Identification and characterization of alpha 2-adrenergic receptors in human myometrium by [3H]rauwolscine binding

Human myometrium contains alpha 3-adrenergic receptors which can be identified by binding of the alpha 2-adrenergic antagonist [3H]rauwolscine. Scatchard analysis of saturation binding data on myometrial membranes revealed that [3H]rauwolscine bound to a single class of noncooperative sites (262 +/- 89 fmol/mg of membrane protein) with high affinity (i.e., with an equilibrium dissociation constant of 5.3 +/- 2.2 nM). The alpha 2-adrenergic nature of these sites was derived from the order of potencies and stereospecificity of alpha-adrenergic agonists and antagonists to compete with [3H]rauwolscine binding.

Measurement of beta-adrenergic receptors on lymphocytes in normal subjects and asthmatics in relation to beta-adrenergic hyperglycaemic response and bronchial responsiveness

The numbers of beta-adrenergic receptors on lymphocytes in normal subjects and asthmatic patients were measured by the use of [125I]hydroxybenzylpindolol. The numbers of beta-adrenergic receptors per lymphocyte in normal subjects, drug-free asthmatics and patients taking beta-stimulants were 1146 +/- 98, 845 +/- 114 and 582 +/- 47 sites/cell (mean +/- SE), respectively. The differences were statistically significant (P less than 0.05) among these groups, while no statistically significant differences were found in dissociation constants. A 42% decrease in the number of beta-adrenergic receptors per lymphocyte after administration of 6 mg/day of terbutaline for 7 days was noted in four volunteers. There was significant correlation (r = 0.68, P less than 0.01) between the number of beta-adrenergic receptors per lymphocyte and the percentage increase in blood sugar 20 min after subcutaneous injection of 4 micrograms/kg epinephrine. There was also significant correlation (r = 0.78, P less than 0.005) between the number of beta-adrenergic receptors per lymphocyte and the respiratory threshold for acetylcholine. These results suggest that beta-blockade and bronchial hypersensitivity in asthmatic patients may in part be due to a decreased number of beta-adrenergic receptors.

Evidence from binding studies for alpha 2-adrenoceptors directly associated with glomeruli from rat kidney

Binding of the alpha 2-adrenoceptor radioligands [3H]clonidine and [3H]rauwolscine but not the alpha 1-adrenoceptor radioligand [3H]prazosin was enhanced in membranes prepared from rat isolated renal glomeruli. [3H]Rauwolscine binding to glomeruli was stereoselective with respect to the (-)-isomer of noradrenaline and the order of potency of a series of antagonists for displacement of binding indicated that the alpha 2-adrenoceptors in this preparation differ somewhat from those in some other species and tissues. Chemical sympathectomy produced no significant change in the number of sites labelled by [3H]rauwolscine indicating that few of the alpha 2-adrenoceptors in glomerular membranes are associated with sympathetic nerve terminals.

Characterisation of postjunctional alpha-adrenoceptors in isolated human femoral veins and arteries

In order to characterise the pharmacological properties of postjunctional alpha-adrenoceptors, both the contractile effects of alpha-adrenoceptor agonists and the blocking potencies of selective alpha-adrenoceptor antagonists were studied in isolated human femoral veins and arteries. The veins were more sensitive to noradrenaline than the arteries. Guanfacine had a higher intrinsic activity in veins than in arteries, whereas the reverse was true for phenylephrine. The antagonists rauwolscine and yohimbine were more potent against noradrenaline in the veins than in arteries, while corynanthine was equally potent in either tissue. They antagonised the noradrenaline response in a competitive manner. Prazosin proved to be the most potent competitive antagonist in arteries, while in veins it exerted weak and non-competitive antagonism. The results suggest that the alpha-adrenoceptor population at the postjunctional site differs between human femoral veins and arteries. The veins seem to contain more alpha 2- than alpha 1-adrenoceptors postjunctionally, whereas in the arteries the alpha 1-subtype prevails. The results indicate the possibility of influencing selectively adrenergic reactions in the capacitance and resistance vessels.

The use of [125I]iodocyanopindolol as a specific probe for beta-adrenergic receptors in differentiating cultured rat skeletal muscle

In order to examine more precisely the role of beta-adrenergic receptors in the process of differentiation we used the new radioligand iodocyanopindolol ([125I]ICYP), which we found to be a very useful probe to identify beta receptors. Binding characteristics conformed to those expected for a physiologically relevant beta receptor. L6E9 cells grown in horse serum, which allows differentiation, exhibit increased beta receptor density in intact cells as a function of age. In contrast, cells grown in fetal calf serum, which does not allow differentiation, exhibit constant beta receptor density. In broken cells, however, both differentiating and non-differentiating cells show an increase in beta receptors. These results suggest that the process of differentiation is associated with an unmasking of beta receptors which are increasing but cryptic in undifferentiated cells.

