Alpha 2-adrenoceptors in the brain of suicide victims: increased receptor density associated with major depression

To examine directly in the brain the status of the alpha 2-adrenoceptor in major depression, the specific binding of the agonists [3H]clonidine and [3H]UK 14304 was quantitated in various brain regions of suicide victims with a retrospective diagnosis of depression or other psychiatric disorders. In depressed suicides, the binding capacity of [3H]clonidine was found to be increased in the hypothalamus (Bmax 35%-55% greater), and to a lesser extent in the frontal cortex, as compared with that in matched controls, schizophrenic suicides, or suicides with various diagnosis. The binding capacity of [3H]UK 14304 also was found increased in the frontal cortex (Bmax 30% greater), and to a lesser extent in the hypothalamus, of depressed suicides. In other brain regions such as the amygdala, hippocampus, and cerebellum there also was a tendency for an increased receptor density associated with suicide. Moreover, in the frontal cortex of suicides, the potency of norepinephrine in displacing the binding of the antagonist [3H]idazoxan also was found increased (Ki decreased eight-fold). The results indicate that the density and affinity of alpha 2A-adrenoceptors in the high-affinity state are increased in the brain of depressed suicides.

[Adrenergic receptors in the liver parenchyma in children with chronic hepatitis]

In the present study adrenergic receptors have been investigated in liver parenchyma, obtained at the resection of extrahepatic portal hypertension children without parenchymal affection (control group, n-7) and the resection of children in parenchymal affection (group of chronic hepatitis children, n-6). It has been shown, that the binding of beta-adrenergic radioligand 3H-dihydroalprenolol (3H-DHA) in liver parenchyma membranes of both control and chronic hepatitis groups was saturable and showed high affinity. The Scatchard analysis of the binding data indicated that the binding site was characterized by Kd and Bmax of 1.2 +/- 0.5 nM, 261.2 +/- 50 fmol/mg, respectively, for the control group; and 0.9 +/- 0.15 nM, 68.5 +/- 18.8 fmol/mg, respectively, for the group of chronic hepatitis patients; (mean+SEM). The binding of alpha 1-adrenergic antagonist 3H-prazosin (3H-PRZ) in liver parenchyma was also saturable and showed high affinity. The binding site is characterized by Kd = 0.6 +/- 0.12 nM, Bmax = 92.8 +/- 8.0 fmol/mg, for the control group; and Kd = 0.8 +/- 0.15 nM, Bmax = 195.0 +/- 22.0 fmol/mg, for the group of chronic hepatitis. It has been found that the number of binding sites of 3H-DHA significantly decreased and the number of binding sites of 3H-PRZ did not change in chronic hepatitis liver parenchyma in comparison with the control group. The results obtained suggest the important role of beta-adrenergic receptors in the pathogenesis of chronic hepatitis and in liver regeneration in children.

[Neuromediator provision of the organs of immune system in benzpyrene intoxication]

The density of adrenergic innervation and relative content of catecholamines were investigated in rat lymphoid organs under different type of benzpyrene treatment. It was found that both ante- and postnatal influence of toxicant leads to a decrease of neurotransmitter providing of the thymus, spleen, mesenterial, iliac and popliteal lymph nodes. On the contrary, when mixed ante- and postnatal benzpyrene influence has place, the adrenergic innervation density and relative content of catecholamines are increased. We suppose that benzpyrene treatment of pregnant animals has specific "training" effect for monoaminergic systems of foetus and causes the increase of neurotransmitter providing of immunocompetent organs in conditions of repeat body and toxicant meeting.

Glucocorticoids and the development of neuronal function: effects of prenatal dexamethasone exposure on central noradrenergic activity

Although glucocorticoids slow the development of most cell types, they have been hypothesized to promote the differentiation of catecholaminergic cells. In the current study, pregnant rats were given dexamethasone on gestational days 17, 18 and 19, and the functional state of noradrenergic synaptic activity was assessed throughout postnatal development by measurements of transmitter levels and turnover, and receptor binding capabilities. Despite growth inhibition caused by dexamethasone, the steroid treatment had little or no effect on transmitter levels or receptor binding and accelerated the maturation of norepinephrine turnover in a regionally selective manner. Effects were most notable in the midbrain and brainstem, where turnover rose to maximum levels 1-2 weeks in advance of controls. Turnover also leveled off prematurely in the dexamethasone group, leading to deficits in the postweaning period and into young adulthood. Although similar patterns were obtained in other, later-developing regions, the effects were less consistent and robust; the smaller effects also extended to dopamine turnover. These results suggest that glucocorticoids have a specific promotional effect on the development of central catecholaminergic activity and that administration of exogenous steroids during critical periods of development can lead to lasting functional abnormalities.

The innervation of the closer muscle of the mesothoracic spiracle of the locust

The closer muscle of the mesothoracic spiracle of the locust, Schistocerca gregaria is innervated by two excitatory motoneurones and also by processes of a peripherally located neurosecretory cell. Within the muscle, ultrastructural studies show the presence of two types of excitatory nerve terminal which differ in the content of dense cored vesicles and in their distribution. The ventral segment of the muscle is innervated predominantly by terminals with small clear vesicles and only an occasional dense-cored vesicle. The central part of the muscle is innervated predominantly by terminals with small clear vesicles and larger numbers of dense-cored vesicles. The dorsal segment of the muscle is innervated exclusively by a neurosecretory type innervation. The small neurohaemal organ of the median nerve close to the spiracle muscle is immunoreactive to an antibody raised against bovine pancreatic polypeptide but no immunoreactive processes enter the muscle itself. The muscle possesses specific octopaminergic receptors that increase cyclic AMP levels and the possibility that the neurosecretory input to the muscle is provided by either a central or peripheral octopamine containing neurone is discussed.

