Myocardial β-adrenergic reactivity in pressure overload-induced cardiac hypertrophy in the rat

Summary— The purpose of this study was to evaluate the changes in myocardial β-adrenergic reactivity in animals undergoing a 4 week cardiac pressure-overload. Abdominal aortic constriction (AAC) or sham operation (sham) were performed in male Wistar rats, and 4 weeks later, isoprenaline dose-effects (chronotropic, inotropic and lusitropic properties) were studied after pithing. Noradrenaline (NA) and adrenaline (A) concentrations and NA turn-over index (DHPG /NE ratio) were evaluated in heart ventricles, while β-adrenoceptor characteristics in ventricle homogenates and slices with [¹²⁵I]iodocyanopindolol and the β(1)/β(2)-adrenoceptor ratio were estimated. Four weeks of cardiac pressure overload resulted in a 70% increase in ventricle weight/body weight ratio (from 2.5 ± 0.1 to 4.2 ± 0.3 mg/g in sham and AAC rats, respectively) and a 24% increase in protein contents (from 11.3 ± 0.7 to 14.0 ± 1.1 mg/100 mg ventricle in sham and AAC rats respectively). The ventricle NA content was similar in AAC and sham, while the ventricle A content and NA ***turn-over index were significantly increased in AAC rats (35 and 80% vs sham, respectively). Dose response of isoprenaline was significantly shifted to the right for all studied effects in AAC rats. However, maximal response (in relative values) was similar in AAC and sham rats only for heart rate but not for parameters depending on left ventricle contractile response. The β-adrenoceptor density was significantly decreased in AAC by 30% without apparent affinity change and due to decreases in β(1)-sites in septum and to β(1)- and β(2)-adrenoceptors in left ventricle endocardium. Decreases in isoprenaline-induced cardiac responses in AAC rats are associated with β(1)-adrenoceptor density reduction and modification of β(1)- and β(2)-adrenoceptor ratio. These modifications are not the only reason for such dose response changes, at least for contractile response.     

Amiodarone: influence of the route of administration on thyroid status and cardiac β-adrenoceptors in the rat

The influence of 2 different routes of amiodarone (AMIO) administration, oral gavage (OG) and subcutaneous injection (SC), on the density of cardiac beta-adrenoceptors (Bmax), hepatic type I 5' iodothyronine deiodinase (5' DI) and thyroid hormone serum concentrations was studied. Compared with respective control values, AMIO treatment (50 mg/kg per day, 7 days) via both OG and SC routes significantly lowered Bmax (OG: 14.6 +/- 1.92 vs 18.2 +/- 1.03 fmol/mg and SC: 16.6 +/- 2.34 vs 19.1 +/- 2.05 fmol/mg) and 5' DI activity (from 409 to 85 and 340 to 47 fmol I-/mg per min, respectively). The SC route induced a fall in thyroid secretion and a generalized hypothyroidism (decreased serum FT4 and FT3, inhibition of body weight gain. The OG route did not modify thyroid secretion. These results demonstrated that the effects on cardiac beta-receptor density in the SC group might be due to the generalized hypothyroidism and that AMIO produced its specific cardiac effects only after oral route medication, suggesting that the oral route is the best choice for studying AMIO cardiac effects on beta-receptor density.     

