Β-adrenergic Action Research Articles

Oleuropein aglycone enhances UCP1 expression in brown adipose tissue in high-fat-diet-induced obese rats by activating β-adrenergic signaling

Oleuropein is the pungent principle of raw olives. Oleuropein aglycone (OA) is a major phenolic compound in extra virgin olive oil and the absorbed form of oleuropein. We aimed to determine the mechanism underlying the nutritional effects of oleuropein and OA on interscapular brown adipose tissue (IBAT) in rats with high-fat (HF) diet-induced obesity by examining the agonistic activity of oleuropein and OA toward the transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1). Four-week-old male Sprague–Dawley rats were fed an HF (palm oil 30% wt:wt) diet alone or with oleuropein (HF-O, 1 g/kg diet) for 28 days. In rats fed HF-O compared to HF, urinary noradrenaline, adrenaline and UCP1 levels in IBAT were significantly higher, whereas plasma leptin levels and the total weight of the abdominal cavity adipose tissue were significantly lower. In anaesthetized 7-week-old male Sprague–Dawley rats, the OA (3.8 mg of intravenous injection)-induced increase in plasma noradrenaline secretion was suppressed by TRPA1 or TRPV1 antagonist and by a β2- or β3-adrenoceptor antagonist. Furthermore, OA-activated rat and human TRPV1s expressed on HEK293 cells at the same level as zingerone (pungent component in ginger). OA also activated humanTRPA1, and its potency was approximately 10-fold stronger than that for TRPV1. These findings suggest that OA is the agonist of both TRPA1 and TRPV1 and that OA enhances UCP1 expression in IBAT with a concomitant decrease in the visceral fat mass of HF-diet-induced obese rats through enhanced noradrenaline secretion via β-adrenergic action following TRPA1 and TRPV1 activation.

Circulating gonadotropins and ovarian adiponectin system are modulated by acupuncture independently of sex steroid or β-adrenergic action in a female hyperandrogenic rat model of polycystic ovary syndrome

Acupuncture with combined manual and low-frequency electrical stimulation, or electroacupuncture (EA), reduces endocrine and reproductive dysfunction in women with polycystic ovary syndrome (PCOS), likely by modulating sympathetic nerve activity or sex steroid synthesis. To test this hypothesis, we induced PCOS in rats by prepubertal implantation of continuous-release letrozole pellets (200 µg/day) or vehicle. Six weeks later, rats were treated for 5–6 weeks with low-frequency EA 5 days/week, subcutaneous injection of 17β-estradiol (2.0 µg) every fourth day, or a β-adrenergic blocker (propranolol hydrochloride, 0.1 mg/kg) 5 days/week. Letrozole controls were handled without needle insertion or injected with sesame oil every fourth day. Estrous cyclicity, ovarian morphology, sex steroids, gonadotropins, insulin-like growth factor I, bone mineral density, and gene and protein expression in ovarian tissue were measured. Low-frequency EA induced estrous-cycle changes, decreased high levels of circulating luteinizing hormone (LH) and the LH/follicle-stimulating hormone (FSH) ratio, decreased high ovarian gene expression of adiponectin receptor 2, and increased expression of adiponectin receptor 2 protein and phosphorylation of ERK1/2. EA also increased cortical bone mineral density. Propranolol decreased ovarian expression of Foxo3, Srd5a1, and Hif1a. Estradiol decreased circulating LH, induced estrous cycle changes, and decreased ovarian expression of Adipor1, Foxo3, and Pik3r1. Further, total bone mineral density was higher in the letrozole–estradiol group. Thus, EA modulates the circulating gonadotropin levels independently of sex steroids or β-adrenergic action and affects the expression of ovarian adiponectin system.

