Contribution of beta 1- and beta 2-adrenoceptors of human atrium and ventricle to the effects of noradrenaline and adrenaline as assessed with (-)-atenolol.

1. (-)-Atenolol was used as a tool to assess the function of beta 1- and beta 2-adrenoceptors in human heart. Right atrial and left ventricular preparations from patients undergoing open heart surgery were set up to contract isometrically. Membrane particles were prepared for beta-adrenoceptor labelling with [3H]-(-)-bupranolol and adenylate cyclase assays. 2. The positive inotropic effects of (-)-noradrenaline were antagonized to a similar extent by (-)-atenolol in atrial and ventricular preparations. (-)-Atenolol consistently antagonized the effects of (-)-adrenaline to a lesser extent than those of (-)-noradrenaline in atrial preparations. In ventricular preparations (-)-atenolol antagonized the effects of low concentrations of (-)-adrenaline to a lesser extent than those of high concentrations. 3. pKB values (M) of (-)-atenolol, estimated with non-linear analysis from the blockade of the positive inotropic effects of the catecholamines, were 7.4 for beta 1-adrenoceptors and 6.0 for beta 2-adrenoceptors. 4. (-)-Atenolol inhibited the binding of [3H]-(-)-bupranolol to ventricular beta 1-adrenoceptors with a pKD (M) of 5.9 and to ventricular beta 2-adrenoceptors with a pKD of 4.6. 5. (-)-Atenolol inhibited the catecholamine-induced adenylate cyclase stimulation in the atrium and ventricle with pKB values of 5.8-6.4 for beta 1- and pKB values of 4.7-5.7 for beta 2-adrenoceptors. The binding and cyclase assays suggest a partial affinity loss for (-)-atenolol inherent to membrane preparations. 6. beta 1-Adrenoceptors mediate the maximum positive inotropic effects of (-)-noradrenaline in both the atrium and ventricle of man. beta 2-Adrenoceptors appear to be capable of mediating maximal positive inotropic effects of (-)-adrenaline in atrium. In contrast, ventricular beta 2-adrenoceptors mediated only submaximal effects of (-)-adrenaline.     

Local modulation of noradrenaline release in vivo: presynaptic beta 2-adrenoceptors and endogenous adrenaline

Isoprenaline bitartrate (0.5 microgram/kg/min i.v.) increased the rate of noradrenaline release into the circulation of pentobarbitone-anesthetized rabbits. This increase was much greater than that produced by an equi-hypotensive dose of the vasodilator hydralazine (0.2 mg/kg i.v.), suggesting that it was only partly due to baro-reflex activation of sympathetic nerves. This facilitatory effect of isoprenaline was also observed in the nephrectomized, pithed rabbit, with electrically stimulated sympathetic outflow, ruling out central nervous system and renin-angiotensin effects. ICI 118,551 HCl (0.3 mg/kg + 0.1 mg/kg/h i.v.) blocked the isoprenaline-induced hypotension, but did not affect the isoprenaline-induced tachycardia, suggesting that it selectively blocked beta 2-adrenoceptors. ICI 118,551 totally abolished the isoprenaline-induced increase in noradrenaline release, suggesting a beta 2-effect. Atenolol (0.3 mg/kg + 0.1 mg/kg/h) blocked the isoprenaline-induced tachycardia, a beta 1-effect, but only slightly attenuated the isoprenaline-induced increase in noradrenaline release. Atenolol by itself decreased heart rate and arterial pressure, but there was no reflex rise in the noradrenaline release rate, which suggests that atenolol impairs baroreceptor activation of sympathetic nerves. In another series of experiments, also in the pentobarbitone-anesthetized rabbit, adrenaline was released into the circulation by splanchnic nerve stimulation. This resulted in prolonged increases of adrenaline levels in heart tissue. After the plasma adrenaline levels had returned to prestimulation values, the rate of noradrenaline release into the plasma was enhanced. This increase was not observed in rabbits treated with either desipramine HCl (1 mg/kg i.v.) or propranolol HCl (2 mg/kg i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of beta 1- and beta 2-adrenoceptors in rat skeletal muscles.

