The control of mucin secretion into the lumen of the cat trachea by α- and β-adrenoceptors,and their relative involvement during sympathetic nerve stimulation

We have tested the effects of phenylephrine, dobutamine and salbutamol, α-, β₁- and β₂-adrenoceptor agonists respectively, on the output of radiolabelled mucins into the cat trachea in situ. Phenylephrine significantly increased mucin output, an effect inhibited by the α-adrenoceptor antagonists, thymoxamine or prazosin, but not by propranolol. Dobutamine increased the output of ³⁵S-labelled mucins greatly and had a smaller effect on ³H-labelled mucins. Propranolol blocked these effects but thymoxamine did not. At high doses atenolol, a β₁-adrenoceptor antagonist, inhibited dobutamine's effect on ³⁵S-labelled mucins. Salbutamol caused a small increase in mucin output and propranolol blocked this increase. Electrical stimulation of the sympathetic nerve supply to the trachea increased mucin output. Propranolol inhibited this effect; thymoxamine did not. We conclude that both α- and β-adrenoceptors increase mucus secretion into the cat trachea but that only the β-adrenoceptors respond to sympathetic nerve stimulation.     

Agonist and Antagonist Properties of β3-Adrenoceptors in Human Omental and Mouse 3T3-L1 Adipocytes

Abstract: The pharmacological properties of the native human β₃-adrenoceptor are poorly defined. In the present study, the agonist and antagonist properties of β₃-adrenoceptors in human omental and mouse 3T3-L1 adipocytes were compared by measuring lipolysis in the absence or presence of adrenoceptor blockers. Methodological experiments revealed that all three β-adrenoceptors were functionally expressed in both types of adipocytes. This makes the human and the mouse cells directly comparable in pharmacological studies. CGP 12177 was a selective partial p₃-adrenoceptor agonist in both cell types with a pD₂ of about 7.5. The order of potency of classical non-selective adrenoceptor agonists, when determined during blockade of β₁, β₂- and α₂-adrenoceptors, was isoprenaline>noradrenaline>adrenaline in both human and 3T3-L1 adipocytes. This is different from the order of potency of the same agonists at the β₁ or β₂-adrenoceptors. The sensitivity of the β₃-adrenoceptor to these catecholamines, expressed as pD₂ values, were virtually identical in both adipocyte types. Isoprenaline, noradrenaline, and adrenaline were almost full agonists in both cell types (intrinsic activity from 74% or 95%) during combined β₁, β₂- and α₂-adrenoceptor blockade. Antagonist potencies (expressed as pA₂ and using CGP 12177 as agonist) at the β₃-adrenoceptor were similar in both adipocyte types: bupranolol>propranolol>meto-prolol. The corresponding pA₂ values for bupranolol, propanolol and metoprolol were about 7, 6 and 5, respectively in both species. In conclusion, the pharmacological properties of classical catecholamines, P-adrenoceptor blockers and CGP 12177 are almost identical at the β₃-adrenoceptors of human omental adipocytes and 3T3-L1 adipocytes.     

beta-Amyrin and alpha-amyrin acetate isolated from the stem bark of Alstonia boonei display profound anti-inflammatory activity

Context: Alstonia boonei De Wild (Apocyanaceae) is used in ethnomedicine for the management of malaria, ulcer, rhematic pain, toothache, and inflammatory disorders.

Objective: To investigate the anti-inflammatory potential of β-amyrin and α-amyrin acetate isolated from the stem bark of Alstonia boonei using animal models.

Materials and methods: Chromatographic purification of the crude methanol extract led to the isolation and structure elucidation of β-amyrin and α-amyrin acetate. Their anti-inflammatory activities were evaluated in rodents using egg albumen-induced paw edema and xylene-induced ear edema models. The gastric ulcerogenic, in vivo leucocyte migration, and RBC membrane stabilization tests were also investigated.