CHARACTERIZATION OF β-ADRENOCEPTORS IN MYOMETRIUM OF PREPARTURIENT RATS

The purpose of this study was to characterize the beta-adrenoceptor subtypes in pregnant rat myometrial membrane fractions and to determine the concentration of beta 2-adrenoceptors in uterus during late pregnancy. Two methods are compared. A non-subtype-selective antagonist radioligand [3H]dihydroalprenolol ([3H]DHA) was used to label all of the beta-adrenoceptors. [3H]DHA bound to both beta 1- and beta 2-adrenoceptors with indistinguishable affinity (KD = 1.31 nM, Bmax = 174 fmol/mg protein). Computer modelling of competition curves of unlabeled selective antagonists or agonists was then required in order to determine reliably beta 1- and beta 2-adrenoceptor affinities and proportions: the beta 1-adrenoceptors represent 35.5% and the beta 2-adrenoceptors 64.5% of the entire beta-adrenoceptor population in rat gravid myometrium at term. The second approach utilized the radioligand [3H]hydroxybenzylisoproterenol ([3H]HBI) which is a very high-affinity beta-adrenoceptor agonist. The characteristics of the [3H]HBI binding sites are essentially those expected of beta 2-adrenoceptors, but the [3H]HBI binding sites represent only 34% of [3H]DHA binding sites and may represent the fraction of beta 2-adrenoceptors that mediate adenylate cyclase stimulation and uterine relaxation. Between 21 d 09 h and 22 d 09 h of gestation, the number of beta 2-adrenoceptors was constant (mean = 225.6 +/- 20.2 fmol/mg protein). At term, the number of [3H]HBI binding sites dropped (-75%) during the last 7 h of pregnancy, suggesting a reduced ability to elicit relaxation through beta-adrenoceptor activation in parturient myometrium of rat.     

Platelet α2- and leucocyte β2-adrenoceptors in phaeochromocytoma: effect of tumour removal

Platelet alpha 2- and leucocyte beta 2-adrenoceptors (as well as noradrenaline and adrenaline plasma levels) were studied in five patients with confirmed phaeochromocytoma using tritiated yohimbine and iodated cyanopindolol, respectively, before and after tumour removal. Patients with phaeochromocytoma had a lower leucocyte iodated cyanopindolol binding than control subjects, but no change in platelet tritiated yohimbine binding. Plasma catecholamine levels were higher than controls. Tumour removal induced a return to normal values of leucocyte iodated cyanopindolol binding and a decrease in plasma catecholamine levels. These results underline the potential interest of leucocyte beta-adrenoceptor quantification in the diagnosis and the follow-up of phaeochromocytoma. Pharmacologically, they show that down-regulation occurs in vivo for leucocyte beta 2-adrenoceptors but not for platelet alpha 2-adrenoceptors.     

Increased α2- but similar β-adrenergic receptor activities in subcutaneous gluteal adipocytes from females compared with males

alpha 2 and beta-adrenergic binding and action were studied in subcutaneous adipocytes from the gluteal region in females and males. The beta-selective antagonist [3H]dihydroalprenolol and the alpha 2-selective antagonist [3H]yohimbine were used to identify the beta- and the alpha 2-receptor, respectively. The biological effects mediated by these receptors were determined by measuring the glycerol release induced by isoproterenol (beta-receptor agonist) and by clonidine (alpha 2-receptor agonist). The study consisted of health volunteers (eighteen females and fifteen males). Compared to men the alpha 2-receptor binding was increased by 73% (P less than 0.01) in adipocytes from females. From Scatchard analysis it was determined that the increased binding was due to an increased receptor number (438 v. 262 fmol mg-1 protein, P less than 0.001) with unaltered Kd (1.18 v. 1.35 nmol l-1, P greater than 0.05). This increased alpha 2-receptor binding in female and adipocytes was associated with a significantly increased sensitivity (P less than 0.05) and maximal antilipolytic effect of clonidine (P less than 0.05). The beta-receptor binding was similar in adipocytes from females and males. However, isoproterenol was significantly more lipolytic in female adipocytes (P less than 0.01). Since the combination of theophylline and adenosine deaminase also was significantly more lipolytic in female adipocytes the enhanced effect of isoproterenol then seemed to be due to mechanisms not directly related to the hormone-beta-receptor binding. Finally, the mixed beta- and alpha 2-receptor agonist, adrenaline showed biphasic effects on lipolysis, with stimulatory effect at low concentrations (less than 500 nmol l-1) and pronounced inhibitory effect at higher concentrations (greater than 1 mumol l-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Whether phenylephrine exerts inotropic effects through α- or β-adrenoceptors depends upon the relative receptor populations

