Increase In Cyclic AMP Content Research Articles

Effects of forskolin on insulin release and cyclic AMP content in rat pancreatic islets.

The effects of forskolin, a diterpene stimulator of adenylate cyclase, on cyclic AMP content and insulin release, have been studied in rat pancreatic islets. In the presence of 2.8 mM glucose, 0.3 to 30 microM forskolin gave concentration-dependent increases in cyclic AMP content to as much as seven-fold without causing any significant increase in insulin release. With 5.6 mM glucose, cyclic AMP contents were elevated by forskolin to the same extent as with 2.8 mM glucose but, under these conditions, insulin release was stimulated. 3 microM forskolin was a maximal concentration with respect to insulin release, but not for the elevation of cyclic AMP levels. Concentration-dependent increases in both insulin release and cyclic AMP content were detected over the range of 0.3 to 3 microM forskolin. The effect of forskolin to stimulate insulin release was rapid and was reversible within 15 minutes of removal of the drug. When tested with 16.7 mM glucose, forskolin potentiated both phases of stimulated release, with the greater effect upon the first phase.

Effects of amino acids, glucagon, insulin and acetylcholine on cyclic nucleotide metabolism and amylase secretion in isolated mouse pancreatic fragments

The effects of amino acids, exogenous islet hormones and acetylcholine on cyclic nucleotide metabolism and amylase secretion in the isolated mouse pancreas have been investigated. The changes in levels of adenosine 3',5'-cyclic monophosphate (cyclic AMP) and guanosine 3',5'-cyclic monophosphate (cyclic GMP) were measured at different times during exposure of pancreatic fragments to amino acids ( l-alanine and l-arginine), islet hormones (insulin and glucagon) or acetylcholine (ACh). lAlanine (1–20 mM) evoked a transient increase in cyclic AMP concentration accompanied by an initial decrease and subsequent increase in the tissue concentration of cyclic GMP. l-Arginine (1–20mM) induced a complex triphasic change in cyclic AMP concentrations involving an initial rise and a delayed sustained elevation. The changes in levels of cyclic GMP increased only transiently. The effects of insulin (10 −6M) and to some extent glucagon (5 × 10 −7M) resembled those seen with l-arginine. The effects of amino acids and islet hormones were all dose-dependent. ACh (10 −7M) elicited a marked reduction in cyclic AMP concentration and this was accompanied by a concomitant increase in the level of cyclic GMP. The amino acids and the islet hormones had no significant effect on amylase secretion whereas ACh, of course, evoked a large increase in amylase output. The results with the amino acids and islet hormones reveal a clear dissociation between cyclic nucleotide changes and amylase secretion and further suggest that the marked reciprocal changes in cyclic AMP and cyclic GMP concentrations may constitute an important physiological role for the cyclic nucleotides to regulate amino acid transport in the pancreas.

The metabolism and hormonal responses of human eccrine sweat glands isolated by collagenase digestion.

1. Collagenase digestion of biopsies of human skin yields eccrine sweat glands that can be picked out under binocular light microscopy. The glands are viable as determined by the exclusion of Trypan Blue, the uptake of Methylene Blue, electron microscopy, the rate of lactate dehydrogenase release, ATP content and the rates of glucose oxidation and lactate release. 2. It is proposed that eccrine sweat glands engage in aerobic glycolysis, which accounts for the high content of lactate in sweat (15--60 mM) and the high lactate/pyruvate ratio (100: 1) [Emrich & Zwiebel (1966) Pfluegers Arch. 290, 315--319]. 3. Acetylcholine causes a 4-fold increase in cyclic GMP content, dilatation of the intercellular canaliculi and a reversible, atropine-sensitive, 2-fold increase in the rates of glucose oxidation and lactate release. 4. Isoprenaline causes a 2.5-fold increase in cyclic AMP content. Phenylephrine does not significantly alter cyclic nucleotide metabolism.