Results: α-Amyrin acetate at 100?mg/kg showed significant (p?p?>?0.01) irritation of the gastric mucosa while significant (p?p?p?Discussion and conclusion: This study generally provided evidence of profound anti-inflammatory activity of β-amyrin and α-amyrin acetate isolated from the Alstonia boonei stem bark.     

Neutrophil-infiltrated paw edema induced by mannose-binding Dioclea violacea lectin

BackgroundThe potential edematogenic effect and the pharmacological characterization of a glucose-mannose-binding lectin from Dioclea violacea (DvL) were investigated.MethodsPaw edema was induced with DvL in control animals, and in animals pretreated with glucocorticoid or with blockers of histamine, nitric oxide synthase, cyclooxygenase, platelet activating factor (PAF), bradykinin and lipoxygenase.ResultsDvL-induced paw edema paralleled with an increase in vascular permeability and myeloperoxidase (MPO) activity. DvL-induced edema could be prevented by pre-treatment with the lectin-binding sugar α-D-methyl mannoside. Dexamethasone, meclizine and N^ω-nitro-L-arginine methyl ester hydrochloride (L-NAME) inhibited this effect.ConclusionsDvL induces edema, increase in vascular permeability and neutrophil infiltration. The edematogenic activity involves the lectin mannose-binding sites and is associated with histamine, cytokines and nitric oxide, since it could be treated with meclizine, dexamethasone and L-NAME.     

In vivo demonstration of α-adrenoceptor-mediated positive inotropy in pithed rats: evidence that noradrenaline does not stimulate myocardial α-adrenoceptors

1 This study examines whether positive inotropy via α-adrenoceptors could be observed in vivo in pithed rats. Cardiac contractility was measured as the maximum rate of rise of left ventricular pressure (dP/dt_max). Heart rate and aortic blood pressure were also recorded. 2 The selective α₁-adrenoceptor agonists, methoxamine, cirazoline, amidephrine and phenylephrine caused dose-related increases in dP/dt_max. This response was progressively reduced by increasing doses of the α₁-adrenoceptor antagonist prazosin. However, since the concomitant increase in diastolic blood pressure (DBP) was also blocked, the changes in dP/dt_max may have been a consequence of increased after load. 3 Adrenaline and noradrenaline also increased dP/dt_max, accompanied by pressor responses. Propranolol (1 mg kg^??1) antagonized the increase in dP/dt_max in response to noradrenaline, suggesting β-adrenoceptor involvement, but not that to adrenaline. The additional presence of prazosin (1 mg kg^??1) further shifted the dose–response curves for both noradrenaline and adrenaline to the right. 4 Analysis of the increases in dP/dt_max at predetermined increases in DBP by each agonist revealed three groups of regression lines. Adrenaline in the presence of propranolol and the four selective α₁-adrenoceptor agonists occupied a common central position. Above this group were adrenaline and noradrenaline in the absence of antagonists; their additional effects on contractility were β-adrenoceptor-mediated since the regression lines were lowered by propranolol. Clearly below the main group of agonists was noradrenaline in the presence of propranolol. 5 Thus, for a given increase in DBP, adrenaline (in the presence of β-blockade) and the α₁-adrenoceptor agonists exert an additional inotropic effect to noradrenaline (also in the presence of β-blockade). This is concluded to be an α-adrenoceptor-mediated increase in cardiac contractility which is not shared by noradrenaline.     

Qualitative Differences between the Inotropic Responses in Rat Papillary Muscles to α-Adrenoceptor and β-Adrenoceptor Stimulation by both Noradrenaline and Adrenaline

