cyclic-gmp and siguazodan

Nonadrenergic, noncholinergic relaxations were elicited by field stimulation (1-16 Hz, 1 msec, 8 V for 15 sec) of guinea pig trachea desensitized with capsaicin (3 microM), pretreated with atropine (1 microM), propranolol (1 microM), indomethacin (3 microM) and treated with alpha-chymotrypsin (2 U/ml) and contracted with 3 microM histamine. The effect of the phosphodiesterase (PDE) isozyme selective inhibitors siguazodan (PDE III-selective), rolipram (PDE IV-selective), denbufylline (PDE IV-selective) and zaprinast (PDE V-selective) was examined on the relaxant responses to field stimulation and on relaxations elicited by the nitric oxide donor 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1). The response to field stimulation in the presence of alpha-chymotrypsin (the putative nitric oxide component), at all the frequencies tested, was potentiated significantly by the PDE IV inhibitors rolipram (1 and 10 microM) and denbufylline (3 and 10 microM) as were responses to SIN-1. The PDE V inhibitor zaprinast (30 microM) potentiated relaxations elicited by field stimulation at 8 and 16 Hz and also potentiated responses to SIN-1. The PDE III inhibitor siguazodan (1 microM), however, was without effect on relaxant responses to field stimulation or to SIN-1. These results suggest that the nitric oxide component of the nonadrenergic, noncholinergic relaxant response is mediated primarily via cyclic AMP whose action is inactivated by a PDE IV isozyme and also by cyclic GMP which is inactivated by a PDE V isozyme.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Animals; Atropine; Cyclic AMP; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 3; Cyclic Nucleotide Phosphodiesterases, Type 4; Electric Stimulation; Guanidines; Guinea Pigs; Indomethacin; Isoenzymes; Muscle Relaxation; Nitric Oxide; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Propranolol; Purinones; Pyridazines; Pyrrolidinones; Receptors, Adrenergic; Receptors, Cholinergic; Rolipram; Trachea; Vasoactive Intestinal Peptide; Xanthines

1. The effects of agents that elevate either cyclic AMP (the phosphodiesterase (PDE) III inhibitor siguazodan, salbutamol) or cyclic GMP (sodium nitroprusside (SNP)) on the relaxant activity of the PDE IV inhibitor, rolipram, were investigated in carbachol (0.1 microM) precontracted guinea-pig tracheal sheets. 2. Rolipram, siguazodan and SNP caused concentration-related reductions in tone of tissues precontracted with 0.1 microM carbachol (EC50 values 12.5; 2.73 and 0.35 microM respectively). Whilst the concentration-response relationship for the PDE III inhibitor, siguazodan, was monophasic that of the PDE IV inhibitor, rolipram, was biphasic. 3. The relaxant activity of rolipram was markedly enhanced in the presence of 10 microM siguazodan (EC50 < 0.01 microM), 0.1 microM salbutamol (EC50 0.03 microM) and 0.3 microM SNP (EC50 0.03 microM). In contrast, the relaxant activity of siguazodan was unaffected by SNP and only modestly enhanced by rolipram (10 microM) and salbutamol (0.1 microM). 4. The relaxant activity of SNP was enhanced by the PDE V inhibitor SK&F 96231 (30 microM: EC50 0.06 microM) and rolipram (30 microM, EC50 0.08 microM) but was unaffected by 30 microM siguazodan. 5. At concentrations up to 10 microM, neither siguazodan nor rolipram elevated tracheal cyclic AMP levels. However, the combination of 10 microM rolipram and siguazodan caused a two fold increase in the cyclic AMP content (from 2.19 to 4.36 pmol cyclic AMP mg-1 protein). SNP (0.1-10 microM) failed to produce a significant increase in tracheal cyclic AMP levels. At 0.1 microM the effect of SNP on tracheal cyclic AMP levels was significantly (P < 0.05) increased in the presence of rolipram but not siguadozan. 6. The results indicate that the relaxant effects of rolipram are markedly enhanced by agents that inhibit PDE III activity or elevate cyclic GMP. They support the hypothesis that SNP potentiates the effects of rolipram via the inhibitory action of cyclic GMP on hydrolysis of cyclic AMP by PDE III. The findings also suggest that whilst PDE III may be more significant in regulating basal smooth muscle tone in the absence of any exogenous stimulus to cyclic AMP accumulation, PDE IV activity may be more tightly coupled to the pool of adenylyl cyclase stimulated by beta2-adrenoceptor agonists.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Animals; Cyclic AMP; Cyclic GMP; Dose-Response Relationship, Drug; Guanidines; Guinea Pigs; In Vitro Techniques; Male; Muscle Relaxation; Nitroprusside; Phosphodiesterase Inhibitors; Pyridazines; Pyrrolidinones; Rolipram; Trachea