Adrenergic and 5-HT2 receptors on the same astroglial cell. A microspectrofluorimetric study on cytosolic Ca2+ responses in single cells in primary culture

Noradrenaline (NA) or 5-hydroxytryptamine (5-HT) evoked cytosolic Ca2+ mobilization in single type 1 astrocytes in primary culture from the cerebral cortex of newborn rat. The Ca2+ indicator dye fura-2/AM was used in a microspectrofluorimetric system to visualize fluctuations in the intracellular Ca2+ concentration. Activation of the adrenergic receptors alpha 1, alpha 2 and beta, or activation of the 5-HT2 receptors elicited different responses of Ca2+ mobilization with different types of Ca2+ spikes or oscillations. Principally, 4 different types of Ca2+ responses could be obtained: a sharp spike, which declined back to baseline; an initial sharp spike, which declined to a smaller but sustained Ca2+ elevation; an initial sharp spike which declined and showed low amplitude oscillations; and a sharp spike which declined back to baseline with baseline oscillations. Applications of the alpha 2 adrenoceptor agonist clonidine to individual astroglial cells evoked Ca2+ transients mostly in young cultures (cultivated for 7-10 days), while applications of the alpha 1 adrenoceptor agonist phenylephrine evoked Ca2+ transients mostly in older cultures (17-21 days of cultivation). Applications of the beta adrenoceptor agonist isoproterenol evoked Ca2+ transients in both young and older cultures, however, more frequent in older cultures. The alpha 2 and beta receptor responses were dependent on external Ca2+ levels. The NA-evoked Ca2+ responses were seen in cultivated cells at all ages, but were more frequent in older cultures. Approximately 50% of the astroglial cells in 8 day old cultures responded to 5-HT with a cytosolic Ca2+ mobilization and 80% of the cells in 21 day old cultures responded.(ABSTRACT TRUNCATED AT 250 WORDS)

[Modeling of hormonal receptors. Application to drug design]

A number of three-dimensional models of serotonin receptor recognition sites which were derived from a conformational analysis of their ligands and successfully used for drug design are reviewed. Models of the complete three-dimensional structure of sequenced G-protein coupled receptors are defined from primary sequence analysis, published experimental data, the crystal structure of bacteriorhodopsin and energy minimizations. Adrenaline, serotonin, dopamine and acetylcholine can thus be docked in their respective binding sites. There is an excellent convergence between the two approaches: modelling of the recognition site from its ligands and modelling of the receptor from its primary sequence.

[Pregnancy-induced changes in adrenergic receptors]

In the 24th and 26th week of pregnancy and also 6 weeks post partum, n = 32 pregnant women were evaluated for the concentration of adrenergic receptors on blood cells by radioligand binding assay and an isoprenaline stimulation of the beta-receptors. The concentrations of estradiol and progesterone in serum were also determined and nephrosonography was carried out. The stimulation and concentration of the beta-receptors were significantly higher during pregnancy than post partum. The alpha-receptors displayed contrary alterations: Here, the concentration evaluated during pregnancy was considerably lower. No connection was determined between the progesterone level in serum and the extent of the receptor alterations. However, one was found with the estrogen level and the dilatation of the upper urinary tract: Pregnant women with pronounced alterations above the median showed a distinct decrease of estradiol and a marked dilatation of the kidney collecting system. Alterations in the adrenergic receptors can therefore be determined during pregnancy. The extent of the receptor fluctuation is connected to the estradiol concentration in serum and the dilatation of smooth muscle hollow organs.

[The formation of the catecholaminergic system of the hypothalamus in rats. Dopamine uptake and release]

The development of the hypothalamic catecholaminergic (CA) system during ontogenesis in rats has been studied with the isotopic biochemical technique in vitro. It has been demonstrated, that at the 15th fetal day, the CA system was functionally inactive at least in its ability for the uptake and K(+)-stimulated release of catecholamines. Since the 16th fetal day, hypothalamic neuronal elements gained an ability for specific uptake and K(+)-stimulated release of the exogenous radioactively labeled dopamine increased significantly. The specific uptake doubled from the 20th fetal till the 9th postnatal day, whereas K(+)-stimulated release doubled between the 9th 45th postnatal days.

Recovery time course of airway hyperresponsiveness to acetylcholine after ovalbumin challenge in guinea pigs

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

[The action of low doses of bromocryptin in experimental morphine abstinence in rats]

In experiments on rats which consumed for a long time morphine solution as a drinking liquid there was studied the effect of low doses of bromocriptine on the behavioural manifestations of morphine abstinence syndrome and the condition of the noradrenergic, dopaminergic and conjugated GABAergic systems of the brain. It was shown that the preliminary administration of bromocriptine decreased the degree of the withdrawal syndrome that correlated with the restoration of dopamine content and the normalization of the condition of D2-dopaminergic receptors in different regions of the brain. Bromocriptine exerted no influence on the morphine withdrawal-induced changes in the condition of GABA receptors of the cerebral cortex.

Pharmacology of airway smooth muscle in chronic obstructive pulmonary disease and in asthma

Only a small number of studies investigating the in vitro pharmacologic properties of airway smooth muscle in asthma and well-characterized COPD have been performed. Further detailed studies on well-defined patient groups are required. The majority of available evidence would suggest that once airway smooth muscle is removed from its in vivo milieu, it loses the characteristics of hyperresponsiveness. This would explain why there are no clear differences in the pharmacologic responsiveness of tissue from patients with asthma or COPD and those with no obstructive disease. Future in vitro studies should be directed towards reproducing the in vivo environment. this would entail the establishment of a chronic inflammatory condition created by the continuous presence of neural and humoral factors.

Adrenoceptors on blood cells from patients with primary Raynaud's phenomenon

1. alpha 2-Adrenoceptors on platelet membranes and beta 2-adrenoceptors on lymphocytes were studied in 24 patients with primary Raynaud's phenomenon and in 24 age- and sex-matched control subjects. In two subgroups, a standardized mental arithmetic test and a finger-cooling test were performed. 2. Baseline blood pressure, heart rate and forearm blood flow did not differ between the two groups. 3. Baseline skin microcirculation (laser Doppler flux) was decreased in primary Raynaud's phenomenon (19 +/- 15 arbitrary units) compared with control subjects (33 +/- 14 arbitrary units) (P less than 0.01). 4. Baseline plasma noradrenaline concentration (2.00 +/- 1.44 versus 1.16 +/- 0.36 nmol/l) and alpha 2-adrenoceptor density (301 +/- 119 versus 210 +/- 82 fmol/mg) were increased in patients with primary Raynaud's phenomenon in comparison with the control subjects. The alpha 2-adrenoceptor density/beta 2-adrenoceptor density ratio in patients with primary Raynaud's phenomenon was, with a value of 0.37 +/- 0.04, higher than in the control subjects, where a value of 0.25 +/- 0.02 was measured (P less than 0.001). Plasma adrenaline concentration, beta 2-adrenoceptor density and the antagonist affinity to both receptor subtypes did not differ between both groups under baseline conditions. 5. Whereas during the finger-cooling test no differences were seen in the responses of the parameters measured, the mental arithmetic test induced an increase in laser Doppler flux in patients with primary Raynaud's phenomenon and a decrease in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular characterization of alpha 1- and alpha 2-adrenoceptors

Three 'alpha 1-adrenoceptors' and three 'alpha 2-adrenoceptors' have now been cloned. How closely do these receptors match the native receptors that have been identified pharmacologically? What are the properties of these receptors, and how do they relate to other members of the cationic amine receptor family? Kevin Lynch and his colleagues discuss these questions in this review.

