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At least 1,441 records · Page 80Linked to original sources
PubMed1982

Prenalterol is an agonist at beta 2- as well as at beta 1-adrenoceptors.

Prenalterol exerted agonist activity in cat, but not guinea-pig, isolated atria, which contain predominantly beta 1-adrenoceptors. Prenalterol relaxed K+ -contracted rat uterus, but not histamine-contracted cat lung strips; both contain predominantly beta 2-adrenoceptors. The effect of prenalterol in rat uterus was antagonised by the selective beta 2-adrenoceptor antagonist ICI 118551 but not by the selective beta 1-adrenoceptor antagonist atenolol. Thus the ability of prenalterol to exert beta-adrenoceptor activity is tissue-dependent, rather than beta-adrenoceptor subtype-dependent.

Adrenergic beta-Agonists↗
PubMed1982

Characterization of the beta-adrenergic inhibition of motility in cat colon strips.

The inhibition of spontaneous contractile activity in isolated cat colon strips by isoprenaline, prenalterol and terbutaline was studied. Isoprenaline produced a concentration-dependent complete inhibition with an EC50 of 6.18 nM. Prenalterol and terbutaline produced a concentration-dependent partial inhibition of 68 and 75% respectively, with EC50 of 0.52 and 0.43 microM respectively. The inhibitory effects of the three agonists were blocked by metoprolol and IPS 339 in such a way as to suggest that the prenalterol effect was mediated by beta 1-adrenoceptors and the terbutaline effect was mediated by beta 2-adrenoceptors, whereas the effect of isoprenaline appeared to be mediated by both types of receptors. Thus, the results indicate that both beta 1- and beta 2-adrenoceptors are involved in the adrenergic inhibition of spontaneous contractile activity in the cat colon strip. Qualitative effects of prenalterol and terbutaline on the spontaneous contractile activity in the cat colon strip indicated that the beta 1-adrenoceptor-mediated effects may be related to inhibition of the activity in cholinergic neurons, whereas the beta 2-adrenoceptors may be acting on the smooth muscle cells per se.

Adrenergic beta-Agonists↗
PubMed1983

Relative inotropic and chronotropic activity of beta-adrenoceptor stimulants in anaesthetised, areflexic dogs.

The use of different methods of measuring contractility and the effects of cardiovascular reflexes are among the factors which complicate the assessment of selective inotropic activity of beta-adrenoceptor agonists. The effects of dobutamine, prenalterol, noradrenaline and isoprenaline on heart rate, iliac blood flow, left ventricular pressure, max dP/dt and (dP/dt) divided by IIT (integrated isometric tension) were evaluated in anaesthetised dogs in which the hearts were denervated and blood pressure held constant. All the drugs caused dose-dependent increases in heart rate and contractility. The relative chronotropic and inotropic activity of each agonist was evaluated. At most doses studied the agonists exerted similar chronotropic and inotropic activity when compared to the non-selective agonist isoprenaline. It is likely that the inotropic selectivity observed with prenalterol and dobutamine in previous studies depends on factors other than direct drug action.

Adrenergic beta-Agonists↗
PubMed1984

Comparison of the beta 1 selective affinity of prenalterol and corwin demonstrated by radioligand binding.

The ability of the beta 1 partial agonists prenalterol and corwin , to displace the binding of [3H]dihydroalprenolol to the heterogeneous populations of beta-adrenoceptors on rat and rabbit lung membranes was compared. Both drugs exhibited higher affinity for the binding sites in rabbit lung (predominant beta 1) as compared to rat lung (predominant beta 2). Curve fitting analysis of the displacement curves into high affinity (beta 1) and low affinity (beta 2) components indicates that both drugs exhibit beta 1 selective affinity. Further competition experiments performed in the presence of carefully calculated concentrations of highly selective beta 1 (atenolol) or beta 2 (ICI 118,551) antagonists to produce homogeneous receptor subtype populations in rat and rabbit lung membranes respectively, confirmed this beta 1 selective affinity. These results suggest an approximate selective affinity ratio (beta 1 to beta 2) of ten and forty fold for prenalterol and corwin respectively.

Adrenergic beta-Agonists↗
PubMed1985

Inotropic selectivity of salbutamol and terbutaline in anaesthetised, areflexic dogs.