Neuropeptide Y is a critical modulator of Leptin's regulation of cortical bone

Leptin signaling is required for normal bone homeostasis; however, loss of leptin results in differing effects on cortical and cancellous bone, as well as altered responses between the axial and appendicular regions. Local β-adrenergic actions are responsible for the greater cancellous bone volume in leptin-deficient (ob/ob) mice; however, the mechanism responsible for the opposing reduction in cortical bone in ob/ob mice is not known. Here we show that blocking the leptin-deficient increase in neuropeptide Y (NPY) expression reverses the cortical bone loss in ob/ob mice. Mice null for both NPY and leptin (NPY(-/-) ob/ob), display greater cortical bone mass in both long-bones and vertebra, with NPY(-/-) ob/ob mice exhibiting thicker and denser cortical bone, associated with greater endocortical and periosteal mineral apposition rate (MAR), compared to ob/ob animals. Importantly, these cortical changes occurred without significant increases in body weight, with NPY(-/-) ob/ob mice showing significantly reduced adiposity compared to ob/ob controls, most likely due to the reduced respiratory exchange ratio seen in these animals. Interestingly, cancellous bone volume was not different between NPY(-/-) ob/ob and ob/ob, suggesting that NPY is not influencing the adrenergic axis. Taken together, this work demonstrates the critical role of NPY signaling in the regulation of bone and energy homeostasis, and more importantly, suggests that reduced leptin levels or leptin resistance, which occurs in obesity, could potentially inhibit cortical bone formation via increased central NPY signaling.

The p75 neurotrophin receptor, semaphorins, and sympathetic traffic in the heart

the sympathetic and parasympathetic branches of the autonomic nervous system control cardiac function through the coordinated activity generated by neurons within the intracardiac autonomic ganglia and central nervous system (3). Activation of the sympathetic efferent projections to the heart increases heart rate, modifies the pattern and conduction velocity of the impulse through the heart, and augments both atrial and ventricular contractility while hastening myocardial relaxation. In the vasculature, the sympathetic nervous system (SNS) reduces venous capacitance and constricts resistance vessels, increasing blood pressure. Conversely, the parasympathetic nervous system (PSNS) decreases heart rate and cardiac impulse conduction. More recent evidence has suggested that the PSNS may also affect ventricular function, indirectly by countering β-adrenergic action or directly via inhibition of L-type Ca2+ channels (34). A transient imbalance between these two branches can lead to increased heart rate and blood pressure when cardiac output is increased. When subnormal cardiac PSNS activity concomitant with sympathetic hyperactivation persists, such as after myocardial infarction, this disequilibrium may increase the risk for cardiac adverse events, including arrhythmias, hypertension, cardiac hypertrophy, and, ultimately, heart failure. This condition is called “autonomic neural remodeling” and can greatly contribute to the induction of ventricular fibrillation, thus increasing the patient's susceptibility to sudden cardiac death (41, 47). It is plausible that neurotrophic factors, target organ-secreted proteins essential for the development and differentiation of neurons, are involved in the remarkable neuroplasticity exhibited by the SNS in the adult life, including autonomic remodeling after infarction and/or in the onset and progression of congestive heart failure (17, 30, 32).

Insulin inhibits β-adrenergic action in ischemic/reperfused heart: a novel mechanism of insulin in cardioprotection