Binding studies with (-)-[125I]cyanopindolol (ICYP) were conducted to characterize beta-adrenoceptors in plantaris and soleus muscles of rats (male, 250-300 g). The distribution of beta 1- and beta 2-adrenoceptors in different muscle fiber types, identified in serial sections by succinic dehydrogenase (SDH) staining, was studied by autoradiography. The densities of binding sites (Bmax, fmol/mg protein) were 5.4 +/- 0.9 (mean +/- SEM) in plantaris and 11.5 +/- 2.0 in soleus muscle. In plantaris muscle, monophasic competition curves were observed when binding experiments were performed using CGP20712A (50 pM to 0.5 mM), a beta 1-adrenoceptor selective antagonist, or ICI 118,551 (50 pM to 20 microM), a beta 2-adrenoceptor selective antagonist, to compete for ICYP binding. Analysis with LIGAND revealed a single binding site with a KD value of 2.41 +/- 0.56 nM (mean +/- SEM) for ICI 118,551 and 8.93 +/- 3.00 microM for CGP 20712A, indicating the presence of a homogeneous population of beta 2-adrenoceptors. In soleus muscle, competition curves were biphasic with 16-21% beta 1-adrenoceptors. Autoradiographic studies supported the findings from binding studies with membrane homogenates. The ICYP binding pattern was associated closely with the muscle fiber types identified by SDH staining. Propranolol-resistant binding sites were observed, and these sites were associated with muscle fibers positive to SDH staining.     

Physiological antagonism between ventricular beta 1-adrenoceptors and alpha 1-adrenoceptors but no evidence for beta 2- and beta 3-adrenoceptor function in murine heart

1. Murine left atrium lacks inotropic beta(2)-adrenoceptor function. We investigated whether beta(2)-adrenoceptors are involved in the cardiostimulant effects of (-)-adrenaline on spontaneously beating right atria and paced right ventricular myocardium of C57BL6 mice. We also studied a negative inotropic effect of (-)-adrenaline. 2. Sinoatrial tachycardia, evoked by (-)-adrenaline was resistant to blockade by beta(2)-selective ICI 118,551 (50 nM) but antagonized by beta(1)-selective CGP 20712A (300 nM). This pattern was unaffected by pretreatment with pertussis toxin (PTX, 600 microg kg(-1) i.p. 24 h) which reversed carbachol-evoked bradycardia to tachycardia. 3. Increases of ventricular force by (-)-adrenaline and (-)-noradrenaline were not blocked by ICI 118,551 but antagonized by CGP 20712A. 4. Under blockade of beta-adrenoceptors, (-)-adrenaline and (-)-noradrenaline depressed ventricular force (-logIC(50)M=7.7 and 6.9). The cardiodepressant effects of (-)-adrenaline were antagonized by phentolamine (1 microM) and prazosin (1 microM) but not by (-)-bupranolol (1 microM). Prazosin potentiated the positive inotropic effects of (-)-adrenaline (in the absence of beta-blockers) from -logEC(50)M=6.2 - 6.8. 5. PTX-treatment reduced carbachol-evoked depression of ventricular force in the presence of high catecholamine concentrations. Inhibition of ventricular function of G(i) protein was verified by 82% reduction of in vitro ADP-ribosylation. PTX-treatment tended to increase the positive inotropic potency of (-)-adrenaline under all conditions investigated, including the presence of ICI 118,551. 6. (-)-Adrenaline causes murine cardiostimulation through beta(1)-adrenoceptors but not through beta(2)-adrenoceptors. The negative inotropic effects of (-)-adrenaline are mediated through ventricular alpha(1)-adrenoceptors but not through beta(3)-adrenoceptors. Both G(i) protein and alpha(1)-adrenoceptors restrain (-)-adrenaline-evoked increases in right ventricular force mediated through beta(1)-adrenoceptors.     

Agonist-specific activation of the beta2-adrenoceptor/Gs-protein and beta2-adrenoceptor/Gi-protein pathway in adult rat ventricular cardiomyocytes

