Functional assessment of beta adrenoceptor subtypes in human colonic circular and longitudinal (taenia coli) smooth muscle.

BACKGROUND AND AIMS: The subtype and species related heterogeneity of beta adrenoceptors prompted a functional reappraisal of these molecular targets of motility inhibition in the human colon. METHODS: Relaxation of muscle strips was measured in vitro. RESULTS: The following agonists had decreasing relaxing potency (effective concentration range 10(-8)-10(-4) mol/l): (-)isoprenaline (non-selective), terbutaline (beta(2) selective), CGP 12177 (beta(3) selective, also beta(1), beta(2) antagonist), and SR 58611A (beta(3) selective). Isoprenaline and terbutaline were more potent on circular than taenia strips; CGP 12177 and SR 58611A weakly and partially relaxed taenia but had little effect on circular strips. The potency of isoprenaline on circular strips was greatly reduced by the beta(1) selective antagonist CGP 20712 (10(-7) mol/l), and less so by ICI 118551 (10(-7) mol/l, beta(2) selective). CGP 20712 and ICI 118551 together (both 3 x 10(-6) mol/l) had no effect on taenia relaxation by SR 58611A and rendered isoprenaline and terbutaline virtually inactive on circular strips, although not on taenia, which was relaxed at higher than control concentrations and maximally by isoprenaline. Propranolol, a beta(1), beta(2) non-selective antagonist, at high concentrations (10(-5) mol/l) prevented taenia relaxation by CGP 12177 and SR 58611A; its quantitative antagonism of isoprenaline (in common with that of CGP 12177 used as an antagonist) was competitive in circular strips but not on taenia. CONCLUSIONS: beta(1), beta(2), and beta(3) adrenoceptors are functionally detectable in the human colon; agonist stimulation of any one type relaxed taenia but only isoprenaline was fully effective at the beta(3) subtype.

The effect of oral terbutaline on maternal glucose metabolism and energy expenditure in pregnancy.

OBJECTIVE: Terbutaline, a selective beta2-agonist, is a frequently used tocolytic known to affect maternal metabolism. The purpose of this study was to evaluate the effect of oral terbutaline on maternal glucose metabolism and energy expenditure. STUDY DESIGN: Six healthy pregnant women with normal glucose tolerance were evaluated between 30 and 34 weeks' gestation. Oral terbutaline was administered to determine the effects on hepatic glucose production with [6-6(2)H2] glucose tracer, insulin sensitivity (hyperinsulinemic-euglycemic clamp), and energy expenditure (indirect calorimetry). Terbutaline, insulin, and glucagon levels were also obtained. Subjects were randomly assigned to either oral terbutaline 5 mg every 6 hours for 24 hours or no medication. Repeat studies were conducted 1 week apart, each subject serving as her own control. RESULTS: In the basal state terbutaline was associated with a trend toward increased basal glucose levels (81.6 +/- 6.6 vs 93.7 +/- 12.0 mg/dl, p = 0.06) but no significant increase in hepatic glucose production (3.2 +/- 0.3 vs 3.6 +/- 0.4 mg/kg fat-free mass/min, p = 0.23). However, there was a significant increase in basal insulin concentration (17.6 +/- 9.2 vs 25.6 +/- 10.4 microU/ml, p = 0.02). There was a 28% decrease in insulin sensitivity as measured by the glucose infusion rate during the euglycemic clamp plus residual hepatic glucose turnover (5.78 +/- 1.91 vs 4.16 +/- 1.49 mg/kg fat-free mass/min, p = 0.005). Glucagon concentration was significantly decreased both in the basal state (163 +/- 26 vs 144 +/- 27 pg/ml, p = 0.0007) and during the clamp (144 +/- 27 vs 133 +/- 27 pg/ml, p = 0.003). Basal oxygen consumption increased 9% (270 +/- 49 vs 294 +/- 50 ml oxygen/min, p = 0.007) and caloric expenditure 14% (1.32 +/- 0.23 vs 1.50 +/- 0.31 kcal/min, p = 0.025) or 260 kcal/day with terbutaline. CONCLUSION: Decreased peripheral insulin sensitivity, and to a lesser degree increased endogenous glucose production, may represent the pathophysiology of abnormal glucose tolerance observed in many women treated with oral terbutaline. Common side effects such as tremors and tachycardia experienced by many women on a regimen of terbutaline are consistent with our finding of a significant increase in basal energy expenditure.

In situ assessment of the role of the beta 1-, beta 2- and beta 3-adrenoceptors in the control of lipolysis and nutritive blood flow in human subcutaneous adipose tissue.

