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PubMedDate not supplied

Evidence for opposing influences of cyclic GMP and cyclic AMP on force of contraction in mammalian myocardium.

The inotropic effects of the 8-Br-derivatives of cyclic GMP and cyclic AMP were investigated in guinea pig or rat auricles and papillary muscles from cats. In guinea pig auricles, 8-Br-cyclic GMP had a concentration-dependent negative inotropic effect, whereas 8-Br-cyclic AMP had a concentration-dependent positive inotropic effect. A negative inotropic effect of 8-Br-cyclic GMP in rat auricles was obtained with 30 times lower doses than in guinea pig auricles; the pacemaker activity of spontaneously beating rat right auricles did not change in response to 8-Br-cyclic GMP. In cat papillary muscles, 8-Br-cyclic GMP (3 X 10(-4) M) also produced a negative inotropic effect. In contrast, 8-Br-cyclic AMP (3 X 10(-4) M) did not affect force of contraction; however, after pretreatment with the strong phosphodiesterase inhibitor papaverine (2 X 10(-5) M) 8-Br-cyclic AMP (3 X 10(-4) M) had a strong positive inotropic effect also in cat papillary muscles. The results suggest opposite influences of cyclic GMP and cyclic AMP on force of contraction in mammalian myocardium.

Animals↗
PubMed1978

Effects of zinc chloride on the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart.

In the presence of 10 micrometer Ca2+ and 5 mM Mg2+ (or 0.25 mM Mg2+), the addition of 100 micrometer Zn2+, Ni2+, Co2+, Fe2+, Cu2+ or 1 mM Mn2+ resulted in varying degrees of stimulation or inhibition of 10(-6) M cyclic GMP and cyclic AMP hydrolysis by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart in the absence or presence of phosphodiesterase activator. The substrate specificity of the enzyme was altered under several conditions. The addition of Zn2+ in the presence of 5 mM Mg2+ and the absence of activator resulted in the stimulation of cyclic GMP hydrolysis over a narrow substrate range while reducing the V 65% due to a shift in the kinetics from non-linear with Mg2+ alone to linear in the presence of Zn2+ and Mg2+. Zn2+ inhibited the hydrolysis of cyclic GMP and cyclic AMP in the presence of activator with Ki values of 70 and 100 micrometer, respectively. Zn2+ inhibition was non-competitive with substrate, activator and Ca2+ but was competitive with Mg2+. In the presence of 10 micrometer Ca2+ and activator, a Ki of 15 micrometer for Zn2+ vs. Mg2+ was noted in the hydrolysis of 10(-6) M cyclic GMP. Several effects of Zn2+ are discussed which have been noted in other studies and might be due in part to changes in cyclic nucleotide levels following phosphodiesterase inhibition.

Animals↗
PubMed1979

Cyclic GMP and cyclic AMP changes in response to folic acid pulses during cell development of Dictyostelium discoideum.

Folic acid pulses induced developmental processes in agip 71, a morphogenetic mutant of Dictyostelium discoideum, strain Ax-2. Cells that had received folic acid pulses were able to form EDTA-stable cell aggregates and to complete full differentiation to fruiting bodies. In these cells no autonomous periodic activities were observed by light scattering. Folic acid pulses elicited increases in the concentrations of cyclic GMP and cyclic AMP. In undifferentiated cells, folic acid caused a rapid increase in the level of cyclic GMP without a significant change in the level of cyclic AMP. In an advanced developmental state folic acid caused an increase in cyclic AMP in addition to two successsive peaks of cyclic GMP. Experiments performed with the parent strain, Ax-2, also showed that during the development towards aggregation competence, cells acquired the ability to produce a cyclic AMP peak in response to folic acid.

Cell Adhesion↗
PubMed1977

Localization of cyclic GMP and cyclic AMP in cardiac and skeletal muscle: immunocytochemical demonstration.

When rat cardiac and skeletal muscle are explored by immunocytochemical procedures designed to show sites of localization of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP), distinct staining patterns for the two nucleotides are seen. Antibody to cyclic AMP is found in the area of the sarcoplasmic reticulum, while antibody to cyclic GMP is found with a periodic distribution corresponding to that of the A band. This suggests a role for cyclic GMP in the regulation of myosin.

