Beta-adrenergic blood pressure regulation in Shy-Drager syndrome and pheochromocytoma

Both Shy-Drager syndrome and pheochromocytoma are characterized by an abnormal catecholamine secretion, e.g. a reduced secretion in Shy-Drager syndrome, and an excessive stimulation in pheochromocytoma resulting in adrenergic dysfunction and in adrenergic hyperactivity, respectively. The relationship between extreme variations in circulating catecholamines and beta-adrenergic receptor activity was studied in two patients with severe orthostatic hypotension (Shy-Drager syndrome) and in a patient with pheochromocytoma with excessive spontaneous catecholamine increases using the lymphocyte beta 2-adrenoceptor assay. In both patients with Shy-Drager syndrome, basal plasma concentrations of epinephrine and dopamine were low under resting conditions and could not be stimulated in the upright position. Norepinephrine was low in the first patient, and could not be stimulated; whereas the second patient had a normal basal concentration of norepinephrine, which could be moderately stimulated. There was no beta-adrenoceptor abnormality in the first patient: however, in the second patient, there were no measurable beta-adrenoceptors on membrane fractions, whereas a population of receptors only in the low affinity state could be identified on intact cells. Alpha-adrenoceptor density on thrombocyte membranes was slightly increased in both patients with Shy-Drager syndrome and showed no substantial change during upright posture. Catecholamine increases in the pheochromocytoma patient were accompanied by a rise in blood pressure, bradycardia, and an acute up-regulation of beta-adrenoceptors. Plasma concentrations of cAMP paralleled the increase in receptor density and blood pressure. The findings in pheochromocytoma add support to the theory that an acute catecholamine stimulation gives rise to an acute beta-adrenergic sensitization leading to blood pressure elevation.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta 2-adrenoceptor response in the rat uterus at the end of gestation and after induction of labor with RU 486

To study the relationship between the progesterone environment and beta-adrenoceptors in the myometrium, rats were treated with the antiprogestin RU 486 (10 mg per rat) at 08:30 h on day 21 of gestation. Under these conditions, more than 60% of animals delivered within 24 h after this treatment, while none of the control animals delivered within the same time period. beta-Adrenoceptors were identified using the radiolabeled antagonist (-)-[125I] iodocyanopindolol. The density (Bmax approximately 33-45 fmol/mg protein) and the affinity (KD approximately 0.105-0.106 nM) were not changed (during the late stages of gestation) in RU 486 treated rats compared with control rats. These results were correlated with the relaxation of longitudinal and circular strips of myometrium placed in high KC1 medium and exposed to beta-adrenoceptor agonists. The adrenoceptors implicated in the relaxation of myometrial strips were mainly of the beta 2-subtype. There was no difference in their affinity between control and RU 486 treated rats. Mean pA2 values were 8.46 for propranolol and 8.27 for ICI 118-551 against salbutamol. Altogether these results indicate in the rat that the blockade of the action of progesterone at its receptor site by RU 486 did not modify either the affinity or the sensitivity of beta 2-adrenoceptors in the myometrium, although it induced parturition.

Beta-adrenoceptor antagonist activities and binding affinities of timolol enantiomers in rat atria

S-Timolol is an effective anti-glaucoma drug, but has potentially hazardous side effects. Recently, R-timolol, also, has been reported to be effective in lowering elevated intraocular pressure. In the present study, the beta-adrenoceptor antagonist activities and binding of R- and S-enantiomers of timolol have been examined on rat atrial preparations. The beta-antagonistic activities were investigated using spontaneously beating rat heart atria. Both timolol enantiomers inhibited (-)-isoprenaline-induced chronotropic action competitively. S-Timolol was about 54 times more potent than R-timolol. The apparent binding affinities of timolol enantiomers to beta 1- and beta 2-adrenoceptors were determined by a radioligand binding assay using (-)-[125I]iodocyanopindolol (ICYP) as a marker and CGP 20712 A as a beta 1- and ICI 118,551 as a beta 2-adrenoceptor antagonist. Both enantiomers of timolol inhibited ICYP binding in nanomolar concentrations with Hill coefficients near unity. Neither enantiomer showed selectivity between beta 1- and beta 2-adrenoceptors, but R-timolol was approximately 30 times less active than S-timolol. It is concluded that R-timolol is a relatively potent non-selective beta-adrenoceptor blocking agent, but may possibly exert a more localized beta-adrenoceptor action in the eye than S-timolol, thus improving the safety of ocular timolol therapy.

