Activation and inhibition of lipolysis in isolated fat cells by various inhibitors of cyclic AMP phosphodiesterase

Summary The effects of methylxanthines, papaverine, dipyridamole and imipramine on lipolysis and phosphodiesterase activity of rat adipose tissue were investigated. Lipolysis in isolated fat cells was stimulated by theophylline and caffeine whereas papaverine, dipyridamole and imipramine had no substantial effect on the basal lipolytic rate. Lipolysis induced by noradrenaline was potentiated by theophylline, but blocked by papaverine, dipyridamole and imipramine at concentrations between 0.02 to 0.2 mM. These agents also depressed lipolysis induced by theophylline and dibutyryl cyclic AMP and reduced the lipolytic activity of homogenates of adipose tissue. The activity of phosphodiesterase assayed over a wide range of substrate concentrations revealed two different Michaelis constants. Both types of phosphodiesterase were inhibited by theophylline, papaverine, dipyridamole and imipramine in a competitive manner, the low K _m enzyme being more sensitive for inhibition than the high K _m enzyme. On both types of phosphodiesterase papaverine and dipyridamole proved to be 10 to 100 times more potent inhibitors than theophylline and imipramine. To explain the antilipolytic effect of phosphodiesterase inhibitors it is assumed that they do not only affect substrate binding of cyclic AMP to phosphodiesterase but also displace cyclic AMP from the binding site on protein kinase, thus acting as inhibitors of the activation process within the lipolytic system.     

The effects of theophylline and cyclic AMP on intestinal smooth muscle contractions

The effects of 10^?4-10^?3 M theopphylline, cyclic 3'5'-adenosine monophosphate (cyclic AMP), dibutyryl cyclic AMP (DBC) and theophylline plus DBC were observed on the spontaneous and potassium (K)-induced contractions of the guinea-pig taenia coli. All of the compounds inhibited spontaneous contractions as well as the phasic and tonic components of the K-contracture. The effects of cyclic AMP, a compound which will not readily penetrate the cell membrane, were similar to those of the other compounds in inhibiting the spontaneous and phasic contractions, but it was a less effective inhibitor of the tonic contracture. Inhibition of spontaneous and phasic activity may occur at the cell membrane while the inhibitory actions on the tonic contracture may depend on cellular penetration by the inhibitor. There was no evidence that theophylline and DBC have different sites of action.     

Inhibition by papaverine of 3′,5′-nucleotide-phosphodiesterase (E.C.3.1.4.1.) from bovine uterus muscle

Summary 3,5-Nucleotide-phosphodiesterase (E.C. 3.1.4.1.) from bovine uterus muscle is inhibited by papaverine at similar concentrations as reported for coronary preparations by Pöch (1971).This work was supported by the Deutsche Forschungsgemeinschaft.     

Inhibition of cyclic-3′,5′-nucleotide-phosphodiesterase as a possible mode of action of papaverine and similarly acting drugs

Naunyn-Schmiedeberg's Archives of Pharmacology -     

Prostaglandin E2 and the stimulation of rat gastric acid secretion by dibutyryl cyclic 3',5'-AMP

In the anaesthetised rat, i.v. injection of dibutyryl cyclic 3′,5′-AMP (dbcAMP) caused a dose-dependent increase in gastric acid secretion during pentagastrin, histamine or carachol stimulation. This was accompanied by a rise in gastric mucosal blood flow. During basal secretion, dbcAMP caused by a relatively small stimulation, atlhough this response was greatly enhanced by threshold doses of pentagastrin or histamine. Cyclic AMP (cAMP) did not stimulate acid secretion, but increased mucosal blood flow and decreased blood pressure. Theophylline had no consistent effect on acid secretion. Prostaglandin E₂, administered i.v. or perfused through the gastric lumen, reduced basal acid secretion but failed to inhibit the secretory response to dbcAMP. These results in the rat support the role of cAMP in gastric acid secretion and suggest that prostaglandins inhibit other secretogogues at a stage prior to cAMP.     

The role of cyclic AMP in temperature-dependent changes of contractile force and sensitivity ot isoprenaline and papaverine in guinea-pig atria.