Autoradiographic localization of autonomic receptors in airway smooth muscle. Marked differences between large and small airways

Autoradiographic methods were used to determine the distribution of autonomic receptors in airway smooth muscle of ferret from trachea to terminal bronchioles; [3H]dihydroalprenolol, [3H]prazosin, and [3H]quinuclidinyl benzilate were used to label beta-adrenergic, alpha-adrenergic, and muscarinic receptors, respectively, using experimental conditions that gave maximal specific receptor binding. Marked differences were found in the longitudinal distribution of each receptor and in distribution of the various receptors in each caliber airway. Beta-receptors were present in high density throughout the airways, with the highest density in bronchioles. Alpha-receptors were sparse in large airways, but numerous in small bronchioles, whereas cholinergic receptors were numerous in bronchial smooth muscle, sparse in proximal bronchioles, and almost absent from distal bronchioles. This method may be useful in studying alterations of autonomic receptors distribution in small and large airways after experimental manipulation and in disease.

Characterization of beta adrenoceptor subtypes in canine airway smooth muscle by radioligand binding and physiological responses

Beta adrenoceptor subtypes in canine tracheal smooth muscle have been investigated by radioligand binding and by physiological responses to beta agonists and sympathetic nerve stimulation in vitro. Specific binding of [3H]dihydroalprenolol to tracheal smooth muscle membranes was of high affinity (Kd = 1.0 +/- 0.08 nM), as in peripheral lung membranes from the same animals, but the concentration of binding sites (95.6 +/- 4.7 fmol/mg of protein) was much lower than in lung (532 +/- 48 fmol/mg of protein). Binding was stereoselective and agonists competed with the rank order of potency isoproterenol greater than epinephrine greater than norepinephrine, signifying a preponderance of beta-2 receptors. Using selective beta antagonists, we determined the ratio of beta-1/beta-2 receptors in tracheal smooth muscle membranes to be 1:4. The relaxation response of tracheal smooth muscle strips to exogenous beta agonists was mediated by beta-2 receptors, with a very small contribution from beta-1 receptors. However, the relaxation response to electrical field stimulation of sympathetic nerves was mediated predominantly by beta-1 receptors. Our results suggest that most beta receptors in dog tracheal smooth muscle are of the beta-2 subtype and mediate responses to circulating catecholamines, but there is a small concentration of beta-1 receptors which mediate the response to neurally released norepinephrine.

Decreased beta-adrenergic receptor density in mononuclear leukocytes from thyroidectomized patients

Beta-adrenergic receptor characteristics were investigated in peripheral blood mononuclear leukocytes taken from patients before and after partial thyroidectomy. In order to discriminate the effect of surgical stress per se from that of thyroidectomy, the analysis was also performed on patients before and after cholecystectomy. Receptor characteristics were determined by using dihydroalprenolol as ligand in direct equilibrium binding experiments. The binding affinity showed no changes either when two different surgical treatments were compared or when the same patient was analysed before and after the operation. On the contrary, a significant decrease in receptor density was found in thyroidectomized patients when compared pre- and post-operatively. This fall in receptor number seems to be linked with thyroid function since no statistically significant changes were observed in cholecystectomized patients in relation to surgical operation. This view is further supported by data on T3 serum levels, which show a significant fall after thyroidectomy but no statistically significant modifications after cholecystectomy. It is concluded that beta-adrenoceptor modulation plays an important role in the relationship between thyroid and beta-adrenergic system.

[Distribution of monoaminergic structures in the amphibian kidney]

Distribution of monoaminergic structures in the kidney of two frog species has been studied by means of the fluorescent-histochemical method. Neural fibers containing catecholamines are revealed in the renal artery wall, in the portal veins walls, in the glomerular arteriole walls. No catecholamine-containing neural fibers have been revealed in the glomerular capillaries. The catecholamine-containing neural fibers tightly adjoining the walls of the proximal and distal parts of the nephron canaliculi have been revealed. The neural structures containing indolamines are not observed.

Alloxan-induced diabetes reduces beta-adrenergic receptor number without affecting adenylate cyclase in rat ventricular membranes

We have investigated alterations in beta-adrenergic receptors and adenylate cyclase activity in myocardial membranes from normal and alloxan-treated diabetic rats. Saturation curves of [3H]dihydroalprenolol binding yielded a Bmax of 96.3 +/- 3.9 fmol/mg protein in normal membranes and 47.6 +/- 3.9 fmol/mg protein in diabetic membranes. Decreased receptor number in membranes from diabetic animals was not accompanied by alteration in receptor affinity for either antagonists or agonists to the beta-receptor. We were unable to detect any alteration in adenylate cyclase activity in similar ventricular membranes. Adenylate cyclase activity in the basal state or in the presence of sodium fluoride, guanyl-5'-yl imidodiphosphate, or isoproterenol, with or without GTP, was not altered by the alloxan-induced diabetic state. Stimulation of adenylate cyclase activity by forskolin, the novel diterpene activator, also was not altered by diabetes. The results suggest that while diabetes reduced beta-receptor number, this is not reflected in any other component of the adenylate cyclase complex.