G protein dependent alterations in [125I]iodocyanopindolol and +/- cyanopindolol binding at 5-HT1B binding sites in rat brain membranes

Several manipulations that affect G protein/receptor coupling also alter the binding of [125I]iodocyanopindolol ([125I]ICYP) and [corrected] +/- cyanopindolol (+/- CYP) to rat brain 5-HT1B binding sites in radioligand binding assays. Inclusion of 5 mM MgSO4 in these assays results in a small but significant increase in the affinity of [125I]ICYP (from KD = 0.046 nM to KD = 0.037 nM). In contrast, 100 microM Gpp(NH)p, GTP, or GDP reduce [125I]ICYP affinity (KD = 0.056 nM with GTP) while ATP and GMP are less effective. +/- CYP affinity for 5-HT1B sites labeled by [3H]dihydroergotamine [( 3H]DE) also displays a small but significant reduction (from Ki = 1.4 nM to Ki = 3.5nM) by the inclusion of 100 microM GTP. Pre-treatment of the brain membranes with N-ethylmaleimide (NEM) in concentrations known to inactivate many G proteins reduces 5-HT1B specific binding of [125I]ICYP. The NEM induced reduction in [125I]ICYP binding can be reversed by reconstitution with purified exogenous G proteins (Go and Gi), demonstrating directly that high affinity binding of [125I]ICYP to 5-HT1B sites is dependent on G proteins. The effects of Mg2+ ion, guanine nucleotides, NEM and G protein reconstitution on [125I]ICYP and +/- CYP binding are all hallmarks of agonist binding to G protein linked receptors. The effect of GTP, however, is quantitatively much less for the binding of these pindolol derivatives than for the binding of 5-HT, a presumed full agonist at 5-HT1B sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Three binding sites of 125I-iodocyanopindolol, i.e. beta 1, beta 2-adrenergic and 5HT1B-serotonergic receptors in rat brain determined by the displacement and Scatchard analysis

The selectivity of binding of 125I-iodocyanopindolol (125I-ICYP) to beta 1-, beta 2-adrenergic and 5HT1B-serotonergic receptors were analysed using both the Scatchard and displacement methods. When the binding of 125I-ICYP to the rat brain membrane was examined by means of the displacement analysis with l-metoprolol, triphasic displacement curves were observed. Analyses carried out on the basis of the displacement of 125I-ICYP by beta-selective antagonists, alpha-adrenergic agonists and antagonists, and serotonergic agonists and antagonists indicated the correspondence of the super high, high- and low-affinity sites of 125I-ICYP binding to beta 2-, beta 1-adrenergic and 5HT1B-receptors, respectively. By contrast, the Scatchard analysis revealed the biphasic character of the 125I-ICYP binding and the complete inhibition of the binding to high- and low-affinity sites by l-metoprolol (30 microM) and 5-hydroxytryptamine (5HT, 10 microM), respectively, suggesting the correspondence of the high- and low-affinity sites to beta-adrenergic and 5HT1B-receptors. Thus, regarding the determination of the selectivity of binding of a radioligand, the displacement analysis is more informative than the Scatchard analysis. In the case of 125I-ICYP the separation of beta 1- and beta 2-adrenergic receptors becomes feasible only with the displacement method.