Sympathetic overactivity is closely connected with cell injury and contractile dysfunction during myocardial ischemia/reperfusion (MI/R). Insulin exerts protection for the I/R heart and the underlying mechanisms remain unclear. This study aimed to investigate the ability of insulin to modulate beta-adrenergic actions on myocardial contraction and post-ischemic injury in acute MI/R and the underlying mechanism. Isolated hearts from adult SD rats were subjected to MI/R (30 min/2 h) and treated with isoproterenol (ISO) or/and insulin. Myocardial contraction, cardiomyocyte apoptosis, myocardial injury and infarction were assessed. In a separate study, isolated ventricular myocytes were subjected to simulated I/R (15/30 min) and myocyte shortening and intracellular Ca2+ transient in response to ISO during reperfusion were assessed with presence or absence of insulin. In isolated I/R hearts, insulin largely reversed the ISO-associated contractile functional impairment at 2 h after MI/R, inhibiting ISO-induced declines in heart rate and left ventricular systolic pressure by 34.0% and 23.0% and preventing ISO-induced elevation in left ventricular end-diastolic pressure by 28.7% respectively (all P < 0.05). In addition, ISO alone resulted in enlarged infarct size, elevated CK and LDH activity and increased apoptotic index in I/R hearts compared with vehicle, which were inhibited by treatment of insulin (all P < 0.05). Interestingly, in SI/R cardiomyocytes, insulin alone at 10(-7 )mol/l increased cell contraction whereas attenuated the positive inotropic response to ISO (10(-9 )mol/l) during R as evidenced by a 18.7% reduction in peak twitch amplitude and a 23.9% reduction in calcium transient amplitude (both P < 0.05). Moreover, insulin blunted ISO-mediated increase in PKA activity, enhanced the PKA-dependent phosphorylation of phospholamban (PLB), resulting in increased sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) activity. Insulin attenuated the contractile response to beta-AR stimulation and suppressed ISO-elicited cardiac dysfunction and cell injury in MI/R. The inhibitory effect of insulin on the beta-adrenergic action involved the inhibition of PKA-mediated Ca2+ transient and promotion of post-ischemic Ca2+ handling.

Possibility of Autocrine β-Adrenergic Signaling in C2C12 Myotubes

Levodopa reportedly inhibits insulin action in skeletal muscle. Here we show that C2C12 myotubes produce levodopa and that insulin-stimulated glucose transport is enhanced when endogenous levodopa is depleted. Exogenous levodopa prevented the stimulation of glucose transport by insulin (P < 0.05) and increased cAMP concentrations (P < 0.05). The decrease in insulin-stimulated glucose transport caused by levodopa was attenuated by propranolol (a beta-adrenergic antagonist) and prevented by NSD-1015 (NSD), an inhibitor of DOPA decarboxylase (DDC; converts levodopa to dopamine). Propranolol and NSD both prevented levodopa-related increases in [cAMP]. However, the effects of levodopa were unlikely to be dependent on the conversion of levodopa to catecholamines because we could detect neither DDC in myotubes nor catecholamines in media after incubation of myotubes with levodopa. The data suggest the possibility of novel autocrine beta-adrenergic action in C2C12 myotubes in which levodopa, produced by myotubes, could have hormone-like effects that impinge on glucose metabolism.

Kyotorphin has a novel action on rat cardiac muscle

Several endogenous peptides for G-protein-coupled receptors have been found to play physiological roles in muscle contraction in addition to their well-demonstrated actions in other tissues. To further identify such peptides, we screened over 400 peptides using an isometric tension assay of rat papillary muscle. Here, we report that kyotorphin, which is known as an analgesic dipeptide, has a cardiac effect. Although kyotorphin had no effect on the twitch tension itself, it inhibited β-adrenergic agonist isoprenaline-induced increases in twitch tension in a dose-dependent manner. Leu-Arg, a selective antagonist of kyotorphin, reversed this inhibitory effect. The inhibitory effect was also reversed by naloxone, an opioid receptor antagonist. These results suggest that kyotorphin may release opioid peptides from rat cardiac muscle and have an indirect regulatory role in β-adrenergic action through cross-talk with opioid receptors.

Vasopressor agents for cardiopulmonary resuscitation.