In rat ventricular cardiomyocytes beta2-adrenoceptors (AR) couple to Gs- and Gi-protein, and evidence has accumulated that beta2-AR agonists can differentially activate either Gs- or Gs- and Gi-protein. In this study, in isolated adult rat ventricular cardiomyocytes, we assessed the effects of pertussis toxin (PTX) on beta2-AR agonist (terbutaline (TER), salbutamol (SAL) and fenoterol (FEN)) evoked inhibition of phenylephrine (PE)-induced increase in the rate of protein synthesis (assessed as [3H]phenylalanine incorporation) to find out which beta2-AR agonist activates selectively Gs- or Gs- and Gi-protein. PE (1 microM) increased the rate of protein synthesis from 100% to 130+/-2% (n = 34). FEN, TER and SAL (1 nM-10 microM) inhibited PE-induced increase in the rate of protein synthesis concentration-dependently. FEN inhibited PE effects almost completely (from 132+/-3 to 101+/-1%), whereas TER and SAL caused only partial inhibition (from 131+/-2 to 114+/-2 and 129+/-1 to 111+/-2%, respectively). Pretreatment of cardiomyocytes with PTX (250 ng ml(-1) for 16 h at 37 degrees C) did not affect FEN effects, but converted TER- and SAL-evoked partial inhibition into complete inhibition.Inhibitory effects of the three beta2-AR agonists were markedly attenuated by beta1-AR selective antagonist CGP 20712A (CGP) (300 nM); in contrast, beta2-AR selective antagonist ICI 118,551 (55 nM) inhibited the inhibitory effects of the three beta2-AR agonists only in PTX-pretreated cardiomyocytes,with beta1-AR blocked by CGP. We conclude that, in adult rat ventricular cardiomyocytes, FEN activates selectively the Gs protein-pathway, while TER and SAL activate the Gs- and Gi-protein pathways. Part of the effects of these three beta2-AR agonists appears to be mediated by beta1-AR.     

Independent regulation of beta 1- and beta 2-adrenoceptors.

1 The down-regulation of beta-adrenoceptors has been postulated as a biochemical marker of antidepressant efficacy. Here we demonstrate that chronic treatment with desipramine down-regulates beta 1-adrenoceptors in rat cerebral cortex and that beta-adrenoceptor subtypes can be independently regulated by treatment with different beta-adrenoceptor agonists. 2 Desipramine, (+/-)-clenbuterol, prenalterol, corwin (20 mg kg-1 daily) and corwin (10 mg kg-1 daily) were administered to male, Sprague-Dawley rats, over eight days, by means of osmotic Alzet pumps placed subcutaneously and removed 24 h before analysis. Control rats received vehicle only. The beta 1- and beta 2-adrenoceptor populations were measured in cerebral cortex by a modified (-)-[125I]-pindolol receptor binding assay. 3 The conventional antidepressant, desipramine, preferentially down-regulated beta 1-adrenoceptors whereas the non-selective beta-adrenoceptor agonist (+/-)-clenbuterol preferentially down-regulated beta 2-adrenoceptors. The beta 1-selective partial agonist, prenalterol, up-regulated beta 1-adrenoceptors perhaps acting more as an antagonist than as an agonist. Finally, neither dose of corwin had any significant effect on beta-adrenoceptor number.     

Effect of overexpressed adenylyl cyclase VI on beta 1- and beta 2-adrenoceptor responses in adult rat ventricular myocytes

1. Adenylyl cyclase VI (ACVI) is one of the most abundantly expressed beta adrenergic receptor (betaAR)-coupled cyclases responsible for cyclic AMP (cAMP) production within the mammalian myocardium. We investigated the role of ACVI in the regulation of cardiomyocyte contractility and whether it is functionally coupled with beta(1) adrenergic receptor (beta(1)AR). 2. Recombinant adenoviruses were generated for ACVI and for antisense to ACVI (AS). Adult rat ventricular myocytes were transfected with ACVI virus, AS or both (SAS). Adenovirus for green fluorescent protein (GFP) served as control. Myocyte contraction amplitudes (% shortening) and relaxation times (R50) were analysed. ACVI function was determined using cAMP assays. 3. ACVI-transfected cells demonstrated a strong 139 kDa ACVI protein band compared to controls. ACVI myocytes had higher steady-state intracellular cAMP levels than GFP myocytes when unstimulated (GFP vs ACVI=6.60+/-0.98 vs 14.2+/-2.1 fmol cAMP/viable cell, n=4, P<0.05) and in the presence of 1 microm isoprenaline or 10 microm forskolin. 4. ACVI myocytes had increased basal contraction (% shortening: GFP vs ACVI: 1.90+/-1.36 vs 3.91+/-2.29, P<0.0001) and decreased basal R50 (GFP vs ACVI: 62.6+/-24.2 ms (n=50) vs 45.0+/-17.2 ms (n=248), P<0.0001). ACVI myocyte responses were increased for forskolin (E(max): GFP=6.70+/-1.59 (n=6); ACVI=9.06+/-0.69 (n=14), P<0.01) but not isoprenaline. 5. ACVI myocyte responses were increased (E(max): GFP vs ACVI=3.16+/-0.77 vs 5.10+/-0.60, P<0.0001) to xamoterol (a partial beta(1)AR-selective agonist) under beta(2)AR blockade (+50 nm ICI 118, 551). AS decreased both control and ACVI-stimulated xamoterol responses (E(max): AS=2.59+/-1.42, SAS=1.38+/-0.5). ACVI response was not mimicked by IBMX. Conversely, response through beta(2) adrenergic receptor (beta(2)AR) was decreased in ACVI myocytes. 6. In conclusion, ACVI overexpression constitutively increases myocyte contraction amplitudes by raising cAMP levels. Native ACVI did not contribute to basal cAMP production or contraction amplitude and only to a minor extent to the forskolin response. beta(1)AR but not beta(2)AR coupling was dependent on ACVI.     