Right and left guinea-pig atria responded to decreasing temperatures (42-27 degrees C) with elevation for force of contraction and concomitant increases in cAMP. When atria were rapidly cooled from 42 to 27 degrees C the increase in cAMP occurred prior to the onset of the inotropic responses. Papaverine (3 X 10(-5) M) potentiated the effects of temperature on cAMP and force of contraction on left atria driven at 0.5 Hz. On right atria beating spontaneously at frequencies above 2 Hz papaverine only potentiated the effect of decreasing temperatures on the response of cAMP but not on that of force of contraction. Time course studies of the effects of isoprenaline (3 X 10(-8) M) on right atria at 27 degrees C showed large inotropic responses to isoprenaline which were accompanied by increases in cAMP. At 42 degrees C the responses of force of contraction and cAMP to isoprenaline occurred faster and were only short-lasting. As with the time courses for isoprenaline, dose-response curves for the effect of isoprenaline and papaverine on cAMP content and force of contraction also appeared to be shifted towards higher levels at hypothemia. However, pD2 values reflected increases in affinity for inotropic, but not for the cAMP responses to isoprenaline and papaverine at hypothermia. These results show that cyclic AMP is involved in the inotropic responses to hypothermia, but not in the supersensitivity of heart to isoprenaline and papaverine as observed at low temperatures.     

Effect of NAD,nicotinamide and nicotinic acid on cyclic AMP accumulation by fat cells

Summary The addition of exogenous nicotinamide adenine dinucleotide (NAD) to isolated rat fat cells at concentrations between 1 and 10 mol markedly inhibited the rise in cyclic AMP accumulation due to norepinephrine. Catabolism of NAD to adenosine did not account for the inhibitory effect since NAD was effective in the presence of adenosine deaminase. The bovine fraction V albumin in which fat cells were incubated contained a substantial amount of glycohydrolase which cleaved NAD to nicotinamide. Incubation of fat cells in albumin-free medium did not abolish the inhibitory effect of NAD, and under these conditions there was little degradation of NAD to nicotinamide during the first 10 min of incubation. Fat cells cleave NAD, in the medium to nicotinamide mononucleotide which does not inhibit cyclic AMP accumulation. NADH, NADP and nicotinic acid mononucleotide were less effective as inhibitors of cyclic AMP accumulation than NAD or deamido NAD. Ineffective as inhibitors were NADPH, nicotinamide mononucleotide, and 1-methyl nicotinamide. N-methyl nicotinamide was as potent as nicotinamide while nicotinic acid was 100- to 500fold more effective than either compound as an inhibitor of cyclic AMP accumulation. Incubation of fat cells with 100 M but not 10 M NAD for 5 min resulted in a decrease in the subsequent accumulation of cyclic AMP by rat fat cell ghosts.Supported by USPHS research grant AM-10149 from the National Institute of Arthritis, Metabolism and Digestive Diseases     

A dual action of papaverine on calcium uptake by microsomal fraction isolated from rat uterus

The effects of papaverine, cyclic AMP and MIX (3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor) on calcium uptake by a microsomal fraction from rat uterus were tested in the presence of 3 mM ATP. Papaverine potentiated calcium uptake in the presence of oxalate but inhibited it in the absence of oxalate. However, cyclic AMP and MIX did not influence calcium uptake, neither in the presence nor the absence of oxalate. These results suggest that calcium uptake by plasma membrane-derived vesicles in the absence of oxalate is inhibited by papaverine and that papaverine potentiated calcium uptake by the internal membranes in the presence of oxalate. They suggest also that the stimulatory action of papaverine involves a cyclic AMP-independent mechanism in addition to the mechanism via cyclic AMP.     

Effects of ethanol on the cyclic AMP system of the dog gastric mucosa.

