Number Of Beta-adrenergic Receptors Research Articles

Defective response to cAMP-dependent protein kinase in non-insulin-dependent diabetic heart

Hearts isolated from 1-yr-old non-insulin-dependent diabetic rats exhibited reduced responsiveness to the beta-adrenergic agonist isoproterenol. Over a concentration range of 3 x 10(-9) to 10(-7) M, isoproterenol-mediated stimulation in the rate of left ventricular pressure decline, a measure of myocardial relaxation, and the rate of left ventricular pressure rise, a measure of myocardial contractility, were significantly depressed in the diabetic hearts. To clarify the basis for this defect, individual steps involved in the actions of the beta-adrenergic agonists were examined. Dihydroalprenolol binding assays revealed that neither beta-adrenergic receptor number nor binding affinity was affected by the diabetic condition. Also unaffected by diabetes was isoproterenol-mediated stimulation of adenylate cyclase activity, myocyte accumulation of adenosine 3',5'-cyclic monophosphate (cAMP), or the increase in cAMP-dependent protein kinase activity ratio. However, it was found that both in the presence and absence of cAMP-dependent protein kinase, activity of the sarcolemmal calcium transporter was significantly depressed in the diabetic heart. Also attenuated was protein kinase-induced enhancement of sarcoplasmic reticular calcium transport. The likelihood that these abnormalities contribute to alterations in calcium homeostasis and myocardial contractile function is discussed.

β-adrenoceptor-agonist and insulin actions on glucose metabolism in rat skeletal muscle in different thyroid states

1. The actions of the beta-adrenoceptor agonist isoprenaline on glucose and glycogen metabolism, in the presence of various concentrations of insulin, were investigated in isolated soleus muscle preparations taken from eu-, hyper- and hypothyroid rats. 2. Hyperthyroidism, induced by 3,3',5-tri-iodo-D-thyronine (T3) administration for 5 days, increased the rate of lactate formation and suppressed the rate of glycogen synthesis in soleus muscle in response to isoprenaline, even in the presence of physiological or supraphysiological insulin concentrations. 3. Hypothyroidism, induced by administration of 6-n-propyl-2-thiouracil for 4 weeks, decreased the rate of isoprenaline-stimulated lactate formation at all insulin concentrations, but significantly decreased the responsiveness of lactate formation only at low insulin concentrations. In the presence of 100 or 10,000 mu-units of insulin/ml, the ability of isoprenaline to suppress the rate of glycogen synthesis was markedly impaired (inhibition at 100 mu-units of insulin/ml and 1 micro-M-isoprenaline: eu- 72.6 +/- 2.9%; hypo-41.0 +/- 2.1%; P less than 0.001). 4. Hyperthyroidism had no effect on the number or affinity of beta-adrenoceptors, defined by 125I-pindolol binding, or beta-adrenoceptor- or forskolin-stimulated adenylate cyclase activity in membrane preparations of gastrocnemius muscle, whereas hypothyroidism increased the beta-adrenoceptor density and decreased the beta-adrenoceptor-stimulated adenylate cyclase activity, without affecting the receptor affinity or forskolin-stimulated adenylate cyclase activity. 5. It is concluded that there is a complex interplay between insulin, catecholamines and thyroid hormones to regulate skeletal-muscle glucose metabolism. The changes observed in muscles in hypothyroidism may be explained, at least in part, by changes in beta-adrenoceptor-G-protein-adenylate cyclase coupling affecting the generation of cyclic AMP and the regulation of some of the key enzymes of glycogen metabolism; in contrast, the changes observed in muscles in hyperthyroidism do not appear to result from alterations at the level of the receptor-mediated second-messenger generation.

Different beta-adrenoceptor-effector coupling in human ventricular and atrial myocardium.