Modulation of noradrenaline release in slices of rat kidney cortex through alpha 1- and alpha 2-adrenoceptors

Slices of rat kidney cortex were incubated in [3H]noradrenaline, then placed in a flow cell and subjected to electrical field stimulation. At a stimulation frequency of 5 Hz, both the alpha 2-adrenoceptor antagonist idazoxan (0.1 microM) and the alpha 1-adrenoceptor antagonist prazosin (0.1 microM) significantly enhanced the stimulation-induced (S-I) outflow of radioactivity from the slice. However, neither clonidine (0.1 microM) nor methoxamine (10 microM), alpha 2- and alpha 1-agonists respectively, affected the S-I outflow of radioactivity at this stimulation frequency. At a lower stimulation frequency (1 Hz), the S-I outflow of radioactivity was not affected by idazoxan or prazosin, but was inhibited by both clonidine and methoxamine. The effect of clonidine was prevented by idazoxan (0.1 microM), but not by prazosin (0.1 microM). The effect of methoxamine was abolished by prazosin (0.1 microM), but not by idazoxan (0.1 microM). The inhibitory effect of methoxamine was not prevented by the prostaglandin synthesis inhibitor indomethacin (10 microM) or the adenosine receptor antagonist 8-phenyltheophylline (1 microM) and thus was not mediated by either prostaglandins or adenosine. The results suggest that both prejunctional alpha 1- and alpha 2-adrenoceptors are directly involved in modulation of noradrenaline release from the renal sympathetic nerves of the rat.     

Overexpression of beta 1-adrenoceptors in adult rat ventricular myocytes enhances CGP 12177A cardiostimulation: implications for 'putative' beta 4-adrenoceptor pharmacology

1. CGP 12177A mediates cardiostimulation by activation of the 'putative' beta(4)-adrenoceptor; however, it has recently been reported that disruption of the beta(1)-adrenoceptor gene abolishes this effect. We have adenovirally overexpressed beta(1)-adrenoceptors in isolated, cultured adult rat ventricular cardiomyocytes and observed the inotropic potency of isoprenaline and CGP 12177A (in the presence of 1 microm propranolol). 2. Isoprenaline was a full inotropic agonist at rat ventricular myocytes (pD(2) 7.69+/-0.12). CGP 12177A was a nonconventional partial agonist (pD(2) 6.34+/-0.09), increasing inotropy and lusitropy, with an intrinsic activity of 0.34 and antagonised by bupranolol. 3. beta(1)-adrenoceptor overexpression enhanced the inotropic potency of isoprenaline by 11.7-fold (pD(2) 8.76+/-0.14) and CGP 12177A by 5.9-fold (7.11+/-0.10), respectively. Green fluorescent protein (GFP) overexpression did not alter the potency of isoprenaline or CGP 12177A (pD(2) 7.41+/-0.24 and pD(2) 6.60+/-0.50, respectively). 4. The cardiostimulant effects of CGP 12177A were enhanced by IBMX (phosphodiesterase inhibitor) and decreased by Rp-cAMPS (cAMP antagonist). CGP 12177A also increased cAMP levels. CGP 12177A but not isoprenaline initiated arrhythmias at lower concentrations following beta(1)-adrenoceptor overexpression. 5. (125)I-Cyanopindolol saturation binding in Adv.beta(1) myocytes demonstrated approximately 18-fold increase in beta(1)-adrenoceptors. (3)H-CGP 12177A saturation binding, in the presence of propranolol, increased approximately 5-fold following overexpression of beta(1)-adrenoceptors. 6. This study demonstrates enhanced cardiostimulation by CGP 12177A (in the presence of propranolol) in rat ventricular myocytes overexpressing beta(1)-adrenoceptors, mediated by a Gs/cAMP signalling pathway. 'Putative' beta(4)-adrenoceptor pharmacology appears to be mediated by activation of a novel affinity state of the beta(1)-adrenoceptor.     

