Rise In Cyclic AMP Concentration Research Articles

The Cytoplasmic Domain of α6A Integrin Subunit Is an in Vitro Substrate for Protein Kinase C

We have investigated whether the cytoplasmic domain of α6A integrin subunit can be phosphorylated by Ser/Thr kinases using synthetic peptides as in vitro substrates. This domain was phosphorylated by protein kinase C (PKC) and cyclic AMP-dependent kinase (protein kinase A, PKA) but not by mitogen-activated protein kinase. While Ser1041 has been shown to be phosphorylated in PMA-stimulated cells in vitro, Ser1048 was phosphorylated by PKA. Furthermore pharmacological agents which induce a rise in cyclic AMP concentration failed to stimulate the phosphorylation of the α6A cytoplasmic domain in intact cells. These results suggest that PKC, but not PKA, is involved in the physiological phosphorylation of the α6A integrin subunit.

The control of glycogen metabolism in yeast. 1. Interconversion in vivo of glycogen synthase and glycogen phosphorylase induced by glucose, a nitrogen source or uncouplers.

The addition of glucose to a suspension of yeast initiated glycogen synthesis and ethanol formation. Other effects of the glucose addition were a transient rise in the concentration of cyclic AMP and a more prolonged increase in the concentration of hexose 6-monophosphate and of fructose 2,6-bisphosphate. The activity of glycogen synthase increased about 4-fold and that of glycogen phosphorylase decreased 3-5-fold. These changes could be reversed by the removal of glucose from the medium and induced again by a new addition of the sugar. These effects of glucose were also obtained with glucose derivatives known to form the corresponding 6-phosphoester. Similar changes in glycogen synthase and glycogen phosphorylase activity were induced by glucose in a thermosensitive mutant deficient in adenylate cyclase (cdc35) when incubated at the permissive temperature of 26 degrees C, but were much more pronounced at the nonpermissive temperature of 35 degrees C. Under the latter condition, glycogen synthase was nearly fully activated and glycogen phosphorylase fully inactivated. Such large effects of glucose were, however, not seen in another adenylate-cyclase-deficient mutant (cyr1), able to incorporate exogenous cyclic AMP. When a nitrogen source or uncouplers were added to the incubation medium after glucose, they had effects on glycogen metabolism and on the activity of glycogen synthase and glycogen phosphorylase which were directly opposite to those of glucose. By contrast, like glucose, these agents also caused, under most experimental conditions, a detectable rise in cyclic AMP concentration and a series of cyclic-AMP-dependent effects such as an activation of phosphofructokinase 2 and of trehalase and an increase in the concentration of fructose 2,6-bisphosphate and in the rate of glycolysis. Under all experimental conditions, the rate of glycolysis was proportional to the concentration of fructose 2,6-bisphosphate. Uncouplers, but not a nitrogen source, also induced an activation of glycogen phosphorylase and an inactivation of glycogen synthase when added to the cdc35 mutant incubated at the restrictive temperature of 35 degrees C without affecting cyclic AMP concentration.

The effects of isoproterenol on intracellular calcium concentration.

beta-Adrenergic agonist, isoproterenol (ISO), is a potent relaxant of tracheal smooth muscle and inhibits carbachol-induced contraction. The effect of ISO on intracellular free Ca2+ concentration ([Ca2+]i) was examined in bovine tracheal smooth muscle strips, employing aequorin as Ca2+ indicator. Surprisingly, 10 microM ISO induces a 5-fold increase in [Ca2+]i which then gradually declines but still remains higher than basal after 1 h of stimulation. The ISO-induced increase in [Ca2+]i is dose-dependent, and the ED50 is approximately 50 nM. The ISO-induced increase in [Ca2+]i is inhibited by a beta-receptor blocker, propranolol, not by an alpha-blocker, phentolamine. The ISO-induced rise in [Ca2+]i is dependent on extracellular Ca2+. Forskolin, an adenylate cyclase activator, and vasoactive intestinal peptide, which is known to stimulate adenylate cyclase via a specific receptor in this tissue, have similar effects on [Ca2+]i, suggesting that a rise in cyclic AMP concentration mediates this effect of ISO on [Ca2+]i. Pretreatment of muscle with 10 microM ISO inhibits both the initial Ca2+ transient and the contractile response induced by 0.3 microM carbachol. Conversely, in carbachol-pretreated muscle strips, addition of ISO causes a fall rather than a rise in [Ca2+]i, and an inhibition of contraction. These results indicate that ISO has effects on cellular Ca2+ metabolism at more than a single site in bovine tracheal smooth muscle, that these effects are different in control and carbachol-pretreated muscle, and that the relaxing effect of ISO is not due solely to its effect on Ca2+ metabolism.