1. We have investigated the bronchodilator potential of type V phosphodiesterase (PDE V) inhibitors in anaesthetized ventilated guinea-pigs using the potent and selective PDE V inhibitor, SK&F 96231. We have compared its activity to that of salbutamol, the PDE III inhibitors, siguazodan and SK&F 95654 and to the PDE IV inhibitor rolipram. 2. Administered as an i.v. infusion SK&F 96231 (0.6 and 1 mg kg-1 min-1, i.v.) caused a slowly developing inhibition of histamine (100 nmol kg-1, i.v.)-induced bronchoconstriction and elevated tracheal cyclic GMP levels in the anaesthetized guinea-pig. SK&F 96231 (0.1 and 0.3 mg kg-1 min-1, i.v.) was without effect on histamine-induced bronchoconstriction. In the presence of a sub-threshold infusion of SNP (0.1 mumol kg-1 min-1, i.v.) there was a marked enhancement of SK&F 96231-induced inhibition of histamine responses such that at infusion rates that were ineffective alone, SK&F 96231 caused a > 50% inhibition of histamine responses. The stimulation of tracheal cyclic GMP accumulation by SK&F 96231 was also potentiated. 3. Administered directly into the airway, SK&F 96231 (300 micrograms in 5 mg lactose carrier) was largely without effect on histamine-induced bronchoconstriction (4.9 +/- 1.9% inhibition). In the presence of SNP (0.1 mumol kg-1 min-1, i.v.) or isosorbide dinitrate (200 micrograms administered by insufflation into the trachea) there was a marked potentiation of the inhibitory activity of SK&F 96231 (40 +/- 4% and 62 +/- 1.8% respectively). 4. Salbutamol and rolipram (3-300 microg by insufflation) caused a dose-related inhibition of histamine responses with a maximum of 91 +/- 2% and 59 +/- 10% respectively. The PDE III inhibitor, siguazodan,was without effect on histamine responses but they were reduced (27.7 +/- 4.8% at 300 microg) by SK&F95654. There was a marked enhancement of the inhibitory activity of rolipram in the presence of SK&F 95654.5. We conclude that SK&F 96231 has weak anti-spasmogenic activity in the guinea-pig in vivo, we suggest that this is primarily a consequence of a low endogenous guanylate cyclase activity in the airway. The potentiation of the anti-spasmogenic activity of SK&F 96231 by SNP suggests that a combination of PDE V inhibitor and guanylate cyclase agonist might provide significant bronchodilator activity.6. We have established that PDE IV inhibitors are bronchodilators when administered directly into the airway of anaesthetized guinea-pigs but that PDE III inhibitors are

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Anesthesia; Animals; Bronchoconstriction; Cyclic GMP; Guanidines; Guinea Pigs; Male; Nitroprusside; Parasympatholytics; Phosphodiesterase Inhibitors; Purinones; Pyridazines; Pyrrolidinones; Rolipram; Trachea

The mechanical and biochemical responses of the canine trachealis to SK&F 94836 [2-cyano-1-methyl-3-[4-(4-methyl-6-oxo- 1,4,5,6-tetrahydropyridazine-3-yl)phenyl]guanidine], a selective inhibitor (ki = 1-3 microM) of the low km cyclic AMP (cAMP) phosphodiesterase, were assessed. Time course studies indicated that SK&F 94836-induced relaxation of trachealis strips contracted with 0.1 microM methacholine was accompanied by an activation of cAMP-dependent protein kinase (cAMP-PK). In subsequent experiments, trachealis strips were contracted with three concentrations of methacholine (0.1, 1.0 or 3.0 microM) or two concentrations of histamine (10 or 300 microM) before being relaxed by the cumulative addition of SK&F 94836. The relaxant response to SK&F 94836 (EC50 = 1-10 microM) decreased progressively as tissues were contracted with higher concentrations of methacholine. In parallel with its inhibitory effect on SK&F 94836-induced relaxation, methacholine suppressed the ability of SK&F 94836 to activate cAMP-PK. Interestingly, the inhibition of cAMP-PK activity was not accompanied by a significant inhibition of SK&F 94836-stimulated cAMP accumulation. Unlike the results with methacholine, the concentration of histamine used to contract tissues had no effect on SK&F 94836-induced relaxation or cAMP-PK activation. To determine the effect of SK&F 94836 on the mechanical and biochemical responses to the beta adrenoceptor agonist isoproterenol, tissues were first contracted with 3.0 microM methacholine and then incubated with 0, 0.3, 3.0 or 30 microM SK&F 94836 before being relaxed by the cumulative addition of isoproterenol. In these experiments, SK&F 94836 potentiated isoproterenol-induced relaxation, cAMP accumulation and cAMP-PK activation in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Animals; Bronchi; Cyclic GMP; Dogs; Dose-Response Relationship, Drug; Guanidines; Histamine; Isoproterenol; Kinetics; Methacholine Chloride; Methacholine Compounds; Muscle Relaxation; Muscle, Smooth; Nitroprusside; Pyridazines; Trachea