The adrenergic system in lymphocytes from children with cystic fibrosis

Several in vivo and in vitro studies have suggested that children suffering from cystic fibrosis (CF) might have a general defect of beta-adrenoceptors on the cell surface which might account for an unbalanced secretory process. In order to investigate if this view holds true, we determined the beta-adrenoceptor density and affinity on lymphocytes by means of radioligand studies using 125-iodo-cyano-pindolol (125-ICYP) in 20 children with CF. Cyclic AMP (cAMP) response was also investigated after specific beta-adrenoceptor stimulation with isoprenaline (IPN) and after direct stimulation of the adenylate cyclase with forskolin in lymphocytes. Children with CF and controls have identical numbers and affinities of beta-adrenoceptors on lymphocytes. The cyclic AMP response was identical in CF- and in age-matched control children regardless whether adenylate cyclase was stimulated directly or via beta-adrenoceptors. In conclusion, the data support the view that no general adrenoceptor or adenylate cyclase defect exists in CF. As several studies have found abnormal reactions to adrenergic stimuli in CF patients, we presume that there is a defect beyond the level of adrenergic receptors and cAMP which remains to be identified.

Identification of two serine residues involved in agonist activation of the beta-adrenergic receptor

Pharmacophore mapping of the ligand binding domain of the beta-adrenergic receptor has revealed specific molecular interactions which are important for agonist and antagonist binding to the receptor. Previous site-directed mutagenesis experiments have demonstrated that the binding of amine agonists and antagonists to the receptor involves an interaction between the amine group of the ligand and the carboxylate side chain of Asp113 in the third hydrophobic domain of the receptor (Strader, C. D., Sigal, I. S., Candelore, M. R., Rands, E., Hill, W. S., and Dixon, R. A. F. (1988) J. Biol. Chem. 263, 10267-10271). We have now identified 2 serine residues, at positions 204 and 207 in the fifth hydrophobic domain of the beta-adrenergic receptor, which are critical for agonist binding and activation of the receptor. These serine residues are conserved with G-protein-coupled receptors which bind catecholamine agonists, but not with receptors whose endogenous ligands do not have the catechol moiety. Removal of the hydroxyl side chain from either Ser204 or Ser207 by substitution of the serine residue with an alanine attenuates the activity of catecholamine agonists at the receptor. The effects of these mutations on agonist activity are mimicked selectively by the removal of the catechol hydroxyl moieties from the aromatic ring of the agonist. The data suggest that the interaction of catecholamine agonists with the beta-adrenergic receptor involves two hydrogen bonds, one between the hydroxyl side chain of Ser204 and the meta-hydroxyl group of the ligand and a second between the hydroxyl side chain of Ser207 and the para-hydroxyl group of the ligand.

Density and functioning of human lymphocytic beta-adrenergic receptors during prolonged physical exercise

In order to study the regulation of beta-adrenergic receptor number and function in response to prolonged physical effort, lymphocytic beta-adrenoceptor density (determined by (-)[125I]iodocyanopindolol binding), lymphocytic basal and isoproterenol-stimulated cyclic AMP (cAMP) production and concentrations of plasma catecholamines were measured before and during 3 h running exercise in eight healthy volunteers. A significant (P less than 0.01) increase of the lymphocytic beta-adrenoceptor density from 45 +/- 4 to 81 +/- 9 fmol mg-1 protein (mean +/- SEM) took place during the first hour of exercise. As the exercise was continued for up to 2.1-3 h, the receptor densities did not change significantly any more and remained elevated (72 +/- 9 fmol mg-1 protein) in comparison to the resting levels (P less than 0.02). The isoproterenol-stimulated cAMP production of the lymphocytes increased during the first hour of running from 190 +/- 36 to 269 +/- 56 pmol mg-1 protein (P less than 0.01) and returned to the resting level at the end of the exercise (182 +/- 38 pmol mg-1 protein). The mean levels of plasma catecholamines increased approximately sixfold during the first hour of exercise and remained elevated until the end of the running. This study demonstrates that the beta-adrenergic receptor system is activated in lymphocytes during prolonged aerobic physical exercise. This activated state becomes, however, attenuated within 2-3 h of exercise as indicated by a diminishing ability of beta-adrenoceptors to mediate catecholamine-induced cAMP production.