The role of cyclic AMP in the positive inotropic effect mediated by beta 1- and beta 2-adrenoceptors in isolated human right atrium.

The time course of the effects of isoprenaline (3 X 10(-7) mol/l) on contractile force and on the cyclic AMP level was studied in the electrically driven isolated muscle strip of the human right atrium. Isoprenaline produced a rise in cyclic AMP content (maximum increase after 60 s) preceding the increase in contractile force. The effects of isoprenaline on contractile force and on the intracellular level of cyclic AMP were enhanced in the presence of the phosphodiesterase inhibitor papaverine (10(-5) mol/l). On the other hand, the beta-adrenoceptor antagonist propranolol (10(-7) mol/l) suppressed isoprenaline-induced cyclic AMP increases, but reduced the increase in force of contraction by only 35%. In addition, both the beta 1-selective antagonist bisoprolol (3 X 10(-9)-3 X 10(-8) mol/l) and the beta 2-selective antagonist ICI 118,551 (3 X 10(-9)-3 X 10(-8) mol/l) inhibited the isoprenaline-induced cyclic AMP increase concentration-dependently; ICI 118,551 produced more pronounced inhibition than bisoprolol. It is concluded that cyclic AMP is involved in the positive inotropic action of isoprenaline evoked by beta 1- and beta 2-adrenoceptor stimulation in isolated human right atrium; however, an additional cyclic AMP independent mechanism cannot be ruled out.

The action of mycophenolic acid on Candida albicans

Mycophenolic acid is an antibiotic fermentation product with known anti-bacterial. anti-fungal, anti-tumour and anti-viral properties (Florey et al., 1946; Gilliver, 1946; Williams et al., 1968; Carter et al., 1969 Suzuki et al., 1969). I t is an inhibitor of DNA synthesis, inhibiting two enzymes, IMP dehydrogenase and GMP synthetase, involved in the biosynthesis of GMP in Landscutz ascites tumour cells (Franklin & Cook, 1969; Sweeney et al., 1972). GMP is also synthesized via the nucleotide-salvage pathway using guanine or guanosine from the culture media (Cline et al., 1969; Sweeney et al., 1972). The activity of mycophenolic acid against the dimorphic pathogenic yeast Candida albicans was investigated and compared with its activity against the monomorphic yeast Succharomyces cerevisiae. Mycophenolic acid has a fungistatic effect on both yeasts, inhibiting the growth of S. cerevisiae by 64% and C . albicans by 71 YO with respect to the controls after incubation at 30°C for 24 h in liquid minimal media supplemented with 0.2 mg of mycophenolic acid/ml. Morphological studies revealed a high proportion of budded cells in mycophenolic acidsupplemented Candida cultures throughout the growth cycle. A large percentage (up to 70%) of these budded cells exhibited unusual morphologies that were not present in the controls or supplemented S. cerevisiae cultures. These cells types (Fig. 1) may be multi-budded and/or contain short mycelia (mycelia have been observed in up to 20% of budded cells). They are observed in populations grown in both minimal and complete mycophenolic acid-supplemented media, and their frequency within a population is similar regardless of the age of the starting culture. Staining with calcofluor (stains birth scars) has shown that these multievaginated cell types can be formed from both daughter and parental cells. Guanine reversed the growth inhibition due to mycophenolic acid, and in the case of C . albicuns the unusual cell types were 110 longer observed. Xanthine, hypoxanthine and adenine did not have this effect. Morphological changes undergone by Candida cultures in mycophenolic acid-supplemented media are possibly related to the dimorphic properties of the organism, as no changes are observed in S. cerevisiae, a monomorphic yeast. Since guanine reverses inhibition due to mycophenolic acid, this suggests that mycophenolic acid inhibits GMP biosynthesis as previously found with viruses (Cline et al., 1969) and with Landschutz acites tumour cells (Franklin et al., 1969; Sweeney et al., 1972). Niinii et al. (1980), investigating the changes in cyclic nucleotide levels and dimorphic transition in C . albicans, showed that germ-tube formation induced bv incubation at 40°C followed a rise in cyclic AMP concentrations, with no accompanying change in cyclic GMP content. We propose a drop in GMP levels results, as available GMP is used in DNA synthesis (it was observed, using mithramycin nuclear staining, that all evaginations from cells contained nuclear material) and mycophenolic acid is blocking the major GMP biosynthesis pathway. The reduction in the GMP pool may cause a relative increase in the AMP pool. This difference in levels could induce the cells towards the mycelial form. The difference in levels may not. be sufficient to induce and maintain 100% mycelia, as other Fig. 1. Candida albican cell types in (a) control and (b) mycophenolic acid (0.05 mg/ml)-supplemented minimal media after 10 h incubation at 30°C