The primary goal of cardiopulmonary resuscitation is to reestablish blood flow to vital organs until spontaneous circulation is restored. Adrenergic vasopressor agents produce systemic vasoconstriction. This increases aortic diastolic pressure, and consequently, coronary and cerebral perfusion pressures. The pharmacologic responses to the adrenergic agents are mediated by a group of receptors that are classified as alpha (alpha), including alpha1 and alpha2, and beta (beta), including beta1 and beta2. Epinephrine, which has each of these adrenergic actions, has been the preferred adrenergic agent for the management of cardiac arrest for almost 40 years. Its primary efficacy is due to its alpha-adrenergic vasopressor effects. This contrasts with its beta-adrenergic actions, which are inotropic, chronotropic, and vasodilator. Accordingly, beta-adrenergic actions prompt increases in myocardial oxygen consumption, ectopic ventricular arrhythmias, and transient hypoxemia due to pulmonary arteriovenous shunting. This may account for the failure to demonstrate that epinephrine improves ultimate outcomes in human victims of cardiac arrest. Major interest has more recently been focused on selective alpha-adrenergic agonists. Both alpha1-agonists and alpha2-agonists are peripheral vasopressors. However, rapid desensitization of alpha1-adrenergic receptors occurs during cardiopulmonary resuscitation. Moreover, alpha1-adrenergic receptors are present in the myocardium, and beta1-agonists, like beta-adrenergic agonists, increase myocardial oxygen consumption. If they cross the blood-brain barrier, alpha2-adrenoceptor agonists also have centrally acting vasodilator effects. In the absence of central nervous system access, alpha2-adrenergic agonists have selective peripheral vasoconstrictor effects. Under experimental conditions of cardiopulmonary resuscitation, selective alpha2-agonists, which do not gain entrance into the brain, produce only systemic vasoconstriction. Experimentally, these selective alpha2-agonists are as effective as epinephrine for initial cardiac resuscitation and have the additional advantage of minimizing myocardial oxygen consumption during the global myocardial ischemia of cardiac arrest. Accordingly, myocardial ischemic injury during cardiopulmonary resuscitation is minimized, and postresuscitation myocardial function is preserved with improved survival.

Pharmacological effects of Eugenia uniflora (Myrtaceae) aqueous crude extract on rat's heart

The effect of aqueous crude extract (ACE) of Eugenia uniflora L. (Myrtaceae) was studied on rat's perfused ventricles. This plant is used in South American traditional medicine as an antihypertensive and we already demonstrated previously its hypotensive properties. In this paper, maximal left intraventriclular pressure ( P) of rat's hearts beating at 0.2 Hz firstly increased to 162.1±11.1% of basal value during 1–3 min of perfusing ACE 0.6%. Maximum rate of contraction (+ P) also increased to duplicating + P/ P ratio. Both types of effect were significantly decreased by either propranolol 0.35 μM, and pre-treatment with reserpine (5 mg/kg), suggesting that they were caused by a compound that releases cathecolamines with β-adrenergic action. Nevertheless, after 20 min of perfusing ACE, ventricles decreased P to about 50% of their basal value, suggesting a negative-inotropic compound present in the extract. The perfusion of 1.2% ACE decreased P in a pressure–[Ca] o curve (0.5–2 mM) in a non-competitive manner, suggesting that an irreversible Ca-blocking compound is also present in the extract. In summary, E. uniflora ACE has a dual effect on the heart related to its hypotensive action and is probably responsible for the therapeutic or adverse effects in patients under cardiac risk.

Nitric oxide inhibits isoproterenol-stimulated adipocyte lipolysis through oxidative inactivation of the β-agonist

Nitric oxide has been implicated in the inhibition of catecholamine-stimulated lipolysis in adipose tissue by as yet unknown mechanisms. In the present study, it is shown that the nitric oxide donor, 2,2-diethyl-1-nitroso-oxyhydrazine, antagonized isoproterenol (isoprenaline)-induced lipolysis in rat adipocytes, freshly isolated from white adipose tissue, by decreasing the potency of the beta-agonist without affecting its efficacy. These data suggest that nitric oxide did not act downstream of the beta-adrenoceptor but reduced the effective concentration of isoproterenol. In support of the latter hypothesis, we found that pre-treatment of isoproterenol with nitric oxide abolished the lipolytic activity of the catecholamine. Spectroscopic data and HPLC analysis confirmed that the nitric oxide-mediated inactivation of isoproterenol was in fact because of the modification of the catecholamine through a sequence of oxidation reactions, which apparently involved the generation of an aminochrome. Similarly, aminochrome was found to be the primary product of isoproterenol oxidation by 3-morpholinosydnonimine and peroxynitrite. Finally, it was shown that nitric oxide released from cytokine-stimulated adipocytes attenuated the lipolytic effect of isoproterenol by inactivating the catecholamine. In contrast with very recent findings, which suggest that nitric oxide impairs the beta-adrenergic action of isoproterenol through intracellular mechanisms and not through a chemical reaction between NO and the catecholamine, we showed that nitric oxide was able to attenuate the pharmacological activity of isoproterenol in vitro as well as in a nitric oxide-generating cellular system through oxidation of the beta-agonist. These findings should be taken into account in both the design and interpretation of studies used to investigate the role of nitric oxide as a modulator of isoproterenol-stimulated signal transduction pathways.