Autoradiography of adrenoceptors in rat and human brain: alpha-adrenoceptor and idazoxan binding sites

This chapter reviews the current classification of adrenoceptors, and notes the difficulties of combining the molecular biological and pharmacological classifications of adrenoceptors. Possibilities for mapping the distribution of the proposed subtypes of adrenoceptors using currently available ligands are discussed, and the autoradiographic visualisation of the broad subtypes of alpha 1-, alpha 2-, beta 1-, and beta 2-adrenoceptors in the rat, monkey and human brain described and illustrated. The non-selectivity of ligands currently being used to label alpha-adrenoceptors is shown; we compare the distribution of [3H]idazoxan binding sites with the distribution of alpha 2-adrenoceptors visualised using other ligands. Resolution limitations of current autoradiographic approaches are considered and we shown how in situ hybridisation can complement data from receptor labelling studies used to localise receptors to pre- or postsynaptic sites.

[A comparative study of the biogenic amine receptors in the muscle tissue of mollusks, echinoderms and tunicates]

Smooth muscles of Mollusca, Echinodermata and Tunicata contain one class of adrenoreceptors with the dissociation constant and maximal specific binding 2.5 and 82 in Anodonta, 2.3 and 320 in Holothuria, 4.9 pM and 232.5 fmol/mg of protein in ascidia. Catecholamines and their antagonists can be ranged in the row as follows: isoproterenol greater than adrenalin greater than propranolol-noradrenaline greater than phentolamine. Negative regulation of the beta-adrenoreceptor affinity to isoproterenol by means of guanine nucleotides (GN) was shown. The muscular tissues of Mollusca, Echinodermata and Tunicata have only one class of the serotonin receptors with the dissociation constant and maximal specific binding 120 and 13.2 in Anodonta, 88 and 192 in Holothuria, 2.6 pM and 54 fmol/mg of protein in ascidia. The GTP negative regulation of serotonin receptors affinity to the hormone was found. The GN regulation of the above receptors affinity to agonist suggests that muscle tissue of the above species has specific GTP [correction of GTR]-binding proteins capable of coupling with these receptors.

Is orthostatic hypotension in the elderly due to autonomic failure?

In order to investigate whether orthostatic hypotension in elderly people is due to autonomic nervous system dysfunction or blood vessel abnormalities, we have measured platelet and lymphocyte adrenoceptor numbers and agonist binding in addition to venous plasma catecholamine concentrations. Eight elderly subjects with orthostatic hypotension and six control elderly subjects were studied. None of the subjects had other symptoms of autonomic failure. There was no significant difference between the heart rate or plasma catecholamine responses to standing of the two groups. The orthostatic hypotension subjects had a significant rise of their plasma vasopressin levels whereas the control group had no significant change. The number of alpha 2-adrenoceptor sites in platelets was lower in the orthostatic hypotensive group compared to the controls and the binding affinity was greater than in the controls. There were no significant differences in beta-adrenoceptor binding sites or affinities in isolated lymphocytes between the two groups. The similar changes in heart rate and catecholamines together with the vasopressin changes suggest that, in these elderly patients with an abnormal drop of blood pressure on standing, there is no dysfunction of autonomic pathways concerned with cardiovascular function. The lower numbers of alpha 2-adrenoceptor sites on isolated platelets in subjects with orthostatic hypotension could indicate reduced alpha 2-adrenoceptor numbers on their blood vessels which could contribute to their inability to maintain blood pressure while standing.

Differential effects of DSP-4 on noradrenaline axons in cerebral cortex and hypothalamus may reflect heterogeneity of noradrenaline uptake sites

The effect of the noradrenergic neurotoxin DSP-4 on high affinity transport of noradrenaline (NAT) was studied using rat brain synaptosomes. DSP-4 decreased NAT with the characteristics of a competitive inhibitor. The neurotoxin was more potent in inhibiting NAT into cortical synaptosomes (Ki = 179 +/- 39 nM) than into hypothalamic synaptosomes (Ki = 460 +/- 35 nM). Differences in NAT into cortical and hypothalamic synaptosomes were also observed with noradrenaline itself (Km = 39.5 +/- 7.5 nM and 100 +/- 12.1 nM, respectively) and with the catecholamine uptake blocker mazindol (Ki = 0.55 +/- 0.05 nM and 0.30 +/- 0.08 nM, respectively). The differences in the pharmacological properties of the noradrenaline uptake carrier in cerebral cortex and hypothalamus may account for the differential effects of DSP-4 on noradrenergic axons in these two brain regions.

Characterization of adrenoceptor subtypes in cat cutaneous vasculature

Experiments were undertaken to characterize the relative contribution of adrenoceptor subtypes in mediating vasoconstriction to exogenous agonists in the digital cutaneous vascular bed of the anesthetized cat using laser-Doppler flowmetry. Intra-arterial administration of (-)-epinephrine and (-)-norepinephrine into the brachial artery caused a dose-related vasoconstriction (decreased flow) with ED50 values of 7 and 21 ng, respectively. Blockade of beta adrenoceptors with propranolol did not alter the response to (-)-epinephrine nor did i.a. isoproterenol produce a significant vasodilation. Vasoconstrictor responses elicited by (-)-epinephrine and (-)-norepinephrine were antagonized by treatment with phentolamine (2.5 mg/kg i.v.) and by yohimbine (0.5 mg/kg i.v.) but were only marginally blocked by prazosin (0.1 mg/kg i.v.). A dose-related depression of cutaneous blood flow was also caused by clonidine at doses virtually identical to those of (-)-norepinephrine. Clonidine-induced vasoconstriction was antagonized by rauwolscine (0.5 mg/kg i.v.) but not by prazosin (0.1 mg/kg i.v.). Dose-response curves to a variety of additional adrenoceptor stimulants were constructed with the potency rank order for all agonists being: (-)-epinephrine greater than B-HT 920 = (-)-norepinephrine = clonidine much greater than (-)-phenylephrine much greater than B-HT 933 greater than methoxamine. Treatment with prazosin (0.1 mg/kg i.v.) antagonized methoxamine induced cutaneous vasoconstriction but not the decreased blood flow caused by B-HT 933. In contrast, rauwolscine (0.5 mg/kg i.v.) blocked the responses to B-HT 933 but not methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic quantification of adrenergic receptors in rat kidney