Mechanism of 3-phenylpyruvate-induced insulin release. Secretory, ionic and oxidative aspects.

1. 3-Phenylpyruvate caused a dose-related stimulation of insulin release from rat pancreatic islets deprived of exogenous nutrient or incubated in the presence of 5.6 or 8.3 mM-D-glucose. 2. 3-Phenylpyruvate inhibited insulin release evoked by high concentrations of D-glucose (16.7 or 27.8 mM) or 4-methyl-2-oxopentanoate (10.0 mM). This inhibitory effect appeared to be attributable to impairment of 2-oxo-acid transport into the mitochondria, with resulting inhibition of D-glucose, pyruvate or 4-methyl-2-oxopentanoate oxidation. 3. 3-Phenylpyruvate failed to affect the oxidation of, and secretory response to, L-leucine, and did not augment insulin release evoked by a non-metabolized analogue of the latter amino acid. 4. L-Glutamine augmented 3-phenylpyruvate-induced insulin release. The release of insulin evoked by the combination of 3-phenylpyruvate and L-glutamine represented a sustained phenomenon, abolished in the absence of extracellular Ca2+ or the presence of menadione and potentiated by theophylline. 5. Whether in the presence or in the absence of L-glutamine, the secretory response to 3-phenylpyruvate coincided with an increase in O2 uptake, a decrease in K+ conductance, a stimulation of both Ca2+ inflow and 45Ca2+ net uptake and an increase in cyclic AMP content. 6. It is concluded that the release of insulin induced by 3-phenylpyruvate displays features classically encountered when the B-cell is stimulated by nutrient secretagogues, and is indeed attributable to an increase in nutrient catabolism.

Biogenic amine-stimulated cyclic adenosine-3',5'-monophosphate formation in the rat carotid body.

The subcutaneous injection of isoprenaline, salbutamol, histamine, and adrenaline to rats, which were subsequently killed by microwave irradiation, resulted in a rapid increase in the cyclic AMP content of the carotid body. On the other hand, noradrenaline, dopamine, adenosine, and 5-hydroxytryptamine, at doses at least 100 times greater than that of isoprenaline, did not significantly alter the cyclic nucleotide content in vivo. The response to isoprenaline was dose related, with an ED50 of 15 micrograms X kg-1, and reached a peak level 1-1.5 min after injection. Incubation of intact carotid bodies with isoprenaline (10(-5) M) in vitro also resulted in a 10-fold increase in cyclic AMP content. The in vivo response to isoprenaline could be blocked stereo-selectively by propranolol, and ICI 118.551, a beta 2-selective antagonist, blocks the isoprenaline-elicited increase in cyclic AMP completely at a dose of 30 micrograms X kg-1; whereas betaxolol, a beta 1-selective antagonist, was ineffective, even at a dose of 300 micrograms X kg-1. Hypoxia (5% oxygen in 95% N2) did not result in a significant increase in the cyclic AMP content, nor did it significantly alter the isoprenaline-stimulated increase in the cyclic AMP content of the rat carotid body. These results suggest that some catecholamines may stimulate cyclic AMP formation by interacting with a beta 2-adrenoceptor in the rat carotid body.

Role of Polyamines in Expression of the Differentiated Phenotype of Chondrocytes: Effect of DL-α-Hydrazino-δ-Aminovaleric Acid (DL-HAVA), an Inhibitor of Ornithine Decarboxylase, on Chondrocytes Treated with Parathyroid Hormone1