Direct demonstration of beta1- and evidence against beta2- and beta3-adrenoceptors, in smooth muscle cells of rat small mesenteric arteries

1 Recent evidence supports additional subtypes of vasodilator beta-adrenoceptor (beta-AR) besides the 'classical' beta(2). The aim of this study was to investigate the distribution of beta-ARs in the wall of rat mesenteric resistance artery (MRA), to establish the relative roles of beta-ARs in smooth muscle and other cell types in mediating vasodilatation and to analyse this in relation to the functional pharmacology. 2 We first examined the vasodilator beta-AR subtype using 'subtype-selective' agonists against the, commonly employed, phenylephrine-induced tone. Concentration-related relaxation was produced by isoprenaline (pEC(50): 7.70+/-0.1) (beta(1) and beta(2)). Salbutamol (beta(2)), BRL 37344 (beta(3)) and CGP 12177 (atypical beta) caused relaxation but were 144, 100 and 263 times less potent than isoprenaline; the 'beta(3)-adrenoceptor agonist' CL 316243 was ineffective. 3 In arteries precontracted with 5-HT or U 46619, isoprenaline produced concentration-related relaxation but salbutamol, BRL 37344, CGP 12177 and CL 316243 did not. SR 59230A, CGP 12177 and BRL 37344 caused a parallel rightward shift in the concentration-response curve to phenylephrine indicating competitive alpha(1)-AR antagonism, explaining the false-positive 'vasodilator' action against phenylephrine-induced tone. Endothelial denudation but not L-NAME slightly attenuated isoprenaline-mediated vasodilatation in phenylephrine and U 46619 precontracted MRA. 4 The beta-AR fluorescent ligand BODIPY TMR-CGP 12177 behaved as an irreversible beta(1)-AR antagonist in MRA and bound to the surface and inside vascular smooth muscle cells in intact vascular wall. Beta-ARs in smooth muscle cells were observed in a perinuclear location, consistent with the location of Golgi and endoplasmic reticulum. 5 Binding of BODIPY TMR-CGP 12177 was inhibited by BAAM (1 microM) in all three vascular tunics, confirming the presence of beta-ARs in adventitia, media and intima. Binding in adventitia was observed in both neuronal and non-neuronal cell types. Lack of co-localisation with a fluorescent ligand for alpha-ARs confirms the selectivity of BODIPY TMR-CGP 12177 for beta-ARs over alpha-ARs. 6 Our results support the presence of functional vasodilator beta(1)-ARs and show that they are mainly located in smooth muscle cells. Furthermore, we have demonstrated, for the first time, the usefulness of BODIPY TMR-CGP 12177 for identifying beta-AR distribution in the 'living' vascular wall.     

Xamoterol activates beta 1- but not beta 2-adrenoceptors in mammalian myocardium: comparison of its affinity for beta 1- and beta 2-adrenoceptors coupled to the adenylate cyclase in feline and human ventricle with positive inotropic effects

