Physiological Temperature Changes Fine-Tune 2- Adrenergic Receptor-Induced Cytosolic cAMP Accumulation

Norepinephrine (NE) controls many vital body functions by activating adrenergic receptors (ARs). Average core body temperature (CBT) in mice is 37°C. Of note, CBT fluctuates between 36 and 38°C within 24 hours, but little is known about the effects of CBT changes on the pharmacodynamics of NE. Here, we used Peltier element-controlled incubators and challenged murine hypothalamic mHypoA -2/10 cells with temperature changes of ±1°C. We observed enhanced NE-induced activation of a cAMP-dependent luciferase reporter at 36 compared with 38°C. mRNA analysis and subtype specific antagonists revealed that NE activates β 2- and β 3-AR in mHypoA-2/10 cells. Agonist binding to the β 2-AR was temperature insensitive, but measurements of cytosolic cAMP accumulation revealed an increase in efficacy of 45% ± 27% for NE and of 62% ± 33% for the β 2-AR-selective agonist salmeterol at 36°C. When monitoring NE-promoted cAMP efflux, we observed an increase in the absolute efflux at 36°C. However, the ratio of exported to cytosolic accumulated cAMP is higher at 38°C. We also stimulated cells with NE at 37°C and measured cAMP degradation at 36 and 38°C afterward. We observed increased cAMP degradation at 38°C, indicating enhanced phosphodiesterase activity at higher temperatures. In line with these data, NE-induced activation of the thyreoliberin promoter was found to be enhanced at 36°C. Overall, we show that physiologic temperature changes fine-tune NE-induced cAMP signaling in hypothalamic cells via β 2-AR by modulating cAMP degradation and the ratio of intra- and extracellular cAMP. SIGNIFICANCE STATEMENT: Increasing cytosolic cAMP levels by activation of G protein-coupled receptors (GPCR) such as the β 2-adrenergic receptor (AR) is essential for many body functions. Changes in core body temperature are fundamental and universal factors of mammalian life. This study provides the first data linking physiologically relevant temperature fluctuations to β 2-AR-induced cAMP signaling, highlighting a so far unappreciated role of body temperature as a modulator of the prototypic class A GPCR.

Visceral Fat: Higher Responsiveness of Fat Mass and Gene Expression to Calorie Restriction than Subcutaneous Fat

Visceral fat accumulation is accompanied by several metabolic disorders. Here, we investigate the improvement of visceral fat accumulation in the early phase of diet. Hyperlipidemic obese patients received a low-calorie diet (1000 kcal/day) for 14 days. Visceral and subcutaneous fat accumulation was analyzed using ultrasonography. After 14 days of the diet, the average visceral fat of obese patients obviously decreased (P < 0.05), as well as the visceral fat-related secreted proteins, whereas subcutaneous fat did not decrease in these patients. These results show that visceral fat is reduced significantly in the early phase of diet therapy in humans. Therefore, to clarify its mechanism, we analyzed the expression of lipid metabolism-related genes in visceral and subcutaneous fat using obese rats. The Long-Evans Tokushima Otsuka (LETO) rats, as an obese model, were divided into two groups: fasting and non-fasting. The gene expressions in visceral and subcutaneous fat were measured by reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of beta(3)-adrenergic receptor (AR), hormone sensitive lipase (HSL), peroxisome proliferator-activated receptor (PPAR)-gamma, and uncoupling protein (UCP)-2 genes increased by 3.2-, 2.3-, 2.2-, and 2-fold in visceral fat (P < 0.01), but remained almost unchanged in subcutaneous fat. Taken together, the responsiveness of lipid metabolism-related genes to fasting is more sensitive in visceral fat than in subcutaneous fat in rats, suggesting that the different responsiveness to calorie restriction in fat tissues is due to the different induction of metabolism-related gene expression.