Previously, it was demonstrated that parathyroid hormone (PTH) induces a series of events, successive increases of the level of cyclic AMP, the activity of ornithine decarboxylase [ODC; EC 4.1.1.17] and glycosaminoglycan synthesis, a characteristic chondrocyte phenotype, in rabbit costal chondrocytes in culture. Cyclic AMP analogues also increase ODC activity and glycosaminoglycan synthesis in these cells. Therefore, in the present work, the role of polyamines in expression of the differentiated phenotype of chondrocytes was investigated. DL-alpha-Hydrazino-delta-aminovaleric acid (DL-HAVA), a potent inhibitor of ODC, inhibited the increase in polyamine levels of quiescent cultures of chondrocytes treated with PTH. DL-HAVA also inhibited stimulation of expression of the differentiated phenotype of chondrocytes by PTH, as judged by decreases in glycosaminoglycan synthesis and metachromasia on toluidine blue staining. Similarly, DL-HAVA inhibited stimulation of expression of the differentiated phenotype of chondrocytes by dibutyryl cyclic AMP. The inhibitory effect on expression of the differentiated phenotype of chondrocytes by DL-HAVA was effectively diminished by addition of polyamines. Under the same conditions, PTH, DL-HAVA, or polyamines had little effect on DNA synthesis. These findings suggest that the rise in polyamine levels induced by PTH, which is mediated by an increase of cyclic AMP concentration, is essential for expression of the differentiated phenotype of chondrocytes.

膜疾患としてのコレラ

Cholera is a disease caused by cholera enterotoxin produced by Vibrio cholerae. Main symptom of cholera is watery diarrhea and it is caused by cholera enterotoxin. Cholera enterotoxin is a protein toxin and its molecular weight is about 84, 000. It consists of two subunits, A and B. B subunit is a binding subunit and it binds to GM1 ganglioside of epithelial cell membrane of intestinal brush border. After the toxin binds to GM1 ganglioside through B subunit, A subunit is incorporated into the cell and it stimulates membrane bound adenylate cyclase. The mechanism of the stimulation of adenylate cyclase by cholera enterotoxin is well established. However, the mechanism how the increase of cyclic AMP concentration in intestinal cell results in an excess secretion of water into intestinal lumen is still not understood.

Comparison of adenylate cyclase activity in segments of rat sciatic nerve with a condition/test or test lesion

A prior “conditioning” lesion enhances the rate of nerve regeneration after a subsequent “test” lesion made proximal to the first injury. This effect has been observed in several species and in both peripheral and central neurons. Nonetheless, the molecular basis of the conditioning effect remains uncertain. The initiation of regeneration and its progress appear to depend on separate processes, and either or both may be affected in different species. This investigation focused on rat sciatic nerve, where only the rate of elongation appears to be consistently enhanced. I investigated the distribution of adenylate cyclase activity in various segments of the injured nerves to determine if cyclic AMP might modulate some aspect of the regeneration process. Adenylate cyclase activity accumulated at the point of injury and was significantly increased in regenerating nerve tips, as determined by the pinch test, in both condition/test- and test-lesion nerves. The sole significant difference between these experimental groups was an increase in adenylate cyclase activity immediately distal to the test lesion and immediately distal to the regeneration point in the condition-lesion nerves. I suggest that an increase in cyclic AMP concentration in nerve segments distal to a lesion may condition the local environment to enhance axon sprouting or elongation. Nerve growth stimulated by a local increase in cyclic AMP, however, may require additional cell body-supplied material to be sustained.

Increases in cyclic AMP potentiate competence formation in BALB/c-3T3 cells.

The ability of platelet-derived growth factor and fibroblast growth factor to stimulate the initiation of DNA synthesis in quiescent BALB/c-3T3 cells was enhanced by cholera toxin. However, the addition of cholera toxin to unsupplemented medium was not mitogenic, nor did cholera toxin increase the mitogenic potential of medium supplemented with platelet-poor plasma. The enhancement of serum-induced DNA synthesis by cholera toxin was due to a specific effect on competence formation and not plasma-controlled progression. Cholera toxin increased the rate of competence formation during a transient exposure of quiescent cells to platelet-derived growth factor; this rate was further increased by the addition of isobutylmethylxanthine, a cyclic nucleotide phosphodiesterase inhibitor. Intracellular cyclic AMP concentrations in quiescent BALB/c-3T3 cells were increased 2- to 3-fold after the addition of cholera toxin., The addition of cholera toxin plus 30 microM isobutylmethylxanthine caused an even greater (7- to 8-fold) increase in the cellular levels of cyclic AMP. That these increases in cyclic AMP concentrations mediated at least part of the increased sensitivity of quiescent cells to competence factors was substantiated by the observation that 0.01 to 1 mM monobutrylcyclic AMP or 8-bromocyclic AMP also caused a concentration-dependent potentiation of competence formation in quiescent cells during a transient exposure to platelet-derived growth factor.