The mode of action of xamoterol, a beta 1-selective partial agonist, was investigated in feline myocardium. Xamoterol bound with an 18-fold greater affinity to ventricular beta 1-adrenoceptors (labeled with [3H](-)-bisoprolol) than to beta 2-adrenoceptors (labeled with [3H]ICI 118,551). Xamoterol had a 10-20-fold higher affinity for ventricular beta 1-adrenoceptors coupled to the adenylate cyclase than for cyclase-coupled beta 2-adrenoceptors. The intrinsic activity of xamoterol with respect to (-)-norepinephrine was 0.5 in right ventricular papillary muscles (force), 0.6 in left atria (force); 0.6 in right atria (sinoatrial rate) and 0.1-0.2 in ventricular membranes (cyclase). The stimulant effects of xamoterol were antagonized by beta 1-specific CGP 20,712 A but not by beta 2-selective ICI 118,551. Xamoterol activated only beta 1-adrenoceptors, while beta 2-adrenoceptors occupied by xamoterol remained silent. The positive inotropic effects of a nearly maximally effective xamoterol concentration were associated with a considerably greater beta 1-mediated cyclase stimulation than the same inotropic effect of (-)-norepinephrine. In human ventricular membranes xamoterol stimulated marginally the adenylate cyclase and antagonized the effects of (-)-norepinephrine with a 30-fold greater affinity for beta 1- than for beta 2-adrenoceptors.     

Binding properties of beta-blockers at recombinant beta1-, beta2-, and beta3-adrenoceptors

The human heart contains at least four distinct beta-adrenoceptor subtypes, three of which have been cloned. However, the binding properties of beta-blockers to the different beta-adrenoceptor subpopulations are not yet thoroughly characterized. Human beta1-, beta2- and beta3-adrenoceptors were expressed in COS-7 cells and [125I]iodocyanopindolol saturation binding, and competition experiments with commonly used beta-blockers were performed in the respective membrane preparations. Atenolol and metoprolol were about fivefold selective for beta1- versus beta2- and beta3-adrenoceptors. Bisoprolol was approximately 15-fold selective for beta1- versus beta2- and approximately 31-fold selective for beta1- versus beta3-adrenoceptors. Carvedilol was nonselective for any beta-adrenoceptor subtype. We conclude that the beta1-selectivities of atenolol, metoprolol, and bisoprolol are lower in COS cell membranes compared with previous investigations performed in native membranes. All beta-blockers investigated bind to beta3-adrenoceptors. Differential binding properties to beta3-adrenoceptors might imply different responses as to body weight, cardiac contractility, heart rate, and growth regulation. This might imply differential indications for the drugs investigated.     

Blockade of beta1- and beta2-adrenoceptors delays wound contraction and re-epithelialization in rats

1. The participation of sympathetic efferent fibres in wound healing is not well understood. The aim of the present study was to investigate the effects of beta(1)- and beta(2)-adrenoceptor blockade on rat excisional cutaneous wound healing. 2. Male rats were treated orally with propranolol dissolved in drinking water (50 mg/kg per day), whereas the control group received drinking water without propranolol. Propranolol was administered daily until rats were killed. A full-thickness excisional lesion was performed. The lesion area was measured to evaluate wound contraction. After rats had been killed, lesion and adjacent normal skin were formol fixed and paraffin embedded. Sections were stained with haematoxylin-eosin, Sirius red or Toluidine blue and immunostained for a-smooth muscle actin or proliferating cell nuclear antigen. 3. Propranolol-treated rats presented delayed wound contraction and epidermal healing and decreased hydroxyproline levels, collagen density and neo-epidermis thickness. Blockade of beta(1)- and beta(2)-adrenoceptors increased epidermal and connective tissue cell proliferation, polymorphonuclear leucocyte migration, myofibroblast density and mast cell migration. The volume density of blood vessels was increased and vessels were more dilated in propranolol-treated animals. 4. Thus, we conclude that beta(1)- and beta(2)-adrenoceptor blockade impairs cutaneous wound healing. This information should be considered by physicians during the treatment of patients who present with hypertension and problems in the healing process (such as venous ulcers).     

A study on the renal action of beta 1- and beta 2-adrenoceptors in rats

The present experiments were designed to study urine volume and urinary sodium excretion effects of beta-antagonists and beta-agonists with reference to beta 1- and beta 2-adrenoceptors in rats. The beta-antagonists used were atenolol as a selective beta 1-antagonist, butoxamine as a beta 2-antagonist and propranolol as a non-selective beta-antagonist. The beta-agonist used were salbutamol as a beta 2-agonist and isoproterenol as a non-selective beta-agonist. Beta-antagonists increased the urine volume and urinary sodium excretion, but beta-agonists decreased the urine volume and urinary sodium excretion. With regards to these effects, atenolol increased the urine volume more than urinary sodium excretion, isoproterenol decreased the urine volume more than urinary sodium excretion, and salbutamol decreased the urinary sodium excretion more than urine volume. When beta-antagonists were infused with a beta-agonist, the original diuretic effects of these beta-antagonists were inhibited by the beta-agonist. In these effects, beta-antagonists infused with isoproterenol inhibited urine volume more than urinary sodium excretion, but beta-antagonists infused with salbutamol inhibited urinary sodium excretion more than urine volume. These results indicate that the urine volume is related to beta 1-adrenoceptors, while the urinary sodium excretion is related to beta 2-adrenoceptors, although there is no selectivity towards either beta 1-adrenoceptors or beta 2-adrenoceptors as far as diuresis or antidiuresis is concerned.     