Cold Exposure Induces Proliferation of Mature Brown Adipocyte in a ß3-Adrenergic Receptor-Mediated Pathway

Hyperplasia of brown adipose tissue (BAT) is a fundamental mechanism for adaptation to survive in the cold environment in rodents. To determine which cell types comprising BAT contribute to tissue hyperplasia, immunohistochemical analysis using a proliferative marker Ki67 was performed on the BAT from 6-week-old C57BL/6J mice housed at 23°C (control) or 10°C (cold) for 5 days. Interestingly, in the control group, the cell proliferative marker Ki67 was detected in the nuclei of uncoupling protein 1-positive mature brown adipocytes (7.2% ± 0.4% of brown adipocyte), as well as in the non-adipocyte stromal-vascular (SV) cells (19.6% ± 2.3% of SV cells), which include preadiopocytes. The percentage of Ki67-positive brown adipocytes increased to 25.6% ± 1.8% at Day 1 after cold exposure and was significantly higher than the non-cold acclimated control until Day 5 (21.8% ± 1.7%). On the other hand, the percentage of Ki67-positive SV cells gradually increased by a cold exposure and peaked to 42.1% ± 8.3% at Day 5. Injection of a ß3-adrenergic receptor (ß3-AR) agonist for continuous 5 days increased the number of Ki67-positive brown adipocytes even at Day 1 but not that of SV cells. In addition, the ß3-AR antagonist, but not ß1-AR antagonist, attenuated the cold exposure-induced increase in the number of Ki67-positive brown adipocytes. These results suggest that mature brown adipocytes proliferate immediately after cold exposure in a ß3-AR-mediated pathway. Thus, proliferation of mature brown adipocytes as well as preadipocytes in SV cells may contribute to cold exposure-induced BAT hyperplasia.

The expression of β3-adrenoceptors and their function in the human prostate

BACKGROUND

Little is known about β3-adrenoceptor (AR) expression and function in human prostate. We examined the expression and distribution of β-AR subtypes in normal prostate and benign prostatic hyperplasia (BPH) tissues, and investigated which selective β-AR subtype agonist was most involved in the relaxation of isolated human prostate strips.

METHODS

Messenger RNA (mRNA) expression for β1-, β2-, and β3 -ARs was investigated using reverse transcriptase-polymerase chain reactions (RT-PCR). Quantitative analysis of mRNA expression of β-AR subtypes between normal prostate and BPH tissues was performed using quantitative RT-PCR (qPCR). Distributions were examined by immunohistochemistry (IHC). Strips of human normal prostate or BPH were suspended in organ baths and exposed to isoproterenol, dobutamine, procaterol, and TRK-380 to investigate their relaxant effects on KCl-induced contractions, and their inhibitory effects on electrical field stimulation (EFS)-induced contractions.

RESULTS

We confirmed the presence of mRNA for β1-, β2-, and β3-ARs both in normal prostate and in BPH tissues. For β3-AR, mRNA expression in BPH tissues was significantly higher than in normal prostate tissues, but there was no significant difference in β1- and β2-AR expression between normal and BPH tissues. IHC revealed differences in staining intensity between smooth muscle cells and glandular cells, with different proportions for different β-AR subtypes. Staining of β3-AR was particularly intense in smooth muscle cells as opposed to glandular cells. Isoproterenol and TRK-380 significantly decreased the tone of KCl-induced contractions of the normal prostate strips. The rank order of relaxant effects was isoproterenol > TRK-380 > procaterol > dobutamine. All selective β-AR agonists significantly decreased the amplitude of EFS-induced contractions of the normal prostate strips. The rank order of inhibitory effects was isoproterenol > dobutamine >TRK-380 > procaterol. In BPH strips, all selective β-AR agonists showed no significant relaxant or inhibitory effects on KCl- or EFS-induced contractions.

CONCLUSIONS

β3 -AR is abundant in human prostate smooth muscle, whose relaxation is mediated by β1- and β3-AR stimulation. β3-AR agonists may have clinical use in the treatment of male non-BPH patients or neurogenic bladder patients with voiding dysfunction.