Effects of adenosine and adenosine analogues on glycogen metabolism in isolated rat hepatocytes

Adenosine and adenosine analogues were incubated with isolated rat hepatocytes. Adenosine and 5′-deoxy-5′-chloroadenosine stimulated glucose release, glycogen loss, and the conversion of glycogen phosphorylase b to a. The effect was of short duration for adenosine, but of long duration for 5′-deoxy-5′-chloroadenosine. The effects on glucose release and phosphorylase were blocked by theophylline, an R-receptor blocking agent, but not by nitrobenzylthioinosine or dipyridamol which are nucleoside transport inhibitors. A dose-dependent rise in cyclic AMP concentration was observed in hepatocytes 1 min after adding adenosine. It is concluded that adenosine exerts these effects in liver by activating adenylcyclase. Adenosine may be involved in the short-term regulation of hepatic glycogen phosphorylase.

Intracellular calcium and adenosine 3',5'-cyclic monophosphate as mediators of potassium-induced aldosterone secretion.

We compared the action of K+ on aldosterone secretion from isolated bovine adrenal glomerulosa cells with that of ionophore A23187. Addition of either 50 nM-A23187 or 8 mM-K+ to perifused cells induces a similar initial aldosterone-secretory responses, and a similar sustained increases in Ca2+ entry. However, K+-induced secretion is more sustained than is A23187-induced secretion, even though each agonist appears to act by increasing Ca2+ entry into the cells. When [3H]inositol-labelled cells are stimulated by 8 mM-K+, a small decrease in phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] is observed. This decrease is not accompanied by an increase in inositol trisphosphate (InsP3) concentration. Also, if [3H]arachidonic acid-labelled cells are exposed to 8 mM-K+, there is no increase in [3H]diacylglycerol production. When [3H]inositol-labelled cells are stimulated by 50 nM-A23187, a small decrease in PtdIns(4,5)P2 is observed. This decrease is not accompanied by an increase in InsP3. The cyclic AMP content of K+-treated cells was approximately twice that in A23187-treated cells. If cells are perifused simultaneously with 50 nM-forskolin and 50 nM-A23187, the initial aldosterone-secretory response is similar to that induced by A23187 alone, and the response is sustained rather than transient, and is similar to that seen during perifusion of cells with 8 mM-K+. This dose of forskolin (50 nM) causes an elevation of cyclic AMP concentration in A23187-treated cells, to a value similar to that in K+-treated cells. These results indicate that, in K+-treated cells, a rise in cyclic AMP content serves as a positive sensitivity modulator of the Ca2+ message, and plays a key role in mediating the sustained aldosterone-secretory response.