Plasma membrane-specific deficiency in cardiac beta-adrenergic receptor in streptozocin-diabetic rats

Cell surface [3H]CGP 12177 binding sites in 10-wk streptozocin-diabetic rats decreased by 41% (P less than 0.01) compared with that in the control rats. In contrast, there was no difference in the total cell receptor concentration between the control and the diabetic rats, which was measured by hydrophobic antagonist [125I]-iodocyanopindolol binding. Forty-eight-hour in vivo insulin treatment significantly (P less than 0.05) increased cell surface beta-adrenergic receptor concentration by 37% above that in diabetic rats without any change in total receptor concentration in the cells. However in vitro treatment of 8 nM insulin, 33 mM glucose, or 10 mM 3-hydroxybutyrate for 2 h showed no effect on [3H]CGP 12177 binding. In contrast, 10 microM isoproterenol-dependent decrease and the recovery of cell surface receptors after the removal of the agonist were significantly (P less than 0.01) impaired in diabetic rats compared with those of control rats. These results indicate that only cell surface beta-adrenergic receptors decrease in diabetic rats, which may be associated with abnormalities in the receptor distribution. The decrease in cell surface receptor number closely associates with the diabetic state and is reversed by the short-term insulin treatment.

Autonomic receptor interactions in isolated cardiac myocytes from hypertensive rats

Isolated ventricular myocytes from adult (16 to 20 weeks) spontaneously hypertensive (SHR) and normotensive (WKY) rats were utilized to examine adrenergic and cholinergic receptor expression and interaction. Binding assays were performed using quinuclidinyl benzilate (QNB) and iodocyanopindolol (ICYP) for cholinergic and beta-adrenergic receptors, respectively. In addition, cAMP was measured as an index of adrenergic-cholinergic control of adenylate cyclase. Data from radioligand binding experiments indicated that muscarinic cholinergic receptors were depressed (22%) in SHR myocytes, while beta-adrenergic receptor density was comparable to that of WKY myocytes. Heterologous receptor modulation in isolated myocytes as assessed by displacement analysis with and without guanosine 5'-triphosphate (GTP), showed that carbachol displacement of QNB was shifted five fold to the right in the presence of GTP and that the beta-adrenergic agonist isoproterenol did not prevent the GTP-mediated binding alteration. In contrast, carbachol modulated the GTP-shift of ICYP displacement by isoproterenol and these effects were comparable in both WKY and SHR myocytes. Furthermore, the ability of carbachol to blunt the stimulation of adenylate cyclase by isoproterenol was also comparable in myocytes isolated from adult SHR and control animals. Thus, the observed decrement in muscarinic cholinergic receptor expression did not alter adrenergic-cholinergic interactions as assessed by displacement assays using guanine nucleotides, or the control of cAMP levels. In addition, isolated myocytes provide a useful system for analyzing receptor expression and regulation and how these parameters may be altered in the hypertensive heart.

The presence of beta-adrenoceptors in rat endometrium is dependent on circulating oestrogen

It has been proposed that the change in sensitivity of the uterus to catecholamines during the oestrous cycle may result from changes in beta-adrenoceptor density in the myometrium. In the present work we applied the technique of light-microscopic autoradiography using the radioligand [125I]iodocyanopindolol to study the density and distribution of beta-adrenoceptors in the rat uterus during the normal oestrous cycle, following ovariectomy, and after ovariectomy with oestradiol replacement. We found that beta-adrenoceptor density in the endometrium, but not the myometrium, varied during the oestrous cycle, being highest during pro-oestrous. The endometrium of the ovariectomized rats was devoid of any beta-adrenoceptors, whilst that of the oestradiol-treated rats was very intensely labelled. Following ovariectomy there was an increase in beta-adrenoceptor density in the myometrium, but this was not observed in the animals given oestradiol replacement. It appears that both the presence and density of beta-adrenoceptors in rat endometrium is dependent on circulating oestrogens.