A carbene-generating photoaffinity probe for beta-adrenergic receptors

A new radioiodinated (2.2 Ci/mumol) iodocyanopindolol derivative carrying a 4-(3-trifluoromethyldiazirino)benzoyl residue has been synthesized. The long-wavelength absorption of the diazirine permits formation of the carbene by photolysis under very mild conditions. [125I]ICYP-diazirine binds with high affinity (Kd = 60 pM) to beta-receptors from turkey erythrocyte membranes. Upon irradiation, [125I]ICYP-diazirine is covalently incorporated in a Mr 40 000 protein. Stereoselective inhibition of photolabeling by the (-)enantiomers of alprenolol and isoproterenol indicated that the Mr 40 000 protein contains a beta-adrenergic binding site. The yield of specific labeling was up to 8.2% of total beta-receptor binding sites. The Mr 40 000 protein photolabeled in the membrane could be solubilized at comparable yield with either digitonin or Triton X-100. Irradiation of digitonin-solubilized turkey erythrocyte membranes with [125I]ICYP-diazirine resulted in specific labeling of two proteins with Mr 40 000 and 50 000. In guinea-pig lung membranes, at least five proteins were photolabeled, of which one (with approximately Mr 67 000) was labeled specifically.

Pulmonary alpha-adrenoceptors: autoradiographic localization using [3H]prazosin

We determined the distribution of pulmonary alpha-adrenoceptors by autoradiographic localisation of [3H]prazosin binding to frozen sections of ferret lung. Specific binding of [3H]prazosin to lung sections was saturable and of high affinity (KD = 0.44 +/- 0.55 nM; mean +/- S.E., n = 5), with a specificity indicating binding to alpha 1-receptors. Autoradiographic showed that alpha 1-receptors were present in highest density in vascular smooth muscle (small vessels greater than large vessels), and were also present in airway submucosal glands and epithelium. There was also scanty labelling of alveolar walls which may be to contractile interstitial cells (Kapanci cells). Although smooth muscle of bronchi showed little labelling, surprisingly that of bronchioles was heavily labelled. The high density of alpha-receptors in small airways may be relevant to asthma in which alpha-adrenergic responses are activated. This method offers a means by which autonomic receptors of small airways may be investigated without the confusing contribution of other contractile elements and larger airways.

Binding of [3H]-dihydroalprenolol and [3H]-acetobutolol to human blood platelets is not related to occupancy of beta-adrenoceptors

Binding of [3H]-dihydroalprenolol to human platelet lysates is inhibited by (+/-)-propranolol and (+/-)-butoxamine, but less effectively by (+/-) practolol. (-)-Isoprenaline causes no significant inhibition of binding where stimulation of adenylate cyclase can be shown. Binding of [3H]-acetobutolol is also inhibited by (+/-)-propranolol. "Specific" binding of [3H]-dihydroalprenolol and [3H]-acetobutolol defined by (+/-) propranolol shows a non-classical saturation curve. 50% maximal binding is observed in the range 15-25 mM. The extent of "specific" binding is 2-fold greater for [3H]-dihydroalprenolol. Similar and rapid rates of binding of [3H]-dihydroalprenolol are observed at 4 degrees C and 20 degrees C. No stereoselectivity is observed for inhibition of [3H]-dihydroalprenolol binding by (+) and (-)-propranolol. Binding of [3H]-dihydroalprenolol and [3H]-acetobutolol may relate to the lipophilic character of these radioligands and does not represent interaction with beta-adrenoceptors.

Demonstration of alpha-adrenoceptors in the rabbit bladder base and urethra with 3H-dihydroergocryptine ligand binding

The purpose of this work was to demonstrate the presence of alpha-adrenoceptors in a crude membrane preparation made from rabbit bladder base and urethra. This was achieved by radioligand binding studies, using 3H-dihydro-alpha-ergocryptine (3H-DHE) as the radioligand. The specific binding, i.e. the binding that could be inhibited by 10(-5) M phentolamine, was saturable with 73 fmol 3H-DHE bound per mg membrane protein. Binding was at steady state after 60 min., and reversible. Rate constants for association and dissociation were 3 X 10(7) M-1 min.-1, and 2 X 10(-2) min.-1, respectively. A number of compounds were tested for their abilities to compete with 3H-DHE for the binding sites. The relative affinity of some adrenoceptor agonists was: (-)-adrenaline greater than (-)-noradrenaline much greater than (+/-)-isoprenaline. Stereoselectivity was shown, since (-)-noradrenaline had 42 times higher affinity than (+)-noradrenaline. Adrenoceptor antagonists inhibited 3H-DHE binding in the following order of potency: DHE greater than phentolamine much greater than (+/-)-propranolol. The dissociation constant, KD, for DHE to the binding sites was estimated in three different ways. The constants were derived from saturation, competition, and kinetic studies, and gave KD values of 1.1, 1.4 and 0.7 nM, respectively. The results suggest that alpha-adrenoceptors were labelled by 3H-DHE in the tissue homogenates.