The adrenergic nervous system is active in kidney function, and the kidney has large numbers of adrenergic receptor subtypes. Because of the cellular complexity of the kidney, it is difficult to obtain direct assessments of adrenergic receptor binding characteristics over specific tissue compartments. Qualitative autoradiography allows the localization of adrenergic receptors over tissue types in the kidney, but quantitative autoradiography allows direct comparison of adrenergic receptor number over different cellular compartments. The purpose of this study was to obtain direct assessments of alpha 1, alpha 2, and beta adrenergic receptor numbers over different tissue compartments of the kidney using quantitative autoradiography. Sections of Sprague-Dawley rat kidney were incubated in several concentrations of 3H-dihydroalprenolol to label beta receptors, 3H-prazosin to label alpha 1 receptors and 3H-rauwolscine to label the alpha 2 receptors. Sections of rat heart incubated in 3H-dihydroalprenolol were included as standards. The sections were then prepared for receptor autoradiography. After processing, the grains were then quantified on an image analysis system, and binding curves constructed from the specific binding. In some animals, the proximal tubules were stained to localize the proximal convoluted tubules. Significant Scatchard analyses were obtained in the glomeruli with dihydroalprenolol (5.18 X 10(9) receptors/mm3) and with rauwolscine (2.48 X 10(9) receptors/mm3). Significant Scatchard analyses were obtained in the cortex with rauwolscine (9.47 X 10(9) receptors/mm3) and with prazosin (3.9 X 10(9)). In addition, specific binding was seen with rauwolscine and prazosin to the kidney arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic receptors. Models for regulation of signal transduction processes

Adrenergic receptors are prototypic models for the study of the relations between structure and function of G protein-coupled receptors. Each receptor is encoded by a distinct gene. These receptors are integral membrane proteins with several striking structural features. They consist of a single subunit containing seven stretches of 20-28 hydrophobic amino acids that represent potential membrane-spanning alpha-helixes. Many of these receptors share considerable amino acid sequence homology, particularly in the transmembrane domains. All of these macromolecules share other similarities that include one or more potential sites of extracellular N-linked glycosylation near the amino terminus and several potential sites of regulatory phosphorylation that are located intracellularly. By using a variety of techniques, it has been demonstrated that various regions of the receptor molecules are critical for different receptor functions. The seven transmembrane regions of the receptors appear to form a ligand-binding pocket. Cysteine residues in the extracellular domains may stabilize the ligand-binding pocket by participating in disulfide bonds. The cytoplasmic domains contain regions capable of interacting with G proteins and various kinases and are therefore important in such processes as signal transduction, receptor-G protein coupling, receptor sequestration, and down-regulation. Finally, regions of these macromolecules may undergo posttranslational modifications important in the regulation of receptor function. Our understanding of these complex relations is constantly evolving and much work remains to be done. Greater understanding of the basic mechanisms involved in G protein-coupled, receptor-mediated signal transduction may provide leads into the nature of certain pathophysiological states.

Binding sites for brain trace amines

1. Neurochemical, neuropharmacological, and neurophysiological studies suggest that some of the so-called trace amines may have a role in the modulation of neurotransmission. This review examines the possible existence and characterization of brain binding sites for the trace amines. 2. The results of radioligand binding studies carried out so far suggest the existence of tryptamine binding sites that possibly constitute a true functional receptor. This is supported by evidence obtained from the saturation studies, drug-mediated inhibition of binding, and the changes in the number of sites induced by pharmacological and lesion studies. In addition, the existence of a functional tryptamine binding site is supported by the increased neurophysiological responses of tryptamine obtained from the striatum of rat with unilateral substantia nigra lesions. 3. It has been shown that the brain contains saturable binding sites for rho-tyramine that appear to be related to the transport of dopamine into synaptic vesicles. There are, however, some questions with respect to the homogenization technique employed and some inconsistencies with respect to the number of binding sites estimated in neuronal membrane preparations. 4. The existence of rho-octopamine binding sites has been demonstrated in crude membranes obtained from fruitflies but not shown so far in vertebrates. 5. The presence of brain binding sites for beta-phenylethylamine are suggested but they are not so well defined and its physiological implication remains to be elucidated.

Development of a photoaffinity ligand for octopamine receptors

Octapamine receptors are widely distributed in invertebrate species, yet little is known about their biochemical structure or tissue localization, in part because there exist no high affinity or irreversible ligands for these receptors. This paper characterizes 2-(2,6-diethyl-4-azidophenylimino)imidazolidine (NC-5Z), a new, high affinity octopamine receptor probe that binds reversibly and, under photolyzing conditions, irreversibly to membrane-associated octopamine receptors. Under reversible conditions NC-5Z is a full agonist, 50-100 times more potent than octopamine in activating the highly enriched and specific octopamine-sensitive adenylate cyclase of the firefly light organ. NC-5Z shows a similar potency in cockroach muscle and thoracic ganglia and in tobacco hornworm nerve cord. Activation of light organ adenylate cyclase by NC-5Z is nonadditive to that caused by octopamine and can be blocked by antagonists, including mainserin (Ki = 0.9 microM), cyproheptadine (Ki = 5 microM), phentolamine (Ki = 20 microM), and propranolol (Ki = 75 microM). These constants agree well with those for the same antagonists in inhibiting stimulation due to octopamine. In physiological studies, NC-5Z mimics the action of, but is more potent than, octopamine in stimulating light emission in intact firefly tails and in disrupting motor behavior and feeding of tobacco hornworms. Under reversible conditions, [3H]NC-5Z, the tritiated derivative of NC-5Z, binds to light organ membranes with an apparent affinity (0.59-0.7 microM) similar to that (0.35-0.7 microM) for NC-5Z in activating adenylate cyclase. Under photolyzing conditions, NC-5Z irreversibly activates light organ adenylate cyclase, and this can be blocked by an excess of octopamine. Under similar conditions, [3H]NC-5Z binds irreversibly to light organ membranes and to membranes from tobacco hornworm nerve ganglia, fat body, and gut. This binding is reduced by prior incubation with octopamine agonists, including octopamine, demethyl-chlordimeform, and 2-(phenylimino)imidazolidines, but not by norepinephrine, dopamine, serotonin, or histamine. Irreversible binding is also reduced by prior incubation with antagonists, most effectively (55% of total binding) by mianserin. The apparent affinity of [3H]NC-5Z for membrane binding, as reflected by its ability to be displaced by mianserin, is altered by GTP. In autoradiographic studies of whole tissue, [3H]NC-5Z shows irreversible, mianserin-displaceable labeling of intact firefly light organs. Taken together, these data indicate that NC-5Z and [3H]NC-5Z are potent and selective agonists of octopamine receptors in a variety of tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracellular distribution of adrenoceptors in the failing human myocardium