Tissue functions mediated by beta(3)-adrenoceptors-findings and challenges

As β₃-adrenoceptor agonists metamorphose from experimental tools into therapeutic drugs, it is vital to obtain a comprehensive picture of the cell and tissue functions mediated by this receptor subtype in humans. Human tissues with proven functions and/or a high expression of β₃-adrenoceptors include the urinary bladder, the gall bladder, and other parts of the gastrointestinal tract. While several other β₃-adrenoceptor functions have been proposed based on results obtained in animals, their relevance to humans remains uncertain. For instance, β₃-adrenoceptors perform an important role in thermogenesis and lipolysis in rodent brown and white adipose tissue, respectively, but their role in humans appears less significant. Moreover, the use of tools such as the agonist BRL 37344 and the antagonist SR59230A to demonstrate functional involvement of β₃-adrenoceptors may lead in many cases to misleading conclusions as they can also interact with other β-adrenoceptor subtypes or even non-adrenoceptor targets. In conclusion, we propose that many responses attributed to β₃-adrenoceptor stimulation may need re-evaluation in the light of the development of more selective tools. Moreover, findings in experimental animals need to be extended to humans in order to better understand the potential additional indications and side effects of the β₃-adrenoceptor agonists that are beginning to enter clinical medicine.

Potent oxindole based human β3 adrenergic receptor agonists

The synthesis and biological evaluation of a series of oxindole beta(3) adrenergic receptor agonists is described. A modulation of rat atrial tachycardia was observed with substitution at the 3-position of the oxindole moiety.

Effect of β-Blockers on β3-Adrenoceptor Expression in Chronic Heart Failure

OBJECTIVES

To investigate the expression of beta(3)-adrenoceptors in rats with chronic heart failure, and to explore the effect of beta-blockers on beta(3)-adrenoceptor expression.

MATERIALS AND METHODS

Thirty-two male Wistar rats were divided into Sham (n = 10) and heart failure (n = 22) groups. The heart failure group was treated with normal saline (Heart Failure Control, n = 6), Metoprolol (n = 8) or Carvedilol (n = 8) for 3 months.

RESULTS

The left ventricular end systolic pressure (LVESP) and the absolute values of maximal rate of rise and fall of left ventricular pressure (+/-dP/dt max) in the heart failure group were lower than in the Sham group (P < 0.01), whereas the left ventricular end diastolic pressure (LVEDP) was higher (P < 0.01). The LVESP and dP/dtmax in the Carvedilol group were higher than the Metoprolol group whereas LVEDP was lower (P < 0.01). The left ventricular mass index (LVMI) in the Carvedilol group was less than the Metoprolol and Heart Failure Control groups (P < 0.01). The level of beta(3)-adrenoceptor expression in the study groups was significantly higher than the Sham group (P < 0.01). beta(3)-adrenoceptor expression in the Carvedilol group was lower than the Heart Failure Control and Metoprolol groups (P < 0.01).

CONCLUSION

beta(3)-adrenoceptor expression is increased in the failing ventricles in rats. Carvedilol is more effective than Metoprolol for improving the hemodynamics and in attenuating ventricular remodeling after heart failure. Carvedilol, rather than Metoprolol, diminishes beta(3)-adrenoceptor expression in the failing ventricles.

The full expression of fasting-induced torpor requires beta 3-adrenergic receptor signaling

Torpor, a controlled rapid drop in metabolic rate and body temperature (Tb), is a hypometabolic adaptation to stressful environmental conditions, which occurs in many small mammals, marsupials, and birds. To date, signaling pathways required for torpor have not been identified. We examined the role of the sympathetic nervous system (SNS) in mediating the torpor adaptation to fasting by telemetrically monitoring the Tb of dopamine beta-hydroxylase knock-out (Dbh-/-) mice, which lack the ability to produce the SNS transmitters, norepinephrine (NE), and epinephrine. Control (Dbh+/-) mice readily reduced serum leptin levels and entered torpor after a fast in a cool environment. In contrast, Dbh-/- mice failed to reduce serum leptin and enter torpor under fasting conditions, whereas restoration of peripheral but not central NE lowered serum leptin levels and rescued the torpor response. Torpor was expressed in fasted Dbh-/- mice immediately after administration of either the nonselective beta-adrenergic receptor agonist isoproterenol or the beta3-adrenergic receptor (AR)-specific agonist CL 316243 [disodium (RR)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxazole-2,2-dicarboxylate], but not after administration of beta1, beta2, or alpha1 agonists. Importantly, the beta3-specific antagonist SR 59230A [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate] severely blunted fasting-induced torpor in control mice, whereas other AR antagonists were ineffective. These results define a critical role of peripheral SNS activity at beta3-AR-containing tissues in the torpor adaptation to limited energy availability and cool ambient temperature.

