isobutyl-methyl-xanthine. Both in the presence and absence of xanthine, the induction of phosphodiesterase was dependent on the FSH concentration, with maximal stimulation achieved with 0.5–1.0 μg FSH/ml. The induction of phosphodiesterase activity by hormone was abolished by cycloheximide treatment. The data suggest that FSH regulates phosphodiesterase activity via changes of cAMP levels in Sertoli cell in culture.     

Exercise-induced increases in myocardial adenosine 3',5'-cyclic monophosphate and phosphodiesterase activity

Numerous cellular biochemical events caused by hormones are mediated through cyclic AMP. Although many changes occur in the cell during exercise that could be attributed to this nucleotide, little evidence is available implicating it as an important regulator of exercise metabolism. In this investigation it was found that a 60 min bout of treadmill exercise caused a 2.4-fold increase in myocardial cyclic AMP immediately following the work. Rather than the immediate nucleotide hydrolysis that was expected, it was found that the elevated cyclic AMP level remained for approx. 24 h before returning to control levels. Cardiac glycogen fell to 30% of control after work but supercompensated 60% above control within 1 h following exercise. Therefore, cardiac cyclic AMP was elevated at a time when glycogen was being synthesized. Study of the temporal relationship between the exercise-induced increase in cyclic AMP and cyclic nucleotide phosphodiesterase indicated that the work caused an increase in the hearts' capacity to hydrolyze cyclic AMP. Measurement of heart phosphodiesterase at substrate concentrations of 1.0 and 100 microM produced significant increases in enzyme activity immediately following exercise which remained elevated for 48 h and was back to control activity 96 h following work. These data present a potentially fascinating model for the study of the dissociation between cyclic AMP, glycogenesis and elevations in phosphodiesterase activity in the heart.     

The effect of manganese on lipogenesis, lipolysis, adenosine 3',5' cyclic monophosphate and cyclic nucleotide phosphodiesterase activity in adipocytes from NZY mice

The insulin-like action of Mn2+ was investigated in adipocytes isolated from male mice of the NZY strain. In agreement with previous reports Mn2+ was found to stimulate both the oxidation of [U-14C]glucose to CO2 and the incorporation of [U-14C]glucose into total lipid and fatty acid, and to inhibit lipolysis stimulated by epinephrine, cyclic AMP or theophylline. The maximum effect of Mn2+ was greater than that of a maximal concentration of insulin and when both agents were present in these concentrations the effect was similar to that observed with Mn2+ alone. Mn2+ lowered the level of cyclic AMP in adipocytes incubated with isoproterenol. The effect was seen as early as 1 minute and it was greater than a maximal concentration of insulin. When Mn2+ was added to suspensions of adipocytes it increased the activity of the membrane-bound low Km cyclic nucleotide phosphodiesterase in subsequently prepared homogenates. The enzyme was stimulated 1.8-fold by Mn2+ compared with a 1.7-fold stimulation by insulin and a 2-fold stimulation in the presence of both Mn2+ and insulin.     

Induction of lysozyme activity by adenosine 3':5' cyclic monophosphate in cultured mouse myeloid leukemic cells.

Mouse myeloid leukemic cells(Ml) could be induced by glucocorticoids to form Fc receptors, phagocytize, migrate in agar, induce lysosomal enzyme activities, and change into forms that were morphologically similar to macrophages and granulocytes. Adenosine 3′:5′ cyclic monophosphate also induced lysosomal enzyme activities, but not the other differentiation-associated properties. The induction of lysozyme activity was marked, the activity reaching about 400 times the initial activity at 5 days after treatment. This suggests that adenosine 3′:5′ cyclic monophosphate may be important in induction of lysozyme activity during differentiation of the cells.     

Localization of the cyclic adenosine 3' : 5' -monophosphate phosphodiesterase activator protein in rat heart.