1. The involvement of beta 1-, beta 2- and beta 3-adrenoceptors in the control of lipolysis and nutritive blood flow was investigated in abdominal subcutaneous adipose tissue of healthy young adults by use of an in situ microdialysis technique. 2. Dialysis probes were infused either with isoprenaline (non-selective beta-adrenoceptor agonist), CGP 12,177 (selective beta 3-adrenoceptor agonist having beta 1-/beta 2-antagonist properties), dobutamine (selective beta 1-adrenoceptor agonist) or terbutaline (selective beta 2-adrenoceptor agonist). The recovery of each probe used for perfusion was calculated by an in vivo calibration method. The local blood flow was estimated through the measurement of the escape of ethanol infused simultaneously with the drugs included in the probe. 3. Isoprenaline infusion at 0.01 microM had a weak effect while higher concentrations of isoprenaline (0.1 and 1 microM) caused a rapid, sustained and concentration-dependent increase of glycerol outflow; the maximum increase was 306 +/- 34% with 1 microM. Isoprenaline also increased the nutritive blood flow in adipose tissue; a significant effect appeared at 0.1 microM isoprenaline and was greater at 1 microM. 4. CGP 12,177 (10 and 100 microM) increased the glycerol concentration in the dialysate (128 +/- 8 and 149 +/- 12%, respectively) and nutritive blood flow. Terbutaline and dobutamine (100 microM) both provoked rapid and similar increases in glycerol outflow (252 +/- 18 and 249 +/- 18%, respectively). Both, terbutaline and dobutamine increased nutritive blood flow. 5. It is concluded that beta 1- and beta 2-adrenoceptor subtypes are both mainly involved in the mobilization of lipids and in the control of nutritive blood flow. beta 3-Adrenoceptors play a weaker role in the control of lipolysis and nutritive blood flow in human subcutaneous abdominal adipose tissue.

Beta 2-agonists and running economy in prepubertal boys.

Asthmatic athletes (adults and junior) have competed successfully at the highest level for many years assisted by pre-event medication with beta 2-agonists. To examine the impact of beta 2-agonists upon submaximal running economy (oxygen consumption at a given submaximal work load), we studied 10 nonasthmatic boys (age, 10.4 +/- 0.48 years, mean +/- SD). They each completed submaximal (speeds, 7.2, 8.0 and 8.8 km/hr) and peak treadmill running protocols preceded by treatment with beta 2-agonist (terbutaline, 500 micrograms via nebuhaler) or placebo in a randomized, crossover single-blind study. No significant differences were found between running economy and heart rate during the submaximal exercise tests or between peak oxygen consumption (VO2), peak respiratory exchange ratio, peak heart rate (HR), or total running time during the peak VO2 test. Pretreatment with terbutaline did produce small but nonsignificant increases in aerobic fractional utilization (percent peak VO2 on drug: 65.9%, 72.6%, and 76.7% vs. placebo: 65.1%, 70%, and 75.5%), at the three submaximal work loads. Respiratory exchange ratio (RER) values were elevated throughout the submaximal tests (on drug: 0.94, 0.93, and 0.94 vs placebo: 0.91, 0.92, and 0.91, P < 0.05). No significant differences were found between drug and placebo for minute ventilation (VE) and ventilatory equivalent for oxygen (VE/VO2), at both submaximal and peak exercise intensities.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of influence of short-term treatment with propranolol and terbutaline on metabolism and energy expenditure of the Na-K pump in human erythrocytes evaluated by microcalorimetry.

A double blind placebo-controlled study was conducted of the effects of oral propranolol (beta 1 beta 2-adrenoceptor antagonist) and terbutaline (beta 2-adrenoceptor agonist) on erythrocyte heat production, measured by direct microcalorimetry under static conditions at 37 degrees C and pH 7.4. Propranolol 80 mg and terbutaline slow-release 7.5 mg were randomly administered twice daily for one week to 15 healthy males, using a cross-over design. No thermogenic difference was detected. Serum potassium was significantly decreased by terbutaline but was only slightly increased by propranolol, but no relationship was found between changes in the extra- and intracellular levels. In the placebo group, 10% of total cell energy was consumed by the Na-K pump, as assessed by ouabain inhibition, and this value was not significantly affected by the treatments. Thus, it seems unlikely that there is a clinically relevant influence on the Na-K pump in erythrocytes during continuous terbutaline or propranolol medication. It is concluded that short term medication with propranolol and terbutaline in therapeutic doses has almost no thermal or metabolic effect on human erythrocytes. The results indirectly imply that no clinically relevant beta-adrenoceptor effects are mediated in erythrocytes and this may also be true with regard to the 'membrane effect' of propranolol.