Beta-Adrenergic action on wild-type and KPQ mutant human cardiac Na+ channels: shift in gating but no change in Ca2+:Na+ selectivity.

Prior studies of the modulation of the Na+ current by sympathetic stimulation have yielded controversial results. Separation of the Na+ and Ca2+ currents poses a problem in myocyte preparations. The gating of cloned Na+ channels is different in oocytes compared with mammalian expression systems. We have examined the sympathetic modulation of the alpha-subunit of the wild-type human cardiac Na+ channel (hH1) and the long QT-associated mutant, delta KPQ, expressed in human embryonic kidney cells. Stable cell lines of hH1 and delta KPQ were established in human embryonic kidney cells. Whole-cell and single-channel currents were measured with the patch-clamp technique. Sympathetic stimulation was effected by exposure to isoproterenol or 8-bromo-cAMP. Na+ channel activation and inactivation were determined using standard voltage clamp protocols. Ca2+:Na+ permeability ratio was determined under bi-ionic conditions. We observed a qualitatively different effect of sympathetic stimulation on the cardiac Na+ current from that reported in frog oocytes: activation and inactivation kinetics were shifted to more negative potentials. This shift was similar for both hH1 and delta KPQ. [delta V0.5 for inactivation: 8.3 +/- 1.7 mV, p < 0.001 (hH1); 6.8 +/- 0.9 mV, p < 0.001 (delta KPQ)]. Increased rate of closed-state inactivation contributed to the shifting of the inactivation-voltage relationship. Open-state inactivation was not affected as mean open times were unchanged. Reversal potential measurement in hH1 suggested a low Ca2+:Na+ permeability ratio of 0.017, uninfluenced by sympathetic stimulation. In delta KPQ, the size of the persistent relative to the peak current was increased with 8-bromo-cAMP from 3.0 +/- 0.7% to 4.3 +/- 0.6% (p = 0.056). Sympathetic stimulation exerts multiple effects on the gating of hH1. Similar effects are also seen in delta KPQ which may increase arrhythmia susceptibility in long QT syndrome by modifying the Na+ channel contribution to the action potential.

Molecular Regulation of Phospholamban Function and Expression

Intracellular levels of cAMP regulated by the β-adrenergic actions of catecholamines play a key in the metabolic, electrical, and mechanical performance of the cardiac muscles. Among a number of biological actions of cAMP, the excitation–contraction coupling process in cardiac myocytes is markedly affected by cAMP through its stimulatory effect on cAMP-dependent protein kinase. Phospholamban, which is expressed in the sarcoplasmic reticulum of cardiac, slow-twitch skeletal, and smooth muscles, is one of the substrates for cAMP-dependent protein kinase. Phospholamban regulates the activity of Ca ATPase in the sarcoplasmic reticulum membranes in a manner dependent on the phosphorylation state of cAMP-dependent protein kinase, thereby changing the mechanical performance of the cardiac muscles. This Ca regulatory mechanism of phospholamban-Ca ATPase system is mediated by a direct protein–protein interaction between two proteins. This review focuses on recent advances in understanding the role of phospholamban molecule in the regulation of Ca transport by cardiac muscle sarcoplasmic reticulum.