Mechanisms underlying regional differences in lipolysis in human adipose tissue

Catecholamine-induced lipolysis was investigated in nonobese females and males. Isolated subcutaneous adipocytes were obtained from the abdominal and gluteal regions. The lipolytic effect of noradrenaline was four to fivefold more marked in abdominal adipocytes than in gluteal fat cells. This regional difference was more apparent in females than in males. No site differences were observed when lipolysis was stimulated with agents acting at different postreceptor levels. The beta-adrenergic lipolytic sensitivity was 10-20 times greater in abdominal adipocytes from both sexes than in gluteal adipocytes. Abdominal adipocytes from females showed a 40 times lower alpha 2-adrenergic antilipolytic sensitivity than did gluteal adipocytes, but the adenosine receptor sensitivity was similar in both sites. Beta-receptor affinity for agonists displayed no site or sex variation. Abdominal adipocytes showed a twofold increased beta-adrenoceptor density than did gluteal cells from both sexes. The alpha 2-adrenoceptor density was similar in all regions, but in females the affinity of clonidine for these sites was 10-15 times lower in the abdominal fat cells compared with gluteal cells. In conclusion, regional differences in catecholamine-induced lipolysis are regulated at the adrenoceptor level, chiefly because of site variations in beta-adrenoceptor density. Further variations in the affinity properties of alpha 2-adrenergic receptor in females may explain why the regional differences in catecholamine-induced lipolysis are more pronounced in women than in men.

Effects of dietary eicosapentaenoate (20:5 n-3) on cardiac beta-adrenergic receptor activity in the marmoset monkey

Eicosapentaenoic acid (EPA; 20:5 n-3; ethyl ester) in combination with atherogenic or non-atherogenic high fat diets was fed to young adult male marmoset monkeys for a period of 30 weeks. EPA markedly reduced the raised plasma cholesterol level evident when feeding an atherogenic diet but did not influence the cardiac membrane cholesterol-to-phospholipid ratio. EPA and its elongation product 22:5 n-3 was incorporated into cardiac membrane phospholipids at the expense of linoleic and arachidonic acids. Dietary EPA increased cardiac beta-AR affinity and reversed the decreased beta-AR affinity evident when feeding an atherogenic diet.

[Identification and characteristics of the beta-adrenergic receptors in the membranes of cultured endothelial cells of the human pulmonary artery]

The properties of beta-adrenoreceptors (beta-AR) have been studied in endothelial cells from the human pulmonary artery (EPA) and umbilical vein (EUV). [125I] Iodosyanopindolol binding assay revealed the amount of 22 and 12 fmol/10(6) cells as well as Kd = 92 and 52 pM for EPA and EUV, respectively. Adrenergic agonists increased the cAMP levels in EPA in the order of potency characteristic for beta 2-AR: isoproterenol greater than epinephrine greater than norepinephrine. Basing on the results obtained in the present study and the literature data a conclusion is made that the properties of beta-AR in vascular endothelial cells do not practically depend on their localization, suggesting universality of their function within the vascular system.

Regulation of beta-adrenergic receptor expression in rat liver

To begin defining the factors regulating neurotransmitter receptor expression, we examined beta-adrenergic receptors in rat liver in vivo and in primary liver cultures under defined hormonal conditions. beta-receptors described a remarkable developmental profile in vivo, increasing fivefold between embryonic days 16 and 20, and decreasing tenfold by early adulthood. The developmental decrease reflected reduced receptor number without a change in receptor properties. The ontogenetic decrease appeared to be specific for beta-receptors; alpha-receptors developed in a hyperbolic fashion, reaching high plateau values by the third postnatal week. Adult rat liver cells plated into culture re-expressed high beta-receptor levels, exhibiting a 4-8-fold increase. A similar pattern of expression of the beta-receptors, having similar pharmacological properties, was observed in primary liver cultures maintained in serum-free medium, in a serum-supplemented medium or in several variations of a serum-free, hormonally defined medium designed for primary liver cultures. Thus, the degree of expression of the beta-receptors was not found affected by various hormones, by serum, or by any medium condition. By contrast, the degree of expression of the beta-receptors was markedly sensitive to cell density. High expression of the beta-receptors was observed at low cell densities (1-3 x 10(6) cells/150 mm dish), and low expression or no expression was observed in confluent cultures (10-20 x 10(6) cells/150 mm dish). Our experiments suggest that beta-receptor expression does not follow an immutable program, but may be regulated by density-dependent cell-cell interactions.