Abstract: Mammalian heart has obviously both α- and β-adrenergic inotropic mechanisms, and stimulation of these two mechanisms by appropriate agonists lead to qualitatively different inotropic responses. This difference can serve to recognize the two adrenergic inotropic effects. In order to explore if the endogenous catecholamines, noradrenaline and adrenaline, could activate both these mechanisms, and if so, to characterize them qualitatively and quantitatively, the mechanical responses in electrically driven rat left ventricular papillary muscles were examined in the absence or presence of appropriate receptor blockade. Isometric tension (T), rate of rise and decline of tension (first derivative = T) and rate of transition from tension rise to tension decline (negative part of second derivative=T) were recorded. α-Adrenergic and β-adrenergic inotropic effects were demonstrated both for noradrenaline and adrenaline. Maximal β-adrenoceptor stimulation (agonist in the presence of an α-adrenoceptor blocker) caused a small increase in T_max, intermediate increases in T'_max and T'_min, and a considerable increase in T_min (β-type effect). Maximal α-adrenoceptor stimulation (agonist in the presence of a β-adrenoceptor blocker) increased all parts of the contraction-relaxation cycle by about the same degree (T_minT_minT'_maxT_max α-type effect). While β-adrenoceptor stimulation gave a dose dependent and pronounced increase in the ratio T_min/T_max (relaxation-onset index), α-adrenoceptor stimulation decreased it to subcontrol values. The time course of the response to the α-adrenoceptor stimulation was characterized by a transient decrease in all qualities followed by an increase which reached maximum at 4–5 min. β-Adrenoceptor stimulation gave a monophasic inotropic response which developed in the course of 1–2 min. Both agents alone gave a monophasic response with the characteristics of a β-type effect (i.e. relative maximal increase of T_minT_minT_maxT_max), and a marked increase in the relaxation-onset index (T_min/T_max). Thus the β-adrenergic inotropic component was the dominating one when the amines were used alone. The two different response patterns probably reflect a dual mechanism of action of the endogenous catecholamines: the β-adrenergic component which is dependent upon an increase in cyclic AMP levels and the α-adrenergic component which is independent on cyclic AMP.     

Functional analysis of a recombinant PIII-SVMP, GST-acocostatin; an apoptotic inducer of HUVEC and HeLa, but not SK-Mel-28 cells

Disintegrins and disintegrin-like peptides interact with integrins and interfere with cell-cell and cell-matrix interactions. A disintegrin-like snake venom gene, Acocostatin was cloned from the venom gland mRNA of Agkistrodon contortrix contortrix. Acocostatin belongs to the PIII-SVMP subfamily of disintegrin-like peptides. The recombinant acocostatin peptide was produced and purified as GST-fusion. The GST-acocostatin peptide, at 44 μg/mL, inhibited platelet aggregation by 30% in PRP and 18% in whole blood. In addition GST-acocostatin, at 220 μg/mL, inhibited SK-Mel-28 cell migration by 48%, but did not inhibit T24 cell migration. The GST-acocostatin peptide ability to induce apoptosis on HUVEC, HeLa, and SK-Mel-28 cells was determined using Annexin V-FITC and chromatin fragmentation assays after 24 h of treatment. At 5 μM GST-acocostatin peptide, 19.68%+/− 3.09 of treated HUVEC, and 35.86% +/− 2.05 of treated HeLa cells were in early apoptosis. The GST-acocostatin peptide also caused chromatin fragmentation of HUVEC and HeLa cells as determined by fluorescent microscopy and Hoechst staining. The GST-acocostatin peptide failed to induce apoptosis of SK-Mel-28 cells. We characterized the HUVEC, HeLa, and T24 integrin expression by flow cytometry, as the first step in determining GST-acocostatin binding specificity. Our results indicate that HUVEC express αv, αvβ3, αvβ5, α6, β1, and β3 integrin receptors. HeLa cells express α1, α2, α6, αv, αvβ5, and β1 integrin receptors. T24 cells express α1, α3, α6, αv, αvβ3, αvβ5, β1, β3, and β6 integrin receptors.     