Phenylephrine produced concentration-related positive inotropic responses in isolated left atria and papillary muscles of guinea-pigs and rats. In rat tissues, these responses were unaffected by propranolol but antagonized by prazosin and therefore mediated via alpha 1-adrenoceptors. The alpha 1-adrenoceptor agonist methoxamine also exerted positive inotropic effects in these rat tissues. The maximum alpha-adrenoceptor-mediated effect of methoxamine (relative to the isoprenaline maximum) was greater than that of phenylephrine in left atria (in the presence of propranolol), whereas in papillary muscles phenylephrine exerted the greater maximum. In guinea-pig papillary muscles, the response to phenylephrine was unaffected by prazosin but was antagonized by propranolol and therefore caused by stimulation of beta-adrenoceptors. Methoxamine had no effect in guinea-pig papillary muscles. Guinea-pig left atria produced biphasic concentration-response curves for phenylephrine, the lower portion being antagonized by phentolamine and was therefore alpha-adrenoceptor-mediated, while the upper portion was antagonized by propranolol and therefore beta-adrenoceptor-mediated. Methoxamine exerted a small inotropic response, the maximum of which was similar to that of the first component of the phenylephrine response. Phenylephrine was a partial agonist for the cardiac beta-adrenoceptor. The density of rat ventricular alpha-adrenoceptors was 4 times greater than beta-adrenoceptor density, as measured by [3H]-prazosin and [3H]-dihydroalprenolol binding. This explains why the responses of rat papillary muscles were alpha-adrenoceptor-mediated. In contrast, the density of beta-adrenoceptor binding sites in guinea-pig ventricles was 6 times greater than the alpha-adrenoceptor density. This explains why the phenylephrine responses were beta-adrenoceptor-mediated in guinea-pig papillary muscles. In the left atria of guinea-pigs, which displayed both alpha- and beta-adrenoceptor-mediated responses, the densities of alpha- and beta-adrenoceptor binding sites were similar. Thus, phenylephrine exerts positive inotropic effects through alpha- or beta-adrenoceptors depending upon their relative densities.     

Differences in β-adrenergic receptor density and adenylate cyclase activity between normal and leukaemic leukocytes

Abstract. An identical class of high-affinity binding sites for the ¹²⁵I-labelled β-adrenergic antagonist hydroxybenzylpindolol, was identified on intact human normal and leukaemic peripheral blood leukocytes. On normal unfractionated lymphocytes, polymorphonuclear leukocytes, and monocytes, receptor density did not differ significantly (1200–1400 receptors per cell; P > 0.3), but it was higher on B- than on T-lymphocytes ( P < 005). In leukaemia, monocytic blast cells expressed highest receptor numbers, whereas very low receptor density was seen on the pathologic B-cells from chronic lymphocytic leukaemia. Among normal leukocytes, adenylate cyclase activation by hormones (isoproterenol, prostaglandin E₁, histamine) and sodium fluoride was strongest in plasma membranes from monocytes, but very weak in polymorphonuclear leukocytes either due to uncoupling of hormone receptors from adenylate cyclase or to low catalytic activity. In T-cells, enzyme activity was significantly lower than in B-cells. Loss of adenylate cyclase sensitivity to hormones and fluoride occurred in leukaemic cells from chronic and acute lymphocytic leukaemia.     

Cardiac β-adrenoceptor sensitivity and Parkinson''s disease

Certain clinical manifestations of Parkinson's disease (PD) (speech or/and balance disturbances) are not linked to brain dopamine deficiency. The purpose of the present study was to search for a possible relationship between those so-called "non-dopamine-dependent" extrapyramidal manifestations and the sensitivity of cardiac beta-adrenoceptors. Fourteen patients aged 51 to 69 were included in the study after having given their informed consent. Any factor or pathology susceptible to modify receptor sensitivity entailed exclusion. In the absence of a reference model for measuring the reactivity of central beta-adrenoceptors, a computation of the isoprenalin dose necessary to increase the resting heart rate by 20 bpm was used as an index for beta-adrenergic system reactivity. In addition to that test, other parameters were recorded: disease duration, motor status scale (Columbia), some cognitive functions (MMS and image differed recall). The cardiac beta-receptor decrease in reactivity to isoproterenol is correlated to PD duration (r = 0.8, P less than 0.001). Conversely, the sensitivity of these receptors appeared to be unrelated to the extrapyramidal severity of the disease, hence to the degree of the so-called "non dopamine-dependent" disturbances. Furthermore, such results raise the meaning of the impairment of peripheral aminergic receptors in the cognitive disturbances linked to ageing and/or PD.     

