The nicardipine-isoprenaline interaction in human and guinea-pig isolated airways

The gastrointestinal effects that may follow the administration of theophylline reflect the pharmacodynamic profiles of both the parent drug and its metabolites

This study investigates the effect of theophylline along the rabbit gastrointestinal tract in comparison with the pharmacodynamic effect produced by the combined application of its three major metabolites. At concentrations up to 10(-3) m, theophylline relaxed, in a declining order from the lower oesophageal sphincter (LOS) to pylorus, all regions of the upper gastrointestinal tract, but only the ascending colon from the intestinal regions studied. At concentrations higher than 10(-3) m, instead of relaxing, theophylline strongly contracted the antrum and pylorus. In all three small intestinal regions, at concentrations up to 10(-3) m, theophylline produced a weak contraction, which at higher concentrations became very strong, and at 10(-2) m was comparable to that produced by a supramaximal dose of acetylcholine. The additive relaxing effect resulting from the combined application of the theophylline's metabolites was, from oesophagus to pylorus, weaker than that produced by theophylline, while on the ascending colon it was comparable to that of the parent drug. In contrast, the additive contractile effect of the metabolites on the three small intestinal regions was four to five times higher the one produced by theophylline. In conclusion, this study shows that the additive effect of the combined application of theophylline's major metabolites on the rabbit gastrointestinal tract plays a major role in the final response of the intestine, and a minor one in the final responses of the gastric regions, while both the parent drug and the metabolites contribute to the final responses of the oesophagus and LOS.

Relaxing and contracting effects of theophylline's metabolites on the rabbit upper gastrointestinal tract

The present study, aimed to clarify whether the gastrointestinal adverse effects following administration of the bronchodilator theophylline are owing to the action of the drug itself or its metabolites, investigates the pharmacodymanic effects of theophylline's metabolites on the spontaneous contractility in the rabbit upper gastrointestinal tract. Comparative examination reveals that while two of the metabolites, namely 1-methylxanthine (1-MX) and 3-methylxanthine (3-MX), cause a similar, but less pronounced than the parent drug, concentration-dependent relaxation on the isolated oesophagus, lower oesophageal sphincter (LOS), fundus, antrum and pylorus, the remaining two metabolites, 1,3-dimethyluric acid (1,3-DMU) and 1-methyluric acid (1-MU), produce either a weak stimulating effect, or an even weaker relaxation. The relaxation which is muscle-mediated, non-adrenergic non-cholinergic (NANC) and nitric oxide (NO)-independent is probably mediated via inhibition of the metabolites on phosphodiesterases (PDEs), while a presynaptic cholinergic pathway is involved in the weak stimulating effect. The effects of all substances are additive. As a consequence, the net result of the cumulative action of all metabolites in the oesophagus, LOS, antrum and pylorus is, at 10(-3) m, comparable with that of theophylline, but in the fundus it is lower than that of the parent drug, because in the latter tissue the stimulating effect of 1,3-DMU and 1-MU counteracts the relaxing effect of the other two metabolites. However, combination of the parent drug with its metabolites leads to a considerable relaxation in all the gastrointestinal regions extending from the oesophagus to pylorus. Conclusively, upper gastrointestinal adverse effects following theophylline's administration are also because of theophylline's metabolites.

Paradoxal effect of salbutamol in an in vitro model of bronchoprotection

Salbutamol-induced hyperresponsiveness to acetylcholine was investigated in human and guinea-pig isolated airways and cultured human airway smooth muscle cells. Salbutamol (10(-7)-10(-5) m) inhibited contractions induced by low concentrations of acetylcholine (10(-8)-10(-7) m) but potentiated contractions induced by higher concentrations of acetylcholine (10(-5)-10(-3) m). Pretreatment with the calcium channel antagonist nicardipine suppressed salbutamol-induced hyperresponse. Stimulation of cultured human airway smooth muscle cells with salbutamol (10(-6) m) amplified intracellular calcium concentration rise induced by acetylcholine (10(-5) m). Propranolol (10(-7) m), a beta1- and beta2-adrenoceptor antagonist, and ICI 118551 (10(-7)-10(-6) m), a beta2-adrenoceptor antagonist, suppressed the inhibitory effect of salbutamol but did not inhibit the hyperresponse on high concentrations of acetylcholine. In contrast, higher concentration of propranolol (10(-6) m) inhibited salbutamol-induced hyperreactivity. Effects of salbutamol were not affected by atenolol, a beta1-adrenoceptor blocker. Salbutamol-induced hyperresponsiveness is mediated through a mechanism involving calcium channel activation.

Effects of verapamil and elgodipine on isoprenaline-induced metabolic responses in rabbits

Verapamil (0.17 microg kg(-1) min(-1) intravenous, i.v.) but not elgodipine (35 ng kg(-1) min(-1)) modestly enhanced the weak blood glucose increase induced by the i.v. infusion of isoprenaline (0.3 microg kg(-1) min(-1)) in conscious rabbits. However, elgodipine but not verapamil suppressed the increase in circulating insulin evoked by the agonist. Both drugs enhanced the rise in plasma lactate mediated by isoprenaline but only elgodipine potentiated the lipolytic effect of the agonist. In isolated islets elgodipine (10(-6) M) blocked forskolin (10(-6) M)-induced insulin release. However, in rabbit adipocytes elgodipine potentiated both glycerol release and cAMP accumulation induced by isoprenaline (10(-8)-10(-6) M). Excess K(+) (40-60 mM) did not alter basal lipolysis or the response to isoprenaline in either rabbit or mouse adipocytes. Therefore, Ca2+ influx through L-type Ca2+ channels does not seem to play a significant role in the lipolytic effect of isoprenaline. Metabolic alterations found with Ca2+ channel antagonists were of minor intensity and probably devoid of pathological implications.