Induction of β3-Adrenergic Receptor Functional Expression following Chronic Stimulation with Noradrenaline in Neonatal Rat Cardiomyocytes

This study aimed to characterize beta(3)-adrenergic receptors (ARs) in rat neonatal cardiomyocytes using the noradrenaline (NOR) properties to modulate the expression and function of the three beta-ARs. We assessed the effect of NOR (physiological nonselective agonist), isoprenaline (ISO, beta-nonselective agonist), dobutamine (DOB, beta(1)-selective agonist), and procaterol (PROC, beta(2)-selective agonist) on cAMP accumulation using cardiomyocytes untreated or treated with 100 microM NOR for 24 h. The inhibition of forskolin-stimulated cAMP accumulation was determined using NOR, isoprenaline, and the beta(3)-selective agonists 4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid (BRL 37344) and 5-[-2-([-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316243). The experiments were performed in the absence or presence of propranolol or 2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide methanesulfonate (CGP 20712A) and/or 1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI 118551) to inhibit beta(1)- and beta(2)-AR stimulation and 1-(2-ethylphenoxy)-3-[[1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino-(2S)-2-propanol hydrochloride (SR 59230A) (beta(3)-selective antagonist). In addition, the level of the three subtypes was determined by reverse transcription polymerase chain reaction and Western blotting. NOR pretreatment decreased the activation of cAMP induced by NOR, isoprenaline, and DOB, whereas PROC response was abolished. The inhibition of NOR response by CGP 20712A or ICI 118551 demonstrated that beta(1)- and beta(2)-ARs are down-regulated and that beta(2)-AR functional activity was also abolished in cardiomyocytes exposed to chronic stimulation. beta(3)-AR function was observed with NOR and ISO when beta(1)-/beta(2)-ARs were blocked and with both beta(3)-selective agonists in NOR-treated cells only. This response was completely inhibited by SR 59230A and involved G(i) protein. Furthermore, the results from functional studies agree well with those from expression experiments. In conclusion, these data provide strong evidence that beta(3)-ARs are functionally up-regulated and coupled to G(i) protein in rat neonatal cardiomyocytes following chronic exposure to NOR when beta(1)- and beta(2)-ARs are down-regulated.

[Vascular beta-adrenergic remodeling in rat transgenic model over-expressing endothelial beta3-adrenoceptors]