Hypertension reduces the number of beta-adrenergic receptors in rat brain microvessels

Beta-adrenergic receptor function was measured in cerebral microvessels of spontaneously and DOCA-salt hypertensive rats using 125I-iodohydroxybenzylpindolol (IHYP). Both in genetic and in experimental hypertension, a significant decrease in the number of beta-receptor sites was observed, without receptor affinity changes. These results suggest that alterations of central adrenergic regulation of small vessels may participate in the pathogenetic mechanisms leading to the development of the central hypertensive disease.

Changes of alpha 1- and beta-adrenergic and cholinergic muscarinic receptors guinea pig lung sensitized with ovalbumin

The effect of immunization of guinea pigs with ovalbumin on the number and affinity of alpha 1- and beta-adrenergic and cholinergic muscarinic receptors was studied in lung membranes by direct binding techniques using 3H-prazosin, 1-3H-dihydroalprenolol and 1-3H-quinuclidinyl benzilate. After immunization by intraperitoneal injection of ovalbumin to guinea pigs, the number and affinity of each receptor in sensitized animals were not significantly different from those of control animals. Sensitization of guinea pigs by an aerosol exposure with the antigen resulted in a decreased number of beta-adrenergic receptor (458 +/- 29 vs. 687 +/- 56 fmol/mg protein; p less than 0.01), and an increased number of alpha 1-adrenergic receptor (36 +/- 2 vs. 25 +/- 2 fmol/mg protein; p less than 0.01), but no change was observed in the number of muscarinic receptors, as compared with control animals. On the other hand, following a prolonged sensitization of guinea pigs with a low dose of the aerosolized antigen, the number of muscarinic receptors was significantly increased in the lung of sensitized animals (50 +/- 2 vs. 42 +/- 2 fmol/mg protein; p less than 0.01); however, we found no significant differences between sensitized and normal animals in the number of alpha 1- and beta-adrenergic receptors. There were no different changes in the affinity of these receptors in all experiments.

Development of beta-adrenergic receptors and their function in glia-neuron communication in cultured chick brain

The beta-receptors of intact neuronal and glial cells of chick embryonic brain were studied via the specific binding of the beta-antagonist [3H]dihydro-L-alprenolol ( [3H]DHA). Cells were cultivated in either highly homogeneous or mixed populations; the neuronal cells were also grown under the influence of glial conditioned medium (GCM) or 10(-11)-10(-10) M L-norepinephrine or L-isoproterenol. The beta-receptors of both neuronal and glial cells proved to be positively cooperative (n = 2.5) and of high affinity, with a Kdapp of 98 and 44 pM, respectively. The Kdapp value was influenced only slightly by the different culture conditions. The receptor concentration was relatively low in the homogeneous neuronal and glial cultures (Bmax = 6.4 and 3.3 fmol/10(6) cells, respectively). It increased by a factor of 2-3 if development of the neuron-glia contacts in the culture was possible (mixed cultures). GCM and beta-agonists elevated the number of beta-receptors of the neuronal cells approximately 4-fold, even in the absence of glial cells. This receptor-number change was preceded by a well observable morphological differentiation. Both the morphological and the beta-receptor effects of L-norepinephrine were antagonized by L-propranolol. The beta-receptor number increased about 2-fold during a 10-day in vitro development, even in neuron-glia mixed cultures.

Biochemical analysis and solubilization of central alpha 1-adrenoceptors in the rat

To study the structure and the molecular mechanisms of action of brain alpha-adrenoceptors, their solubilization was undertaken. alpha 1-Adrenoceptors were first successfully solubilized from fresh rat brain membranes by treatment with 0.3 percent deoxycholate, after prelabeling of the binding site by the highly specific tritiated antagonist 3H-prazosin. The complex thus solubilized underwent a rapid loss of activity at 25 degrees C. Direct solubilization of brain alpha 1-adrenoceptors was obtained by treatment with a new zwitterionic derivative of cholic acid (CHAPS) at a concentration of 5 to 10 mM. The soluble complex was detected by precipitation by polyethylene glycol 6,000 with gamma globulin as a carrier. Binding of 3H-prazosin at 25 degrees C was rapid; at 4 degrees C the steady state was obtained within two hours and remained unchanged for at least six hours. The affinity of the soluble binding site, determined by Scatchard analysis (congruent to 0.6 nM), varied with the concentration of detergent. Specificity of the membrane-bound receptor was preserved as demonstrated by incubation in the presence of alpha 1- and alpha 2-antagonists at various concentrations (by order of potency: prazosin greater than phentolamine greater than yohimbine). Stereoselectivity was also retained in the solubilized binding protein. The solubilization of an active brain alpha 1-adrenoceptor will allow further investigation at the molecular level.