Regulation of beta 1- and beta 2-adrenoceptors following chronic treatment with beta-adrenoceptor antagonists

The effect of chronic pretreatment of guinea pigs with various beta-adrenoceptor antagonists on the binding characteristics of the radioligand 125I-cyanopindolol (ICYP) and responsiveness of adenylate cyclase to isoprenaline in the gastrocnemius muscle (beta 2-adrenoceptors) and the left ventricle (beta 1-adrenoceptors) were compared. Pretreatment of guinea pigs with propranolol or ICI 118,551 for one week significantly increased the density of the beta 2-adrenoceptors in the gastrocnemius muscle. Atenolol pretreatment for one week did not affect the density of the receptors. Pretreatment of the animals with pindolol for one week reduced the density of beta 2-adrenoceptors in skeletal muscle. In the left ventricle pretreatment of the guinea pigs with any of the antagonists did not alter either the density or the KD of beta 1-adrenoceptors. The responsiveness of adenylate cyclase to isoprenaline (10(-4) M) in the left ventricle or skeletal muscle was not affected when the guinea pigs were pretreated with propranolol. Pretreatment of the guinea pigs with reserpine (0.5 mg.kg-1) intraperitoneally for one week, to deplete catecholamines did not affect beta-adrenoceptor density or KD in the left ventricle or skeletal muscle. We conclude that the regulation of beta-adrenoceptors by the antagonist may not be caused by the prevention of the access of endogenous agonists to beta-adrenoceptors and it is dependent on the selectivity of the antagonist and on the susceptibility of the receptors to regulation.     

Blockade of beta 1- and desensitization of beta 2-adrenoceptors reduce isoprenaline-induced cardiac fibrosis

The aim of the present study was to analyse the role of beta(1)- and beta(2)-adrenoceptors in the catecholamine-induced myocardial remodeling, especially the interstitial fibrosis. Wistar rats were subjected to a 2-week chronic isoprenaline administration (30 microg/kg/h). Rats received a concomitant treatment with the selective beta(1)-adrenoceptor antagonist, bisoprolol (50 mg/kg/day p.o.) or were chronically pretreated with the selective beta(2)-adrenoceptor agonist salbutamol (40 microg/kg/h) for 1 week to induce beta(2)-adrenoceptor desensitization. The pretreatment with salbutamol induced a 59% down-regulation of left ventricular beta(2)-adrenoceptors compared to control. The extent of the isoprenaline-induced left ventricular fibrosis was significantly reduced in both the bisoprolol and salbutamol groups compared with the control isoprenaline-treated group especially in the apical region (1.7+/-0.6% and 1.4+/-0.3% versus 6.0+/-1.3%, respectively, P<0.005). beta(1)-adrenoceptor blockade and beta(2)-adrenoceptors down-regulation provided similar protection against isoprenaline-induced cardiac interstitial fibrosis suggesting that both beta-adrenoceptors are involved in such cardiac remodeling process.     

Functional beta1- and beta2-adrenoceptors in the left and right atrium of pre-hypertensive rats