Effects of some adrenergic and cholinergic drugs on isolated spleen strips from the COD, Gadus morhua

The effects of drugs on isolated spleen strips from the cod, Gadus morhua, have been investigated. Affinities and intrinsic activities for various agonists were determined from cumulative dose-respinse curves. Contractions were produced by acetylcholine, methacholine or carbachol. The response to acetylcholine was considerably potentiated by the acetylcholinesterase inhibitor BW 284 C51. Methacholine-induced responses were competitively blocked by atropine (pA₂ = 8.2), indicating the presence of muscarinic receptors. Nicotine did not contract the spleen strips. Adrenaline, noradrenaline or phenylephrine contracted the preparations and so did isoprenaline in high concentrations. Competitive blockade of the noradrenaline-induced contraction was obtained with yohimbine (pA₂ = 6.1), phentolamine (pA₂ = 6.0) and propranolol (pA₂ = 3.4), and non-competitive blockade with phenoxybenzamine (pM₅₀ = 7.0), indicating that α-adrenoceptprs mediate the contractions produced by the adrenergic agonists. Isoprenaline caused a slight relaxation of preparations precontracted with methacholine. This effect was abolished by propranolol suggesting the presence of β-adrenoceptors. Judged from the pA-values for the competitive antagonists, arterial and capsular/trabecular smooth muscles have slightly different α-adrenoceptor properties.     

Beta-adrenoceptors invloved in inhibition of histamine release from sensitized guinea-pig lung.

Selective β-adrenoceptor agonists and antagonists were used to study the type of β-adrenoceptors involved in inhibiting antigen-induced histamine release from actively sensitized guinea-pig lung. Results obtained with six non-catechol β-adrenergic agonists were compared with those found in guinea-pig atrial (β₁) and tracheal (β₂) preparations. In terms of rank order the relative activities of the compounds differed in the three preparations. Dissociation constants (K_B values) for the cardioselective antagonist H93/26 were assessed using (?)-isoprenaline as an agonist. The K_B value for inhibition of histamine release was significantly different from, and intermediate between, the K_B values obtained in atria and trachea. In the guinea-pig tissues H35/25 was not a selective β-adrenoceptor antagonist; K_B values were not significantly different in the three preparations. The results using the β-adrenoceptor agonists and antagonists suggest that the β-receptors involved in inhibition of antigen-induced histamine release in the guinea-pig lung differ from those found in guinea-pig atria and trachea.     

Preliminary report: Comparison of the potencies of clonidine,B-HT 920, and B-HT 933 in reversing reserpine-induced ptosis in the mouse

The potencies of the α-adrenoceptor agonists clonidine, B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[5,4-d]-azepin), and B-HT 933 (2-amino-6-ethyl-4,5,7,8,-tetrahydro-6H-oxazolo-[5,4-d]-azepin; Azepexole) in reversing reserpine-induced ptosis in male NMRI mice were determined. Reserpine (2.5 mg/kg, i.p.) was administered 4 hr before intraperitoneal injection of the α-adrenoceptor agonists. All three α-adrenoceptor agonists produced dose-dependent reversal of ptosis, this effect being maximal at about 15–30 min after injection. At 30 min postinjection, on a mg/kg basis, clonidine-HCl was about 23 times more potent than B-HT 920-2 HCl and about 375 times more potent than B-HT 933 2-HCl in reversing ptosis. Although reversal of reserpine-induced ptosis in the mouse is not selective for α₂-adrenoceptor agonists, these results indicate that this test can be used to compare the relative potencies of three substances with pronouced α₂-adrenoceptor agonist activity.     

Differences between α-Adrenergic and β-Adrenergic Inotropic Effects in Rat Heart Papillary Muscles