Catechol-O-methyltransferase activity and aminergic binding sites distribution in human peripheral blood lymphocyte subpopulations

We have studied the binding of [3H]dihydroalprenolol, a beta-adrenergic ligand, and [3H]spiroperidol, a dopaminergic ligand, to human peripheral blood lymphocyte subpopulations. The catechol-O-methyltransferase activity on these different cells was also determined. On intact living cells, an unequal distribution of both beta-adrenergic and dopaminergic binding sites was found between B- and T-lymphocyte subpopulations. In each binding, T cells exhibited a lower number of binding sites than B cells. On particulate preparation, catechol-O-methyltransferase activity showed a similar distribution, but binding data with such material were quite different. Although it was not possible to detect dopaminergic binding sites on particulate preparation, T and B lymphocytes contained equivalent numbers of beta-adrenergic binding sites. Different explanations for these results are proposed.

alpha- and beta-adrenergic binding sites in sheep cerebral cortex: characterisation, effects of photoperiod and treatment with estrogen/progesterone

The radioligands [3H]-dihydroergocryptine and [3H]-dihydroalprenolol were used to characterise alpha- and beta-adrenergic binding sites, respectively, in membrane fractions of sheep cerebral cortex. In terms of affinity, density and specificity these sites possess properties similar to those previously characterised in rat brain. Further, in preliminary studies, these sites also appear to be responsive to treatment with estradiol/progesterone as well as to photoperiod. Thus, estrogen treatment can elevate both alpha- and beta-adrenergic binding sites in cortical tissue of sheep kept in natural light. In contrast, artificial light either has no effect or inhibits binding in response to estrogen.

Alpha- and beta-adrenergic and muscarinic cholinergic binding sites in the bladder and urethra of the rabbit

The affinities of a number of alpha- and beta-adrenergic binding sites and muscarinic cholinergic binding sites in rabbit urethra and bladder have been determined, using specific radioligand receptor binding assays. There was a greater density of beta-binding sites than alpha-binding sites in the bladder, while, in the urethra, there was a greater density of alpha-binding sites than beta-binding sites. The number of alpha-binding sites was fourfold greater in the urethra, whereas there were fewer beta-binding sites in the urethra. There were fewer muscarinic binding sites in the urethra than in the bladder. The dissociation constant for [3H]dihydroalprenolol at the beta-binding site was 6.4 nM, for [3H]dihydroergocryptine at the alpha-binding site was 2.11 nM, and for 3H-labelled l-quinuclidinyl benzilate at the muscarinic binding site was 0.22 nM.

Low beta-adrenergic receptor concentration on human thymocytes

Several agents are known that can elevate cyclic AMP levels in lymphoid cells, e.g. isoproterenol, PGE1 and adenosine. We have studied the cyclic AMP increasing effect of these agents on thymocytes from mouse and man and on human peripheral T lymphocytes. In contrast to mouse thymocytes and human peripheral T lymphocytes, human thymocytes appeared to be insensitive to isoproterenol, but did respond to PGE1 and adenosine. Furthermore, the density of beta-adrenergic receptors on the cells was determined by measuring the specific binding of 3H-dihydroalprenolol. A correlation was found between the receptor density on the cells and the rise in intracellular cyclic AMP induced by isoproterenol: human thymocytes appeared to have very few beta-adrenergic receptors, in contrast to thymocytes from mouse or to T lymphocytes from human blood. We conclude that the development of beta-adrenergic receptors in T cell ontogeny is different for mice and human beings. Comparison of animal models with the situation in man should be made with caution.

A rapid method for isolation of human mononuclear cells free of significant platelet contamination

In order to obtain mononuclear cells from peripheral human blood for the study of cell surface receptors, it was necessary to effectively eliminate contaminating platelets. The usual Hypaque-Ficoll isolation procedures were found to produce mononuclear cells contaminated with 10-1000 platelets per mononuclear cell (by phase microscopy). Multiple slow speed centrifugations reduced the contamination to 5-10 platelets per mononuclear cell. However, centrifugation of EDTA-anticoagulated blood through Hypaque (D20(20) 1.060) at 400 X g for 5 min at 22 degrees C followed by the usual Hypaque-Ficoll gradient reduced platelet contamination to less than 1 platelet per 2 mononuclear cells. Thus, a rapid and simple gradient procedure is capable of significantly reducing platelet contamination of mononuclear cell preparations and should facilitate the analysis of mononuclear cell receptors and functions.