Inhibition by SR 59119A of isoprenaline-, forskolin- and VIP-induced relaxation of human isolated bronchi

In the human isolated bronchus (HIB) it has been shown that beta(3)-adrenoceptor stimulation fails to induce relaxation of airway smooth muscle. It has however been reported in human ventricular endomyocardial biopsies that beta(3)-adrenoceptor stimulation induced a marked negative inotropic effect which could be linked to Gi protein activation. The aims of this study were: (1) to determine in HIB (internal diameter 1-2 mm) whether the selective beta(3)-adrenoceptor agonist SR 59119A (N[7-methoxy-1,2,3, 4-tetrahydronaphthalen-(2R)methyl]-(2R)-2-hydroxy-2-(3-chloroph eny l)e thanamine hydrochloride) was able to inhibit adenylate-cyclase-mediated airway smooth muscle relaxation induced by isoprenaline, forskolin or vasoactive intestinal peptide (VIP) and (2) to investigate the role of the Gi protein in this interaction. SR 59119A (0.1 microM and 1 microM) induced a shift to the right of concentration response curve for isoprenaline (-0. 15+/-0.06 and -0.54+/-0.21 log unit, P<0.05 and P<0.01 respectively), forskolin (-0.12+/-0.02 and -0.30+/-0.05 log unit, P<0.001), and VIP (-0.42+/-0.12 log unit, P<0.01 with SR59119A 10(-6)M). The inhibitory effect of SR 59119A was (1) abolished by an incubation of HIB with pertussis toxin (1 microg/ml, during 15 h in Krebs-Henseleit solution, at 21 degrees C), which is known to inactivate the Gi protein and (2) increased after an incubation of HIB with the pro-inflammatory cytokine IL-1beta (10 ng/ml, during 15 h in Krebs-Henseleit solution, at 21 degrees C), which is known to up-regulate Gi protein expression. Our results suggest that the selective beta(3)-adrenoceptor agonist SR59119A might inhibit the cAMP-dependent relaxation of human isolated bronchus through Gi protein-mediated inhibition of adenylate cyclase.

In vitro studies on the interactions of beta2-adrenoceptor agonists, methylxanthines, Ca2+-channel blockers, K+-channel openers and other airway smooth muscle relaxants in isolated guinea-pig trachea

Pharmacodynamic interactions in vitro between different types of airway smooth muscle relaxants were systematically and quantitatively evaluated by using a new methodological technique. Relaxant concentration-effect curves for terbutaline, theophylline, cromakalim, sodium nitroprusside and isradipine were obtained in isolated guinea-pig trachea contracted by histamine (1 microM). The effects of three different fixed concentrations of each airway smooth muscle relaxant were initially attained and concentration-effect curves for combinations with increasing concentrations of either one of the other relaxants were produced. Based on pharmacodynamic parameters obtained by non-linear regression analysis of experimental data for the relaxants alone theoretical concentration-effect curves for predicted additive interaction were constructed by using the isobolic method. Synergistic (over-additive) interaction was defined as existing when data points and derived pharmacodynamic parameters obtained with combinations of the relaxants showed statistically significant deviation from the predicted additive interaction curve and its functional parameters. Significant synergistic interaction with terbutaline was found for both theophylline (70 or 200 microM), cromakalim (0.1, 0.3 or 1 microM), sodium nitroprusside (30 or 100 nM) and isradipine (1, 3 or 10 nM). Theophylline showed synergistic interaction with cromakalim (0.1, 0.3 or 1 microM), sodium nitroprusside (10 nM) and isradipine (1, 3 or 10 nM). Interactions between cromakalim and sodium nitroprusside (10, 30 or 100 nM) were also synergistic, whereas cromakalim and isradipine (1, 3 or 10 nM) produced only additive interaction. Possible mechanisms underlying the interactions are discussed on basis of existing knowledge with special regards to phosphodiesterase isoenzymes, K+ and Ca2+ channels.

Functional, biochemical and morphological studies on human bronchi after cryopreservation

1. Human isolated bronchi have been investigated as fresh tissue or after storage (7 and 30 days) at -196 degrees C in foetal calf serum containing 1.8 M dimethyl sulphoxide. 2. After cryopreservation, the maximal contractile response to acetylcholine (3 mM) was reduced (approximately 25%) but the difference did not reach significance statistically. Maximal responses to other spasmogens tested (histamine, [Nle10]NKA(4-10), bradykinin, leukotriene D4, U46619, and KCl) did not differ between unfrozen and frozen/thawed tissues. The sensitivity of cryopreserved tissues to the constrictor agents tested was similar to that of fresh tissues. 3. The accumulation of inositol phosphates produced by acetylcholine in human bronchus in vitro was similar in fresh and cryostored (30 days) tissues. 4. Relaxant responses of acetylcholine (0.3 microM)-precontracted preparations to theophylline, isoprenaline, rolipram and sodium nitroprusside were unchanged after storage with the exception of the sensitivity to rolipram which was diminished in the 30-days cryostorage group. 5. Light microscopic examination of sections taken from 30 days cryostored tissues indicates that the epithelium, submucosal tissue and smooth muscle were well preserved. 6. These experiments suggest that cryopreservation of human bronchi results in maintenance of several morphological, functional (contraction/relaxation) and biochemical properties.