There is a small increase in the functional beta2-adrenoceptor response on the spontaneously hypertensive rat (SHR) left atrium in the early stages of hypertension. In the present study, the functional beta1- and beta2-adrenoceptors of the left and right atrium in SHR pre-hypertension and age-matched (5-week-old) Wistar Kyoto (WKY) rats were characterized. Contractility methods with isoprenaline, T-0509 (a selective beta1-adrenoceptor agonist) and procaterol (a selective beta2-adrenoceptor agonist) were used. At 5 weeks, the SHRs were pre-hypertensive. Isoprenaline was more potent on the left atrium of 5-week-old SHRs than WKY rats. Bisoprolol, a selective beta1-adrenoceptor antagonist, was more potent against isoprenaline and T-0509 on the SHR than WKY rat left atrium. ICI 118,551, a selective beta(2)-adrenoceptor antagonist, was more potent against procaterol and T-0509 on the SHR than WKY rat left atrium. The results with bisoprolol and ICI 118,551 suggest that there are more functional beta(1)- and beta(2)-adrenoceptors on the left atrium of 5-week-old SHRs than WKY rats. Isoprenaline, T-0509 and procaterol were equipotent on the right atrium of 5-week-old WKY rats and SHRs. Bisoprolol was more potent against isoprenaline, T-0509 and procaterol on the SHR than WKY rat right atrium. ICI 118,551 was more potent against T-0509, but not isoprenaline and procaterol, on the SHR than WKY rat left atrium. This suggests there are more functional beta1-adrenoceptors, and probably more functional beta2-adrenoceptors, on the right atrium of 5-week-old SHRs than WKY rats. These functional differences in beta1- and beta2-adrenoceptor-mediated responses of the left and right atria of pre-hypertensive SHRs cannot be caused by hypertension, and may be associated with the onset of hypertension.     

Demonstration of both beta 1- and beta 2-adrenoceptors mediating relaxation of isolated ring preparations of rat pulmonary artery.

1 Cumulative concentration-response (relaxation) curves to three beta-adrenoceptor agonists, fenoterol (beta 2-selective), isoprenaline (non-selective) and noradrenaline (beta 1-selective) were obtained on isolated ring preparations of rat pulmonary artery contracted with 15 mM KCl. alpha-Adrenoceptors and neuronal and extraneuronal uptakes were blocked with phenoxybenzamine. The agonist concentration-response curves were reproducible. 2 Responses to each of the three agonists could be blocked by the beta-adrenoceptor antagonists atenolol (beta 1-selective) or ICI 118,551 (beta 2-selective) confirming the presence of beta-adrenoceptors. 3 The relative potencies of the agonists were isoprenaline : fenoterol : noradrenaline = 100 : 38 : 1.4. This indicated that the predominant beta-adrenoceptor type was beta 2. 4 Schild plots were obtained for atenolol and ICI 118,551 using the three different agonists. For each antagonist the location of the Schild plot varied depending on which agonist was used. This indicated that the beta-adrenoceptor population mediating relaxation responses to beta-adrenoceptor agonists was not homogeneous. 5 Atenolol was most potent when noradrenaline was the agonist and ICI 118,551 was most potent when fenoterol was the agonist. 6 It is concluded that isolated pulmonary artery ring preparations of the rat contain a mixed population of beta 1- and beta 2-adrenoceptors both mediating relaxation.     

The effects of adrenaline, noradrenaline and isoprenaline on inhibitory α- and β-adrenoceptors in the longitudinal muscle of the guinea-pig ileum

1. Two preparations, a segment of the ileum and the myenteric plexuslongitudinal muscle preparation, have been used for an analysis of the inhibitory effects of adrenaline, noradrenaline and isoprenaline on the contractor responses of the longitudinal muscle to acetylcholine or to electrical, coaxial or field, stimulation.2. Since the inhibitory effects of adrenaline, noradrenaline and isoprenaline on the acetylcholine-induced contractions were not affected by phenoxybenzamine but were antagonized by propranolol, it is concluded that beta-adrenoceptors are present on the muscle cells.3. The responses to electrical stimulation were suppressed by adrenaline or noradrenaline but only partly inhibited by isoprenaline. Propranolol antagonized the effect of isoprenaline and, to some extent, that of noradrenaline, but scarcely affected the action of adrenaline. Phenoxybenzamine, on the other hand, antagonized most of the effect of adrenaline and, to some extent, that of noradrenaline; it usually potentiated the effect of isoprenaline.4. The output of acetylcholine evoked by electrical stimulation was diminished by adrenaline or noradrenaline but was not affected by isoprenaline. The depressant effect on acetylcholine release was antagonized by phenoxybenzamine but not affected by propranolol; therefore these effects of adrenaline and noradrenaline are mediated by alpha-adrenoceptors.5. It may be assumed that alpha-adrenoceptors in situ are stimulated mainly by circulating adrenaline and possibly noradrenaline and thus cause a prejunctional inhibition at the nerve-smooth muscle junction.