Prostaglandins and cyclic AMP stimulate creatine kinase synthesis but not fusion in cultured embryonic chick muscle cells

Cyclic AMP levels have been measured in cultures derived from 12-day-old chick embryonic muscle. A rise in concentration was found after the onset of myoblast fusion. Cells cultured at a medium Ca 2+ concentration of 0.1 μM did not fuse and exhibited only a small rise in cyclic AMP concentration during culture. Addition of 1.4 mM Ca 2+ to these cells after 50 h in culture caused rapid, synchronous fusion with a concomitant rise in cyclic AMP levels. Indomethacin, an inhibitor of prostaglandin synthesis, did not inhibit fusion, but inhibited the rise in cyclic AMP concentration. Indomethacin-treated cultures exhibited lower creatine kinase levels, though no change in the ratio of the three isoenzymes was observed. Addition of prostaglandins E 1 and E 2 to indomethacin-treated cultures overcame this inhibition. We propose that prostaglandin synthesis is a consequence of the stimulation of myoblast fusion and that via cyclic AMP it stimulates protein synthesis.

Cyclic GMP mediates neurogenic relaxation in the bovine retractor penis muscle.

Field stimulation of the non-adrenergic, non-cholinergic inhibitory nerves to the bovine isolated retractor penis muscle evoked a relaxation that was preceded by a rise in the tissue content of cyclic GMP. There was no change in the content of cyclic AMP. The selective cyclic GMP phosphodiesterase inhibitor, 2-o- propoxyphenyl -8- azapurin -6-one (M&B 22948), elevated the tissue's cyclic GMP content, and potentiated both the relaxation and the rise in cyclic GMP produced by inhibitory nerve stimulation. Sodium nitroprusside and an inhibitory factor extracted from the bovine retractor penis muscle mimicked the effects of inhibitory nerve stimulation in that they each produced relaxation associated with a selective rise in cyclic GMP concentration. Haemoglobin (in the form of erythrocyte haemolysate) and N- methylhydroxylamine , which are known to block guanylate cyclase, blocked the relaxation and the rise in cyclic GMP content produced by inhibitory nerve stimulation, inhibitory factor and sodium nitroprusside. Haemoglobin itself caused a rise in muscle tone and at the same time reduced the cyclic GMP content of the tissue. 8-Bromocyclic GMP, a permeant derivative of cyclic GMP, produced a relaxation of the muscle that, as expected, was not blocked by haemoglobin. Vasoactive intestinal polypeptide, prostaglandin E1 and forskolin each produced relaxation associated with a selective rise in cyclic AMP content. Their effects were not blocked by haemoglobin or N- methylhydroxylamine . It is concluded that inhibitory nerve stimulation in the bovine retractor penis muscle produces a relaxation that is mediated by cyclic GMP, although some substances relax the muscle without affecting cyclic GMP levels. The results are also compatible with the view that the extracts of muscle contain the inhibitory neurotransmitter.

Cyclic AMP in macrophages from experimental granulomas and the effect of prostaglandin E2

Leucocytes were isolated by pronase digestion from granuloma tissue at different stages in inflammation induced by carrageenin-soaked sponge implants in rats and cyclic AMP was measured in these cells. In a mixed cell suspension, containing granulocytes and macrophages, the cyclic AMP levels increased during the early stages of inflammation but decreased when the granuloma became established. However, after correction for the proportion of infiltrating macrophages, as the inflammation progressed only a fall in cyclic AMP content was observable. Exposure of granuloma-derived cells to PGE2 resulted in a rise in cyclic AMP content, which was more pronounced in cells isolated during a later rather than an earlier stage of granuloma development. The results provide support for the earlier proposal that the anti-inflammatory effect of E-type prostaglandins on granulomas is partially explicable on the basis of cyclic AMP changes in infiltrating macrophages.

Changes in cyclic AMP and cyclic GMP concentrations during the action of 5-hydroxytryptamine on an insect salivary gland.