To examine whether the downregulation of beta-adrenoceptors is accompanied by reduced beta-adrenoceptor-mediated effects in atrial as well as in ventricular myocardium, we investigated the beta-adrenoceptor-effector coupling in atrial and papillary muscle strips from patients with terminal heart failure (heart transplantation because of dilated cardiomyopathy; New York Heart Association Class IV, NYHA IV) and moderate heart failure (mitral valve replacement, NYHA II-III) and in tissue from non-failing hearts. The isometric force of contraction induced by isoprenaline (0.001-1 mumoll-1) or Ca2+ (1.8-15 mmoll-1) in atrial muscle strips and papillary muscle strips has been measured. We also examined the number of beta-adrenoceptors in both tissues by radioligand binding. The degree of heart failure affected neither the potency (EC50: control: 0.01 (0.001-0.082) mumoll-1; NYHA II-III: 0.01 (0.001-0.125) mumoll-1; NYHA IV: 0.01 (0.001-0.160) mumoll-1) nor the efficacy (NYHA IV: 7.8 +/- 1.0 mN; NYHA II-III: 6.1 +/- 0.7 mN; control: 7.7 +/- 0.9 mN) of the isoprenaline-mediated increase in force of contraction in atrial muscle strips. This is in spite of a reduced number of beta-adrenoceptors in moderately (NYHA II-III) and terminally (NYHA IV) failing atrial myocardium compared to non-failing atrial myocardium (P less than 0.05). In contrast, in papillary muscle strips increasing degrees of heart failure were accompanied by a progressive reduction of the isoprenaline-mediated increase in force of contraction (P less than 0.05) as well as by a progressive decrease of beta-adrenoceptors (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

High density of beta 2-adrenoceptors in a human keratinocyte cell line with complete epidermal differentiation capacity (HaCaT).

A non-tumorigenic keratinocyte cell line with complete epidermal differentiation capacity (HaCaT) was used in radioligand binding experiments to determine the number of beta-adrenoceptors. Intact cells were saturated with 3H-labelled (-)CGP-12177 (CGP), a hydrophilic non-selective beta-adrenergic antagonist as radioligand. In order to investigate the beta-adrenergic subtype selectivity, displacement experiments were performed with different antagonists and agonists. Binding of CGP to keratinocytes has been shown to be reversible and saturable and to have high affinity (Bmax = 114.0 +/- 8.8 fmol/10(7) cells with 6866 receptors/cell, KD = 0.095 +/- 0.017 nmol/l; n = 11). Beta-adrenergic antagonists inhibited binding yielding monophasic displacement curves. IC50-values (nmol/l) were: propranolol (non-selective) 1.68; CGP-12177 (non-selective) 1.08; ICI 118,551 (beta 2-selective) 2.92; bisoprolol (beta 1-selective) 1230; and CGP-20712 (beta 1-selective) 24,980. Agonists displaced CGP in the order isoprenaline greater than adrenaline greater than noradrenaline. We conclude that HaCaT cells express a high density of beta2-adrenoceptors providing a good model system to study adrenergic receptor mechanisms under reproducible experimental conditions in keratinocytes.

Chronic propranolol treatment in developing rats: Acute and lasting effects on monoamines and beta-adrenergic receptors in the rat brain

During early postnatal development rat pups were treated twice daily with the beta-adrenergic antagonist propranolol (15 mg/kg) in order to study the acute and long-lasting effects of early blockade of noradrenergic beta-mediated neurotransmission. Treatments from postnatal days 1–10 or days 11–20 did not induce alterations in the number of beta-adrenergic receptors as measured three days after the last injection, nor could lasting effects be shown at 60 days of age. The day 1–10 treatment, however, had a significant effect on the regional brain levels of noradrenaline (NA) and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), measured 90 min after the last injection. The metabolite had increased by 40% in all brain regions examined. On day 60, the MHPG concentrations were still increased when compared to postnatally saline-treated animals. Propranolol treatment from day 11–20 only marginally increased MHPG on day 20 and induced no lasting differences. These results suggest that propranolol treatment during the first ten days of life produces a long-lasting increase in NA metabolism, possibly reflecting an increased neuronal NA turnover.