EFFECT OF DOPAMINE, IBOPAMINE, AND EPININE ON α- AND β-ADRENOCEPTORS IN CANINE PULMONARY CIRCULATION

Dopamine has been widely utilized in the treatment of acute congestive heart failure, ibopamine, the diisobutyrate ester of N-methyldopamine (epinine), is a novel inotropic agent that, unlike-dopamine, is orally active. In clinical studies at doses that produce favorable hemodynamic responses, ibopamine and dopamine can evoke a slight and transient increase in pulmonary artery pressure and pulmonary capillary wedge pressure, an effect that is no longer apparent 1 h after administration. We have previously demonstrated in anesthetized dogs that this effect is due to stimulation of alpha-adrenoceptors in the pulmonary circulation by dopamine and ibopamine, as well as by the active form of ibopamine, epinine. The aim of the present investigation was to determine how dopamine, ibopamine, and epinine interact with beta-adrenoceptors in the canine pulmonary circulation, since this activity may serve to offset the alpha-adrenoceptor-mediated pulmonary vasoconstrictor responses. Intraarterial injection of dopamine, ibopamine, and epinine resulted in dose-dependent pulmonary vasoconstrictor responses with a maximum increase of approximately 50-60% above resting pulmonary vascular tone. When animals were pretreated with propranolol (1 mg/kg iv) to block beta-adrenoceptors, pulmonary vasoconstrictor responses to dopamine were unchanged, whereas pulmonary vasopressor responses to ibopamine and epinine were significantly potentiated, especially for epinine. Upon intraduodenal administration of a therapeutically effective dose of ibopamine (i.e. 36 mg/kg) to normal dogs, virtually no pulmonary pressor response was observed. However, administration of this same dose of ibopamine to dogs pretreated with propranolol (1 mg/kg iv) resulted in a marked pulmonary pressor response. These data indicate that epinine, and therefore the parent compound ibopamine, have the capacity to stimulate beta 2-adrenoceptors in the pulmonary circulation to a far greater degree than dopamine, and that this activity serves to offset, at least in part, the alpha-adrenoceptor-mediated pulmonary vasoconstriction that occurs in response to ibopamine.     

Differential activation of β1-, β2- and β3-adrenoceptors by catecholamines in white and brown adipocytes

Summary— This review summarizes the experiments performed by various groups to determine how the activation of the different β-adrenoceptors (β-ARs) is ordinated when they are present in the same fat cell and involved in the same biological event. When expressed after the transfection of their genes in Chinese hamster ovary cell (CHO cells), β₁- and β₂-ARs present a higher affinity for catecholamines than β₃-ARs. In vitro, the lipolytic effect induced by low concentrations of catecholamines in dog and rat white fat cells is due to the selective activation of β₁- and/or β₂-ARs. Higher concentrations only are able to activate β₃-ARs. Similar results have been obtained in rat brown adipocytes. On the other hand, the lipolytic effect of catecholamines in human and primate adipocytes does not involve a β₃-AR component whatever the concentration used. In vivo experiments in the dog have also shown that lipomobilization induced by low doses of isoprenaline only involved β₁- and β₂-AR activation, this effect being blocked by β₁-/ β₂-antagonist pretreatment. However, in the same blockade conditions, perfusion of a 10-fold higher dose of isoprenaline revealed a β₃-AR contribution in the lipomobilizing effect. These data showed that brown and white adipocyte β₃-ARs possess a lower affinity for catecholamines than β₁- and β₂-ARs and are only recruited by high concentrations of the amines. Thus, even if the β₃-AR plays an indisputable role in the white and brown adipose tissue of some species, its physiological status and its expression are still subject to debate in human white fat cells.     