Salivary glands from adult blowflies (Calliphora erythrocephala Meigen) were studied in vitro. The time course of changes in cyclic AMP content of the glands was followed at different concentration of 5-hydroxytryptamine. There was an immediate biphasic rise and fall in cyclic AMP content, following by a slower rise and subsequent gradual decline. The initial rise preceded the onset of fluid secretion by the glands. Rises in cyclic AMP content were inhibited by compound RMI 12330 A (an adenylate cyclase inhibitor) and were halted after about 15-20s if the glands were deprived of Ca2+. Theophylline (a phosphodiesterase inhibitor) abolished the decline phase of the fast response, Losses of cyclic AMP from the glands either to the bathing medium or to the saliva were small and could not account for the rapid fall found. Evidence is presented that cyclic GMP is not involved in the process of initiating secretion in the blowfly salivary gland.

Changes in cyclic AMP levels during development in Myxococcus xanthus

Cyclic AMP levels doubled in Myxococcus xanthus under conditions in which cells aggregate and form fruiting bodies. In liquid medium, glycerol- or dimethyl sulfoxide-induced sporulating cultures exhibited a sharp but transient rise in cyclic AMP concentration after 45 min.

Development of Secretory Function in Rat Parotid Gland

Summary: Because very little is known regarding the control of enzyme secretion in developing parotid glands, the effects of various secretagogues on cyclic AMP levels and amylase release were studied in rats at various times after birth. In parotid fragments or slices incubated with isoproterenol or epinephrine (40 μM) in vitro, neither cyclic AMP elevation nor amylase release was achieved at 8 days postnatally. In in vivo studies, secretion of amylase at this age was also refractory to stimulation with these hormones or carbamylcholine. In animals older than 15 days, highly significant rise in cyclic AMP content occurred 5 min after exposure of the glands to the catecholamines in vitro, and the magnitude of this elevation was incremental with age. Thus, in 15-day-old animals adrenergic stimulation produced a 2-fold rise in cyclic AMP levels (from 9.3 ± 1.0 pmol/mg protein to 20.9 ± 4.7, mean ± SE); at 25 days the increase was 7–8 times the basal value (from 2.7 ± 0.3 to 21.3 ± 3.9); and at 8 weeks the rise was 8-fold with epinephrine (from 3.2 ± 0.3 to 24.4 ± 7.5) and 12-fold after isoproterenol (from 3.2 ± 0.3 to 39.2 ± 9.2). At these ages, adrenergic stimulation led to a 2− to 3-fold increase in amylase secretion compared to unstimulated control levels. When isoproterenol (16 μg/g body weight) was injected intraperitoneally in intact animals 15 days of age or older cyclic AMP levels 5 min later were increased 2–3 times in 15− and 25-day-old animals (from 13.9 ± 4.4 to 49.3 ± 3.9 and 31.3 ± 4.0, respectively) and >100-fold in mature animals (1211 ± 437). Greater than 40% of the stored amylase was released from the glands in 30 min, a quantity comparable to that found in vitro. The data demonstrate that the responsiveness of the parotid gland to catecholamines is age dependent, and that development of secretory function precedes full morphologic and biochemical development. Speculation: The identification of a stage in exocrine development when the immature parotid glands are refractory to secretory stimuli represents an important model for the study of stimulus-secretion coupling. The acquisition of mature secretory function may depend upon the relationship between the number of cell surface hormone receptors and acinar maturation.

Formation of guanosine 3′,5′-cyclic monophosphate by thyroliberlin in cultured rat pituitary cells a possible role in stimulation of prolactin synthesis

In a clonal strain of rat pituitary tumour cells (GH 4C 1 cells), thyroliberin stimulated prolactin secretion and synthesis: effects that could be demonstrated after 5 min and 4–5 h of treatment, respectively. Within 0.5–5 min after addition of thyroliberin, maximal increases (2–4 hold) in cellular cyclic GMP concentrations were observed, and this rise preceded or occurred simultaneously with that of cyclic AMP. After 60 min of treatment the concentrations of the cyclic nucleotides had returned to control values. Half maximal and maximal stimulation of cyclic GMP elevations were obtained with approx. 2·10 9 and approx. 27·10 −9 thyroliberin, respectively. Aminophylline increased both cyclic GMP and cyclic AMP, and potentiated the stimulatory effects of thyroliberin on both cyclic nucleotides. The dibutyryl derivative of cyclic GMP (10 −4–10 −6 M) stimulated prolactin synthesis, but not hormone release. Prostaglandin E 2 (3·10 −7 M) stimulated cellular cyclic AMP concentrations, but did not affect cyclic GMP levels. We conclude that thyroliberin in the GH 4C 1 ccell strain stimulates cyclic GMP formation, in addition to elevate cyclic AMP concentrations. The stimulatory effect on cyclic GMP is probably not secondary to the rise in cyclic AMP concentration, since prostaglandin E 2 elevates only cyclic GMP is involved in the action of thyroliberin on prolactin, the present results suggest a role on hormone synthesis.