Recovery Time Course of Airway Hyperresponsiveness to Acetylcholine After Ovalbumin Challenge in Guinea Pigs

Sequential changes in airway and adrenergic responsiveness after ovalbumin (OA) challenge were studied in guinea pigs. Airway responsiveness, alpha 1- and beta-adrenoceptor numbers and adenylate cyclase activity was determined after increasing doses of acetylcholine aerosol were administered before, 0, 3, 7, and 14 days after exposure to 2 percent OA or physiologic saline solution for 10 consecutive days. The antiasthmatic agent, azelastine (1 mg/kg/day, intraperitoneal), was administered for 14 days after the tenth exposure to OA in some animals. Airway responsiveness increased significantly after OA exposure, beta-adrenoceptor numbers decreased by 35 percent, and adenylate cyclase activity decreased by 54 percent (p less than 0.01). Values remained significantly different than control animals for 7 days and required 14 days to normalize completely. Azelastine decreased the recovery period to seven days. Azelastine may affect airway responsiveness, at least in part, by increasing beta-adrenergic responsiveness.

?-Adrenergic receptor activity of cerebral microvessels is reduced in aged rats

The effect of age on beta- (beta) adrenergic receptor number (Bmax) and adenylate cyclase (AC) activity was determined in microvessels isolated from male F-344 rats at 3, 18, and 24 months of age. Scatchard analysis of [125I]iodocyanopindolol (ICYP) binding indicated reduced Bmax (fmol/mg) of microvessels isolated from 24 month old rats (27.2 +/- 4.9) compared with 3 month old (50.4 +/- 5.2) and 18 month old rats (p less than 0.01) (61.4 +/- 7.6). The basal AC activity (pmol cAMP/mg) in 24 month old rats (32.0 +/- 6.7) and in 18 month old rats (30.4 +/- 2.1) were significantly reduced compared to the basal activity in the young (50.1 +/- 4.2). The net isoproterenol or NaF stimulated AC activity in 24 month old rats (zero and 15.6 +/- 8.5 respectively) was also reduced compared to young rats (10.1 +/- 3.9 and 166.0 +/- 21.2 respectively). It is concluded that aging is associated with reduced isoproterenol stimulated AC activity of cerebral microvessels. This reduction is the product of reduced beta-adrenergic receptor number and reduced activity of AC in aged rat cerebral microvessels.

Adipocyte Beta-Adrenoceptor numbers in growing pigs of different genotypes

Catecholamines are the major lipolytic agents in fat cells and are mediated primarily by beta-adrenergic receptors. The present experiment was designed to study p-receptor numbers in growing pigs of various genotypes in relation to their body compositions.Fat samples from 5 representative pigs of each genotype were removed immediately after slaughter, at about 60 kg body weight, and stored at -80°C prior to analysis. Adipocytes were extracted by incubation with 1 mg/g (w/v) collagenase in a tris/MgCl2/ EDTA/Bovine serum albumin buffer (pH 7.4) for 1 hour at 37°C. Cells were mechanically ruptured and membranes were removed by ultracentrifugatlon (37,000 rpm for 20 minutes). Recovery was estimated by protein assay using the method of Lowry (1951). Approximately 20 μg of adipocyte membrane protein in 300 μl tris/MgCl2/EDTA assay buffer was added to graded concentrations of the125I-labelled β-antagonist Iodocyanopindolol (100 μl) together with 100 μl of either assay buffer or the non-specific β-antagonist propanolol (to determine non-specific binding). Samples were then incubated for 1 hour at 37°C. Total β-receptor numbers (maximum binding - Bmax) expressed as pmol/g protein, were estimated by Scatchard analysis using the computer programme ‘EBDA’ by Elsevier - BIOSOFT, Cambridge.

Age-related changes in adrenergic alpha 1, alpha 2, and beta receptors of rat white fat cell membranes: an analysis using [3H]bunazosin as a novel ligand for the alpha 1 adrenoceptor.