The effect of ethanol on the cyclic AMP system of the dog fundic mucosa was studied in vitro. The gastric mucosal content of cyclic AMP was increased by 2.5% ethanol, whereas 10 and 20% ethanol decreased the mucosal content of cyclic AMP. The activity of adenylate cyclase was increased by 2.5 and 5% ethanol, whereas 10% ethanol did not significantly affect it. The activity of cyclic AMP phosphodiesterase was inhibited by ethanol in a competitive manner. The increase in the gastric mucosal content of cyclic AMP, induced by low concentrations of ethanol, is apparently due to the stimulation of adenylate cyclase and inhibition of phosphodiesterase. Changes in the phosphodiesterase or adenylate cyclase activites do not explain the decrease of the mucosal content of cyclic AMP by higher concentrations of ethanol. The mechanism of the decrease is discussed.     

Stimulation of cyclic adenosine 3′,5′-monophosphate accumulation and lipolysis in fat cells by adenosine deaminase

Summary The basal lipolytic activity of isolated fat cells of the rat was greatly enhanced in the presence of 0.01 to 30 g adenosine deaminase (ADA) per ml. This effect was more pronounced in dilute (20000 cells/ml) than in concentrated cell suspensions (100000 cells/ml); this is possibly due to the presence, in the incubation medium, of a high concentration of inosine which is formed by the deamination of the large amounts of adenosine released from high concentrations of fat cells. Inosine, although less potent than adenosine as an antilipolytic agent, markedly inhibited ADA-induced lipolysis at concentrations between 10 to 100 M. The lipolytic effect of ADA was identical with the stimulation of lipolysis by 1 M noradrenaline or 1 mM theophylline, while 1 mM dibutyryl cyclic AMP yielded two-fold higher values. The effects of ADA and lipolytic agents at maximally stimulating concentrations were not additive.After 5 min of incubation maximally effective concentrations of ADA which were also maximal with respect to lipolysis caused a 3- to 6-fold elevation of cyclic AMP levels in fat cells. A similar increase was observed with maximally effective concentrations of theophylline, whereas noradrenaline produced a 100- to 200-fold elevation. This indicates that a small accumulation of cyclic AMP may be sufficient to trigger the full lipolytic response. Furthermore, ADA, like theophylline, acted synergistically with noradrenaline and prevented the fall of cyclic AMP levels during 30 min of incubation.Insulin (100 U/ml) and nicotinic acid (0.1 M) decreased cyclic AMP accumulation and glycerol production induced by ADA.The results support the hypothesis that adenosine is released from isolated fat cells and that this nucleoside may serve as an inhibitor of adenyl cyclase activity, thus regulating cyclic AMP-dependent processes in adipose tissue.     

Adenosine 3′,5′-monophosphate in cultured neuroblastoma cells: Effect of adenosine,phosphodiesterase inhibitors and benzazepines

Summary The effect of various neurohormones on intracellular levels of adenosine 3,5-monophosphate were evaluated in a neuroblastoma cell line both, in the presence and in the absence of the phosphodiesterase inhibitors isobutylmethylxanthine and papaverine. Without the phosphodiesterase inhibitors only prostaglandin E₁ increased intracellular adenosine 3,5-monophosphate levels. In the presence of isobutylmethylxanthine and/or papaverine, however, adenosine stimulated adenosine 3,5-monophosphate formation and the effect of prostaglandin E₁ was greatly potentiated. Treatment of the cells with dopamine, 5-hydroxytryptamine, noradrenaline, adrenaline, histamine and prostaglandin F₁ was without effect on adenosine 3,5-monophosphate levels either in the presence or absence of the phosphodiesterase inhibitors. The adenosine concentration for a half maximal effect was about 75 M. The effect of 0.1 mM adenosine was not antagonized by 1 mM theophylline. Several adenosine analogs were tested and found to have little or no effect on adenosine 3,5-monophosphate levels in neuroblastoma N4TG3. Diazepam and to a lesser extent chlordiazepoxide act like phosphodiesterase inhibitors when incubated together with prostaglandin E₁.Part of this work was done during a visit of the authors to NIH, U.S.A., J. S. being a fellow of the Deutsche Forschungsgemeinschaft and B. H. of the Max-Planck-Gesellschaft.     

Positive dromotropic effect of dibutyryl cyclic adenosine 3',5'-monophosphate on the atrioventricular node.