Guanylate cyclase activity and cyclic nucleotide concentrations during liver regeneration after experimental injury.

Cyclic nucleotide concentrations and guanylate cyclase activity were measured in regenerating rat liver. Previous work has shown that in livers of partially hepatectomized rats the activity of a membrane-bound guanylate cyclase increases considerably during the early replicative phase [Kimura & Murad (1975) Proc. Natl. Acad. Sci. U.S.A.72, 1965-1969; Goridis & Reutter (1975) Nature (London) 257, 698-700]. Over the same time period after partial hepatectomy, increased tissue concentrations of cyclic GMP were found when the rats were killed under pentobarbital anaesthesia, but not when anaesthesia was omitted. The results obtained on hepatectomized livers were compared with the changes in guanylate cyclase activity and cyclic nucleotide concentrations during the response to galactosamine treatment. Here, a peak of guanylate cyclase activity and of cyclic GMP concentrations occurred at 8h, that is before the beginning of the proliferative response. Both parameters were normal at the time of increased DNA synthesis. There does not, therefore, seem to be a consistent correlation between changes in guanylate cyclase activity or concentrations of cyclic GMP and an increase in liver DNA synthesis. A modest rise in cyclic AMP concentrations was found, however, in livers of galactosamine-treated rats, which was coincident with the time of DNA synthesis.

Increase in pituitary adenosine 3':5'-cyclic monophosphate content and potentiation of growth-hormone release from heifer anterior pituitary slices incubated in the presence of 3-isobutyl-1-methylxanthine.

The release of growth hormone from heifer anterior pituitary slices and the cyclic AMP content of the slices were increased by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, both increases being related to inhibitor concentration over the range 0.1-1.0mm. Neither Ba(2+) (6.9 or 2.3mm), K(+) (72mm), nor p-chloromercuribenzoate (20mum) had any effect on pituitary cyclic AMP content over a 20min period. 3-Isobutyl-1-methylxanthine potentiated the release of growth hormone in response to Ba(2+) (2.3mm) and K(+) (24mm), but the degree of potentiation did not depend on inhibitor concentration in the same way as did tissue cyclic AMP content. 3-Isobutyl-1-methylxanthine decreased the concentration of K(+) required to give maximum stimulation of growth-hormone release, but did not significantly increase the maximum response to Ba(2+). Growth-hormone release in the presence of prostaglandin E(2) (1mum) was increased by 3-isobutyl-1-methylxanthine and was inhibited by the prostaglandin antagonist, 7-oxa-13-prostynoic acid, although this antagonist increased the pituitary cyclic AMP concentration and potentiated the prostaglandin E(2)-induced rise in cyclic AMP content. The stimulation of growth-hormone release by p-chloromercuribenzoate was not potentiated by 3-isobutyl-1-methylxanthine. The data suggest that Ba(+) and K(+) act at the same point in the secretory process as 3-isobutyl-1-methylxanthine, although by a different mechanism, and that p-chloromercuribenzoate has a different point of action.

The role of calcium in fly salivary gland secretion analyzed with the ionophore A-23187

The ionophore A-23187 at a concentration of 10 −6 M stimulates fluid secretion, increases calcium influx and efflux, and alters the trensepithelial potential in the isolated fly salivary gland but causes a fall in cyclic AMP concentration. In this regard, it mimics all the effects of 5-hydroxytryptamine of this tissue, except that 5-hydroxytryptamine causes a rise in cyclic AMP concentration. These data in conjunction with past evidence indicate that calcium, as well as cyclic AMP, is a second messenger in the action of 5-hydroxytryptamine upon fly salivary gland secretion.