Although it is increasingly recognized that the density of cardiac membrane-bound beta adrenoceptors declines in heart failure, the mechanisms involved are unclear. Furthermore, it is not known whether cardiac alpha-1 adrenoceptors are similarly affected. Inasmuch as agonist-induced desensitization results in translocation of adrenoceptors from the plasma membrane to an intracellular vesicular fraction, we determined the intracellular distribution of cardiac adrenoceptors in two groups: group 1 (n = 9) consisted of papillary muscles from patients with mild-to-moderate heart failure undergoing valve replacement, and group 2 (n = 8) consisted of severely failing hearts removed during orthotopic cardiac transplantation. The density of cardiac beta adrenoceptors was lower in membranes from group 2 (17.8 +/- 3.3 fmol/mg protein vs 27.8 +/- 3.7 fmol/mg in group 1; (p less than 0.01), and the percentage of beta receptors recovered in the vesicular fraction was higher in group 2 (47.1 +/- 3.3% vs 36.8 +/- 5.0% in group 1; p less than 0.01). In group 1 but not group 2 there was a significant inverse correlation (r = -0.87; p less than 0.001) between the density of membrane-bound beta receptors and the percentage of beta receptors recovered in the vesicular fraction. Alpha-1 adrenoceptors were lower in both membrane and vesicular fraction of group 2 compared to group 1; in group 2 but not group 1 there was a significant negative correlation between the density of membrane-bound alpha-1 adrenoceptors and the percentage of alpha-1 receptors in the vesicular fraction (r = -0.8; p less than 0.01). These results suggest that the regulation of alpha-1 and beta adrenoceptors differs in the failing myocardium. Furthermore, agonist-induced desensitization may play a predominant role only in mild-to-moderate heart failure.

Modulation of pyloric motor activity via adrenergic receptors

The influences of adrenergic nerves on pyloric motor function and the locus and types of receptors involved were examined. Using glyoxylic acid fluorescence a dense adrenergic innervation of the inner pyloric muscle ring was demonstrated. Pyloric motor activity was monitored while close i.a. injections of a selective alpha-1 adrenoceptor agonist, phenylephrine, or a selective alpha-2 adrenoceptor agonist, B-HT-920, were given. Neither agonist affected basal pyloric motor activity, but both inhibited pyloric activity when it was stimulated by duodenal field stimulation or by intraduodenal acid infusion. The actions of each of the inhibitory agonists, phenylephrine or B-HT-920, were blocked selectively by prazosin or rauwolscine, respectively. Injection of isoproterenol usually had no effect or excited basal pyloric activity. This excitation could be antagonized selectively by propranolol or by atropine. Injection of isoproterenol after neural blockade by tetrodotoxin inhibited pyloric motor activity. Receptor binding studies carried out with subcellular nerve or muscle enriched membrane fractions of canine pyloric muscle with [3H]prazosin, [3H]rauwolscine and [125I]cyanopindolol revealed a dual location of alpha-1, alpha-2 and beta receptors on both nerve membranes and smooth muscle membranes. These results suggest that adrenergic effects on the pyloric muscle can be exerted by pre- and postsynaptic beta receptors which, respectively, excite by releasing acetylcholine and inhibit by acting on receptors on the pyloric muscle. Also inhibitory alpha-1 and alpha-2 receptors are present on cholinergic nerves. The functions of postsynaptic alpha-1 and alpha-2 adrenoceptor binding sites on smooth muscle are so far unknown.

Human tissue adrenergic receptors are not predictive of responses to epinephrine in vivo

To test the hypotheses that adrenergic receptor and adenylate cyclase characteristics of easily accessible circulating cells reflect those of relatively inaccessible extravascular catecholamine target tissues in a subtype-specific fashion and that these characteristics predict responses to catecholamines in vivo, we studied 22 normal humans. Adrenergic receptors and their linked adenylate cyclase systems were measured in mononuclear leukocytes (MNL; beta 2), platelets (alpha 2), skeletal muscle membranes (beta 2), and fat cells (B1 and alpha 2) and compared with the responses to stepped, intravenous epinephrine infusions in vivo. MNL beta 2-adrenergic receptor densities (but not antagonist affinities) were correlated (r = 0.627; P less than 0.01) with skeletal muscle beta 2-adrenergic densities. However, other adrenergic receptor characteristics and basal and maximally stimulated adenosine 3',5'-cyclic monophosphate (cAMP) contents of MNL and all adrenergic receptor characteristics and cAMP contents of platelets were unrelated to the corresponding measurements in skeletal muscle and fat. Furthermore, there were no consistent relationships between tissue adrenergic receptor-adenylate cyclase characteristics and the chronotropic, diastolic depressor, lipolytic, ketogenic, glycemic, or glycogenolytic-glycolytic responses to epinephrine in vivo. Thus the data support the hypothesis that adrenergic receptor densities on circulating cells reflect those of extravascular target tissues in a subtype-specific fashion. On the other hand, the data do not support the hypothesis that physiological interindividual variation of adrenergic receptor characteristics is of sufficient magnitude to alter sensitivity to epinephrine in vivo.