On the Use of Microwave Radiation Energy for Brain Tissue Fixation

Abstract: Focused microwave irradiation (MWR) is an increasingly accepted method of sacrifice of laboratory animals such as the mouse or rat. By fixing the brain within a fraction of a second with heat inactivation, the investigation of fast neurochemical events may be obtained. Even though the technique is widely utilized, its application is inconsistent. This report illustrates some of the requirements necessary for the proper application of MWR for the sacrifice of animals, particularly those related to the length of time MWR is applied and the efficiency with which generated MWR power is coupled to the brain tissue. Studies were performed on the mouse, using either a 2.5 KW or 6.3 KW generator with a focused, closed system waveguide at time intervals of 350 or 500 ms or 1.4 s. During each of these intervals MWR was varied so that core brain temperatures for all groups were held between 83 and 95°C. In contrast with reported studies that used full animal restraint, all animals were minimally restrained for less than 1 s before sacrifice. Tissue content of cyclic AMP, an index of neuronal activity grossly affected by subtle changes in the activity of adenylate cyclase and/or phosphodiesterases, was monitored. No differences in tissue cyclic AMP content in any of 12 brain regions were detected after MWR, either at 350 or 500 ms. A substantial increase in cyclic AMP content occurred in 8 of 12 brain regions examined following microwave irradiation for 1.4 s. On the basis of these experiments, accurate determination of cyclic AMP in rodent brain requires that the maximum time interval of MWR exposure should not exceed 500 ms.

Adenosine-elicited accumulation of adenosine 3', 5'-cyclic monophosphate in the chick embryo retina.

The cyclic AMP level of 17-day-old chick embryo retina increased from 20 to 331 pmol/mg protein when the tissue was incubated for 20 min in the presence of 4-(3-butoxy-4-methoxybenzyl-2-imidozolinone) (RO 20-1724). The addition of 0.5 mM-3-isobutyl-1-methylxanthine (IBMX) or 0.5 units/ml of adenosine deaminase (EC 3.5.4.4) to the medium reduced the increase of cyclic AMP content from 20 to 100 pmol/mg protein. Dipyridamole did not interfere with the rise of the retinal cyclic AMP level observed with RO 20-1724. The EC50 of 6-amino-2-chloropurine riboside (2-chloroadenosine)-elicited accumulation of cyclic AMP of retinas incubated in the presence of RO 20-1724 plus adenosine deaminase was approximately 1 microM. When retina incubation was carried out in the presence of 0.5 mM-IBMX, the 2-chloroadenosine dose-response curve was shifted to the right two orders of magnitude. Maximal stimulation of the cyclic AMP level of 17-day-old chick embryo retina incubated in the presence of 0.5 mM-IBMX was observed at 1 mM-adenosine concentration. This effect was not blocked by dopamine antagonists. Guanosine and adenine did not affect the retinal cyclic AMP level. AMP and ATP had a slight stimulatory effect. Adenosine response of embryonic retina increased sharply from the 14th to the 17th embryonic day. A similar, but not identical adenosine effect was observed in cultured retina cells.

Fetal and Early postnatal development of adenylate cyclase and cyclic AMP phosphodiesterase activities in rat brain.