Age-related changes in alpha 1-, alpha 2-, and beta-catecholamine receptors on membrane of rat epididymal fat cells were investigated. Both young (6 weeks old, weight about 190 g) and aged (20 weeks old, weight about 490 g) Sprague-Dawley male rats were used. For the alpha 1-adrenoceptor binding experiment, we developed a novel analytical method using the hydrophilic alpha 1-receptor selective antagonist, [3H]bunazosin. The binding of [3H]bunazosin to its binding sites was rapid, reversible, saturable, and stereospecific. Scatchard binding analysis showed a single class of binding site. The sites were characterized as alpha 1-adrenoceptors by inhibition experiments using various agonists and antagonists. The number of maximum binding sites (Bmax) of alpha 1-receptor binding was 37.0 +/- 6.5 (young) versus 24.0 +/- 3.2 (aged) fmol/mg protein (P less than 0.01). [3H]Rauwolscine and [3H]CGP-12177 were used for alpha 2- and beta-receptor binding, respectively. In alpha 2-receptor detection using [3H]rauwolscine as a ligand, Bmax increased markedly from 19.8 +/- 4.9 to 86.2 +/- 19.5 fmol/mg protein (P less than 0.01). In contrast, Bmax for beta-receptor decreased from 69.7 +/- 9.7 to 45.4 +/- 13.9 fmol/mg protein with increasing rat age (P less than 0.05). Kd showed no change in each of the binding experiments between young and aged rats. The cell volume increased from 0.07 +/- 0.02 to 0.15 +/- 0.06 nl. It is implied that anti-lipolytic activity strengthened on the whole mainly with the marked increase of alpha 2-receptor number and decrease of beta-receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Ovariectomy and Regional Fat Distribution on the Membranous Transducing System Controlling Lipolysis in Rat Fat Cells*

The mechanism by which sex steroid hormones modulate the lipolytic process in fat cells is still not completely understood, particularly at the level of the membrane. As estrogens seem to have regional influence on adipose tissue, we have compared the effects of long term ovariectomy (3 weeks) on the membranous transducing system controlling lipolysis in two rat fat deposits, the femoral sc and the parametrial adipose tissue. These experiments demonstrate the following. 1) Compared to parametrial adipocytes, sc adipocytes have a reduced cAMP production and a decreased beta-adrenoceptor number associated with a reduced lipolytic activity. 2) In parametrial adipocytes, ovariectomy induces a decrease in cAMP production and in both the beta-agonist-stimulated response and the catalytic activity of adenylate cyclase in association with a decreased lipolysis. In contrast, these parameters are unaltered by ovariectomy in sc adipocytes. This study, which reveals site-related differences in the sensitivity of the fat cell adenylate cyclase system to ovarian status, suggests that these differences may explain some of the sex-related regional specificities of adipose tissue metabolism and distribution.

Effects of chronic administration of carteolol on beta-adrenoceptors in spontaneously hypertensive rat heart.

We studied the effects of chronic administration of beta-adrenoceptor antagonists with and without intrinsic sympathomimetic activity (ISA): carteolol (with ISA) and propranolol (without ISA), respectively, on the heart of spontaneously hypertensive rat (SHR) and Wistar Kyoto rat (WKY). Six-week-old SHRs and WKYs were orally given carteolol or propranolol for ten weeks. The heart rate was reduced in propranolol-treated SHR, but not in carteolol-treated ones. In WKY, carteolol-treatment increased the heart rate. The number and affinities of beta-adrenoceptors were analyzed using [3H]dihydroalprenolol as a ligand. Propranolol at 30 mg/kg increased the number of cardiac beta-adrenoceptors in both SHR and WKY. In contrast, 10 mg/kg carteolol significantly decreased the number of cardiac beta-adrenoceptors in SHR, but not in WKY. These data indicate that carteolol, a beta-adrenoceptor antagonist with ISA, does not cause up-regulation of the number of cardiac beta-adrenoceptors in the rat and suggest that this fact is related to a possible lack of "rebound phenomena" after sudden discontinuation of chronic carteolol-therapy in humans.

Testosterone Increases Lipolysis and the Number of β-Adrenoceptors in Male Rat Adipocytes*

The influence of androgen status on the regulation of lipolysis and number of beta-adrenoceptors in isolated adipocytes was studied in male rats. Castration resulted in decreased catecholamine-induced as well as forskolin-induced lipolysis. beta-adrenoceptor number, examined by a whole cell cyanopindolol binding assay, was also diminished to a similar extent. Testosterone treatment of castrated rats normalized lipolysis as well as beta-adrenoceptor number. These results demonstrate that testosterone stimulates catecholamine-induced lipolysis in vivo by increasing the number of beta-adrenoceptors as well as the activity of adenylate cyclase, confirming previous in vitro studies performed in adipose precursor cells.