β-Adrenoceptor density in patients with left-sided valvular regurgitation

Summary— Aortic regurgitation differs from mitral regurgitation in that it is a result of combined volume and pressure overload, while the latter represents an almost pure volume overload. In this study, we tested the possibility that these two forms of left ventricular volume overload exert different effects on β-adrenoceptor density. Lymphocyte (n = 33) and myocardial (n = 22) β-adrenoceptor densities were evaluated by [¹²⁵I]-iodocyanopindolol binding in volume-overloaded patients with left heart valvular disease, compared with 31 healthy donor blood and 15 donor heart controls, made available as a result of failing to get matching recipient. The total lymphocyte (LC) β-adrenoceptor density decreased from 43.4 ± 5.5 fmol mg^?1 protein in controls to 9.2 ± 2.7 fmol (P < 0.001) in heart valvular patients. In the myocardial controls, the left ventricular (LV)-receptor density was 126.7 ± 19.5 fmol; right ventricular (RV), 123.1 ± 14.6 fmol; left atrial (LA), 81.6 ± 10.5 fmol; and right atrial (RA), 108.1 ± 14.5 fmol mg^?1 protein. Compared to this group, the total LV-receptor density of the patients decreased by 63%, RV by 54%, LA by 31% and RA by 34%. The decrease in receptor density exhibited a positive correlation with increasing ejection fractions in both the left (r = 0.38) and right (r = 0.44) ventricles, indicating that the former was dependent on the extent of the disease. These changes were accompanied by a 44% increase in plasma epinephrine, 13% in norepinephrine and a 27% decrease in dopamine levels. Based on the predominant left ventricular volume overload classified as aortic regurgitation (AVR), mitral regurgitation (MVR) and mixed aortic and mitral regurgitation (MOL), the attenuation in myocardial-receptor densities showed the following trend: MOL > MVR > AVR. The results show a global reduction in myocardial and LC β-adrenoceptor density, which depends on the origin and the gravity of the LV volume overload.     

Cardiac β-adrenoceptors and adenylyl cyclase activity in human left ventricular hypertrophy due to pressure overload

Summary— The effect of left ventricular hypertrophy (LVH) due to chronic pressure overload on right atrial (RA) and left ventricular (LV) myocardial β-adrenergic receptor (β-AR) density and subtypes, adenylyl cyclase (AC) activity and ADP-pertussis toxin ribosylated proteins was investigated in humans with LVH due to aortic stenosis and in patients without LVH undergoing heart surgery for mitral stenosis or coronary artery disease taken as controls. Both groups presented normal systolic function or plasma catecholamine levels. In LVH and controls, β-AR density was similar in RA (62 ± 6 vs 77 ± 12 fmol·mg^?1 protein) and LV (39 ± 7 vs 32 ± 2 fmol·mg^?1 protein). In LVH, β₁-AR percentage was < than in controls in LV (35 ± 11 vs 73 ± 5%, P < 0.05) but not in RA (79 ± 5 vs 73 ± 8%). Basal AC activity in RA (19 ± 4 vs 21 ± 6 pmol·;mg^?1 protein) and LV (22 ± 5 vs 27 ± 3 pmol·mg^?1 protein) was similar in LVH and in controls. Isoprenaline-induced stimulation of AC in RA was similar in LVH and in controls (51 ± 18 vs 36 ± 18%) but < in LV of LVH (7 ± 6 vs 45 ± 6%, P < 0.05). In the presence of ICI-118,551 (a β₂-adrenoceptor antagonist), isoprenaline failed to induce any increase in cAMP in LVH. The quantification of ADP-pertussis toxin ribosylated proteins indicated a lower concentration of substrates in LV myocardial membranes from LVH. These data indicate that in LVH due to pressure overload, there is a down-regulation of β₁-AR and an increase in β₂-AR density. This is associated with alterations of the transmembrane signalling marked by a decreased capacity of isoprenaline to stimulate AC and an impaired expression of Gi proteins.     

β-adrenergic priming of rats in vivo modulates the effect of β-agonist in vitro on surfactant phospholipid metabolism of isolated lungs