Alliin and volatile sulfur-containing compounds in garlic enhance the thermogenesis by increasing norepinephrine secretion in rats

The effects of alliin and volatile sulfur-containing compounds in garlic on thermogenesis were investigated in rats. Rats were fed high-fat diet with or without a ethanol extracted-garlic powder (EE-garlic) supplemented at 0.8% for 28 days. After feeding, mitochondrial protein content in interscapular brown adipose tissue (IBAT) and plasma norepinephrine secretion were significantly greater in rats given EE-garlic as compared with control rats. The effects of the administrations of EE-garlic and alliin on norepinephrine secretions were evaluated in anesthetized rats. The norepinephrine concentrations of arterial blood were significantly increased by EE-garlic and alliin administration, and these increases were dose dependent. The administration of allylsulfides having a different number of sulfur atoms (diallyldisulfide and diallyltrisulfide) also significantly increased the norepinephrine secretion. The effects of the administration of EE-garlic, alliin, and diallyldisulfide on thermogenesis were examined by the direct measurement of IBAT and rectal temperatures in anesthetized rats. The temperatures were significantly increased by the administration of these compounds, and the effect of diallyldisulfide disappeared in the presence of β-adrenergic blocker. These results suggest that the administration of alliin and volatile sulfur-containing compounds in garlic enhance the thermogenesis by increasing norepinephrine secretion via β-adrenergic action.

Cardiopulmonary resuscitation: a promise as yet largely unfulfilled.

After failure of initial external defibrillation, restoration of spontaneous circulation is largely contingent on rapid and effective reversal of myocardial ischemia by both mechanical and pharmacologic means. Despite the introduction of modern cardiopulmonary resuscitation (CPR) more than 35 years ago, its universal acceptance, and its wide implementation, no improvements in outcome excepting early defibrillation have been documented over these many years. The science of CPR therefore is still in its infancy. It was incorrectly assumed that all that needs to be known is known and that the need for scientific research was therefore not apparent. Accordingly, serious resuscitation research was neither encouraged nor equitably supported. The ABCs of CPR currently provide for the establishment of a patent airway (A) and intermittent positive pressure ventilation, preferably with oxygen-enriched air (B). These are to be immediately followed with precordial compression (C). This ordering of priorities, however, is based on consensus rather than objective outcome measurements. The ABCs recently have been seriously challenged on the basis of results of both experimental and clinical studies. Conventional external precordial compression restores systemic blood flow. It may be used by both professional and nonprofessional CPR providers, especially bystanders, because of its apparent simplicity and noninvasiveness. However, manual or mechanical external precordial compression typically generates cardiac outputs that represent less than 30% of normal values. Coronary blood flow, which is critical for restoration of spontaneous circulation, is correspondingly reduced. Accordingly, several alternatives to conventional precordial compression have been proposed with the intent of increasing cardiac output and both coronary and cerebral blood flows. Among the large number of pharmaceutical agents initially recommended for cardiac resuscitation, only agents that produce peripheral vasoconstriction are of proved benefit. Epinephrine has been the preferred vasopressor agent for the management of cardiac arrest for more than 35 years because of its alpha-adrenergic effects. However, the potentially adverse effects of epinephrine are related to its beta-adrenergic inotropic actions. The beta-adrenergic actions account for disproportionate increases in myocardial oxygen consumption with increased severity of myocardial ischemic injury and provocation of ectopic ventricular tachycardia and ventricular fibrillation. Nevertheless, epinephrine remains the drug of choice, although adrenergic drugs with selective alpha-adrenergic actions or nonadrenergic vasoconstrictor drugs are likely to emerge as useful alternatives. Experimental and clinical observations have led to identification of continuous monitoring of both end-tidal carbon dioxide and ventricular fibrillation waveforms as practical noninvasive guides because they are highly correlated with both cardiac output and coronary blood flow. Both end-tidal carbon dioxide and ventricular fibrillation waveforms now serve as predictors of the likelihood of successful resuscitation. These two measurements may now be used to guide interventions and especially to assure optimal precordial compression. It is well established that sudden death among adults is predominantly due to malignant ventricular arrhythmias and ventricular fibrillation. Early defibrillation serves as an unequivocally effective immediate intervention. Minimally trained first responders and members of the general public are being enfranchised to use automated external defibrillators for very early defibrillation. Use of these devices by bystanders is the most promising new intervention since CPR was first proposed in the early 1960s. Postresuscitation ventricular dysrhythmias and heart failure are now called postresuscitation myocardial dysfunction. This complication has been recognized as a leading cause of the high postresuscitation mor