Abstract: α-And β-adrenergic inotropic effects have been shown to be qualitatively different. In order to further characterize these differences we compared the mechanical responses to α- and β-adrenoceptor stimulation, respectively, in electrically driven left ventricular papillary muscles from rat heart. The muscles were stimulated by either isoprenaline (β-adrenoceptor stimulation), phenylephrine in the presence of propranolol (α-adrenoceptor stimulation) or phenylephrine alone (combined α- and β-adrenoceptor stimulation). Isometric tension (T), rate of rise and decline of tension (first derivative = T′) and rate of transition from tension rise to tension decline (negative part of second derivative = T″) were recorded. These recordings disclosed qualitative differences between the α- and β-inotropic response both in dose-response and time course experiments. Maximal β-adrenoceptor stimulation caused a small increase in T_max (18%), intermediate increases in T′_max (45%) and T′_min (68%) and a considerable increase in T″_min (145%) (“β-type” effect). Maximal α-adrenoceptor stimulation increased all qualities by about the same degree (23–24%) (“α-type” effect). While β-adrenoceptor stimulation gave a dose-dependent and pronounced increase in the ratio T″_min/T′_max (relaxation-onset index), α-adrenoceptor stimulation decreased it to subcontrol values and phenylephrine alone gave a small dose-dependent increase at higher doses. The time course of the α-adrenoceptor stimulation was characterized by a transient decrease in all qualities followed by an increase which reached maximum at 4–5 min. β-Adrenoceptor stimulation gave a monophasic response which reached maximum after 1–2 min. Phenylephrine alone gave mainly an “α-type” effect although T″_min increased significantly more in the absence than in the presence of propranolol and T″_min/T′_max showed a small increase which developed slowly. Thus β-adrenoceptor stimulation activated relaxation compared to contraction by a higher degree than did α-adrenoceptor stimulation. This probably reflects different mechanisms of action. While the α-effect may rely primarily on an increased calcium influx, the β-effect probably is the final result of several subcellular effects of cyclic AMP.     

Protective effects of the β3-adrenoceptor agonist CL316243 against N-methyl-D-aspartate-induced retinal neurotoxicity

We have previously reported that β₃-adrenoceptor agonists dilate retinal blood vessels, but their effects on retinal neurons have been unclear. In this study, we examined the action of the β₃-adrenoceptor agonist CL316243 against retinal damage induced by intravitreal injection of N-methyl-D-aspartate (NMDA) in rats. CL316243 was injected into the vitreous cavity before, with, or after intravitreal NMDA injection. Seven days after NMDA injection, cell loss in the ganglion cell layer (GCL) and thinning of the inner plexiform layer were observed. The reduction in the number of cells in the GCL was diminished by injection of CL316243 at 15, 30, 60, or 120?min after NMDA injection, whereas no significant protective effect was observed when CL316243 was administered 240?min after NMDA injection. Neither preinjection of CL316243 30?min before NMDA nor simultaneous injection of CL316243 with NMDA exerted any protective effect. The β₃-adrenoceptor antagonist L748337 almost completely abolished the protection conferred by CL316243 injection 120?min after NMDA injection. The number of parvalbumin-positive amacrine cells was decreased in eyes examined 1?day after NMDA treatment, but this was prevented by CL316243 injection at 120?min after NMDA injection. These results suggest that CL316243 exerts protective effects against NMDA-induced damage by stimulation of β₃-adrenoceptors. β₃-adrenoceptor agonists may be effective candidates for the treatment of retinal diseases associated with glutamate-induced excitotoxicity, including glaucoma and diabetic retinopathy.     

Inhibition of platelet aggregation by papaverine-like drugs: evidence for a novel mechanism of action.