In rat thoracic aorta, the stimulation of endothelial beta3-adrenoceptors (beta-AR) produces a vasorelaxation through activation of a NO synthase pathway and an increase in cGMP levels. In hypertension, a global decrease of the beta-AR response has been described. In spontaneously hypertensive rats (SHR), we have shown that beta3-adrenoceptor-mediated relaxation was not modified in SHR aorta at the age of 12 weeks, in spite of an upregulation of beta3-adrenoceptors. In order to determine the consequences of an over-expression of the beta3-AR, we have developed a transgenic rat over-expressing specifically in endothelial cells the human beta3-AR (Tg beta3). By real-time quantitative PCR, we have determined the expression level of the different beta-AR subtypes. We confirmed an over-expression of the beta3-AR transcripts in Tg beta3 (ratio = 3.39 +/- 0.8; n=3 for Tg beta3 vs wild type [WT] animals). Surprisingly, we observed in Tg beta3 a decrease of beta1-AR transcripts (ratio = 0.76 +/- 0.03; n=3 for Tg beta3 vs WT animals) and no variation for beta2-AR transcripts (ratio = 1.95 +/- 0.60; n=3 for Tg beta3 vs WT animals). In aorta rings from WT and Tg beta3, the isoproterenol-induced relaxation was similar (WT: Emax = 82 +/- 6%, n=6; Tg beta3: Emax = 85 +/- 6, n=6). By contrast, in the presence of 10 microM nadolol, a beta1-, beta2-AR antagonist, the isoproterenol-induced response was significantly increased in Tg beta3 (WT: Emax = 68 +/- 6%, n=6: Tg beta3: Emax = 86 +/- 3; p < 0.01 vs WT). This effect was loss on denuded aortic rings. In conclusion, our study reported similar results to those obtained in hypertension in which a decrease of the beta-AR expression was associated to an elevation of the beta3-AR density. Moreover, this over-expression in our transgenic model is associated to a potential response induced by beta3-AR. Therefore, an activation of beta3-AR could supply the beta1- / beta2-AR decrease. Then, our transgenic model should be used to characterize the physiological consequences of this over-expression as well as to determine the putative involvement of this receptor in the pathogenesis of hypertension.

Evidence for the Presence of Beta-3-Adrenoceptors Mediating Relaxation in the Human Oviduct

Beta1- and beta2-adrenoceptors mediate relaxation in the oviductal smooth muscle. This study examines the existence and function of beta3-adrenoceptors in the human oviduct. Ring segments of the oviduct were set up for isometric tension recording. The effect of isoprenaline and BRL 37344 on smooth muscle tone was examined. The expression of beta3-adrenoceptors in the oviduct was also examined. Isoprenaline and BRL 37344 concentration-dependently relaxed circular muscles of the oviduct. BRL 37344 was less potent than isoprenaline and was a partial agonist. Propranolol shifted isoprenaline but not BRL 37344 concentration-response curve to the right without reducing the maximum response. Cyanopindolol (1 micromol/l), a beta3-adrenoceptor antagonist, shifted the isoprenaline concentration response curve to the right. The -log K(B) value of 7.8 indicates activation of beta3-adrenoceptors by isoprenaline. mRNA for beta3-adrenoceptors was expressed in the oviduct. These results suggest that beta3-adrenoceptors, mediating relaxation, are expressed in the human oviduct.

Endothelial beta3-adrenoceptors mediate vasorelaxation of human coronary microarteries through nitric oxide and endothelium-dependent hyperpolarization

BACKGROUND

Coronary vessel tone is modulated in part by beta-adrenergic relaxation. However, the implication of specific beta-adrenoceptor subtypes and their downstream vasorelaxing mechanism(s) in human coronary resistance arteries is poorly defined. beta3-Adrenoceptors were recently shown to vasodilate animal vessels and are expressed in human hearts.

METHODS AND RESULTS

We examined the expression and functional role of beta3-adrenoceptors in human coronary microarteries and their coupling to vasodilating nitric oxide (NO) and/or hyperpolarization mechanisms. The expression of beta3-adrenoceptor mRNA and protein was demonstrated in extracts of human coronary microarteries. Immunohistochemical analysis revealed their exclusive localization in the endothelium, with no staining of vascular smooth muscle. In contractility experiments in which videomicroscopy was used, the nonspecific beta-agonist isoproterenol and the beta3-preferential agonist BRL37344 evoked an approximately 50% relaxation of endothelin-1-preconstricted human coronary microarteries. Relaxations were blocked by the beta1/beta2/beta3-adrenoceptor antagonist bupranolol but were insensitive to the beta1/beta2-adrenoceptor antagonist nadolol, confirming a beta3-adrenoceptor-mediated pathway. Relaxation in response to BRL37344 was absent in human coronary microarteries devoid of functional endothelium. When human coronary microarteries were precontracted with KCl (thereby preventing vessel hyperpolarization), the relaxation to BRL37344 was reduced to 15.5% and totally abrogated by the NO synthase inhibitor L-omega-nitroarginine, confirming the participation of a NO synthase-mediated relaxation. The NO synthase-independent relaxation was completely inhibited by the Ca2+-activated K+ channel inhibitors apamin and charybdotoxin, consistent with an additional endothelium-derived hyperpolarizing factor-like response. Accordingly, membrane potential recordings demonstrated vessel hyperpolarization in response to beta3-adrenoceptor stimulation.