Alpha 1-adrenoceptor function and autoradiographic distribution in human asthmatic lung

1. The autoradiographic distribution of alpha 1-adrenoceptors was investigated in non-diseased and asthmatic human lung by use of [3H]-prazosin (H-PZ). To validate binding and autoradiographic methods, H-PZ binding was also measured in rat heart. 2. Significant levels of specific H-PZ binding were detected in sections of rat heart. This binding was associated with a single class of non-interacting sites of high affinity (dissociation constant, Kd = 1.17 +/- 0.26 nM). The maximum binding capacity (Bmax) was 59.5 +/- 4.5 fmol mg-1 protein. 3. In sharp contrast, very low levels of specific H-PZ binding were found in both human nondiseased and asthmatic bronchus, although a high level of binding of [125I]-iodocyanopindolol (I-CYP, 50 pM) to beta-adrenoceptors was detected in these airways. Furthermore, very low levels of autoradiographic grains representing specific H-PZ binding were found in all airway structures in human non-diseased or asthmatic lung parenchyma. 4. Consistent with these data, the alpha-adrenoceptor agonist phenylephrine failed to induce significant increases in tone in bronchi isolated from either non-diseased or asthmatic human lung. Results indicate that asthma does not involve significant increases in airway alpha 1-adrenoceptor function.

Function, characterization and autoradiographic localization and quantitation of beta-adrenoceptors in cardiac tissues

1. This paper demonstrates the use of organ bath, radioligand binding and autoradiography to detect beta 1- and beta 2-adrenoceptors in human and guinea-pig cardiac tissues. 2. In organ bath experiments, non-selective and beta 1- and beta 2-adrenoceptor selective agonists produced concentration-dependent inotropic responses in human right atrial appendage. Both subtypes mediate inotropic responses. In guinea-pig right atria chronotropic responses were mediated predominantly through beta 1-adrenoceptors. 3. Receptor binding studies using (-)[125I]-cyanopindolol (CYP) and beta 1- and beta 2-adrenoceptor selective antagonists showed that beta 2-adrenoceptors comprised 25% of the total population of beta-adrenoceptors in guinea-pig right atria. In human right atria the proportion is higher (40%). 4. Quantitative autoradiography was used to determine the location and densities of beta 1- and beta 2-adrenoceptors in guinea-pig heart. Both beta 1- and beta 2-adrenoceptors were distributed on myocardium. The atrioventricular conducting system had a higher density of beta 2-adrenoceptors compared with myocardium.

Selectivity of bunitrolol for beta 1- and beta 2-adrenergic receptors and 5HT1B-receptors: assessment by biphasic Scatchard plots and biphasic displacement curve analysis with 125I-iodocyanopindolol and 3H-CGP12177

The preference by bunitrolol for beta 1- and beta 2-adrenoceptors of the rat brain, heart and/or lung was assessed by the radioligand binding assay method with 125I-iodocyanopindolol (125I-ICYP) or 3H-CGP12177. Scatchard plots of 125I-ICYP binding in the presence of bunitrolol were found to be non-linear. The inhibition constants (Ki) of bunitrolol for high (beta 2-) and low affinity sites (beta 1-) were: 0.42 +/- 0.16 nM for beta 1 and 3.55 +/- 1.61 nM for beta 2 (beta 1 greater than beta 2), respectively. Displacement experiments conducted with the preparations of the rat brain using 125I-ICYP or with the preparations of the rat heart using 3H-CGP12177 yielded Ki values for bunitrolol of 0.53 +/- 0.20 (beta 1) and 2.37 +/- 0.78 (beta 2) nM for 125I-ICYP binding and 2.01 +/- 0.38 (beta 1) and 12.67 +/- 6.54 (beta 2) nM for 3H-CGP12177 binding. In addition, the Ki value for 5HT1B-receptors assessed in displacement experiments conducted with 125I-ICYP in the presence of 30 microM I-metoprolol in the rat brain was 10.54 +/- 5.92 nM. Thus, bunitrolol is a beta 1-selective antagonist.