Trimethoquinol [6,7-dihydroxy-1-(3′,4′,5′-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline] (TMQ) was chosen as a model compound for studying inhibition of platelet aggregation in vitro, because of its β-adrenoceptor agonist properties and structural resemblance to the anti-aggregatory agent, papaverine. TMQ inhibited collagen-induced aggregation of human platelet-rich plasma (I₅₀, 2 μM), the second wave of aggregation induced by 2.5 μM ADP (I₅₀, 0.9 μM), and the second wave of aggregation induced by 45 μM epinephrine (I₅₀, 2.5 μM). Collagen-induced aggregation of human washed platelets was inhibited by TMQ (I₅₀, 1 μM). TMQ was a better inhibitor than aspirin and papaverine and had an inhibitory activity similar to indomethacin in all of the systems studied. TMQ retained inhibitory activity in the presence of both β-adrenoceptor antagonist: propranolol (50 μM), and α-adrenoceptor antagonist: phentolamine (2.5 μM). Platelet adenylate cyclase was not activated and neither cAMP nor cGMP-phosphodiesterase activities were inhibited by TMQ, PGF_2α, biosynthesis by aggregating platelets during the coagulation of blood obtained from rats pretreated with aspirin (10 mg/kg, p.o.) or indomethacin (1 mg/kg, p.o.) was inhibited. However, similar pretreatment with TMQ (100 mg.kg, p.o.) and papaverine hydrochloride (100 mg/kg, p.o.) had no effect. TMQ acted synergistically with the aggregation inhibitors: papaverine, aspirin, and PGE₁. The in vitro inhibitory action of papaverine, aspirin, and TMQ was enhanced by increasing calcium concentration. These data indicate that the platelet anti-aggregation activity of TMQ, in contrast to its myocardial stimulating and bronchodilating mechanism, is independent of adrenergic activation. Cyclic AMP accumulation or prostaglandin biosynthesis also seem not to be involved in TMQ action. Therefore, it appears that TMQ may have a novel anti-aggregatory mechanism of action.     

Vascular permeability, neutrophil migration and edematogenic effects induced by the latex of Cryptostegia grandiflora

Inflammatory responses have been described as occurring after exposure to some latex materials. In this study pro-inflammatory activity in the latex of Cryptostegia grandiflora was investigated. The soluble proteins of the latex (CgLP) were isolated from the whole latex and evaluated by in vivo assays. CgLP induced strong inflammatory activity mediated by neutrophil migration, enlarging vascular permeability and increasing myeloperoxidase activity locally in rats. CgLP-induced inflammation was observed in peritonitis, paw edema and air push models. In addition, CgLP caused hyperemia in a healing model. The peritonitis effect was lost when CgLP was previously boiled suggesting the involvement of pro-inflammatory proteins. Thioglycollate increased the neutrophil migration induced by CgLP, but not by fMLP. Mast cell depletion provoked by 40/80 compound did not modify the course of inflammation triggered by CgLP, being similar to fMLP, which suggested that neutrophil migration was induced by direct mechanism mediated by macrophages. Neutrophil migration stimulated by CgLP was strongly inhibited by Dexamethasone and to a lesser extent by Thalidomide, indicating the involvement of cytokines in mediating neutrophil infiltration. Celecoxib and Indomethacin were inhibitory suggesting the involvement of prostaglandins. Cimetidine was effective only in the initial phase of edema. PCA 4248 was ineffective. It is concluded that the latex of C. grandiflora is a potent inflammatory fluid, and also that laticifer proteins may be implicated in this process.     

Effects of propranolol and L-NAME on β-adrenoceptor-mediated relaxation in rat carotid artery

1 The properties of β-adrenoceptors mediating vascular relaxation in rat isolated carotid artery were investigated. Ring segments of arteries were preconstricted with the thromboxane A₂ receptor agonist U-46619 and relaxation to β-adrenoceptor agonists determined. 2 Isoprenaline produced a concentration-dependent relaxation of U-44619-constricted arteries. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (1 μm ) although the shift was less (105 fold; pA₂, 8.02) than would be expected for an effect of isoprenaline at classical β-adrenoceptors (300–1000 fold; pA₂, 8.5–9). L-NAME (100 μm ) significantly reduced responses to isoprenaline, lowering the slope of the CRC and reducing the maximum response. 3 The selective β₃-adrenoceptor agonists, BRL 37344 and ZD2079, also produced concentration-dependent relaxation of the arteries. L-NAME (100 μm ) shifted the BRL 37344 CRC to the right 15 fold with no reduction in the slope or maximum response. L-NAME (100 μm ) had no significant effect on the ZD2079 CRC. 4 In conclusion, relaxation to isoprenaline in rat carotid artery is inhibited by propranolol in a manner suggesting a mixed population of classical (β₁-/β₂-) and atypical (β₃-) adrenoceptors. The presence of β₃-adrenoceptors was confirmed by the relaxant effects of the selective β₃-adrenoceptor agonists BRL 37344 and ZD2079. L-NAME attenuated responses to both isoprenaline and the β₃-adrenoceptor agonist BRL 37344, suggesting a role for endothelial release of nitric oxide in β-adrenoceptor mediated relaxation. However, the relaxant effect of BRL 37344 was attenuated by L-NAME to a lesser extent than that of isoprenaline. In addition, L-NAME had no effect on relaxation induced by ZD2079. These results suggest that there may be a differential contribution of endothelium to classical β-and β₃-adrenoceptor-mediated effects, with endothelium contributing less to β₃-adrenoceptor-mediated relaxation.     