A cyclic adenosine 3′ : 5′ — monophosphate phosphodiesterase activator protein has been partially purified from rat heart by a procedure involving ammonium sulfate fractionation and affinity column chromatography with cyclic AMP phosphodiesterase bound to Sepharose 4B. Freezing and thawing of the rat heart was essential for solubilization of the activator protein in the crude homogenate. Activator activity was localized on sarcoplasmic reticulum isolated from fresh heart which could be solubilized with a low yield that resulted in a labile product. Maximal activation of cyclic AMP phosphodiesterase with excess protein activator was 100%.     

Lipolysis and reesterification: effects of some inhibitors of adenosine 3',5'-cyclic monophosphate phosphodiesterase

Theophylline and three lipolytic agents, 2,5-bis(2-chloroethylsulfonyl)-pyrrole-3,4-dicarbonitrile (substituted pyrrole), 2,4-diamino-6-butoxy-s-triazine (substituted triazine), and 2,3-dihydro-5,6-dimethyl-3-oxo-4-pyridazinecarbonitrile (substituted pyridazine), stimulate basal lipolysis in adipose tissue in vitro. They also cause an increased release of free fatty acids, but not glycerol, from adipose tissue in which lipolysis is already maximally stimulated by epinephrine. The four compounds also inhibit cyclic AMP phosphodiesterase and the conversion of [1-(14)C]glucose to (14)CO(2). Evidence is presented that free fatty acids accumulate as the result of inhibited reesterification. The substituted pyridazine and triazine, but not the pyrrole, elevate plasma free fatty acids after oral or intraperitoneal administration in rats.     

Mediation of macrophage collagenase production by 3'-5' cyclic adenosine monophosphate

The production of collagenase by lipopolysaccharide-(LPS) activated guinea pig macrophages is mediated by prostaglandins (PG) of the E series. After stimulation of guinea pig macrophages with LPS, extracellular PGE levels and cellular cAMP levels are elevated. Indomethacin inhibits not only PG synthesis, but also cAMP and collagenase production in LPS-stimulated macrophage cultures. In these indomethacin-inhibited cultures containing LPS, dibutyryl (dB) cAMP, or cholera toxin can restore macrophage collagenase production but not PG synthesis. Moreover, dBcAMP and cholera toxin enhance collagenase production in LPS-activated cultures. Initial activation of the macrophages by an agent such as LPS is a prerequisite for synthesis of collagenase, since in the absence of LPS, dBcAMP or cholera toxin alone are ineffective stimuli. These findings clearly demonstrate a role for PG-induced elevations of cAMP in the production of collagenase by LPS-activated macrophages.     

Effect of adenosine 3',5'-cyclic monophosphate derivatives on alpha-amylase release, protein kinase and cyclic nucleotide phosphodiesterase activity from rat parotid tissue.

Several 8-substituted derivatives of cyclic AMP were tested for their effects on alpha-amylase release. None of the 8-substituted compounds were more active than N6,O2-dibutyryl- or N6-monobutyryl adenosine 3',5'-monophosphate in causing alpha-amylase release. The rat parotid was found to contain a high (105 muM) and a low (1.15 muM) Km cyclic AMP phosphodiesterase activity. All of the 8-substituted cyclic AMP compounds inhibited the hydrolysis of 1 muM cyclic AMP. However, there was only a partial correlation between the ability to cause alpha-amylase release and inhibit cyclic AMP hydrolysis. Extracts of parotid tissue contained a cyclic AMP-dependent protein kinase activity. None of the compounds were as effective as cyclic AMP in activating the protein kinase. As in the case of inhibition of cyclic AMP hydrolysis, the ability of the 8-substituted cyclic AMP compounds to increase protein kinase activity did not correlate with their effects on alpha-amylase release. It is concluded that factors in addition to the in vitro inhibition of cyclic AMP hydrolysis and activation of protein kinase are important in determining the net result of the 8-substituted cyclic AMP compounds on parotid gland function. These additional factors might include differences in the rate of uptake and differences in rats of conversion to compounds with modified activity.     