Effects of Aging and Drugs on Myocardial β-Adrenergic Receptors in M-SHRSP and SHRSP

Myocardial beta-adrenergic receptors were measured in membrane fractions from malignant SHRSP (M-SHRSP), SHRSP and WKY at different ages using [3H]-dihydroalprenolol (DHA) as a radioligand. The effects of isoproterenol (ISP) and chemical sympathectomy (6-hydroxydopamine treatment) on myocardial beta-receptors were also investigated in 10 and 24 week-old SHRS and WKY to examine the effects of hypertension and aging on receptor regulation. The number of myocardial beta-receptors in M-SHRSP at 4 weeks of age (W) and 10 W were significantly lower than those in age-matched SHRSP and WKY. In addition, the values in SHRSP at 4 and 10 W were significantly lower than those in age-matched WKY, but the numbers in SHRSP at 1, 24 and 48-54 W were not significantly different from age-matched WKY. The dissociation constant and activity of 5'-nucleotidase, which is a marker enzyme of cell membrane, were not significantly different among the three groups. ISP treatment significantly reduced the numbers of myocardial beta-receptors in 10 week-old SHRSP and 10 and 24 week-old WKY, but did not in 24 week-old SHRSP. The extent of this decrease of beta-receptors was lower in 10 week-old SHRSP than in 10 week-old WKY, and it was also lower in 24 week-old WKY than 10 week-old WKY. 6-Hydroxydopamine treatment significantly increased the number of myocardial beta-receptors in 10 and 24 week-old WKY, but did not in SHRSP. The extent of this increase of beta-receptors was lower in 24 week-old WKY than in 10 week-old WKY. These results suggest that the decrease of myocardial beta-receptor numbers in 4 and 10 week-old M-SHRSP and SHRSP does not appear to be genetically determined, but rather is caused by accelerated sympathetic activity, and that the regulation of myocardial beta-receptor is impaired in young and aged SHRSP and in aged WKY.

Experimental congestive heart failure due to myocardial infarction: sarcolemmal receptors and cation transporters.

Rats, subsequent to loss of a large amount of left ventricular free wall due to surgically-induced myocardial infarction, form a good model of congestive heart failure. Since depressed cardiac pump function is the hallmark of heart failure, it is suspected that decreased influx of Ca2+ into the cardiac cell is responsible for depressed contractile function. Because Ca2+ movements in the sarcolemmal membrane are known to involve Ca(2+)-channels, Na(+)-Ca2+ exchange, Ca(2+)-pump, Na(+)-K+ ATPase, beta-adrenoceptors and alpha-adrenoceptors directly or indirectly, the status of these mechanisms was examined by employing rats at different degrees of congestive heart failure. The left coronary artery was ligated and hearts were examined 4, 8, and 16 weeks later; sham-operated animals served as controls. The number of Ca2+ channels in the myocardium was depressed in moderate and severe stages of heart failure. Furthermore, depressions in sarcolemmal Na(+)-Ca2+ exchange activity and beta-adrenoceptor number were associated with the development of early stages of heart failure, whereas sarcolemmal Na(+)-K+ ATPase activity was decreased and the number of alpha-adrenoceptors was increased at moderate and severe stages. The Ca(2+)-pump activities were not altered in failing hearts. Thus it appears that changes in Na(+)-Ca2+ exchange as well as beta-adrenoceptors and Ca2+ channels may contribute towards decreasing Ca2+ influx at early and moderate stages of congestive heart failure, respectively. On the other hand, changes in alpha-adrenoceptors and Na(+)-K+ ATPase may act as compensatory mechanisms for maintaining Ca2+ influx at moderate and late stages of congestive heart failure.