Structure of the adrenergic and related receptors

The isolation and sequencing of a number of G protein-coupled receptors has now provided extensive primary structure information for this family of homologous proteins. The diverse nature of these receptors suggests that the family of proteins may grow to include receptors for many neurotransmitters and perhaps many peptide hormones. The topography of these receptors, a single polypeptide with seven transmembrane segments, appears to have features well suited for the transmission of signals, via conformational changes, to the interior of the cell. Detailed site-directed mutagenesis studies are now underway in many laboratories to understand the significance of the topography and also the regions of homology evident in the structures of all of these receptors. Obvious features of interest are the precise residues involved in the coupling of the receptors to the G-proteins and the identification of the residues required for ligand binding in each of the receptors, as well as domains of these receptors involved in the regulation of receptor function. In addition, the availability of molecular probes for this family of proteins will permit the elucidation of mechanisms of regulation at the gene level.

Adrenergic receptors. Evolving concepts on structure and function

During the past 15 years there has been a striking increase in the understanding of the molecular basis of cellular response to catecholamines. In addition to the two principal subtypes of beta-adrenergic receptors (beta 1 and beta 2), there are at least two (alpha 1, alpha 2) and very likely additional subtypes of alpha-adrenergic receptors. The discovery of guanine nucleotide binding (G) proteins as transducers of receptor occupancy to activation of second messenger systems provides a common theme in cellular regulation by catecholamines. Application of techniques such as radioligand binding and photoaffinity labeling have facilitated the direct identification, quantitation, and ultimately purification of alpha 1, alpha 2, beta 1, and beta 2 receptors. Each is a plasma membrane glycoprotein with a subunit molecular weight (without the carbohydrate portion of the glycoprotein) of 40,000 to 55,000 kDa. The recent cloning and sequencing of cDNAs for alpha 2-, beta 1-, and beta 2-adrenergic receptors has revealed that although each has a unique molecular structure, they appear to share several common features, including extracellular amino terminus, seven plasma membrane spanning domains, and intracellular carboxy terminus. The application of molecular biological techniques together with antireceptor antibodies, which will allow studies of adrenergic receptors independent of binding or functional properties, should help in answering the many unresolved questions related to activation and regulation of adrenergic receptors. Foremost among these is whether diseases such as hypertension are characterized by alterations in one or more adrenergic receptor subtypes.

Inhibitory effect of norepinephrine on the single-unit activity of caudally projecting paraventricular neurons

The role of norepinephrine (NE) in controlling the single-unit activity of paraventricular (PVN) neurons projecting to or passing through the caudal ventrolateral medulla (CVLM) was investigated in adult male rats anesthetized with urethane. Of 72 PVN neurons studied, 19 were antidromically activated by CVLM stimulation (Group I) and 48 were antidromically activated by posterior pituitary (PP) stimulation (Group II). The remaining 5 neurons were antidromically driven by both CVLM and PP stimulation (Group III). In 14 of the 19 Group I neurons and in all the 5 Group III neurons, iontophoretically applied NE was demonstrated to be inhibitory to the single-unit activity. No excitatory effect of NE was observed. In contrast, both excitatory and inhibitory actions of NE were observed in the Group II neurons. Of 37 Group II neurons tested, 28 were excited and 7 were inhibited by NE. The inhibitory effect of NE in Group I and Group III neurons was selectively blocked by the alpha antagonist, phentolamine, that was coiontophoresed with NE, but not by the beta antagonist, timolol (n = 9). The unit activity of Group I neurons that were inhibited by NE was not altered by an increase in arterial blood pressure (n = 3), whereas the unit activity of one NE-insensitive Group I neuron was decreased by an increase in blood pressure. Taken together, the results suggest that NE plays an alpha-adrenoreceptor-mediated inhibitory role in controlling the single-unit activity of caudally projecting PVN neurons. These neurons include a subpopulation of PVN neurons that project caudally as well as to the PP. The possible function associated with the NE-sensitive, caudally projecting PVN neurons may be other than the regulation of blood pressure.

Further characterisation of the dopamine-inhibitory receptor in Helix and evidence for a noradrenaline-preferring receptor

1. The cells in this study responded with a hyperpolarization to the following agents in this order of potency; dopamine greater than noradrenaline phenylephrine = octopamine. 2. 6,7 ADTN had a relative potency of 0.1 compared to dopamine. 5,6 ADTN did not inhibit the cells in this study. 3. The D1 receptor agonists SKF38393 and dihydroxynomifensine mimicked the effect of dopamine on these cells but were over 100 times less active, whereas the D2 selective agonists quinpirole and RU24213 were without effect. 4. Both the D1 antagonist SCH23390 and the D2 antagonist sulpiride antagonised the dopamine response with pA2 values of 6.1 and 6.7, respectively. 5. Five cells that responded to dopamine with a hyperpolarization were depolarized by noradrenaline. The order of potency of compounds at eliciting this depolarization, noradrenaline greater than phenylephrine greater than octopamine indicated that this response may be mediated by a noradrenaline-preferring receptor.

A possible new class of octopamine receptors coupled to adenylate cyclase in the brain of the dipterous Ceratitis capitata. Pharmacological characterization and regulation of 3H-octopamine binding

Octopamine exerts its effects in insects through interaction with at least two classes of receptors, designated octopamine-1 and octopamine-2. Octopamine-2 receptors are positively coupled to adenylate cyclase, while octopamine-1 receptors are not coupled to this enzyme system. Ceratitis capitata brain appears to have octopamine receptors as unique aminergic receptors coupled to adenylate cyclase. These receptors show some pharmacological analogies with respect to octopamine-2 receptors, however they should constitute a new class of octopamine receptors. C. capitata brain octopamine receptors have also been characterized by [3H]octopamine-binding studies, exhibiting similar regulatory mechanisms to other receptors coupled to adenylate cyclase activation.

