Adenosine promoted accumulation of adenosine 3′,5′-monophosphate in rabbit vagus nerve

Summary Desheathed rabbit vagus nerve has been found to form cyclic AMP when incubated with adenosine. This accumulation of cyclic AMP is inhibited by theophylline but not by antiadrenergic agents, anticholinergic agents or local anaesthetics. Depolarizing media are not able to promote cyclic AMP accumulation in this preparation.Acknowledgment. We gratefully acknowledge Mr.G. Jones for valuable discussion, MrsM. Moosmayer and Mr.S. Ferrara for expert technical assistance and Swiss National Science Foundation for grant support (Nr. 3.478.0.75).     

Role of adenosine A1 and A2 receptors in the regulation of aldosterone production in rat adrenal glands

To investigate the roles of adenosine A1 and A2 receptors in the regulation of aldosterone production, we examined the effects of adenosine and adenosine agonists (N6-cyclohexyl adenosine; selective adenosine A1 receptor agonist and 5'-N-ethylcarboxamine adenosine; selective adenosine A2 receptor agonist) on aldosterone and cyclic AMP production in rat adrenal capsular cells. Neither adenosine nor 5'-N-ethylcarboxamine adenosine caused significant effects on basal aldosterone or cyclic AMP production. Also, adenosine (10(-3) M) showed no consistent effects on aldosterone and cyclic AMP production induced by ACTH. On the other hand, N6-cyclohexyl adenosine exhibited a significant inhibition of basal aldosterone and cyclic AMP production at doses of 10(-4) M and 10(-3) M; furthermore, 10(-3) M N6-cyclohexyl adenosine inhibited aldosterone and cyclic AMP production stimulated by ACTH. These results suggest that adenosine A1 receptors are coupled to and inhibit adenylate cyclase and may be involved in the inhibition of aldosterone production.     

Adenosine promoted accumulation of adenosine 3',5'-monophosphate in rabbit vagus nerve.

Desheathed rabbit vagus nerve has been found to form cyclic AMP when incubated with adenosine. This accumulation of cyclic AMP is inhibited by theophylline but not by antiadrenergic agents, anticholinergic agents or local anaesthetics. Depolarizing media are not able to promote cyclic AMP accumulation in this preparation.     

Influence of cyclic nucleotides on protein synthesis in vascular smooth muscle.

The incorporation of leucine-14C into protein in bovine mesenteric arteries was augmented by cyclic GMP (10-3 M) and decreased by cyclic AMP (10-3 M). There was no effect of 5'AMP (10-3 M). The phosphodiesterase inhibiting drugs theophylline (10-3 M) and papaverine (5 x 10-5 g/ml) both decreased the leucine-14C incorporation.     

Increase of interferon antiviral activity by exogenous cyclic adenosine-3':5'-monophosphate (cAMP).

Some effects of cAMP on replication of Semliki Forest Virus in chick embryo fibroblast cell cultures are described. Depending on concentration, the incorporation of [3H]-uridine into viral RNA or the formation of plaque-forming units is inhibited; the highest concentration tested was 8 mM. Cyclic AMP has an effect of its own and increases the Interferon action in the lower concentration ranges of Interferon (up to 1 unit/ml). The effect of cyclic AMP is fast, needs no induction and is also visible in late phases of viral replication. However, these experiments do not establish a causal relation between cAMP and Interferon.     

Inhibition of prostaglandin-induced cyclic AMP accumulation in the rat anterior pituitary by alrestatin.

Alrestatin at 25-1 X 10(-4) M inhibited the accumulation of cyclic AMP induced by prostaglandin E2, but not theophylline, in the rat anterior pituitary in vitro. Somatostatin, at lower concentrations, inhibited both; maximal inhibition of the prostaglandin effect was greater with alrestatin. As cyclic AMP is considered to be a mediator in induced-hormonal release, it appears from the present findings that alrestatin may be of potential use in altering hormonal release.     

Plasma cyclic 3',5'-guanosine monophosphate and cyclic 3',5'-adenosine monophosphate response to methacholine in man

Cholinergic agents are known to induce increases in tissue and plasma levels of cyclic GMP in experimental animals. We observed that i.m. injection of methacholine, a cholinergic agent, caused significant increases in plasma cyclic GMP and cyclic AMP in man.     

Role of adenosine A1 and A2 receptors in the regulation of aldosterone production in rat adrenal glands

Summary To investigate the roles of adenosine A₁ and A₂ receptors in the regulation of aldosterone production, we examined the effects of adenosine and adenosine agonists (N⁶-cyclohexyl adenosine; selective adenosine A₁ receptor agonist and 5-N-ethylcarboxamine adenosine; selective adenosine A₂ receptor agonist) on aldosterone and cyclic AMP production in rat adrenal capsular cells. Neither adenosine nor 5-N-ethylcarboxamine adenosine caused significant effects on basal aldosterone or cyclic AMP production. Also, adenosine (10^–3M) showed no consistent effects on aldosterone and cyclic AMP production induced by ACTH. On the other hand, N⁶-cyclohexyl adenosine exhibited a significant inhibition of basal aldosterone and cyclic AMP production at doses of 10^–4 M and 10^–3 M; furthermore, 10^–3 M N⁶-cyclohexyl adenosine inhibited aldosterone and cyclic AMP production stimulated by ACTH. These results suggest that adenosine A₁ receptors are coupled to and inhibit adenylate cyclase and may be involved in the inhibition of aldosterone production.     