Long-term multicentre trial in chronic nonspecific lung disease: methodology and baseline assessment in adult patients. Dutch CNSLD Study Group.

Airways obstruction and airways hyperresponsiveness are two dominant features in patients with chronic nonspecific lung disease (asthma and chronic obstructive pulmonary disease (COPD)). We set up a study to determine whether long-term (3 yrs) therapeutic intervention directed at airways obstruction and hyperresponsiveness is superior to one directed at airways obstruction alone. Patients were selected on functional criteria (age, baseline forced expiratory volume in one second (FEV1), and airways hyperresponsiveness) and, furthermore, extensively characterized by history, smoking habits, allergy, reversibility of airways obstruction and quality of life. The methodology and practical problems of setting up this large multicentre study are outlined, together with an analysis of baseline data. Standardization of methods and techniques and recruitment of patients required much effort, recruitment taking about twice as long as expected. A 3 month feasibility study allowed us to eliminate minor problems in the protocol. Over a 16 month period, 274 adult patients (18-60 yrs) from the out-patient clinics of six university centres entered the study; 99 met the diagnostic criteria for asthma, 51 for COPD, 88 for asthmatic bronchitis, and 36 could not be classified. Their mean (SD) FEV1% pred was 65.1 (15.2)%. Their geometric mean provoking concentration of histamine producing a 20% fall in FEV1 (PC20 histamine) was 0.28 mg.ml-1. In a multiple regression analysis, more severe airways hyperresponsiveness was associated with lower prechallenge FEV1% pred (p less than 0.0001), higher pack-years of smoking (p = 0.0099), blood eosinophil count (p = 0.0004), skin test reactivity (p = 0.0047) and with female sex (p = 0.0302). We conclude that setting up long-term multicentre trials in chronic nonspecific lung disease (CNSLD) is feasible and that these may offer valuable information on treatment and outcome of the disease.

The ventilatory and oxygen costs in the anesthetized rhesus monkey of inhaling drugs used in the therapy and diagnosis of asthma.

We examined in male Rhesus monkeys the effects on oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart and respiratory rates, and functional residual capacity (FRC) of breathing normal saline (NS), salbutamol (albuterol), methacholine (MCh), sodium cromoglycate (SCG), epinephrine (adrenaline), and terbutaline in doses commonly prescribed to human infants and children. We studied 10 anesthetized and intubated monkeys with a mean age and weight of 6.0 yr and 9.1 kg, respectively. VO2 increased over control, by 46.5% after salbutamol (p less than 0.0005), 25% after methacholine (p less than 0.001), 13.2% after epinephrine (p less than 0.01), and 16% after terbutaline (p less than 0.001), but it did not increase after either SCG or NS. VE increased by 82% after MCh and salbutamol (p less than 0.001), less dramatically after epinephrine and terbutaline at 50.5 and 31.5% (p less than 0.02 and p less than 0.001), respectively, and not at all after SCG and NS. Heart rate response was greatest after salbutamol, and nodal and ventricular arrhythmias were noted in four of 10 monkeys after MCh challenge. FRC did not change significantly except after salbutamol, where there was a small rise of 1.8 ml/kg (p less than 0.05).

Assessment of beta-1 selectivity of bisoprolol and atenolol by means of their influence on the lipolytic response to an infusion of terbutaline.

We have investigated the beta-1 selectivity of a new beta-blocker, Bisoprolol, by comparing its effect on lipolysis induced by intravenous terbutaline infusion with that of Atenolol. At a dose of 5 mg, Bisoprolol had virtually no beta-2 blocking activity as measured by free fatty acid (FFA) release during terbutaline infusion. At a dose of 10 mg, Bisoprolol had a small but statistically insignificant effect on FFA release similar to 50 mg Atenolol. At a dose of 20 mg, Bisoprolol had significant beta-2 blocking activity. At lower doses, therefore, Bisoprolol is a very selective beta-blocker.

Two-week stimulation or blockade of the sympathetic nervous system in man: influence on body weight, body composition, and twenty four-hour energy expenditure.