CONCLUSIONS

Beta3-adrenoceptors are expressed in the endothelium of human coronary resistance arteries and mediate adrenergic vasodilatation through both NO and vessel hyperpolarization.

β3-Adrenoceptors: relaxant function and mRNA detection in smooth muscle cells isolated from the human colon

Functional involvement of β3-adrenoceptors in controlling human gastrointestinal motility has not been unequivocally assessed yet. The direct myogenic contribution of these receptors was examined, by in vitro functional studies and analysis of mRNA expression, on smooth muscle cells separately isolated from taenia coli and circular muscle layers of the human colon. Isoproterenol, a nonselective β-adrenoceptor agonist, relaxed, in a concentration-dependent manner, both human taenia coli and circular colonic smooth muscle cells, although displaying a higher intrinsic activity (65.3 ± 2.3 vs. 55.2 ± 1.4% maximal relaxation) and potency (pEC50: 7.41 ± 0.07 vs. 6.32 ± 0.08) were greater on taenia coli than circular cells. In the presence of the β1-antagonist CGP20712A and of the β2-antagonist ICI 118,551, a 25–30% decrease in isoproterenol intrinsic activity was observed on both cell types and on taenia coli, the nonselective β1/β2-antagonist propranolol produced a rightward shift of the isoproterenol concentration-response curve with mean estimated pKB values (8.12 ± 0.27 at 0.1 µM and 6.45 ± 0.13 at 1 µM) lower than that expected for both β1- and β2-adrenoceptors. CGP12177A and SR 58611A, two β3-adrenoceptor agonists, presented an intrinsic activity comparable to that of isoproterenol in the presence of β1- and β2-antagonists, the former being more potent on taenia coli than on circular smooth muscle cells. β3-Adrenoceptor mRNA was detected by reverse transcription PCR on both cell types. These results strongly suggest a direct functional role of β3-adrenoceptors in the human colon.Key words: adrenoceptors, β3-adrenoceptors, smooth muscle cells, taenia coli, human colon.

Differences in the expression of lipolytic-related genes in rat white adipose tissues

We have investigated in vivo whether the gene expression of the beta3-adrenergic receptor (beta3-AR), perilipin A, hormone-sensitive lipase (HSL), and adipocyte lipid-binding protein (ALBP/aP2) is regulated in a site-specific manner. To induce lipolysis and discriminate between short- and long-term modifications, rats were submitted to an experimental fast for one or five days followed or not by refeeding. The mRNA encoding beta3-AR in retroperitoneal adipose tissue (RP) was significantly increased by one and five days of fasting (4-fold) and then lowered by one day of refeeding (2-fold) compared to fed rats. The reverse trend was observed for perilipin A expression in one day fasted rats. HSL mRNA concentrations were significantly induced (2.2-fold) by five days of fasting relative to fed animals and remained high after refeeding. ALBP/aP2, peroxisome proliferator-activated receptor gamma, and CAAT/enhancer binding protein alpha mRNA levels were essentially unaffected by dietary manipulations. Fasting and/or refeeding were similarly ineffective at regulating gene expression in SC. These data provide a molecular basis for regional differences at different steps of the lipolytic process.