The effect of atrioventricular (A-V) conduction of N6-2'-0-dibutyryl cyclic 3',5'-adenosine monophosphate (dibutyryl cyclic AMP) was investigated in comparison with those of norepinephrine, cyclic 3',5'-adenosine monophosphate (cyclic AMP), adenosine-5'-monophosphate (5'-AMP), and adenosine by the use of the isolated, blood-perfused A-V node preparation of the dog. Single injections of dibutyryl cyclic AMP (3-300 micronmol) and norepinephrine (0.1-1 nmol) into the posterior septal artery of the preparation (the upper part of the A-V node is mainly perfused through this artery) produced a dose-dependent decrease in the A-V conduction time. The time to the peak effect and the duration of the effect of dibutyryl cyclic AMP were much longer than with norepinephrine. The positive dromotropic effect of dibutyryl cyclic AMP was resistant to the beta-adrenoceptor blocking action of propranolol. Unlike dibutyryl cyclic AMP, cyclic AMP (above 30 nmol), 5'-AMP and adenosine (above 1 nmol) injected into the posterior septal artery prolonged the A-V conduction time in a dose-dependent manner. The results indicate that dibutyryl cyclic AMP has a mode of action on A-V nodal cells which differs distinctly from that of either norepinephrine or cyclic AMP, 5'-AMP, and adenosine.     

Effect of the phosphodiesterase inhibitor 4-(3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone (ZK 62711) on gastric secretion and gastric mucosal cyclic AMP

Summary The effect of the phosphodiesterase inhibitor 4-(3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone (ZK 62711) on gastric secretion and the cyclic AMP system of the gastric mucosa was studied in rats and guinea pigs. In rats, 0.03–0.3 moles/kg ZK 62711 i.v. stimulated acid and pepsin secretion in a dose-dependent manner and 0.03 moles/kg i.v. enhanced the effect of histamine. In guinea pigs no reproducible stimulation was found after intravenous injections of ZK 62711. The stimulation of gastric secretion in the rat by 0.3 moles/kg ZK 62711 i.v. was not affected by vagotomy but was totally inhibited by 10 moles/kg cimetidine i.v. The structurally related phosphodiesterase inhibitor, 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidine (Ro 20-1724), at the dose of 3.3 moles/kg i.v. stimulated gastric secretion in anaesthetised rats to a similar extent as 0.3 moles/kg ZK 62711 i.v. The content of cyclic AMP in the rat gastric mucosa in vivo was slightly increased by 10 moles/kg ZK 62711 i.v, whereas lower doses did not change it. Accumulation of cyclic AMP in the rat gastric mucosa by 50 moles/kg histamine i.v. was enhanced by simultaneous injections of 3.3 moles/kg ZK 62711 i.v. In rat gastric tissue slices in vitro 1–50 M ZK 62711 increased the level of cyclic AMP but 100 M histamine had no effect in the absence or presence of ZK 62711. In gastric mucosal slices of the guinea pig 10 and 50 M ZK 62711 increased the cyclic AMP content which effect was inhibited by 100 M cimetidine and enhanced the stimulatory effect of 100 M histamine on cyclic AMP. The activity of soluble cyclic AMP phosphodiesterase was inhibited by ZK 62711 in the rat (IC₅₀=18 M) and guinea pig gastric mucosa (IC₅₀=1.5 M). Adenylate cyclase was not affected in the homogenate of the guinea pig gastric mucosa. The results indicate that the phosphodiesterase inhibitor ZK 62711 which increases cyclic AMP levels in the gastric mucosa in vivo and in vitro, is a potent stimulator of gastric acid secretion.     