Current and future pharmacotherapy for treating overactive bladder

Introduction: Drugs which prevent acetylcholine mediated involuntary detrusor contractions are the mainstay of overactive bladder(OAB) treatment but there are now several alternative therapeutic options available.

Areas covered: Current and future drug therapies for OAB are highlighted. These include novel antimuscarinic molecules (imidafenacin and tarafenacin); novel combination therapies with β3-adrenoceptor agonists or muscarinic agonists (tolenix) and a novel vaginal delivery method for oxybutynin. β3-adrenoceptor agonists(β3-AR) have been shown to be efficiacious in the management of OAB. The evidence supporting the first licensed β3-AR agonist, mirabegron, is assessed, as well as other putative β3-AR agonists in development such as solabegron, ritobegron, aryloxypropanolamine, TRK-380, and CL 316,243. The role of vaginal oestrogen is highlighted followed by a detailed analysis of botulinum-A toxin.

Expert opinion: Anticholinergics were the first OAB drug therapy on the market and have the largest dataset available. Despite obvious limitations, these are still first line medical therapy. There are a number of new OAB therapies under investigation and we await their contribution to the management armamentarium. Other novel drugs have been licenced and these are now vying for pole position in the treatment algorithm. One must exercise caution however until the long term effects of any new medicines are known.     

Both α1- and β-Adrenoceptor Stimulation Determine the Time Course of the Inotropic Effect of Noradrenaline in Rabbit Heart

It has been a matter of controversy whether α₁-adrenoceptor stimulation contributes to the final inotropic and lusitropic responses in mammalian myocardium to noradrenaline during concomitant and unopposed β-adrenoceptor stimulation. In the present paper we report studies that compare time courses of the inotropic and lusitropic responses to separate and combined α- and β-adrenoceptor stimulation, respectively, in electrically driven rabbit papillary muscles by a submaximal concentration of noradrenaline. Separate α₁- or β-adrenoceptor stimulation (presence of appropriate receptor blocker) showed the characteristic slow and fast development, respectively, of the inotropic responses. Qualitatively, the respective characteristic changes were also observed: α₁-adrenoceptor stimulation caused a negative lusitropic effect giving a prolongation of the time to peak tension (TPT), while β-adrenoceptor stimulation caused a pronounced positive lusitropic effect giving a shortening of TPT. The time course of the inotropic response to combined adrenoceptor stimulation had characteristics that deviated from the respective time courses to separate α₁- or β-adrenoceptor stimulation thus indicating a contribution from both adrenoceptor populations to the final inotropic response. Combined α₁- and β-adrenoceptor stimulation gave a pronounced positive lusitropic response as might be expected due to the obviously dominating role of the β-adrenergic component. However, the maximal lusitropic effect and the shortening of TPT were both slightly less during combined adrenoceptor stimulation compared to separate β-stimulation thus indicating an influence of the α₁ -adrenoceptor mediated negative lusitropic effect. Quantitatively, the separate α₁ - and the separate β-adrenoceptor mediated inotropic effects were not additive. In accordance with other recent studies, this indicated an inhibitory interaction between the two adrenergic receptor populations in myocardium.     