Functional postsynaptic alpha 2- but not alpha 1-adrenoceptors in dog saphenous vein exposed to phenoxybenzamine

Phenoxybenzamine greatly attenuated phenylephrine-induced contractions of dog saphenous vein in vitro, but had less effect on contractions induced by clonidine. The phenoxybenzamine-resistant responses to clonidine were not affected by prazosin or by corynanthine but were competitively antagonized by yohimbine (pA2 8.2). It is concluded that exposure of saphenous vein to phenoxybenzamine resulted in blockade of alpha 1-adrenoceptors to the extent that there remained a virtually homogeneous population of postsynaptic alpha 2-adrenoceptors. The effects of agents at postsynaptic alpha 2-adrenoceptors can be studied on this preparation without the complications caused by the presence of functional alpha 1-adrenoceptors.

Characterization of (-)-[3H]dihydroalprenolol binding to intact and broken cell preparations of human peripheral blood lymphocytes

In this study we compared characteristics of (-)-[3H]dihydroalprenolol ([3H]DHA) binding sites in crude membrane preparations of human peripheral blood lymphocytes with those of intact, viable cells. A valid determination of specific beta-adrenergic receptor binding in both preparations was obtained by defining non-specific [3H]DHA binding with 10(-6) M l- or dl-propranolol or 10(-3) M l-isoproterenol. Higher concentrations of propranolol were used in prior reports on lymphocyte membranes. We showed that these concentrations may inhibit non-specific binding, causing non-saturability and inhomogeneity of the estimated 'specific' binding. In the intact cell preparations, inclusion of 10(-4) M phentolamine was necessary to reduce the high degree of non-specific binding. By contrast, phentolamine (10(-4) M) showed no effect on the [3H]DHA binding to membrane preparations. At 37 degrees C the [3H]DHA binding to beta-adrenergic receptor sites in both intact and broken cell preparations was rapid and reversible. The sites were stereoselective, as l-propranolol was about two orders of magnitude more potent to inhibit [3H]DHA binding than was the d-isomer. In both preparations, agonists competed for specific binding with a rank order of potency isoproterenol greater than epinephrine greater than norepinephrine, which indicated a beta 2-type of adrenergic receptor. The specific [3H]DHA binding was saturable and Scatchard analysis revealed comparable numbers of homogeneous, non-cooperative binding sites (approximately 1250 receptors/cell in the membrane preparations and 1700 receptors/cell in the intact cells). In spite of these similarities the membrane sites showed a lower affinity for the antagonists [3H]DHA and propranolol than did the intact cell sites, whereas their affinity for the agonists was increased. These differences indicate that the membrane system might be less suited to provide physiologically significant information about the beta-adrenergic receptor system.

Evidence for the existence of alpha- and beta-adrenoceptors on cultured glial cells--an electrophysiological study

The action of adrenergic alpha- and beta-agonists and antagonists has been studied on the membrane potential and resistance of glial cells of cultured rat central nervous system. Noradrenaline and the alpha-adrenoceptor stimulating agents phenylephrine and clonidine (10(-7) to 10(-4)M) depolarized the glial membrane, whereas the beta-agonist isoprenaline caused a hyperpolarization at low concentrations (10(-7) and 10(-6)M). The effects of noradrenaline and phenylephrine were reversibly blocked by the alpha-antagonist phentolamine, whereas those of isoprenaline were antagonized by the beta-blocker atenolol. Atenolol did not affect the depolarization by noradrenaline. The glial depolarization induced by the alpha-agonists was not the consequence of a change in the extracellular K+-concentration unlike that produced by amino acid transmitters. The present results, together with those of biochemical and autoradiographic binding studies, suggest that alpha- and beta-adrenoceptors occur on glial cells and that the glial depolarization is mediated by alpha-receptors, whereas the hyperpolarization is due to activation of beta-receptors.

Age-dependent decrease of beta-adrenoceptor density in the submandibular glands of mice and its modulation by the thymus

Beta-adrenergic receptors were characterized in submandibular glands of ageing mice and old mice grafted with a neonatal thymus. No statistically significant changes of receptor affinity were found in the animal models investigated. On the contrary, receptor density showed a progressive decrease with advancing age. The age-related decrease has been found partially corrected in thymus-grafted old animals, which show a statistically significant recovery of receptor density when compared to their untreated littermates. Receptor modulation can be responsible for the age-related impairment and the thymus-dependent correction of beta-adrenergic responsiveness of submandibular glands previously observed in vivo. Hormonal balance and thyroid hormones, in particular, are suggested as being involved in the age- and thymus-dependent regulation of receptor density. In the accompanying Appendix, we describe the mathematical method used to calculate both specific and nonspecific binding from total binding data.