Inhibition of cyclic AMP phosphodiesterase activity and myocardial contractility: effects of cilostamide, a novel PDE inhibitor, and methylsiobutylxanthine on rabbit and canine ventricular muscle

The effects of cilostamide (N-cyclohexyl-N-methyl-4-[6-carbostyriloxy]butyramide; OPC-3689), a novel cyclic AMP phosphodiesterase (PDE) inhibitor were compared with those of 1-methyl-3-isobutylxanthine (IBMX) on the rabbit and canine heart preparations. Cilostamide was about three times less potent than IBMX in inhibiting the crude PDE activity of rabbit and canine heart in the cell-free system, while it was 10 times more potent than IBMX in enhancing the positive inotropic action of isoprenaline in the rabbit and canine ventricular myocardium: 10^?6 M cilostamide shifted the concentration-response curve for isoprenaline to the left in a parellel manner to the same extent as did 10^?5 M IBMX. Thus, cilostamide enhanced β-adrenoceptor stimulation more potently than did IBMX and the substances examined previously. Accumulation of intracellular cyclic AMP caused by 10^?6 M isoprenaline in the isolated canine ventricular myocardium was significantly enhanced by 10^?6 M cilostamide and 10^?5 M IBMX; isoprenaline (10^?6 M) induced cyclic AMP accumulation was greater with IBMX (10^?5 M) than with cilostamide (10^?6 M). The threshold concentration for cilostamide itself to induce positive chronotropic and inotropic actions in the rabbit heart was lower than that for IBMX, while the intrinsic activity of IBMX was greater than that of cilostamide. In the canine ventricular myocardium, the positive inotropic actions of cilostamide were comparable to those of IBMX; the action of cilostamide in concentrations of 10^?5 M and higher was partly inhibited by a β-adrenoceptor blocking agent, pindolol (3 × 10^?8 M). During the washout period of the drugs after the maximal response to the drugs had been reached, the positive inotropic action of cilostamide disappeared more rapidly than that of IBMX. The present results suggest that cilostamide is able to permeate the myocardial cell membrane more easily than IBMX and reach the PDE in the functionally important cyclic AMP compartment. The difference in turnover rate of cyclic AMP even in the same tissue in the physiological condition may also affect the direct action of the PDE inhibitors thereon.     

Binding of alpha-and beta-adrenergic ligands to cerebral cortical membranes: effect of 6-hydroxydopamine treatment and relationship to the responsiveness of cyclic amp-generating systems in two rat strains.

The binding of an α-adrenergic antagonist, WB 4101 and of a β-adrenergic antagonist, dihydroalprenolol, to cerebral cortical membranes fromo two rat strains, Sprague-Dawley and F-344, was examined after intraventricular administration of 6-hydroxydopamine. Cyclic AMP-generating systems in cerebral cortical slices from Sprague-Dawley rats respond to norepinephrine with an accumulation of cyclic AMP which is increased twofold after 6-hydroxydopamine treatment, while the cyclic AMP systems in slices from F-344 rat respond to norepinephrine with a relatively large accumulation of cyclic AMP which is not further increased after 6-hyxdroxydopamine treatment. The binding of WB 4101 to cerebral cortical membranes was similar in both rat strains and was unchanged after 6-hydroxydopamine treatment. The binding of dihydroalprenolol to membranes was similar in both rat strains and increased about 25% in both strains after 6-hydroxydopamine. Thus, the number of binding sites for these ligands does not correlate well with the magnitude of responses of cyclic AMP-generating systems to norepinephrine. Activity of cyclic AMP-phosphdiesterases in cerebral cortical homogenates was similar in both rat strains and was unchanged after 6-hydroxydopamine. Fluoride-stimulated adenylate cyclase activity in cerebral cortical homogenates appeared to be slightly higher in F-344 rats compared to Sprague-Dawley rats before but not after 6-hydroxydopamine treatment suggesting that changes in responsiveness of the cyclic AMP system might not be dependent upon changes in receptor density but in a post-receptor alteration such as adenylate cyclase activity.     