Characterization of the adrenoceptors in coronary arteries of pigs

The effects of phenylephrine and norepinephrine and the influence of adrenoceptor blockers on them were investigated on isolated strips of pig coronary arteries of different diameter. Phenylephrine contracted large coronary arteries, an effect inhibited by phentolamine, but was ineffective on small coronary arteries. Norepinephrine either relaxed large coronary arteries or occasionally contracted them. Phentolamine potentiated the relaxing effect of norepinephrine and propranolol inhibited or even reversed it into a contraction.Small coronary arteries were without exception relaxed by norepinephrine. This effect was not influenced by phentolamine but was inhibited by propranolol. These findings prove the presence of α-adrenoceptors in pig coronary arteries with a large diameter although β-adrenoceptors predominate; α-adrenoceptors are not found in coronary arteries with a small diameter.The classification of β-adrenoceptors in the coronary musculature into one of the two β-types was determined by comparing the affinities of propranolol, practolol and H 35/25 on the β-adrenoceptors of isolated atrial preparation of guinea pigs and of strips of pig coronary arteries. While the affinities of propranolol were the same to both organs the affinity of practolol to the myocardium was 100 times higher than to the coronary arteries. On the other hand the affinity of H 35/25 to the coronary arteries was three times higher than to the myocardium.The selective effects of the β₁-adrenoceptor blocker practolol on the myocardium and the β₂-adrenoceptor blocker H 35/25 on the coronary arteries indicate that the β-adrenoceptors of the coronary arteries should be classified as β₂-adrenoceptors.     

β2-adrenoceptor agonists can both stimulate and inhibit glucose uptake in mouse soleus muscle through ligand-directed signalling

The β-adrenoceptor agonists BRL37344 and clenbuterol have opposite effects on glucose uptake in mouse soleus muscle, even though the β₂-adrenoceptor mediates both effects. Different agonists may direct the soleus muscle β₂-adrenoceptor to different signalling mechanisms. Soleus muscles were incubated with 2-deoxy[1-¹⁴C]-glucose, β-adrenoceptor agonists, other modulators of cyclic AMP, and inhibitors of intracellular signalling. The adenylyl cyclase activator forskolin (1 μM), the phosphodiesterase inhibitor rolipram (10 μM) and BRL37344 (10, but not 100 or 1,000, nM) increased, whereas clenbuterol (100 nM) decreased, glucose uptake. Forskolin increased, whereas clenbuterol decreased, muscle cyclic AMP content. BRL37344 (10 nM) did not increase cyclic AMP. Nevertheless, protein kinase A (PKA) inhibitors prevented the stimulatory effect of BRL37344. Nanomolar but not micromolar concentrations of adrenaline stimulated glucose uptake. After preincubation of muscles with pertussis toxin (100 ng/ml), 100 nM clenbuterol, 0.1-10 μM adrenaline and 100 nM BRL37344 stimulated glucose uptake. Clenbuterol increased the proportion of phosphorylated to total β₂-adrenoceptor. Inhibitors of phosphatidylinositol 3-kinase (PI3K) and the stress-activated mitogen-activated protein kinase (MAPK), but not of the classical MAPK pathway, prevented stimulation of glucose uptake by BRL37344. Elevation of the cyclic AMP content of soleus muscle stimulates glucose uptake. Clenbuterol, and high concentrations of adrenaline and BRL37344 direct the β₂-adrenoceptor partly to Gα_i, possibly mediated by β₂-adrenoceptor phosphorylation. The stimulatory effect of 10 nM BRL37344 requires the activity of PKA, PI3K and p38 MAPK, consistent with BRL37344 directing the β₂-adrenoceptor to Gα_s. Ligand-directed signalling may explain why β₂-adrenoceptor agonists have differing effects on glucose uptake in soleus muscle.