Brain cyclic AMP metabolism was studied in rat offspring at 17, 19 and 21 days of intrauterine life and 0, 1 and 4 postnatal days. Wet weight and protein and DNA and RNA concentrations in brain increased in parallel with body weight until the 4th postnatal day although during the perinatal phase some of these parameters suffered a manifest temporal retardation. In the brain, similar qualitative changes were observed in both adenylate cyclase and high Km cyclic AMP phosphodiesterase activity while the low Km enzyme showed a rise from 17-day fetuses to those of 19 days with no further changes. The increase in cyclic AMP concentration was very mild and the values found in the 21-day fetuses were already similar to those in adults. In the mother's brain a significant reduction in adenylate cyclase activity appeared at 19 and 21 days of gestation. The retardation in the ontogenic development of cyclic AMP metabolism during the perinatal phase in offspring is probably a consequence of their specific metabolic situation while in the mother it may be the result of its endocrine preparation for parturition.

Effects of trifluoperazine and pimozide on stimulus-secretion coupling in pancreatic B-cells. Suggestion for a role of calmodulin?

The possible involvement of calmodulin in insulin release was evaluated by studying the effects on intact islets of trifluoperazine and pimozide, two antipsychotic agents known to bind strongly to calmodulin in cell-free systems. Trifluoperazine (10-100mum) produced a dose- and time-dependent inhibition of the two phases of glucose-stimulated insulin release. The effect was not reversible by simple washing of the drug, but could be prevented by cytochalasin B or theophylline. Trifluoperazine also inhibited the release induced by glyceraldehyde, oxoisocaproate, tolbutamide or barium, but not that stimulated by 10mm-theophylline or 1mm-3-isobutyl-1-methylxanthine. Pimozide (0.5-10mum) also produced a dose-dependent inhibition of insulin release triggered by glucose, leucine or barium, but did not affect the release induced by methylxanthines. Glucose utilization by islet cells was not modified by trifluoperazine (25mum), which slightly increased cyclic AMP concentration in islets incubated without glucose. The drug did not prevent the increase in cyclic AMP concentration observed after 10min of glucose stimulation, but suppressed it after 60min. Basal or glucose-stimulated Ca(2+) influx (5min) was unaffected by 25mum-trifluoperazine, whereas Ca(2+)net uptake (60min) was inhibited by 20%. Glucose-stimulated Ca(2+) uptake was almost unaffected by pimozide. In a Ca(2+)-free medium, trifluoperazine decreased Ca(2+) efflux from the islets and did not prevent the further decrease by glucose; in the presence of Ca(2+), the drug again decreased Ca(2+) efflux and inhibited the stimulation normally produced by glucose. In the absence of glucose, trifluoperazine lowered the rate of Rb(+) efflux from the islets, decreased Rb(+) influx (10min), but did not affect Rb(+) net uptake (60min). It did not interfere with the ability of glucose to decrease Rb(+) efflux rate further and to increase Rb(+) net uptake. The results show thus that trifluoperazine does not alter the initial key events of the stimulus-secretion coupling. Its inhibition of insulin release suggests a role of calmodulin at late stages of the secretory process.

Muscarinic-dopaminergic synergism on retinal cyclic AMP formation

The cholinergic agonist, carbachol, produces a small increase in cyclic AMP concentration in the isolated rat retina, and markedly potentiates dopamine-stimulated cyclic AMP formation. This effect of carbachol is mediated through a muscarinic receptor, is calcium-independent, and is not due to inhibition of phosphodiesterase activity. Activation of miscarinic receptors may potentiate dopaminergic responses in the retina by enhancing coupling of the dopamine receptor to adenylate cyclase.

Cardiac effects of prostaglandins E1 and F1 alpha.