Effect of nedocromil sodium on down-regulation of pulmonary beta-adrenoceptors

1. We have studied the effect of the anti-inflammatory anti-asthma drug, nedocromil sodium, on down-regulation of pulmonary beta-adrenoceptors in guinea-pig lung. 2. Incubation of minced lung with isoprenaline (10 mumol/l) resulted in a reduction in maximum binding capacity of [125I]iodocyanopindolol to lung membranes from 246 +/- 4 to 169 +/- 6 fmol/mg of protein (mean +/- SEM, P less than 0.01, n = 18). 3. Nedocromil sodium, which had no direct effect on [125I]iodocyanopindolol binding, prevented isoprenaline-induced down-regulation, giving complete protection at a dose of 100 mumol/l. 4. The mechanism of this effect is not certain, but nedocromil sodium may interfere with the internalization of beta-adrenoceptors in pulmonary parenchymal cells. This may have some therapeutic relevance.

Plasma catecholamines and adrenoceptors after chronic sinoaortic denervation in dogs

Chronic sinoaortic denervation (SAD) performed by section of both carotid and aortic nerves induced a significant and sustained increase in blood pressure and heart rate in conscious dogs; under our experimental conditions, the values of systolic blood pressure and heart rate were never lower than 190 mmHg and 120 beats/min, respectively. The present long-term study (8 mo) investigated the time-course of plasma catecholamine levels and circulating blood cell adrenoceptor (leukocyte beta 2 and platelet alpha 2) number. Catecholamine plasma levels were highly correlated with the variations of leukocyte beta adrenoceptors (measured by [125I]cyanopindolol binding and characterized as a beta 2 receptor in dogs). These two parameters followed a biphasic pattern after SAD: during the first 2 mo, significant increases in noradrenaline and adrenaline levels were associated with a decrease in leukocyte beta 2 adrenoceptor number; from the 4th month, they slowly returned to normal values, although blood pressure remained elevated. By contrast, platelet alpha 2 adrenoceptor number (measured by [3H]yohimbine binding) did not follow this pattern since it remained lower than before SAD during the whole experiment. Finally, the development (but not the maintenance) of SAD-induced hypertension is associated with an increase in sympathetic tone. Only leukocyte beta 2 (and not platelet alpha 2) adrenoceptors are directly regulated by the endogenous levels of catecholamines.

Autoradiographic localization of changes in pulmonary beta-adrenoceptors in an animal model of atopy

Vaccination of guinea pigs with Haemophilus influenzae leads to an impairment of beta-adrenoceptor function in lung. We have used an autoradiographic technique to study the distribution of changes in lung beta-adrenoceptor density. H. influenzae induced a decrease in beta-adrenoceptors in peripheral lung membranes of 22 +/- 5% (mean +/- S.E.M., n = 7), while the affinity of binding was unaffected. Tracheal beta-adrenoceptor binding was not influenced by H. influenzae. Autoradiography revealed a 27% reduction in beta-adrenergic binding sites on alveolar septa. Bronchial epithelial beta-adrenoceptors were decreased for 36%, and vascular smooth muscle and endothelial beta-adrenoceptors were also reduced. beta-Adrenoceptors on airway smooth muscle were unaffected. H. influenzae affected both the beta 1- and beta 2-subtypes of receptors. It is concluded that in this animal model of atopy beta-adrenoceptors may be decreased on several different cell types within the lungs, which may influence overall airway and vascular reactivity.