Regulation of adrenergic receptor number following chronic noradrenaline infusion in the rabbit

In order to study noradrenaline-induced regulation of alpha- and beta-adrenoceptors, groups of male New Zealand White rabbits (n = 8) were treated with intravenous noradrenaline (0.09 mumol/kg x h) or ascorbate (0.1%) for 10 days via osmotic minipumps implanted in the femoral vein, and the number of cardiac, lung and lymphocyte beta-adrenoceptors as well as renal and platelet alpha 2-adrenoceptors were determined. 1. The mean arterial blood pressure, heart rate and catecholamine levels were measured before commencing, and after 24 h and 10 days infusion. Circulating noradrenaline concentrations were elevated approximately 6-fold at 24 h and were sustained at these levels after 10 days administration of noradrenaline. There were no significant alterations in the blood pressure while a significant decrease in the heart rate was observed at 24 h. 2. Alpha 2-adrenoceptor density was assessed using [3H]-yohimbine. A significant decrease in the number of alpha 2-adrenoceptors in the kidney was observed following the 10 days infusion with noradrenaline. This down-regulation was in marked contrast to the lack of alteration in platelet alpha 2-adrenoceptor number and the platelet alpha 2-adrenoceptor mediated aggregatory response. 3. The density of beta-adrenoceptors in lymphocytes, heart and lung were quantified using (-)[125I]iodocyanopindolol (ICYP). The noradrenaline infusions caused significant reductions in beta-adrenoceptor number in the heart and lung (containing predominantly beta 1-adrenoceptors) but not in lymphocytes (possessing mainly beta 2-adrenoceptors). The KD-values (pM) for ICYP binding to heart and lung were also significantly decreased in the present studies.(ABSTRACT TRUNCATED AT 250 WORDS)

[Atraumatic approach in myocardial perfusion, metabolism and receptors by positron emission tomography]

Positron emission tomography (PET) is a noninvasive visualization method that provides a quantitative representation of radioactive molecule distribution on a tissue section within an organ. PET may be compared to the quantitative autoradiography performed in animals on heart sections with carbon 14- or tritium-labelled molecules, but it has the advantages of being applicable to human beings and enabling time-related concentration studies to be carried out on various substances. By using mathematical models fatty acid consumption or cholinergic receptor density can then be measured in e.g. the interventricular septum. Myocardial perfusion is routinely measured using such tracers as rubidium 82, nitrogen 13-labelled ammonia or even oxygen 15 water or gallium 68-labelled albumin microspheres. 82 Rb and 13NH3 ammonia are strongly taken up by the myocardium. 82 Rb has properties that are similar to those of 201Tl used in nuclear medicine, and the kinetics of 13NH3 depend on both myocardial perfusion and myocardial metabolism. The myocardium can metabolize fatty acids, glucose, ketone-bodies and lactic acid. 11C-palmitate is ideal to evaluate the regional utilization of fatty acids. It has been extensively studied in dogs, where a good correlation was found between the size of experimental infarcts and that of the region where a reduction in palmitate concentration was observed. Glucose metabolism is studied by means of an 18F-labelled analogue: fluoro-deoxyglucose. Using this analogue and 11C-palmitate jointly in animals or patients with myocardial ischaemia showed an increase of glucose myocardial extraction and a decrease of palmitate uptake in the ischaemic areas. In necrotic areas, both fluoro-deoxyglucose and palmitate uptakes were extremely low.(ABSTRACT TRUNCATED AT 250 WORDS)

The response of autonomic receptors to castration and testosterone in the urinary bladder of the rabbit

The effects of castration and testosterone on the autonomic receptor density and contractility in the urinary bladder smooth muscle of male rabbits were compared to untreated animals. Four groups of rabbits were studied over a similar time span with Group 1 animals serving as the untreated controls. Two groups (Groups 2 and 3) were castrated 28 days prior to sacrifice, Group 2 animals received corn oil for 14 days, and Group 3 animals received testosterone, 10 mg./day, for 14 days. The Group 4 animals were non-operated and received testosterone 10 mg./day for 14 days. Ligand saturation binding studies for alpha adrenoceptors in the bladder base and proximal urethra were performed with [3H]dihydroergocryptine ([3H]DHE). Muscarinic cholinergic receptors (MChR) were assayed with [3H]quinuclidinyl benzilate ([3H]QNB) and beta adrenoceptors with [125I]iodocyanopindolol ([125I]CYP) on the detrusor smooth muscle. Castrated Group 2 animals showed no significant change in receptor density with either [3H]QNB or [125I]CYP in detrusor muscle, but did exhibit a significant reduction (59%) of alpha adrenoceptors in the bladder base-urethra. The testosterone treated castrate and testosterone treated non-operated animals had significant increases in the MChR density, but no change in the alpha adrenergic, or beta adrenergic receptor density as compared to untreated controls. Cumulative dose response contractile studies were performed with carbachol on detrusor muscle strips and with phenylephrine on bladder base strips in isolated organ baths. The contractile studies on muscles from Groups 1, 2 and 3 showed no change in the ED50 or maximal contractile strength between control, castration or testosterone treated castrated animals. The ratio of wet bladder weight as compared to total body weight between each of the treatment groups showed a slight increase in both of the testosterone treatment groups. It was concluded that castration down regulates the alpha adrenergic receptors of the bladder base, while testosterone treatment increases the density of MChRs, and increases the ratio of the bladder to total body weight. Although no contractile changes were observed in the bladder base tissue it is conceivable that longer chronic testosterone deficits might ultimately affect the bladder outlet resistance in the male because of the reduced alpha adrenergic receptor density.

Alpha-adrenergic agonists stimulate neonatal glucose production less than beta-adrenergic agonists in the lamb

Epinephrine, a catecholamine with both alpha (alpha)- and beta (beta)-adrenergic agonist effects, may produce clinical hyperglycemia in the adult by increasing glucose production and decreasing glucose clearance. However, the relative contribution of alpha v beta adrenergic agonists in control of neonatal glucose kinetics has not been defined. Twenty-three term lambs (weighing 4.4 +/- 0.2 kg, mean +/- SEM, and aged 3.8 +/- 0.4 days) were infused with 0.9% NaCl at 0.6 mL.kg-1 min-1 + 100 microCi/kg D[6-3H]-glucose by prime plus constant infusion for 210 minutes. Ra (rate of production) was measured during infusion of variable doses of epinephrine with or without variable doses of propranolol, a competitive beta-adrenergic antagonist to isolate the alpha-adrenergic agonist effects. All basal kinetic data were comparable. Under conditions of epinephrine infusion, the plasma glucose concentration increased from 95 +/- 10 mg/dL to 129 +/- 18 mg/dL (50 ng.kg-1 min-1 epinephrine; P less than .0001) and from 85 +/- 6 mg/dL to 253 +/- 8 mg/dL (500 ng.kg-1 min-1 epinephrine; P less than .00001) compared with controls (96 +/- 7 mg/dL to 95 +/- 8 mg/dL). When epinephrine and propranolol were infused simultaneously, plasma glucose concentration increased from 95 +/- 10 mg/dL to 122 +/- 12 mg/dL (50 ng.kg-1 min-1 epinephrine + 1.1 micrograms.kg-1 min-1; P less than .0001) and from 78 +/- 9 mg/dL to 134 +/- 12 mg/dL (500 ng.kg-1 min-1 epinephrine + 11 micrograms.kg-1 min-1; P less than .0001) compared with controls (no epinephrine, no propranolol).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of adrenergic receptors of rat ascites hepatoma AH130 cells with those of normal rat hepatocytes