Altered responsiveness of hypertrophied rat hearts to alpha- and beta-adrenergic stimulation

Inotropic responsiveness to α- and β-adrenergic agents was examined in pressure-overload hypertrophied rat hearts. Pressure overload was induced in rats by abdominal aortic constriction. Three weeks post-constriction, hearts were isolated and perfused with buffer containing various concentrations of (1) calcium (2) isoproterenol (3) forskolin, or (4) phenylephrine. The change in rate of left ventricular pressure development ( Δ + dP dt ) with increasing perfusate calcium concentrations was comparable in hypertrophied hearts of aortic-constricted rats (AC) and hearts of sham-operated rats (SO). However, with isoproterenol or forskolin stimulation, inotropic responsiveness ( Δ + dP dt ) was 50% lower in hypertrophied hearts of AC. This was associated with significantly lower tissue cAMP levels. Beta-adrenoceptor number and affinity were unchanged in the hypertrophied myocardium. Maximum inotropic responsiveness to phenylephrine was also lower in hypertrophied hearts and was associated with reduced α-adrenoceptor numbers. The data suggest that altered inotropic responsiveness to α-adrenergic stimulation may, in part, be due to reduced cardiac α-adrenoceptor density. However, post-receptor mechanisms including alterations in cAMP metabolism may contribute to the reduced responsiveness to β-adrenergic stimulation in hypertrophied hearts of AC.

Influence of short- and long-term inhalation of salbutamol on lung function and beta 2-adrenoceptors of mononuclear blood cells in asthmatic children.

Clinical observations have shown that some asthma patients develop tachyphylaxis to beta-sympathomimetic drugs. As down-regulation of the number of beta-adrenoceptors in different human tissues after exposure to catecholamines and beta-adrenergic drugs is well known, we investigated whether a interrelation exists between beta-adrenoceptor down-regulation and clinically detectable beta-adrenergic subsensitivity during beta-sympathomimetic treatment. The following results were obtained: 1. beta 2-Sympathomimetic inhalation treatment with salbutamol in therapeutic doses led to a significant down-regulation of beta 2-adrenoceptors and consecutive cyclic adenosine monophosphate response to isoprenaline. This effect was already detectable after short-term treatment of 3-7 days in 9 asthmatic children. 2. In the long-term study over 6 months, salbutamol inhalation in 12 asthmatic children led to a significant down-regulation of beta-adrenoceptor binding sites on mononuclear blood cells (MNC) from 1539 +/- 91 to 1115 +/- 99 after 14 days, remaining in this range thereafter. 3. The mean airway resistance (Raw) of these 12 patients decreased significantly within 14 days from 8.1 +/- 0.8 to 5.7 +/- 0.5 cm H2O/l/s to remain stable throughout the 6 months of salbutamol treatment. The differences in Raw before and immediately after inhalation of 0.2 mg salbutamol (2 puffs) were unchanged during the study period. It is concluded, that long-term inhalative treatment with salbutamol over a period of 6 months does not result in refractoriness to beta-adrenergic drugs in the airways of asthmatic children, even though a significant down-regulation of beta 2-receptors on peripheral MNC occurs.

Beta-adrenergic receptors in lymphocyte subsets after exercise. Alterations in normal individuals and patients with congestive heart failure.

Dynamic exercise increases the number of beta-adrenergic receptors in mixed lymphocytes by a mechanism that is incompletely understood. In a set of in vivo studies, we have investigated the effects of dynamic exercise on the subset distribution of circulating lymphocytes and on the number of beta-adrenergic receptors in each of these subsets in two groups of patients. In healthy subjects, exercise increased plasma norepinephrine and epinephrine and caused lymphocytosis. Whereas the number of Thelper cells increased only modestly, the number of Tsuppressor/cytotoxic and natural killer cells more than tripled. The number of beta-adrenergic receptors varied among subsets but was not significantly altered by dynamic exercise in any subset except natural killer cells (35% increase, p = 0.0302). In a group of patients with congestive heart failure, dynamic exercise increased plasma norepinephrine but did not alter plasma epinephrine and did not cause significant lymphocytosis. We did not detect any significant alterations of circulating leukocyte subsets or beta-adrenergic receptors in any of these subsets after exercise. A combined analysis of healthy patients and heart failure patients revealed a significant correlation between increases in plasma epinephrine and increases in circulating lymphocytes. We conclude that the exercise-induced increase in beta-adrenergic receptors of mixed lymphocytes is predominantly caused by a redistribution of circulating cell subsets that differ in their beta-adrenergic receptor number. This appears to be mediated by epinephrine rather than norepinephrine.