Abstract. To evaluate the effects of multiple β -adrenergic stimulations on pulmonary surfactant phospholipids, perfused lungs from β -adrenergic primed and non-primed rats were challenged with the β -agonist terbutaline in vitro . Cell-free lung lavage, lavagable alveolar cells and lung tissue were analysed for phospholipid content and incorporation of precursors. In lung lavage, terbutaline in vitro doubled the incorporation of ¹⁴C-choline and ³H-palmitate into total phosphatidylcholine (PC) and of ³H-palmitate into phosphatidylglycerol (PG). β -adrenergic priming in vivo prior to terbutaline in vitro lowered the increase of precursor incorporation. For lavagable cells, terbutaline in vitro increased the incorporation of ³H-palmitate into PC. Priming in vivo reduced this effect and diminished the specific ³H-choline incorporation into lavagable cell PC below control level. For lung tissue, priming increased the amounts of PC and disaturated PC (DSPC) whereas terbutaline in vitro decreased DSPC in both primed and non-primed lungs. Terbutaline in vitro slightly increased the incorporation of ¹⁴C-choline and ³H-palmitate into PC and DSPC in non-primed but not in primed lungs. β -adrenergic blockade by ICI 118.551 prevented all effects but generally increased ³H-palmitate incorporation into the phospholipids and, in lavagable cells, the amount of PC. We conclude that long-term β -adrenergic treatment may alter the metabolism of pulmonary surfactant phospholipids by increasing tissue PC and DSPC and by decreasing the secretion of newly-synthesized PC.     

Primary headaches: reduced circulating β-lipotropin and β-endorphin levels with impaired reactivity to acupuncture

Eleven patients affected by common migraine (CM), eleven affected by daily chronic headache (DCH), and eight healthy volunteers were studied. Plasma levels of beta-endorphin (beta EP), beta-lipotropin (beta LPH). ACTH and cortisol were measured in basal conditions and after traditional Chinese acupuncture (TCA). Basal beta LPH and beta EP plasma levels (pg/ml) in the DCH patients (57.6 +/- 9.5 and 16.8 +/- 2.5, respectively; M +/- SE) were lower than those found in the controls (83.6 +/- 13.7 and 26.0 +/- 6.1; p less than 0.001), while those found in the CM cases showed inter-mediate values (75.3 +/- 12.0 and 24.4 +/- 5.8). ACTH and cortisol concentrations in both the CM and DCH patients were in the same range as those of the control group. TCA caused an increase in beta LPH and beta EP plasma concentrations in the control group (beta LPH: 117 +/- 16.9; beta EP: 44.1 +/- 6.7). Opioid plasma levels, however, remained unmodified after TCA in both the CM and DCH groups. ACTH plasma levels remained stable after TCA in all three subject groups. Patients suffering from primary headache are characterized by low beta LPH and beta EP plasma levels and by a poor reactivity of circulating opioids to non-stressful stimuli.     

Triiodothyronine and amiodarone effects on β3-adrenoceptor density and lipolytic response to the β3-adrenergic agonist BRL 37344 in rat white adipocytes

Summary— The β-adrenergic effects of catecholamines are potentiated by thyroid hormones in adipose tissue. Amiodarone (AM) is structurally similar to thyroid hormones and was used to explore the mechanism of the triiodothyronine (T₃) effect on β-adrenergic receptors (β-ARs) in adipose tissue. AM decreases the expression of some T₃ sensitive genes in various tissues and antagonizes the effect of T₃ on its nuclear receptors. In this study, the T₃, AM and AM + T₃ effects on the β1- and β₃-AR density were assessed on rat white adipocytes by radioligand binding using [³H]CGP 12177 after characterization of these subtypes by displacement of [³H]CGP 12177 binding by isoproterenol, BRL 37344 and noradrenaline. BRL 37344 was used to study β₃-AR lipolysis. White adipocytes from hyperthyroid rats had increased responsiveness (E_max × 2) and sensitivity (+ 38%) to BRL 37344, while those given AM alone had decreased values. Moreover, AM antagonized the T₃ effect on lipolysis. The β₁-binding characteristics (receptor density [B_max]: 45 ± 4 fmol/mg of proteins; dissociation factor [K_d]: 0.96 ± 0.10 nM) were not modified by either compound. Finally, T₃ significantly increased β₃-AR density (587 ± 69 versus 363 ± 25 fmol/mg of proteins) and K_d (38 ± 2 versus 23 ± 3 nM), while AM alone had no effect and did not antagonize the T₃ effect on β₃-AR number. In conclusion, the hyperthyroid state in the rat potentiated the lipolytic response of white adipocytes to a specific β₃-agonist and increased the β₃-AR density without changing in β₁-AR number and affinity. Furthermore, the lack of antagonism between AM and T₃ on β₃-AR expression suggests that T₃ does not work directly on the β₃-AR gene. Moreover, AM induced a functional tissular hypothyroid-like effect and its antilipolytic effect probably occurred at a postreceptor level.     