Effects of rearing temperature on sympathoadrenal activity in young adult rats

Animals reared at 18 degrees C exhibit enhanced innervation of brown adipose tissue (BAT) and greater cold tolerance as adults, yet gain more weight when fed an enriched diet compared with rats reared at 30 degrees C. To explore this paradox, sympathoadrenal activity was examined using techniques of [(3)H]norepinephrine ([(3)H]NE) turnover and urinary catecholamine excretion in male and female rats reared until 2 mo of age at 18 or 30 degrees C. Gene expression in BAT was also analyzed for several sympathetically related proteins. Although [(3)H]NE turnover in heart did not differ between groups, [(3)H]NE turnover in BAT was consistently elevated in the 18 degrees C-reared animals, even 2 mo after removal from the cool environment. Gene expression for uncoupling proteins 1 and 3, GLUT-4, leptin, and the alpha(1A)-adrenergic receptor was more abundant in BAT and the increase in epinephrine excretion with fasting suppressed in 18 degrees C-reared animals. These studies demonstrate that obesity consequent to exposure to 18 degrees C in early life occurs despite tonic elevation of sympathetic input to BAT. Diminished adrenal epinephrine responsiveness to fasting may play a contributory role.

Enhanced cAMP response of naturally occurring mutant of human beta3-adrenergic receptor

We have examined the functional significance of the naturally occurring mutation at position 64 of human beta3-adrenergic receptor (beta3AR), which changes the amino acid from tryptophan to arginine (W64R-beta3AR). The affinities of betaAR agonists for W64R-beta3AR expressed in COS-7 cells were not significantly different from those for wild type beta3AR. When two receptors are expressed at various expression levels, and stimulated with CGP12177A, they showed essentially the same EC50 values and maximal responses. Overexpression of Gi and Go, or the treatment with pertussis toxin did not affect the agonist-induced cAMP response, suggesting that Gi and Go did not contribute to the beta3AR-induced cAMP response. However, the enhanced cAMP response was observed when W64R-beta3AR was coexpressed with the adenylyl cyclase type III isoform, and stimulated by CGP12177A and isoproterenol. These results indicate that the cAMP response of W64R-beta3AR can be enhanced under the particular condition that adenylyl cyclase type III was coexpressed.

Effect of oleoyl-estrone treatment on the expression of beta1- beta2- and beta3-adrenoreceptors in rat adipose tissues

Adult female rats received a constant i.v. infusion of oleoyl-estrone (3.5 pmol/kg day) in a lipidic suspension for 14 days. On days 0 (no treatment), 3, 6, 10 and 14, as well as on day 14 for controls (receiving only the lipid); the rats were killed and the expression of the beta1-, beta2- and beta3-adrenoceptor genes, in brown adipose tissue and in subcutaneous and periovaric white adipose tissue, were measured by RNA protection assay, and compared with that of cyclophyllin. The beta3-adrenoceptor was the most expressed in all adipose tissues, whereas beta2 was the less expressed in brown adipose tissue. Oleoyl-estrone significantly, but moderately, increased the expression of beta-adrenoceptors in the three adipose tissues: beta1 increased in subcutaneous, beta2 and beta3 in periovaric and beta3 in brown adipose tissue. Oleoyl-estrone also decreased beta3 expression in subcutaneous white adipose tissue. On day 10, adipocytes isolated from periovaric white adipose tissue of oleoyl-estrone-treated rats showed higher cAMP response to an isoproterenol challenge than the controls. The mechanism by which oleoyl-estrone elicits the wasting of fat reserves could be mediated by adrenergic pathways, at least in part.

Beta3-adrenoceptors in the cardiovascular system

beta-Adrenoceptors of the beta1 and beta2 subtypes classically mediate the effects of catecholamines on the contractility of cardiac muscle and the relaxation of vascular smooth muscle. Since the molecular characterization of the beta3-adrenoceptor in 1989, most studies of this adrenoceptor subtype have focused on its control of lipolysis in adipose tissues. However, more recent studies have investigated the involvement of beta3-adrenoceptors in the physiological control of cardiac and vascular contractility. In this article, the pharmacological and molecular evidence that supports the functional role of beta3-adrenoceptors in cardiovasculartissues of various species, including humans, will be discussed. These data might provide new insights into our understanding of the abnormal responsiveness of the cardiovascular system to catecholamines in heart failure and its treatment with beta3-adrenoceptor antagonists.