The cardiovascular effects of the selective beta 2-adrenoceptor agonists salbutamol and terbutaline have been evaluated in anaesthetised, areflexic dogs. The preparation was designed to reduce the effects of changes in cardiac function mediated via reflex responses to changes in blood pressure. The effects of the selective beta 2-adrenoceptor agonists on heart rate, hindlimb blood flow, left ventricular pressure, max dP/dt and (dP/dt)/IIT (integrated isometric tension) were compared to those of isoprenaline, while blood pressure was held constant. All three drugs produced dose-dependent increases in heart rate, myocardial contractility and iliac blood flow. When equiactive inotropic doses of isoprenaline and salbutamol were compared, salbutamol produced a significantly lower chronotropic effect. A similar inotropic selectivity was found when terbutaline was compared to isoprenaline. beta 2-Adrenoceptor blockade abolished this selectivity. It is concluded that, in the absence of autonomic reflex activity, the beta 2-selective adrenoceptor agonists are relatively selective inotropic stimulants.

Albuterol↗
PubMed1985

Comparison of the effects of forskolin and isoprenaline on tracheal, cardiac and skeletal muscles from guinea-pig.

Forskolin, a potent activator of adenylate cyclase, and isoprenaline, an unselective beta-adrenoceptor agonist, were studied in vitro on tissues from guinea-pig with respect to relaxation of the carbachol-contracted trachea, increase in the force of contraction of the papillary muscle and depression of subtetanic contractions of the soleus muscle, three well-characterized beta-adrenoceptor-mediated effects. Forskolin and isoprenaline relaxed the trachea and increased the force of contraction of the papillary muscle. Isoprenaline but not forskolin caused a depression of the subtetanic contraction of the soleus muscle. Forskolin did not seem to potentiate the effects of isoprenaline on the tissues studied; the combined effects appeared to be a mere addition. Forskolin did not increase the efficacy of the partial agonist prenalterol either. It is concluded that there is no simple relation between c-AMP generation and the functional response to beta-adrenoceptor agonists. Forskolin should not be used uncritically to probe beta-adrenoceptor-mediated effects.

Animals↗
PubMed1984

X-ray microanalysis of the rat parotid gland after chronic sympathectomimetic stimulation.

The effects of chronic treatment with isoproterenol, reserpine, prenalterol, and terbutaline on rat parotid gland were investigated by electron microscopy and X-ray microanalysis. Chronic isoproterenol treatment induced lower potassium and calcium concentrations in the acinar cells. The cells were enlarged and contained more and larger zymogen granules than acinar cells in the controls. The zymogen granules contained markedly less sulfur, potassium, and calcium than in control animals. Prenalterol had effects similar to those of isoproterenol, but less pronounced, whereas terbutaline had no significant effects. Chronic treatment with reserpine caused a decrease in calcium levels but did not affect potassium levels. The changes in elemental composition in parotid acinar cells after chronic treatment with isoproterenol and reserpine differed from those induced by the same treatment in the submandibular gland of the rat.

Animals↗
PubMed1986

Beta-adrenergic control of motility in the rat colon. I. Evidence for functional separation of the beta 1- and beta 2-adrenoceptor-mediated inhibition of colon activity.

The beta-adrenoceptor-mediated inhibitory response in isolated rat colon strips of beta-adrenoceptor agonists (isoproterenol, terbutaline, prenalterol) in the absence and presence of the selective beta-adrenoceptor antagonists metoprolol (beta 1) and IPS 339 (beta 2) demonstrates that both beta 1- and beta 2-adrenoceptors are involved in the inhibition of colonic motility. Neuronal blockade induced by tetrodotoxin suppressed the relatively high (68%) maximal response of prenalterol (partial beta-adrenoceptor agonist) to 23%. The concentration-response curves for terbutaline (beta 2-selective agonist) and isoproterenol (nonselective agonist) were not influenced by tetrodotoxin. The results thus indicate that the beta-adrenergic inhibition of spontaneous activity in the rat colon strip may be mediated at two functional levels within the colon wall: either by beta 2-adrenoceptors in the smooth muscle layer or by beta 1-adrenoceptors in the intramural ganglionic plexuses, which by neuronal elements are coupled to the effector smooth muscle.

Adrenergic beta-Agonists↗