Evidence for the existence of alpha- and beta-adrenoceptors on neurones and glial cells of cultured rat central nervous system--an autoradiographic study

The cellular localization of the binding of radioactive noradrenaline and alpha- and beta-adrenoceptor antagonists was studied in organotypic cultures of rat cerebellum, brain stem and spinal cord using autoradiography. In cerebellar cultures, many neurones, which appeared to be Purkinje cells, were labelled by [3H]noradrenaline and by the beta-antagonists [3H]dihydroalprenolol and [3H]carazolol, whereas no binding of the alpha-antagonists [3H]prazosin and [3H]rauwolscine was detected. In cultures of spinal cord and brain stem, [3H]noradrenaline and the beta-antagonists were bound to many large neurones. Binding of [3H] alpha-antagonists was observed to a small number of brain stem and spinal neurones, the labelling being much weaker than that produced by the [3H] beta-antagonists. The antidepressant [3H]desmethylimipramine was bound to many neurones and glial cells in cerebellar, brain stem and spinal cord cultures. Glial cells also possessed binding sites for [3H]noradrenaline and alpha- and beta-adrenoceptor antagonists, findings that are consistent with recent electrophysiological observations which indicate the existence of alpha- and beta-adrenoceptors on cultured astrocytes.

Characterization of the rat mast cell beta-adrenergic receptor in resting and stimulated cells by radioligand binding

Rat serosal mast cell beta-adrenergic receptors were characterized both functionally by assessing changes in histamine release and cyclic 3',5' adenosine monophosphate (cAMP) levels and directly by radioligand binding studies using [3H]dihydroalprenolol ([3H]DHA), a beta-adrenergic antagonist. Mast cells were obtained by lavage of the pleural and peritoneal cavities of Sprague-Dawley rats and were purified on metrizamide gradients to greater than 95% purity. Resting mast cells stimulated with beta-adrenergic agonists demonstrate a marked rise in cAMP levels after a 15-sec incubation. However, the same concentrations of these agonists have no effect on IgE-mediated mast cell histamine release. [3H]DHA binding to intact mast cells is rapid, reversible, saturable, and stereoselective. The cells possess 40,000 +/- 14,000 beta-adrenergic receptors/cell and demonstrate a binding affinity of 1.58 +/- 0.56 nM for [3H]DHA. Competition studies reveal that 83.5% of the receptors are of the beta 2 subtype and 16.5% are beta 1. Neither sensitization with anti-DNP-BSA IgE nor subsequent challenge with specific antigen alters mast cell beta-adrenergic receptor characteristics. Rat mast cells possesses large numbers of high affinity beta-adrenergic receptors, primarily of the beta 2 subtype, coupled to adenylate cyclase, but the role of these receptors in mast cell secretory events is not yet established.

The beta-adrenergic system and allergic bronchial asthma: changes in lymphocyte beta-adrenergic receptor number and adenylate cyclase activity after an allergen-induced asthmatic attack

Beta-adrenergic receptor characteristics and adenylate cyclase responses to different stimuli were measured in lymphocyte membrane preparations of six normal control subjects and five allergic asthmatic patients with mild airways disease and increased bronchial reactivity to histamine and acetylcholine. The determinations were performed just before and 24 hr after inhalation challenge with house-dust mite antigen to investigate the influence of an allergen-induced asthmatic attack on the beta-adrenergic receptor system. Before the house-dust mite challenge, the lymphocyte membranes of the patients showed a normal receptor density, dissociation constant for (-)3H-dihydroalprenolol, and adenylate cyclase response to isoproterenol, guanyl-5'-yl-imidodiphosphate, (GppNHp) and NaF. After the allergen-induced asthmatic reaction, however, the beta-adrenergic receptor number in the patients was significantly reduced by 21%, while the basal adenylate cyclase activity and isoproterenol-, GppNHp-, and NaF-induced cyclic AMP responses were simultaneously reduced by about 40%. The allergen challenge had no significant effect on the lymphocyte membranes of the control subjects. These results suggest (1) that a reduced beta-adrenergic function is not an intrinsic component of allergic bronchial asthma but is rather the consequence of an active disease state, and (2) that next to changes in beta-adrenergic receptor number, alterations distal to the receptor may play an important role in the observed decrease in beta-adrenergic responsiveness.