Effects of protein kinase inhibitor, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, on beta-2 adrenergic receptor activation and desensitization in intact human lymphocytes

To investigate the role of protein kinases in agonist-mediated beta-2 adrenergic receptor regulation, the effects of the protein kinase A and C inhibitor, H-7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine], on isoproterenol-induced beta adrenoceptor activation and desensitization have been studied in intact human lymphocytes. In the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, H-7 potentiated 10(-8) to 10(-4) M isoproterenol or prostaglandin E1-induced cyclic AMP (cAMP) accumulation in a dose-dependent manner. We failed to observe any effect of H-7 on forskolin-induced cAMP accumulation. These effects of H-7 are probably not due to its inhibition of phosphodiesterase. In addition, whereas up to 10(-3) M H-7 had no beta adrenergic receptor blocking effect, preincubation of intact cells with 10(-3.5) M H-7 partially prevented 50 nM isoproterenol-induced beta-2 adrenergic receptor desensitization in terms of decreases in beta adrenoceptor density (maximum binding), isoproterenol-mediated cAMP responsiveness and high affinity receptor binding for agonist. Interestingly, 10(-3.5) M H-7 alone treated cells also showed an up-regulation of cell surface beta receptor density (maximum binding) and increased cAMP responsiveness to isoproterenol stimulation. The mechanisms are unclear. If these effects occur as a result of inhibition by H-7 of protein kinase A and/or C, it may suggest an important role of protein kinase A and/or C in agonist-induced beta-2 adrenergic receptor regulation.

Lymphocyte beta-adrenoreceptor density in patients with unipolar depression and normal controls

Values of binding maximum (Bmax) and dissociation constant (Kd) of (-)3-[125I]iodocyanopindolol (ICYP) were determined in beta-adrenergic receptors of membranes of peripheral lymphocytes in 32 patients with unipolar depression (DSM-III-R) and 31 normal controls. Results were analyzed by a two-way Analysis of Covariance method. A significant difference was noted for group assignment (patient versus control, p less than 0.05). Mean Bmax (fmol ICYP bound/mg lymphocyte membrane fraction total protein) of patients was 31.9 +/- 3.84 (SE) and controls 46.3 +/- 3.92 (SE). A significant interaction was found between group membership and gender (p less than 0.05). In the female patient group (n = 14), mean Bmax was 30.5 +/- 5.79 (SE); in female controls, mean Bmax was 56.0 +/- 5.15 (SE). Differences between male patients and male controls were not significant. Mean values of Kd (pmol/liter) showed a trend for patient values to be lower than control values [69.0 +/- 13.66 (SE) versus 108.5 +/- 14.42 (SE), respectively]. A significant inverse relationship was noted between lymphocyte beta-receptor Bmax and frequency of panic attacks during the depressive episode in 18 patients (p = 0.05). No relationship was found between values of Kd and frequency of panic attacks in these patients. Thus, preliminary evidence is provided for relationships among altered beta-adrenergic receptor binding, gender, and indices of panic-anxiety in unipolar depressed patients.

Beta-adrenoceptor binding potencies of new aliphatic and alicyclic oxime ethers and their relevance to intraocular pressure control

The selectivity and binding potency of a series of alkyliminoxypropanolamines characterized by the lack of an aromatic nucleus are studied using a new non-selective radioligand, (-)-(125I)-Iodocyanopindolol. The relationship between the effectiveness in lowering the intraocular pressure (IOP) in experimental hypertensive rabbit eyes and their capacity to bind to ciliary processes beta 2-adrenoceptors is discussed. The inhibition constant (Ki) and beta 2/beta 1 ratios indicate a beta 2-selectivity for the tested drugs. Cyclopropyl, dicyclopropyl, cyclopentyl and cyclohexyl derivatives displayed a potent binding to ciliary processes beta 2-adrenoceptors and lowered the IOP about -18%. These compounds induced a lowering in IOP equal to that produced by timolol and appear to be effective and safe beta-adrenergic antagonists in open-angle glaucoma therapy. Decreasing the size of the alkyl group of the oxime, removing the oxime function or modifying the beta-hydroxyl group from the side chain led to a significant decrease in beta 2-adrenoceptor binding and induced weak hypotensive ocular activity. Since the tested alkyliminoxypropanolamine series has very similar physicochemical characteristics and therefore, ruled out the differences in their ability to reach, through the cornea, the targeted ciliary processes, it was demonstrated that contrary to generally held views, the action of the new beta-antagonist series on IOP is related to their ability to antagonize ocular beta 2-adrenoceptors.