The brachymorphic mutation of mice and altered developmental patterns of limb bud 3':5' cyclic adenosine monophosphate

Concentrations of cyclic AMP (cAMP) were determined in paired fore and hind limbs from day 12-16 of development in murine fetuses homozygous for the brachymorphic (bm) mutation and normal controls. A developmental rise in cAMP occurred 1 day earlier in bm/bm than in +/+ hind limbs and cAMP was higher in day-13 bm/bm than in +/+ fore limbs. Since cAMP is well documented to stimulate chondrogenic differentiation, premature cartilage determination secondary to altered levels of cAMP could play a role in bm/bm short-limbed dwarfism.     

3'5'-Cyclic AMP phosphodiesterase activity in the internal and external layers of human myometrium at the end of pregnancy]

The hydrolysis of cAMP by phosphodiesterase was studied in whole homogenate from human myometrium at the end of the pregnancy before onset of labour. Tissue samples were taken from outer and inner layers of placental and anti-placental sites. Kinetic analysis shows in every case two apparent Km values for low and high cAMP concentrations in the order of 1 x 10(-5) M and 1 x 10(-4) M. On the other hand Vmax values are lower for the enzyme isolated from the placental site than for the one isolated from the anti-placental area. In the 4 zones studied, an appreciable proportion of the low Km enzyme is present.     

Stimulation of ribonuclease activity and its isoenzymes in germinating seeds of cowpea (Vigna sinensis) by gibberellic acid and adenosine-3',5-cyclic monophosphate.

Application of GA3 and cyclic AMP to cowpea seedings caused a 2-3 fold stimulation of RNAase activity, together with the augmentation of RNAase isoenzymes. Inhibitor studies indicated the requirement of fresh RNA and protein synthesis for enzyme stimulation.     

Specific inhibition of a calcium dependent activation of brain cyclic AMP phosphodiesterase activity by vinblastine.

Vinblastine selectively inhibits the activation of brain cyclic AMP phosphodiesterase activity by Ca++-protein activator (50% inhibition by 2 x 10(-5) M). This inhibitory effect was reversed by excessive amounts of the activator, whereas large quantities of Ca++ caused only a slight suppression of the vinblastine effect. This result of vinblastine suggests a new site of its action and also suggests the possible role of protein activator, phosphodiesterase proteins or cyclic nucleotides in the previously known effects of vinblastine in vivo and in vitro.     

VIP and histamine H2 receptor activity in human fetal gastric glands

Vasoactive intestinal peptide (VIP, EC50 = 6.4 X 10(-10)M) and histamine (EC50 = 3 X 10(-6)M) activated the cyclic AMP generating system in gastric glands isolated from two human fetuses at 23 weeks gestation. Histamine antagonism by the H2 receptor blockers cimetidine (Ki = 0.35 X 10(-6)M) and ranitidine (ki = 0.51 X 10(-7)M) clearly characterized the histaminic activation as being of the H2 type. It is suggested that these two vasoactive hormones may operate as neurocrine/paracrine regulators of the differentiation and/or function of the human gastric mucosa in utero.     

Vasoactive intestinal peptide (VIP): specific receptors and adenylate cyclase activation in a human prolactin-secreting pituitary tumor]

Receptors for the Vasoactive Intestinal Peptide (VIP) were characterized in particles enriched in plasma membranes obtained from a human prolactin-secreting pituiatry tumor. Native VIP inhibited competitively the binding of 125I-VIP to the particles and stimulated cyclic AMP production; both these effects were observed at concentrations of VIP as low as 10(-11)-10(-10) M, which are compatible with VIP concentrations in the hypothalamopituitary portal blood.     

The response of cyclic 3',5'-AMP and cyclic 3',5'-GMP phosphodiesterases to experimental diabetes

Alloxan diabetes caused a decrease in cyclic AMP phosphodiesterase in all affected rat tissues. Cyclic GMP phosphodiesterase activity was, however, decreased in adipose and liver, but increased increased in heart and uterus.     

Purification of the glutamate decarboxylase from human brain]

A method of purifying the glutamate decarboxylase from human brain is described. The enzyme was purified 8 000 fold in regard to the initial homogenate and appears homogenous by electrophoresis, both in denaturing and non-denaturing conditions. The molecular weight of the native enzyme and its subunits indicate that GAD from human brain is formed by two similar if non identical polypeptide chains. The Km for glutamate and pyridoxal phosphate found for the human enzyme, respectively 1,2.10(-3) M and 0,13.10(-6) M, are close to the Km found for the Mouse enzyme.     

Neuronal responses to extracellularly applied cyclic AMP: Role of the adenosine receptor

Summary At low doses, theophylline blocks the neuronal depressant effects of 5-AMP, but not cyclic AMP. Higher doses (100 mg/kg) block cyclic AMP responses and reduce the effects of noradrenaline and GABA. It is concluded that cyclic AMP does not depress neurones via the adenosine receptor.We are grateful to the Wellcome Trust and Royal Society for travel grants.     

Cyclic AMP is a likely mediator of ovulation in the tsetse fly.

Ovulation in tsetse flies is normally induced by mating, but virgins can be stimulated to ovulate with an injection of dibutyryl cyclic AMP, cholera toxin (a cyclic AMP generator), or aminophylline (a phosphodiesterase inhibitor). Thus, elevation of cyclic AMP is a likely link in the events leading to ovulation.     

Fetal calf serum alters cyclic adenosine 3',5'-monophosphate's effect on heme synthesis in vitro.

An investigation of the effect of cAMP on heme synthesis of rat bone marrow cells revealed that at 10(-2) M this cyclic nucleotide inhibits heme synthesis and that optimum stimulation occurs at 10(-4) M. Some unidentified constituent of fetal calf serum in the culture medium modifies the direction and degree of cAMP's effect.