Adenosine 3′, 5′-cyclic monophosphate in [formula omitted

Homogenates of adult Schistosoma mansoni (blood flukes), isolated from the porto-mesenteric veins of infected mice, contain substantial activities of adenylyl cyclase, cyclic AMP phosphodiesterase, and a cyclic AMP stimulated protein kinase. The adenylyl cyclase, which is largely sedimentable at 10,000xg, is stimulated 20-fold by 10mM sodium fluoride and 1.4 to 2-fold by serotonin, glucagon, prostaglandins E 1, E 2 or B 1. The phosphodiesterase, which is largely sedimentable at 10,000xg, is inhibited by both aminophylline and papaverine but is not influenced by 10mM sodium fluoride. The protein kinase, which is present in the 10,000xg supernatant is stimulated 4 to 8-fold by either cyclic AMP or cyclic GMP. There is a preference for cyclic AMP ( K 1 2 = 1.1×10 −7 M ) over cyclic GMP ( K 1 2 = 4.5×10 −6 M ). If intact worms are incubated in a glucose free medium there is a mobilization of glycogen stores which is preceded by a rise in cyclic AMP concentration. In a medium with 5mM glucose there is neither a rise in cyclic AMP nor mobilization of glycogen.

Stimulation of cyclic AMP production in the rat ovary by luteinizing hormone: Independence of prostaglandin mediation

In cubation of intact juvenile rat ovaries with luteinizing hormone (LH; 10 μ g/ml) for 20 min caused a ten-fold rise in cyclic AMP concentration, without increasing the activity of “prostaglandin synthetase” in the tissue. Flufenamic acid [N-(α,α,α- trifluoro-m-tolyl) anthranilic acid], aspirin or indomethacin (100 μ g/ml of each added to the incubation medium) inhibited “prostaglandin synthetase” activity by 90%, 97% and 70%, respectively, but did not prevent the stimulatory effect of LH on cyclic AMP formation. Prostaglandin E 2 (10 μ g/ml) also stimulated cyclic AMP formation in vitro, but this action was abolished by flufenamic acid. These findings argue against the hypothesis proposed in the literature that prostaglandins of the E-type are essential for the LH effect on ovarian adenylate cyclase and thus serve as obligatory mediators of cyclic AMP-dependent actions of LH on the ovary.

Cyclic adenosine 3',5'-monophosphate concentration in the pancreas following stimulation by secretin, cholecystokinin-pancreozymin and acetylcholine.

1. Following an I.V. injection of secretin into anaesthetized cats, the pancreatic cyclic AMP concentration rose within 30 sec and reached near-maximal values within 1 min. Pancreatic secretion began only after 45 sec. As secretion declined, the cyclic AMP concentration also fell. However, after 40 min, when secretion had ceased, the concentration again rose, reaching a maximum after about 80 min and returned to basal values within 140 min.2. During secretin infusion the pattern of cyclic AMP changes was the same, except that the initial rise was maintained as long as secretin was infused.3. Following either pancreozymin or acetylcholine, alone or super-imposed on secretin stimulation, similar changes in cyclic AMP concentration were observed. However, the initial rise lasted only 30 sec, basal concentrations being approached within 1 min, and was accompanied by enzyme secretion. The concentration of cyclic AMP subsequently rose and fell again, in the absence of enzyme secretion, exactly as after secretin stimulation.4. Similar observations were made using an isolated, saline-perfused preparation of the cat's pancreas.5. By using very low doses of pancreozymin it was possible to observe the first rise in cyclic AMP concentration in the absence of enzyme secretion. Similarly atropine, while blocking enzyme secretion, did not affect the rise in cyclic AMP concentration after acetylcholine. The second increase in concentration was never associated with secretion (it may have been connected with the synthesis of exportable enzymes by the gland).6. While these observations suggest that cyclic AMP may be involved in the response of the pancreas to secretin, pancreozymin and acetylcholine, no simple relation exists between cyclic AMP concentration and secretion.