The effects of prostaglandin E1 (PGE1) and prostaglandin F1 alpha (PGF1 alpha) were studied on perfused rat hearts and isolated rat atria. Both PGE1 and PGF1 alpha produced dose-dependent increases in right atrial rate but had no effect on left atrial tension development. PGE1 (10(-4) M) increased right atrial cyclic AMP content without changing phosphorylase a activity. PGF1 alpha (10(-4) M) did not change right atrial cyclic AMP or cyclic GMP content. Both prostaglandins had no effect on left atrial cyclic nucleotide content. When infused at a rate of 1 microgram/min, PGE1 produced a time-dependent increase in cyclic AMP content in the Langendorff perfused hearts but did not alter contractile force development or phosphorylase a activity. An infusion of PGF1 alpha produced a dose-dependent increase in tension development which was secondary to a negative chronotropic effect. PGF1 alpha (1 microgram/min) did not produce any changes in cyclic nucleotide levels or phosphorylase a activity in the Langendorff perfused hearts. These results show that PGE1 can selectively increase myocardial cyclic AMP content without altering contractile force or phosphorylase activity and that PGF1 alpha does not increase rat cardiac AMP levels.

Cyclic 3′,5′-adenosine monophosphate levels during the developmental cycle of Trypanosoma brucei brucei in the rat

Intracellular content of cyclic 3′,5′-adenosine monophosphate was determined in several strains of Trypanosoma brucei brucei during their growth in rats. In non-relapsing infections with the cloned monomorphic strain 110M and with the cloned pleomorphic strain YTatl, the amount of cyclic AMP per 10 9 trypanosomes increased from 30 to over 90 pmol as the parasitemia increased from patency to over 10 9 organisms per ml. This increase was not observed during non-relapsing infections with strain 427. During infections with strain YTatl in both immunocompetent and lethally X-irradiated rats, cyclic AMP content of the parasite increased from 20-20 pmol per 10 9 cells early in logarithmic growth to 65–70 pmol per 10 9 cells at peak parasitemia, then decreased as the transition to intermediate and short stumpy forms commenced. At crisis, basal levels were reestablished when long slender forms were the lowest percentage of the total population and intermediate and short stumpy forms predominated, suggesting a correlation between morphologic type and level of cyclic AMP per cell during fluctuations in parasitemia. Increases in intracellular cyclic AMP were measured during in vitro incubation of the parasite in medium containing potential effectors of the trypanosome cyclic AMP system. Sodium fluoride, adenosine and methyl xanthines stimulated increases in cyclic AMP content while isoproterenol, prostaglandin E 1, serotonin, histamine and several trypanocidal drugs were ineffective. The results are discussed in terms of the possible regulatory role of cyclic AMP in differentiation of trypanosomes.

The increase in cyclic AMP content in the isolated guinea pig gastric mucosa during histamine-stimulated acid secretion.

Using the isolated guinea pig gastric mucosa perfused in vitro with a constant acid secretion and potential difference, the cyclic AMP (cAMP) contents in the gastric mucosa and in the serosal solution were measured during the course of acid secretion stimulated by histamine or dibutyryl cyclic AMP (db-cAMP). (1) The acid-secreting response of the gastric mucosa to histamine was reproduced by addition of db-cAMP. (2) The acid secretion stimulated by db-cAMP was not inhibited. (3) The increase in mucosal cAMP content was accompanied by histamine-stimulated acid secretion. (4) The increase in the mucosal cAMP content preceded the increase in acid secretion stimulated by histamine. From these findings, it has been concluded that cAMP plays an important role in the mechanism of histamine-stimulated acid secretion, including the morphological transformation of parietal cells, although its role as the intracellular mediator of the stimuli for the hydrogen ion pump itself requires further investigation.

In vivo and in vitro effects of proteases upon adenylate cyclase activity of liver cells and plasma membranes.