Animals↗
PubMed1979

Cyclic GMP and cyclic AMP levels in median eminence, hypothalamus and pituitary gland of the rat after decapitation or microwave irradiation.

Cyclic AMP and cyclic GMP content of the median eminence (ME), medial basal hypothalamus (MBH), posterior pituitary (PP) and anterior pituitary (AP) of inact male rats was measured by radioimmunoassay following decapitation or exposure to microwave irradiation (MW). Levels of both nucleotides in MW irradiated animals were higher in all three nervous tissues studied than in the AP. Following decapitation cyclic AMP levels increased strikingly in the MBH and ME, slightly in the AP, but remained unchanged in the PP. Cyclic GMP levels increased more markedly in the ME than in the MBH, slightly in the PP and did not change in the AP. The distinct synthesizing capability of the cyclic AMP and cyclic GMP generating systems in the ME, a region rich in neurohormones known to control anterior pituitary function, raises the possibility that these nucleotides are involved in the process of neurohormone secretion by the ME.

Animals↗
PubMed1978

Effects of CuCl2 on the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart.

CuCl2 non-competitively inhibited the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent phosphodiesterase from bovine heart in the presence of 5 mM Mg2+, 10 muM Ca2+ and phosphodiesterase activator with Ki values of approximately 2 muM for both substrates. CuCl2 inhibition was also non-competitive with Mg2+, Ca2+ and phosphodiesterase activator. Dialysis demonstrated that CuCl2 inhibition is reversible. Treatment of the enzyme with p-hydroxymercuribenzoate resulted in the loss of enzyme activity, suggesting the presence of sulfhydryl groups essential for enzyme activity. The inhibitory activity of CuCl2 was not additive with that of p-hydroxymercuribenzoate, therefore CuCl2 may inhibit enzyme activity by binding to one or more essential sulfhydryl groups. CuCl2 also inhibited the hydrolysis of cyclic AMP by the cyclic AMP-specific phosphodiesterase from bovine heart with an I50 value of 18 muM. Several effects of Cu2+ are discussed which have been noted in other studies and might be due, in part, to changes in cyclic nucleotide levels following alterations in phosphodiesterase activity.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Regulation of intracellular cyclic GMP and cyclic AMP levels in mouse lung fragments by disodium cromoglycate, beta-adrenergic agonists, cholinergic activators, and histamine.

The effects of adrenergic and cholinergic agents as well as the effects of disodium cromoglycate (DSCG) on the levels of cyclic AMP and cyclic GMP in mouse lung fragments were studied. Levels of cyclic AMP were enhanced by two of the known beta-adrenergic agonists, epinephrine and isoproterenol. This increase was abolished by propanolol, a recognized beta-adrenergic antagonist. Disodium cromoglycate, a proposed inhibitor of phosphodiesterases, alone caused a slight, significant increase in cyclic AMP. However, in the presence of epinephrine, levels of cyclic AMP were potentiated by DSCG. DSCG behaves, therefore, as a typical cyclic AMP phosphodiesterase inhibitor. Cyclic GMP levels were increased by carbachol, acetylcholine, and the phosphodiesterase inhibitor, aminophylline, but not by DSCG, or beta-adrenergic agonists.

Adrenergic beta-Agonists↗
PubMed1975

The antagonistic action of cyclic GMP and cyclic AMP on proliferation of B and T lymphocytes.

The effect of c-AMP, c-GMP and both substances together on (3H)-thymidine incorporation into nuclear DNA was investigated using spleen cells of normal and athymic nude mice. c-GMP induces DNA synthesis in both normal and nude spleen cell populations. c-AMP inhibited the stimulatory activity of c-GMP as well as the phytohaemagglutinin (PHA) and lipopolysaccharide (LPS) response of spleen cells. The inhibitory activity of c-AMP on the PHA and LPS responses can be reversed by c-GMP. The possible role of cyclic nucleotides in the regulation of cell proliferation and of the immune response is discussed.

Animals↗