Effect of a novel inhibitor of cyclic AMP phosphodiesterase,E-1020, on cytosolic Ca++ level and contraction in vascular smooth muscle

Summary 1. The effects of a novel cyclic AMP phosphodiesterase inhibitor, E-1020 (1,2-dihydro-6-methyl-2-oxo5-(imidazo[1,2-a]pyridin-6-yl)-3-pyridine carbonitrile hydrochloride monohydrate), on cytosolic Ca⁺⁺ level ([Ca⁺⁺]_cyt) and muscle tension were examined in rat aorta using a fluorescent Ca⁺⁺ indicator, fura-2. 2. The sustained contraction induced by norepinephrine was more strongly inhibited by E-1020 than that induced by high K⁺. The contraction induced by a higher concentration of the stimulant was less sensitive to E-1020 than that due to a lower concentration. 3. Contractions induced by high K⁺ and norepinephrine followed the increase in [Ca⁺⁺]_cyt. E-1020 inhibited the increments in [Ca⁺⁺]_cyt and muscle tension. A Ca⁺⁺ channel blocker, verapamil, inhibited the norepinephrine-stimulated [Ca⁺⁺]_cyt more strongly than the contraction. E-1020 inhibited the verapamil-insensitive portion of the norepinephrine-stimulated [Ca⁺⁺]_cyt and contraction. 4. Norepinephrine transiently increased [Ca⁺⁺]_cyt and muscle tension in Ca⁺⁺-free solution. E-1020 inhibited the transient contraction but not the stimulated [Ca⁺⁺]_cyt. 5. E-1020 increased the cyclic AMP content of the muscle. The effects of E-1020 on cyclic AMP content and contraction were potentiated by an activator of adenylate cyclase, forskolin. 6. These results suggest that E-1020 inhibits the vascular contractility by the decrease in [Ca⁺⁺]_cyt and decrease in Ca⁺⁺ sensitivity of contractile elements. These effects may be mediated by the increase in cyclic AMP content of the muscle. Send offprint requests to M. Täjimi at the above address     

Heterologous sensitization of adenylate cyclase activity by serotonin in the rat cerebral cortex

In vitro exposure of rat cerebrocortical slices to μM concentrations of serotonin (5HT) results in an increased response of adenylate cyclase to isoproterenol (ISO). No change in the affinity of the β-adrenoceptor toward the agonist was found after 5HT exposure when measuring ISO displacement of [³H]CGP 12177 binding. A similar increase of adenylate cyclase response was also found when using VIP as a stimulatory agent. The dose-response curve of adenylate cyclase to the GTP analogue, GppNHp, was modified by 5HT, which promotes a significantly higher maximal response without altering the potency of GppNHp. Forskolin-stimulated adenylate cyclase activity was not affected by 5HT. Serotonergic 5HT₂ receptors are involved in the sensitization of adenylate cyclase to GppNHp, since the selective 5HT₂ antagonist ketanserin inhibits the effect of 5HT, whereas the 5HT₂ agonist DOI mimics 5HT. The involvement of 5HT₂ receptor-coupled activation of protein kinase C is also demonstrated: direct protein kinase C activators such as phorbol esters and s,n-dioctanoylglycerol behave in the same manner as 5HT, while the protein kinase C inhibitor CGP 41251 prevents 5HT from increasing adenylate cyclase responsiveness to GppNHp. Moreover, in vitro exposure of cortical slices to 5HT results in reduced inhibition of adenylate cyclase by somatostatin. Since no change was observed at the receptor level and in the direct stimulation of the catalytic subunit of the enzyme, we propose that 5HT might accomplish the sensitization of adenylate cyclase through protein kinase C by inactivating the inhibitory coupling protein Gi and facilitating the interaction of the exogenous GppNHp with the stimulatory coupling protein Gs.     

Prevention of nitroglycerin tolerance in vitro by T0156, a selective phosphodiesterase type 5 inhibitor