Reduced β-adrenergic sensitivity in healthy volunteers induced by hypoglycemia

Summary— A single causative mechanism for development of hypoglycemia unawareness in insulin-dependent diabetes mellitus (IDDM) is not yet apparent. Reduced adrenergic sensitivity may be part of the explanation. This study was carried out to investigate the effect of hypoglycemia on β-adrenergic sensitivity. Ten healthy male subjects (age 19–23 years) gave informed consent to take part in the study. They were hospitalized overnight at the University Hospital of Tromsø, Department of Clinical Research, on two occasions. Isoprenaline and metoprolol sensitivity tests were performed the morning after hospitalization: once after an intravenous (iv) injection of placebo (0.9% NaCl), and once after an iv injection of insulin (0.15 IU insulin/kg body weight) to induce hypoglycemia. The dose of isoprenaline needed to increase heart rate (HR) by 25 beats per minute (bpm) (I₂₅), and the dose of metoprolol (M_–12.5) needed to inhibit I₂₅ with 50% or 12.5 bpm, when injected simultaneously, were used as determinants of isoprenaline and metoprolol sensitivity. In this study, there was a significant ( p < 0.05) increase both in I₂₅ and M_–12.5 after hypoglycemia. The dose-response curve of isoprenaline/HR was significantly shifted to the right after hypoglycemia. This study shows that acute hypoglycemia induces a reduction in β-adrenegic sensitivity, and it supports the hypothesis of reduced β-adrenergic sensitivity as an important pathophysiological mechanism in hypoglycemia unawareness in IDDM.     

Glucocorticoid modulation of muscarinic and β-adrenergic receptors in guinea pig lung

Summary— We investigated the effect of the in vivo treatment of guinea pigs with methylprednisolone, 10 mg/kg daily, on lung muscarinic and β-adrenergic receptors. Receptor densities were assessed by saturation experiments of tritiated N-methylscopolamine and dihydroalprenolol binding to lung membranes. After 3 h of treatment, methylprednisolone induced a decrease of 19.2% ( P < 0.05) of muscarinic receptors but was without effect on β-adrenergic receptor density. After 24 h, an increase of 39.7% ( P < 0.01) and 16.9% ( P < 0.05) was observed for muscarinic and β-adrenergic receptors, respectively. For muscarinic receptors, this increase reached 53.4% ( P < 0.01) within 48 h and stayed at this level until 96 h. The increase of β-adrenergic receptors was maximal (24.9%) after 72 h and returned to the control value after 96 h. The dissociation constant (K_d) values of both ligands were not affected by the glucocorticoid treatment. Functional studies showed that the 96 h treatment did not affect the contractile response of guinea pig lung parenchymal strips to carbachol since the 50% concentration value (EC₅₀) and the maximal contraction value (E_max) were not significatively different from control values. These data show that glucocorticoids control the expression of both muscarinic and β-adrenergic receptors in guinea pig lung but with different time courses and to a larger extent for muscarinic receptors. The glucocorticoid treament did not modify the contractile response of lung strips to carbachol, confirming the absence of effect on the affinity of muscarinic receptors and suggesting that the receptor reserve exceed the increase of their density by the steroid.     

Effects of AT1- and β-adrenergic receptor antagonists on TGF-β1-induced fibrosis in transgenic mice