Cardiovascular Effect of a Senso (Toad Venom)-Containing Drug in Anesthetized Dogs (2): Influence of Propranolol

Effects of a Senso (toad venom)-containing drug KY on systemic hemodynamics were examined, and participation of beta-adrenoceptor in its action was evaluated by using propranolol in anesthetized dogs. KY produced a positive inotropic action, and decreased total peripheral (TPR) and coronary vascular resistances (CR), while renal vascular resistance (RR) was increased. After propranolol, KY significantly increased TPR, CR, vertebral vascular resistance and RR. KY-induced positive inotropic action was partly diminished but not abolished by beta-blockade. These results indicate that the beta-adrenergic action may be involved in the vasodilating effect of KY and partly in the positive inotropic action.

Adrenergic blockade paradoxically increases lipogenic response of brown adipose tissue to sympathetic nerve stimulation

Intermittent electrical stimulation of sympathetic nerves entering the interscapular brown adipose tissue (BAT) in rats increased the rate of glyceride glycerol synthesis in BAT but the fatty acid synthesis did not change. Simultaneous administration of phenoxybenzamine and propranolol paradoxically increased the fatty acid synthesis in response to the nerve stimulation whereas the glyceride glycerol synthesis was inhibited. Propranolol alone was also effective in mimicking the effects of adrenergic blockade, but guanethidine selectively eliminated the lipogenic response to the nerve stimulation. These results indicate that synthesis of glyceride glycerol induced by sympathetic nerve stimulation is largely due to β-adrenergic action of noradrenaline, whereas synthesis of fatty acids may be mediated by non-adrenergic transmission of the sympathetic nerves.

Interactive α- and β-adrenergic actions of norepinephrine in rat cardiac myocytes

We investigated the effects of the physiological neurotransmitter norepinephrine on the contractile properties and Ca 2+ dynamics of isolated cardiac myocytes, with particular emphasis on possible interactions between α- and β-adrenergic effects. Individual rat ventricular myocytes were electrically stimulated at a frequency of 1 Hz. Norepinephrine (10 −9 to 10 −5 m) increased extent and velocity of shortening and decreased the contraction duration. β-Adrenergic activation gave a greater enhancement of extent and velocity of shortening than did norepinephrine alone (i.e. α plus β). Neither α 1 nor α 2 adrenergic activation individually produced a significant impact upon contraction. Using suspensions of myocytes loaded with Quin-2, we also studied resting levels of cytosolic Ca 2+ ([Ca 2+] c), the increase of [Ca 2+] c due to caffeine-addition (as an index of sarcoplasmic reticulum Ca 2+ content) and the subsequent increase in [Ca 2+] c due to depolarization with 30 m m K + (as an index of sarcolemmal voltage-dependent Ca 2+ channel activity). Norepinephrine decreased resting [Ca 2+] c, increased sarcoplasmic reticulum Ca 2+ content and increased Ca 2+ channel activity. β-Adrenergic activation produced the same effect on resting [Ca 2+] c and sarcoplasmic reticulum content, but gave significantly greater activation of sarcolemmal Ca 2+ channel activity, than did norepinephrine (α plus β). By contrast, α-adrenergic stimulation had no effect on resting [Ca 2+] c or sarcoplasmic reticulum Ca 2+ content. We conclude that β-mediated effects predominate in the action of the physiological agonist norepinephrine on cardiac myocytes. However, α (specifically α 1)-adrenergic effects are significant in diminishing the potentiation of the extent and velocity of shortening, and of depolarization-induced entry of Ca 2+ into the cell, which is seen on β-stimulation alone. Thus, there may be an intrinsic feedback effect in the actions of norepinephrine on the cardiac myocyte.