Seven lean healthy young men were studied for 6 weeks during exposure to pharmacologic inhibition or stimulation of the sympathetic nervous system. For a period of 2 weeks their beta-adrenergic receptors were either blocked with propranolol hydrochloride (160 mg/d) or stimulated with terbutaline sulphate (15 mg/d). After a further 2 weeks of placebo administration (500 mg lactose/d), the subjects crossed over to the drug they had not been taking at the beginning of the experiment for another 14 days. During the last five days of each 2-week period, the subjects consumed a weight-maintaining diet, composed of 12% protein, 48% carbohydrate, and 40% fat. They consumed exactly the same menus on the same days during the subsequent study periods. Body weight and physical activity were measured every day for 6 weeks. Daily heart rate and nitrogen excretion were measured continuously for days at the end of each 2-week period, the last two days of which were spent in a respiration chamber where energy expenditure and a variety of metabolic parameters were measured. In the respiration chamber on the propranolol, placebo, and terbutaline treatments, respectively, significant differences were observed in mean daily heart rate (65 +/- 3, 75 +/- 4, and 84 +/- 4 beats/min), mean sleeping heart rate (51 +/- 2, 56 +/- 3, and 62 +/- 3 beats/min), nitrogen excretion (13.6 +/- 0.7, 12.6 +/- 0.6, and 11.9 +/- 0.6 g/d), fat oxidation (+1,045 +/- 95, +1,243 +/- 148, and +1,278 +/- 84 kcal/d) and thyroid hormones (12.0 +/- 0.7, 15.7 +/- 0.9, and 17.2 +/- 1.0 T3/T4 ratio).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic beta-receptor stimulation on sympathetic nervous system activity, energy expenditure, and thyroid hormones.

The effects of hyper- and hypothyroidism on sympathetic nervous system activity and energy expenditure are well recognized. The impact of altered sympathetic nervous system activity on energy expenditure and thyroid hormone metabolism has not been well studied. We investigated the effects of orally administered terbutaline sulfate, a beta 2-receptor agonist (5 mg, three times per day for 2 weeks), on the activity of the sympathetic nervous system, energy expenditure, and thyroid hormone metabolism in six normal men, aged 21-36 yr. The cardiovascular, metabolic, and thermogenic responses to an infusion of the beta-adrenergic agonist isoproterenol were clearly blunted after 2 weeks of treatment with terbutaline sulfate, indicating down-regulation of beta-receptors and/or development of reduced sensitivity. There were no significant changes in the cardiovascular, metabolic, or thermogenic responses to an infusion of the alpha-adrenergic agonist phenylephrine. Basal metabolic rate was significantly increased by the chronic administration of terbutaline sulfate [5.040 +/- 0.167 (+/- SE) vs. 5.421 +/- 0.234 kJ/min; P less than 0.05]. There was a highly significant change in the serum T3 to T4 ratio (19.4 +/- 1.0 vs. 24.4 +/- 1.0; P less than 0.001). This was a result of increased serum T3 concentrations (136 +/- 9 vs. 160 +/- 14 ng/dl; P less than 0.05) and decreased serum T4 concentrations (7.2 +/- 0.8 vs. 6.7 +/- 0.8 micrograms/dl; P = NS). Chronic beta-receptor stimulation with terbutaline sulfate increases the basal metabolic rate and T3 concentrations. These changes occurred despite down-regulation of beta-receptors and/or decreased sensitivity in response to chronic terbutaline administration.

Theoretical and practical problems with the assessment of intrinsic efficacy of agonists: efficacy of reputed beta-1 selective adrenoceptor agonists for beta-2 adrenoceptors.

Agonist effects of the reputedly beta-1 selective adrenoceptor agonists prenalterol, dobutamine and tazolol were compared, in rat uterus, with those of the reportedly beta-2 selective agonist, terbutaline. Butoxamine was a simple competitive antagonist of responses to all agonists with a 10 to 16 times greater potency in rat uterus than in guinea-pig left atria. Similarly, atenolol was 50 to 80 times less potent as an antagonist of all agonists in rat uterus than guinea-pig left atria. The Schild regressions for both antagonists, when subjected to analyses of covariance of regression lines, yielded no evidence to suggest that the reputedly beta-1 selective agonists activated receptors different from those activated by terbutaline in rat uterus. These data indicated that the responses produced by these agonists in rat uterus were due to stimulation of beta-2 adrenoceptors under current classifications. An analysis of the relative intrinsic efficacy of prenalterol on beta-2 as opposed to beta-1 adrenoceptors indicated a nonselective efficacy at the receptor level. The implications of these data in terms of tissue-related efficacy (i.e., intrinsic activity) and receptor-related intrinsic efficacy (as defined by Furchgott) are discussed as a caveat to ascribing tissue selectivity to receptor selectivity without the appropriate data. Specifically, estimates of selective agonist efficacy at receptors should be made on the basis of selective intrinsic efficacy and not on measurements of agonists potency or maximal responses.