Background Transforming growth factor‐β1 (TGF‐β1) is involved in interstitial remodelling promoting collagen synthesis and suppressing collagen degradation by inhibition of collagenases. TGF‐β1 mediates angiotensin II‐dependent effects and modulates β1‐adrenergic signalling. To study the effect of neuroendocrine antagonism on TGF‐β‐induced hypertrophic and fibrotic phenotype, we treated TGF‐β1 (Cys223,225Ser) transgenic mice (TGF‐β1‐TG) with either the β1‐receptor blocker metoprolol (MET), the angiotensin II type I (AT1)‐receptor antagonist telmisartan (TEL) or an antibody blocking TGF‐β1 signalling (TGFβ1‐sR‐Ab). Material and Methods Transforming growth factor‐β1‐TG mice (8 weeks) overexpressing TGF‐β1 were treated with either TEL (10 mg kg^?1), MET (350 mg kg^?1) or a soluble TGF‐β1 receptor antibody (1 mg kg^?1) for 6 weeks. Morphological analyses of interstitium and cardiomyocytes were related to expression of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) by immunoblotting and zymography. Results In TGF‐β1‐TG mice, myocardial interstitial total collagen content was fourfold elevated compared to that of controls (P < 0·05) and was lowered under the treatment with TEL (P < 0·05). Protein expression of TIMP‐1 and ‐4 was increased in TGF‐β1‐TG but inhibited by TEL (TIMP‐1 and TIMP‐4) and MET (TIMP‐1), while collagenase activity was decreased in TGF‐β1‐TG and normalized by treatment with TEL (MMP‐1 and MMP‐13) and MET (MMP‐1) (P < 0·05). Morphometric measurements of cardiomyocyte diameter and area demonstrated similar antihypertrophic effects for all treatment groups. Conclusion The AT1‐antagonist TEL reduced myocardial hypertrophy and interstitial fibrosis in TGF‐β1‐TG mice by normalizing MMP/TIMP ratio. β1‐Adrenergic inhibition by MET as well as TGF‐β1 antagonism induced antihypertrophic rather than antifibrotic effects. Inhibition of both renin‐angiotensin system and β1‐adrenergic system may exert different but synergistic effects to reduce myocardial remodelling.     

Changes in plasma glucose and lactate evoked by α and β2-adrenoceptor stimulation in conscious fasted rabbits

In conscious fasted rabbits, the iv infusion of salbutamol (3 micrograms/kg per min) and clonidine (2 micrograms/kg per min) induced a blood glucose increase amenable to blockade, respectively by ICI 118551 (1 micrograms/kg per min) and idazoxan (20 micrograms/kg per min). Amidephrine (10 micrograms/kg per min) and salbutamol mediated an increase in plasma lactate which was attenuated by prazosin (50 micrograms/kg, sc) and ICI 118551 respectively. Clonidine did not alter basal plasma lactate. The iv infusion of adrenaline (0.3 micrograms/kg per min) evoked an increase in plasma lactate more sensitive to blockade by ICI 118551 than by prazosin. ICI 118551 also shortened the hyperglycaemic response to adrenaline, 3-Mercaptopicolinic acid (25 mg/kg) reduced salbutamol- and adrenaline-mediated hyperglycaemia and increased at the same time the lactate/glucose ratio. Our data show that plasma lactate levels may be regulated by alpha 1- and beta 2-excitatory adrenoceptor stimulation. However, only the increase in blood lactate derived from beta 2-adrenergic stimulation seems to contribute to the overall catecholamine-mediated hyperglycaemia.     

Flerobuterol: a potential antidepressant drug related to β-adrenergic agonists. Experimental profile in mice

The potential antidepressant effect of flerobuterol (dl-(fluoro-2 phenyl)-1 t-butylamino-2 ethanol), a new drug related to beta-adrenoceptor agonists, was evaluated and compared with imipramine and salbutamol using classical psychopharmacological tests in mice. Like imipramine and salbutamol, flerobuterol (0.5-32 mg kg-1, ip) fully prevented apomorphine (16 mg kg-1, sc)- and partly reversed reserpine- and oxotremorine-induced hypothermia. At higher doses (16-32 mg kg-1), flerobuterol enhanced the toxic effects of yohimbine. Unlike imipramine, flerobuterol and salbutamol did not reduce immobility duration in the behavioural despair test. Salbutamol and flerobuterol decreased locomotor activity. Flerobuterol did not induce mydriasis, did not prevent oxotremorine-induced tremors or salivary and lacrimal gland secretion and did not reduce reserpine-induced palpebral ptosis. Propranolol (8 mg kg-1, ip) but not alpha-methyl-paratyrosine (75 mg kg-1, ip) prevented the flerobuterol-induced antagonism of apomorphine-induced hypothermia. Our results suggest that flerobuterol demonstrates potential antidepressant activity, which could be related to beta-adrenoceptor activation in mice.