Effect of Aging on the Response of Guinea Pig Trachea to Isoprenaiine

To study the effect of aging on the β-adrenergic receptor potency of isoprenaiine, tracheas from 3-, 6-, 10-, 40- and 100-week-old guinea pigs were used as test tissues. The pD2 values (potency) of isoprenaiine increased with age in tracheas treated with corticosterone, but decreased in untreated tracheas. The pA2 value of propranolol against isoprenaiine estimated in the treated tracheas did not change with age. Specific binding of [3H]-dihydroalprenolol to the microsomal fractions from the tracheal muscles from 6-, 10- and 40-week-old guinea pigs was analyzed with Scatchard plots. The capacity of maximum binding sites of [3H]-dihydroalprenolol increased with increasing age, while its dissociation constant did not change. Age-related increase in the potency of isoprenaline in the tracheas treated with corticosterone is considered to be due to the increase in the total amount (density) of β-adrenoceptors. However, the potency of the drug in untreated tracheas decreased with age. These results suggest that extraneuronal uptake plays an important role in the β-adrenergic action of isoprenaline in older (40 and 100 weeks) guinea pigs.

Dopamine inhibition of superoxide anion production by polymorphonuclear leukocytes

To examine the modulatory effects of catecholamines on the respiratory burst in polymorphonuclear leukocytes (PMNs), dopamine was tested for its capacity to modify the superoxide anion (O 2 −) production by PMNs under their stimulation with several stimuli. Dopamine inhibited the O 2 − production by PMNs when PMNs were stimulated with N-formylated chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), phorbol myristate acetate, or opsonized zymosan, whereas dopamine did not alter the PMN mobility. The values of percentage inhibition of the O 2 − production by FMLP-stimulated PMNs were 57% under treatment with 10 −5 mol/L and 83% with 10 −4 mol/L of dopamine. Isoproterenol also inhibited PMN O 2 − production in response to FMLP. Although a β-adrenergic blockade, propranolol, diminished the isoproterenol-induced inhibition of the O 2 − production, it did not affect the inhibitory effect of dopamine. The increase in intracellular cyclic AMP levels in dopamine-treated PMNs was much smaller than the increase in isoproterenol-treated cells. Furthermore, dopamine inhibited the reduced nicotinamide-adenine dinucleotide phosphate-dependent O 2 − production by subcellular particles. These results indicate that dopamine inhibits PMN O 2 − production through its effect on PMN reduced nicotinamide-adenine dinucleotide phosphate-oxidase system rather than through its β-adrenergic action.

24] Reconstitution of calcium pumping of cardiac sarcoplasmic reticulum

This chapter describes the reconstitution of cardiac SR transport function, which has provided new insight into the nature of the modulation of Ca 2+ transport. The β-adrenergic action of catecholamines on heart muscle is, in part, explained by modulation of Ca 2+ fluxes by way of the action of their intracellular second messengers, such as cAMP and Ca 2+ itself. At the level of cardiac sarcoplasmic reticulum (SR), the Ca 2+ -pump, which transports Ca 2+ from the cytoplasm into the lumen of the SR, can be modulated by cAMP and Ca 2+ -calmodulin. In cardiac SR, phospholamban is phosphorylated by adding catalytic subunit of cAMP-dependent protein kinase or via an intrinsic Ca 2+ -calmodulin-dependent protein kinase. Phospholamban in the reconstituted vesicles is also phosphorylated by the catalytic subunit of cAMP-dependent protein kinase to about the same extent as that in the original vesicles. In the original cardiac SR, it is known that a significant stimulation of Ca 2+ loading is observed when phospholamban is phosphorylated, by way of a decrease in the Ca 2+ concentration for the half-maximal Ca 2+ -loading rate (Kc a ).