An affinity label for alpha 2-adrenergic receptors in rat brain

Clonidine, a potent and highly selective alpha 2-adrenergic agonist of the central nervous system, was modified. Insertion of the strong alkylating isothiocyanate group (NCS) group, at its aromatic residue, makes clonidine a potential affinity label of the alpha 2-adrenergic receptors. In displacement of [3H]clonidine and p-[3H]aminoclonidine from rat brain membrane preparations, clonidine-NCS demonstrates high affinity for the alpha 2-adrenergic receptors (Kd = 50 mM). The covalent labelling of the central alpha 2-receptors requires higher concentrations of the irreversible ligand (1-70 microM), thus indicating possible non-productive interactions at the environment of the receptor site. Only partial protection of the receptors is observed with a reversible alpha 2-agonist. The new clonidine analog appears to be a general ligand for the alpha 2-adrenergic receptors and might serve as a potential affinity probe for these receptors.

Rat lung cholinergic receptor: characterization and regulation by corticosteroids

Muscarinic cholinergic receptors have been implicated in the regulation of bronchomotor tone, bronchial mucus secretion, and lung mast-cell mediator release. Rat lung membranes prepared by homogenization, sonication, and sedimentation of 37,000 g in sucrose have been demonstrated to possess muscarinic cholinergic receptors as assessed by radioligand binding employing l-quinuclidinyl[phenyl-4-3H]benzilate ([3H]QNB). QNB binding was saturable, stereoselective, and reversible in the presence of 1 microM atropine. The rat lung muscarinic receptor demonstrated a Kd of 0.268 +/- 0.126 (+/- SD) nM and a density of 35.4 +/- 4.6 fmol/mg protein by Scatchard analysis. The Hill coefficient was 1.015 +/- 0.085, indicating noncooperative binding. Muscarinic cholinergic receptors in the rat lung were equal in number to alpha 1-adrenergic receptors, but beta-adrenergic receptors are 14 times more prevalent as defined by [3H]prazosin and l-[propyl-2, 3-3H]dihydroalprenolol ([3H]DNA) binding. Dexamethasone (140 micrograms) administration in vivo caused an increase in all three receptor types by 24-48 h, suggesting steroids regulate not only the number of beta-receptors but also that of alpha- and cholinergic receptors. These data suggest new avenues by which steroids may regulate lung function.

Pharmacological experiments demonstrate that toad (Bufo marinus) atrial beta-adrenoceptors are not identical with mammalian beta 2- or beta 1-adrenoceptors

Chronotropic responses to sympathomimetic amines of isolated atrial preparations from toads (Bufo marinus) were mediated by beta-adrenoceptors since isoprenaline was more potent than adrenaline and noradrenaline, and propranolol was a potent antagonist (pA2, adrenaline as agonist = 9.33). The beta-adrenoceptors had some of the characteristics of mammalian beta 2-adrenoceptors in that (i) adrenaline was more potent than noradrenaline and (ii) the pA2 values of two selection beta-adrenoceptor antagonists, atenolol (pA2 = 5.84) and alpha-methylpropranolol (pA2 = 8.42), were close to the values reported on beta 2-adrenoceptors in mammalian tissues. However, the relative potencies of adrenaline, isoprenaline, noradrenaline, rimiterol, salbutamol and fenoterol (1 : 45.8 : 0.07 : 3.3 : 1.05 : 0.32) did not correspond to the relative potencies reported for these agonists on mammalian tissues which contain predominantly beta 2-adrenoceptors. Also the pA2 value for the beta 2-selective antagonist, ICI 118,551 (7.89, adrenaline as agonist) was lower than its reported pA2 on beta 2-adrenoceptors in mammalian tissues. There was no evidence that the response was mediated by both beta 1- and beta 2-adrenoceptors since Schild plots for ICI 118,551 using three agonists of differing selectivity (adrenaline, rimiterol and noradrenaline) were superimposed. It is concluded that, although toad atrial beta-adrenoceptors have several characteristics in common with beta 2-adrenoceptors in mammalian tissues, these amphibian beta-adrenoceptors are not identical with mammalian beta 2-adrenoceptors.

Cardiac beta-receptor variation in rat strains selectively bred for differences in susceptibility to stress

The radioligand 3H-DHA was used to estimate the density and affinity of cardiac beta-receptors in rat strains selectively bred for differences in response to stress. Maudsley Reactive rats selected for heightened reactivity to stress had a greater density of beta-adrenergic binding in cardiac membranes than rats of two genetically distinct Maudsley Non-Reactive strains selected for decreased reactivity to stress, and compared with one of these Non-Reactive strains the MNR/Har, increased affinity for 3H-DHA. Together with previous findings the present results demonstrate a negative correlation between estimates of basal sympathetic activity on the on hand, and post-synaptic beta-receptors in heart on the other, that are consistent with the notion that these receptor alterations have occurred as a result of long-term differences in pre-synaptic release of transmitter. The Maudsley strains may, therefore, provide a useful model for the study of beta-adrenergic receptors as a physiological locus for regulation of end-target responsiveness to sympathetic stimulation.