The effects of cyclic 3'5' adenosine monophosphate on the acute tolerance induced by ethanol in male rats.

The effect of cyclic 3′5′ adenosine monophosphate (cAMP) on the acute tolerance induced by ethanol was studied in male rats. The acute tolerance was measured with a hexobarbital anesthesia method, where the dose of hexobarbital needed to obtain a burst suppression of 1 second or more in EEG is determined. Ethanol 2.0 g/kg was given ip 0.25 or 3 h prior to the threshold determination. cAMP 10 mg/kg or saline was given iv 6 h prior to the threshold determination.After saline pre-treatment less hexobarbital was needed 0.25 h after ethanol administration compared to 3 h after ethanol administration, although the blood levels were similar. An acute tolerance had developed. Pre-treatment with cAMP had no effect on the dose of hexobarbital needed without ethanol nor on the dose needed 3.0 h after ethanol administration. 0.25 h after ethanol more hexobarbital was needed in the animals pre-treated with cAMP compared with the corresponding saline treated animals. The dose of hexobarbital was as large as the one needed 3.0 h after ethanol. Thus cAMP seems to facilitate the induction of acute tolerance to ethanol while the hexobarbital threshold as such is uninfluenced.     

Opposite effects of dibutyryl adenosine 3':5' cyclic monophosphate and serum on growth of Chinese hamster cells

The effect of dibutyryl adenosine cyclic 3′:5′ monophosphate and testosterone on growth, response to serum and transport properties of Chinese hamster ovary cells was studied. There was a marked depression of growth in the presence of both compounds. A change of medium was sufficient to permit a partially synchronized burst of growth of the treated cells either in the presence or absence of dibutyryl adenosine cyclic 3′:5′ monophosphate plus testosterone. However, in the presence of these compounds a second round of cell division was prevented. Initiation of the cell cycle by cells exposed to dibutyryl adenosine cyclic 3′:5′ monophosphate plus testosterone displayed a greater serum requirement than untreated cells. It is concluded that serum and cyclic AMP could have antagonistic interactions in growth regulation. The treated cells had a reduced ability to accumulate amino-isobutyrate and glutamine, but no difference was observed with uridine uptake. The data suggest that a functional alteration of the membrane is induced by the exposure to dibutyrl adenosine cyclic 3′:5′ monophosphate plus testosterone.     

Mode of death effect on rat liver iodothyronine 5' deiodinase activity: role of adenosine 3',5' monophosphate

Liver thyronine 5'-deiodinase activity assayed in crude homogenates in the absence of dithiothreitol (DTT) is increased in rats killed by asphyxia when compared to that of animals killed by phenobarbital injection or decapitation. The addition of cyclic adenosine monophosphate leads to a consistent decrease in observed deiodinase activity, suggesting the possible involvement of this nucleotide in the regulation of this enzyme. The addition of DTT eliminates this effect and suggest a dual regulation of the enzyme by cAMP and physiological sulfhydryl compounds.     

Elevation of cyclic 3'5' adenosine monophosphate levels by cholera toxin inhibits the generation of interleukin 2 activity

Several molecules can interact with membrane receptors on mononuclear cells to increase intracellular levels of cyclic adenosine monophosphate (cAMP). We used the cholera toxin (CT), a cAMP elevating agent, to study the influence of this nucleotide on the production of interleukin 2 (IL-2) by human peripheral blood mononuclear cells stimulated by phytohemagglutinin and phorbol myristate acetate. Stimulated generation of IL-2 activity was inhibited by CT but not by its B subunit. The inhibition was potentiated by addition of theophylline. Therefore the synthesis and/or release of IL-2 is controlled by intracellular cAMP levels and may be modulated by agents active on this nucleotide system, such as bacterial toxins, glycoprotein hormones, or neurotransmitters.