Differences and similarities between guanosine 3',5'-cyclic monophosphate phosphodiesterase and adenosine 3',5'-cyclic monophosphate phosphodiesterase activities in neuroblastoma cells in culture.

There are phosphodiesterase activities in both particulate and supernatant fractions which hydrolyze guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) with an apparent Km of 2-8 muM and with an apparent Km of 44-222 muM. 4-(3-Butoxy-4-methoxybenzyl-2-imidazolidinone (RO20-1724) did not inhibit cGMP phosphodiesterase activity in homogenates of mouse neuroblastoma cells, but markedly inhibited cAMP phosphodiesterase activity. Papaverine and theophylline inhibited both cGMP and cAMP phosphodiesterase activities to about the same extent. The former was more potent than the latter. The specific activity of cGMP phosphodiesterase as a function of protein concentrations first increased and then decreased. The specific activity of cAMP phosphodiesterase decreased under a similar experimental condition.     

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.     

Adenosine 3' , 5'-cyclic monophsphate phosphodiesterase activities in the x-irradiation induced rat small bowel adenocarcinoma.

The adenosine 3′, 5′-cyclic monophosphate phosphodiesterase (PDE) activities were evaluated in X-irradiation induced Holtzman rat small bowell adenocarcinoma and age-matched normal small intestine. Within normal small intestine, PDE activity was optimal at pH 7.4, and highly dependent upon the addition of Mg²⁺ or Mn²⁺. Analyses of the rat small bowel adenocarcinoma revealed significantly elevated PDE activities above the normal small bowel which were found to be relatively constant throughout the length of the ileum and jejunum. These findings suggest that the diminished intracellular adenosine 3′, 5′-cyclic monophosphate levels observed in this lesion (1) may be the consequence of elevated PDE activities.     

Insulin-sensitive adenosine 3',5'-cyclic monophosphate phosphodiesterase of hepatocyte plasma membrane.

Adenosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.17) has been investigated in rat liver as to its insulin sensitivity. Hormone action has been assayed in vitro on a liver homogenate purified by DEAE-cellulose column chromatography, on isolated hepatocytes, on isolated plasma membranes. The DEAE-cellulose chromatography purified homogenate showed no sensitivity to insulin, whereas isolated hepatocytes incubated in presence of insulin showed increased phosphodiesterase activity in a plasma membrane-containing fraction. The plasma membrane-bound enzyme, which shows both high and low affinity components, was significantly stimulated after hormonal treatment; this effect being dependent on a V increase of the low Km form.     

Circadian variations in plasma 3':5'-cyclic adenosine monophosphate and 3':5'-cyclic guanosine monophosphate of normal adults.

Circadian variations in plasma cyclic AMP and cyclic GMP were studied in thirteen male subjects (20–22 years old) under controlled invironmental condition. Plasma collections were made every six hours. Cyclic AMP and cyclic GMP were determined by radioimmunoassay. Individual values of plasma cyclic AMP at 0800 are between 13.0 and 25.8 pmole/ml, and cyclic GMP between 2.5 and 7.0 pmole/ml. Cyclic AMP demonstrated the circadian variation with the maximum level at 1400 and the minimum at 0200, and cyclic GMP with the highest level at 1400 and the lowest level at 0800.     

Inhibition of adenosine-3',5'-cyclic monophosphate phosphodiesterase by potential antiallergic compounds.

The potential antiallergic compounds doxantrazole (3- (5-tetrazolyl)-thioxanthone 10, 10-dioxide) and CTD (3- carboxythioxanthone 10, 10-dioxide) are inhibitors of the phosphodiesterases of human and guinea pig lung and beef heart. Disodium cromoglycate is a weak inhibitor of all these enzymes. It is suggested that the antiallergic activity of doxantrazole and CTD is due, at least in part, to their ability to elevate intracellular cAMP levels by inhibiting phosphodiesterase activity.     

Effects of adenosine 3':5'-cyclic monophosphate and guanosine 3':5'-cyclic monophosphate on 3H-uridine incorporation into glomerulosal cells of hypophysectomized rat adrenal cortex.

The effects of cyclic AMP and cyclic GMP on the incorporation of 3H-uridine into glomerulosal cells of hypophysectomized rats were investigated by high resolution autoradiography. The quantitative analysis of autoradiographs shows that cyclic nucleotides, like ACTH, enhance the tracer incorporation into both nuclear and mitochondrial compartments. These findings are discussed in relation to previous results indicating that both cyclic nucleotides function as intracellular mediators of the trophic action of ACTH on the rat adrenal zona glomerulosa. The hypothesis that the mechanism of the glomerulotrophic action of ACTH and cyclic nucleotides involves the stimulation of nuclear and mitochondrial RNA synthesis is discussed.     

Adenosine 3',5'-cyclic monophosphate modulates the mitogenic responses of murine B lymphocytes

Adenosine 3',5'-cyclic monophosphate (cAMP) acts to inhibit a number of lymphocyte activities. The extent of this inhibition was tested by evaluating the effects of two cAMP-raising agents on B cell S phase entry induced by several different mitogenic regimens. It was found that both dibutyryl cAMP (dbcAMP) and isobutylmethylxanthine (IBMX) enhanced S phase entry induced by some regimens but inhibited S phase entry induced by others. The observed enhancing activity stands in contrast to the general notion of cAMP as being a "negative regulator," and it confirms that the observed inhibiting activity does not simply reflect cytotoxicity. Mitogenic regimens that appear to mimic each other, such as F(ab')2 fragments of goat anti-mouse immunoglobulin and the combination of a calcium ionophore and a phorbol ester, were distinguished by their responses to the addition of the two cAMP-raising agents. B cell responses were enhanced or inhibited even when dbcAMP was added 18-24 hr after the establishment of cultures. Cyclic AMP may regulate in a complex fashion S phase entry in cells of the immune system.