β-Agonistic properties of tulobuterol, a newβ-sympathicomimetic Drug, and its effects on pulmonaryβ-adrenoceptor characteristics

Radioligand binding studies have been developed to determine pharmacologic receptor characteristics in vitro. With this assay, not only the number and dissociation constant (KD) can be studied, but also the interaction of agonists with the receptor. We used this method to study a new beta 2-sympathicomimetic drug, tulobuterol (1-(0-chlorophenyl)-2-butylamino-ethanol hydrochloride). Two sets of experiments were performed. One set of experiments investigated the effects of tulobuterol and terbutaline in chronic administration, while the second set compared the beta-adrenoceptor-stimulating properties of tulobuterol with terbutaline and salbutamol. The effects of 10 days' administration of tulobuterol and terbutaline on beta-adrenergic characteristics in rats were assessed biochemically by means of radioligand binding studies on pulmonary membranes and functionally using isolated tracheal spirals. It was found that: (1) In vivo treatment with both drugs induced a reduction of the number of beta-adrenoceptors bound by 3H-dihydroalprenolol (3H-DHA); however, tulobuterol also induced an increased affinity for beta-adrenoceptor binding. (2) Tulobuterol induced a significant increase in the sensitization of tracheal smooth muscle, facilitating the relaxation of airway smooth muscle. The inhibition of 3H-DHA binding with the three drugs was best fit in a two-binding site model, showing high- and low-affinity binding sites. The high-affinity sites had similar KD values for terbutaline and tulobuterol (1.6 x 10(7) and 1.5 x 10(-7), respectively). The high-affinity sites for salbutamol had a higher KD value (9.4 x 10(-7), suggesting a lower affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

β-Adrenergic Sensitivity in Parkinsonʼs Disease

The beta-adrenergic sensitivity in never-treated and levodopa-treated patients with Parkinson's disease (PD) was studied through the evaluation of lymphocyte beta-adrenoceptor number ([125I]cyanopindolol binding sites) and chronotropic and metabolic (plasma nonesterified fatty acids--NEFA) responses to isoproterenol. No change was found in Bmax values or affinity constant Kd between never-treated patients, levodopa-treated patients with PD, and controls. At rest, no difference was observed in heart rate, plasma catecholamine, or NEFA levels between the three groups. Isoproterenol sensitivity (chronotropic response and plasma NEFA increase) was similar in never-treated and treated PD. The results suggest that peripheral beta-adrenergic sensitivity is unaffected either by the pathophysiological process of PD or by levodopa treatment.

Effect of oxygen tension on catecholamine-induced formation of cAMP and on swelling of carp red blood cells

We studied the effects of beta-adrenergic stimulation on the formation of adenosine 3',5'-cyclic monophosphate (cAMP) and on the cell volume in carp red blood cells in normoxia (PO2 = 150 mmHg) and hypoxia (PO2 = 8 mmHg). Accumulation of cAMP was the prerequisite for adrenergic cell swelling. Cell swelling was induced by beta-agonists, forskolin, and 8-bromo-cAMP. The amount of cAMP required for adrenergic swelling was minimal; swelling was observed at cAMP concentrations greater than 100 nM. Maximal increase in cell volume was observed at 200 nM cAMP. These values were independent of both the oxygen tension and the beta-agonist used. Norepinephrine caused the largest accumulation of cAMP, followed by isoproterenol and epinephrine. At hypoxic conditions, the cAMP concentrations obtained after stimulation with the natural catecholamines norepinephrine and epinephrine were greater than at normoxic conditions. The catecholamines caused appreciable cell swelling at lower concentrations in hypoxia than in normoxia. Thus the number of beta-adrenergic receptors, and their inherent ligand affinities, may be higher in hypoxic than in normoxic carp red blood cells. Oxygen tension had a pronounced effect on the magnitude of the adrenergic swelling. The maximal increase in cell volume was 5-7% in hypoxia, whereas in normoxia it was only approximately 2%. This was not due to differences in cAMP formation, but possibly to a greater activity of the Na(+)-H+ exchanger in hypoxic than in normoxic conditions.