1. 1. Several hours after an intraperitoneal injection of papain (3 mg) the marked stimulation of adenylate cyclase activity was observed as well as the significant increase in cyclic AMP content of rat livers. The fluoride-sensitive adenylate cyclase activity was stimulated more than the basal activity. Trypsin, which is not mitogenic, was much less effective on both events, as compared to papain which is mitogenic to the liver in vivo. 2. 2. Papain stimulated the basal adenylate cyclase activity of isolated liver cells in vitro at concentrations larger than 2.5 μg papain per ml, but the sensitivity of adenylate cyclase activity to fluoride was completely lost upon increasing the papain concentration. Trypsin, on the other hand, gave no effect on the basal adenylate cyclase activity of isolated liver cells at enzyme concentrations from 0 to 500 μg/ml. The fluoride sensitivity was lost upon increasing trypsin concentration similarly to the case of papain. 3. 3. Adenylate cyclase activity (both basal and fluoride-sensitive) of isolated liver plasma membranes was stimulated by papain (but not by trypsin) at concentrations as low as about 0.25 μg papain/ml, similarly to the in vivo effect of proteases. Upon increasing the protease (papain, trypsin) concentration further, both the basal and fluoride-sensitive activities of plasma membranes were markedly reduced. 4. 4. Acid mucopolysaccharides of liver plasma membranes were released almost completely by treatment with papain at concentrations larger than 25 μg/ml, whereas trypsin was less effective in degrading proteoglycans associated with plasma membranes. 5. 5. The results were discussed in relation to the possible involvement of protease in mitogenesis of liver cells through the alteration of cell surface architecture and function.

Activation of cyclic AMP-dependent protein kinase. A common step in vasopressin- and hypertonicity-induced water flow.

Abstract Water flow across the amphibian urinary bladder can be induced by either vasopressin or serosal hypertonicity. In an effort to determine the common intracellular steps mediating both responses, we determined the in situ activation of cyclic AMP-dependent protein kinase in bladders stimulated by vasopressin or hypertonicity. Treatment of bladders with vasopressin (1 mU/ml) caused in situ activation of cytosolic cyclic AMP-dependent protein kinase of epithelial cells, with a rise in the kinase ratio and cyclic AMP content. Similarly, hyperonicity increased the kinase ratio, but this occured without a measurable increase in cyclic AMP content per mg protein. Because of the hypertonicity-induced cell shrinkage, epithelial cell water decreased by 20%, which may result in a proportionate increase in cyclic AMP concentration (per ml cell water). Furthermore, cell shrinkage also increases intracellular electrolyte concentration, which, in turn, should delay reassociation and consequent inactivation of the predominant Type II cyclic AMP-dependent protein kinase of the epithelial cells. Thus activation of cyclic AMP-dependent protein kinase during hypetonicity may be the result of cell shrinkage, with an associated increase in cyclic AMP and electrolyte concentrations. Studies with prostaglandin synthesis inhibitors and colchicine, a microtubule disrupting agent, also indicated common pathways for vasopressin and hypertonicity. Both naproxen and meclofenamate significantly enhanced the hypertonicity response. Colchicine pretreatment, on the other hand, caused a small (18%) but significant inhibition of the hypertnicity response, similar to its effect on the vasopressine response (25% inhibition). Thus, the increased water permeability of the toad bladder in response to both vasopressin and hypertonicity follows a similar pathway. Activation of cyclic AMP-dependent protein kinase represents the first common step yet identified.

Cyclic nucleotide metabolism and reactive oxygen production by macrophages

The production of reactive oxygen species by elicited rat peritoneal macrophages was assessed by in vitro measurement of chemiluminescence in the presence of luminol. The divalent ion ionophore A23187 stimulated the production of reactive oxygen species. This action was inhibited by monobutyryl and dibutyryl derivatives of cyclic AMP but was not affected by derivates of cyclic GMP. Cyclic AMP and cyclic GMP concentrations increased rapidly in macrophages exposed to A23187 or zymosan. Indomethacin (20 μmol/1) inhibited the increase in cyclic AMP concentration but not the increase in cyclic GMP concentration. Neither A23187 nor zymosan stimulated adenylate cyclase activity in broken cell preparations of macrophages. The observations are consistent with the hypothesis that PGE produced by macrophages after phagocytotic stimuli may inhibit certain macrophage functions and perform a regulatory role in these cells. This action of PGE may be mediated by cyclic AMP.