The efficacy of nitroglycerin as a vasodilator is limited by tolerance, which develops shortly after treatment begins. The present study aims to examine whether T0156, a newly developed potent and selective inhibitor of phosphodiesterase type 5 (PDE5), could attenuate the tolerance to nitroglycerin on rat aortas. Rat aortic rings were suspended in organ bath for the measurement of changes in isometric tension and nitrate tolerance was acutely induced by preceding exposure for 90 min to 30 microM nitroglycerin. Concentration-response curves to nitroglycerin were obtained on aortic rings pre-contracted with phenylephrine. Pre-exposure of rings with or without endothelium to nitroglycerin reduced the relaxations to nitroglycerin. The tissue levels of cyclic GMP were measured by enzyme immunoassay kit. Treatment with T0156 inhibited and prevented the reduced relaxation and cyclic GMP levels in response to nitroglycerin in tolerant rings. In contrast, nitroglycerin-induced tolerance was unaffected by cilostazol (PDE3 inhibitor) and rolipram (PDE4 inhibitor). Finally, incubation of aortic rings with thromboxane prostanoid receptor antagonist, cyclooxygenase inhibitor, or endothelin ET(A) receptor antagonist did not inhibit the development of tolerance. The present results suggest that nitroglycerin tolerance may involve an increased activity of PDE5 but not PDE3 or PDE4 isoforms in vascular smooth muscle cells since T0156 prevents the development of tolerance. Thromboxane A(2), cyclooxygenase (COX)-dependent prostaglandins and endothelin 1 play little role in the acute induction of nitroglycerin tolerance.     

The PDE4 inhibitor rolipram reverses object memory impairment induced by acute tryptophan depletion in the rat

Rationale The selective type IV phosphodiesterase inhibitor, rolipram, has been shown to improve long-term memory and can reverse the cholinergic deficit caused by scopolamine. However, the underlying mechanisms of action of rolipram remain obscure. Objectives The present study investigates the effect of rolipram in a serotonergic-deficit model of acute tryptophan depletion (ATD). In addition, the levels of plasma tryptophan (TRP) were compared to object recognition performance. Materials and methods The experiments were conducted using male Wistar rats. The time-dependent effect of ATD treatment (a gelatin-based protein mixture) on plasma TRP levels (0, 1, 3, and 6 h after injection) and object recognition task (ORT) performance (0.5, 1, 3, and 6 h after ATD treatment) was examined. The effect of rolipram (0, 0.01, 0.03, and 0.1 mg/kg, i.p.) was tested in the condition in which ATD induced a clear memory deficit. Results ATD significantly lowered the plasma TRP ratio (TRP/Σlarge neutral amino acid) with a maximum of 48%, approximately 1 h after administration. Furthermore, ATD impairs ORT performance when administered 3 h before testing. Rolipram (0.1 mg/kg) reversed the memory deficit induced by ATD in a dose-dependent manner. Conclusions On the basis of previous studies and the ability to reverse a serotonergic deficit, we suggest that rolipram may act through elevation of cyclic adenosine monophosphate levels and subsequent increase in neurotransmitter release.     

Inhibition of fluid transport in the isolated gall bladder of the guinea pig by isoprenaline,theophylline and cyclic adenosine 3′,5′-monophosphate

Summary The isolated gall bladder of guinea pigs was used to study the effects of isoprenaline and orciprenaline on fluid transport. Both drugs in the range 10^–8 M to 10^–4 M inhibited fluid transport 20–50 min after application, when applied to the serosal side. The maximum inhibition observed was 49±3.9% by a concentration of 10^–5 M. After this inhibitory phase the transport rate returned to control values. Doubling the concentration did not evoke a new inhibitory response, but washing gall bladders with fresh Ringer's solution restored the sensitivity to isoprenaline. Isoprenaline was ineffective when added to the mucosal side. Propranolol but not practolol, prevented the action of isoprenaline. Theophylline inhibited fluid transport in the range 10^–3 M to 10^–2 M. Cyclic adenosine 3,5-monophosphate (cyclic AMP) 3.3×10^–3 M decreased fluid transport only when added to the serosal side. In contrast to isoprenaline, both theophylline and cyclic AMP caused a prolonged decrease in fluid transport. The results are in accordance with the assumption that the inhibition of fluid transport in the gall bladder by -sympathomimetic drugs may be caused by an increase of the intracellular cyclic AMP level.Part of this work was presented at the 14th meeting of the Deutsche Pharmakologische Gesellschaft in Mainz, 1973.This work was supported by a grant from the Deutsche Forschungsgemeinschaft given to the Sonderforschungsbereich 160, Eigenschaften biologischer Membranen, Projekt T.