The pharmacological specificity of adrenergic receptors in the plasma membrane of rat ascites hepatoma AH130 cells was compared with that in normal rat hepatocytes. The number of [125I]iodocyanopindolol-binding sites was much greater in AH130 cells than in the hepatocytes. We characterized the alpha-adrenergic receptor subtypes using the alpha 1-selective ligand [3H]prazosin and the alpha 2-selective ligand [3H]clonidine. AH130 cells had fewer prazosin-binding sites than the hepatocytes and about 8 times as many clonidine-binding sites of high affinity. The results showed that the adrenergic receptors in AH130 cells have pharmacological properties that are very different from those of the receptors in normal rat hepatocytes.

Pharmacological characterization of human ciliary muscle adrenoceptors in vitro

The in vitro pharmacological characteristics of adrenoceptors of the human ciliary muscle were investigated. Tissue was obtained from 30 eyes used previously for corneal transplantations which had been enucleated 6-24 hr after death. Experiments were performed within 2 days of enucleation. Strips of the meridional and circular portion of the ciliary muscle were attached to a tension gauge in an organ bath and the effect of drugs added to the perfusion medium was monitored isometrically. The muscle was precontracted with physostigmine (10(-5) M) and acetylcholine (10(-5) M). The non-selective beta adrenoceptor agonist isoproterenol (10(-6)-10(-3) M) caused a dose-related relaxation of the ciliary muscle, an effect which was completely inhibited by the non-selective beta adrenoceptor antagonist timolol (10(-5) M), while the beta 1 adrenoceptor antagonist betaxolol (10(-5) M) had no effect. The beta 2 adrenoceptor agonist salbutamol (10(-6)-10(-3) M) produced a dose-related relaxation of the ciliary muscle, an effect which was completely blocked by the beta 2 adrenoceptor antagonist L1 32-468 (10(-5) M). The non-selective alpha adrenoceptor agonist noradrenaline (10(-6)-10(-3) M) also caused a dose-related relaxation of the ciliary muscle. The non-selective alpha adrenoceptor antagonists phentolamine (10(-5) M) and thymoxamine (10(-5) M) and the alpha 1 adrenoceptor antagonist prazosin (10(-5) M) partially blocked the response to noradrenaline, while the alpha 2 adrenoceptor antagonist idazoxan (10(-5) M) and timolol (10(-5) M) had no effect. The alpha 1 adrenoceptor agonist phenylephrine (5 X 10(-6)-5 X 10(-3) M) caused a dose-dependent relaxation in five out of 12 isoproterenol-sensitive muscle strips. Further, it was not possible to block the phenylephrine-induced relaxation with thymoxamine (10(-5) M). The alpha 2 adrenoceptor agonist clonidine (10(-6)-10(-3) M) had no effect. No qualitative difference between drug effects on the meridional and circular ciliary muscles was observed. We conclude from these data that beta 2, and most probably alpha 1, adrenoceptors are present on both the meridional and circular portions of the ciliary muscle of the human eye.

Characterization of dopamine-induced potassium efflux in rat parotid acinar cells

The effects of dopamine and noradrenaline on potassium efflux from rat parotid gland were studied in a perifusion system. Tissue specimens were preincubated with 86RbCl and the efflux of 86Rb+ was used as a marker for potassium efflux. Noradrenaline induced 86Rb+ efflux more effectively than dopamine. The noradrenaline-induced efflux was inhibited by alpha-adrenoceptor blockers, especially the alpha 1-antagonist prazosin. The dopamine-induced 86Rb+ efflux was blocked by alpha-adrenoceptor antagonists, non-selective dopamine antagonists and a D-1 selective dopamine antagonist. The D-2 selective drug, sulpiride, did not affect the dopamine-induced 86Rb+ efflux. The dopamine effect was abolished when reserpinized animals were used, whereas the effect of noradrenaline was unaffected. The results suggest that dopamine has a presynaptic stimulatory effect in rat parotid gland, and that the presynaptic effect on potassium efflux seems to be mediated via the D-1 receptor subtype. Whether activation of the presynaptic D-1 receptors leads to noradrenaline release, or whether the D-1 receptor is coupled to the catecholamine transporter system remains to be studied further.

Postjunctional alpha 2-adrenoceptors in blood vessels of human nasal mucosa

Human nasal mucosa has various types of blood vessels and is a good tissue for demonstrating receptors for many vasoactive substances, including alpha-adrenoceptors. In contrast to the large contractile response induced by alpha 1-agonists, our studies have shown that alpha 2-agonists produce a small maximal contraction. This alpha 2-induced response was easily blocked by alpha 1-antagonists, indicating that it is evoked, at least partially, by the stimulation of alpha 1-adrenoceptors. Noradrenaline (NA)-induced contractions could not be abolished by either alpha 1- or alpha 2-antagonists alone, but were almost completely blocked by the combination of both antagonists. This suggests the presence of postjunctional alpha 2-adrenoceptors. The low-maximal responsiveness to alpha 2-agonists and calcium independency of NA-induced contractions were distinct from our former results obtained on canine nasal specimens.

Comparison of cortical adrenergic, cholinergic and benzodiazepine receptors between albino rat and desert rat (Mastomys natalensis) using radioreceptor binding

Cortical alpha-adrenergic, beta-adrenergic, cholinergic (muscarinic) and benzodiazepine receptors have been studied in the albino rat and Mastomys natalensis (desert rat) using radioligand binding. Scatchard analysis was performed to determine affinity (Kd) and density (Bmax) of receptors. Compared to the albino rat, the desert rat was found to have higher affinity and density of alpha-adrenergic receptors. Beta-adrenergic receptors had similar Kd in both species but Bmax was significantly lower in the desert rat as compared to the albino rat. Cholinergic (muscarinic) receptors as well as the benzodiazepine receptors were in significantly higher density in the desert rat. The affinity was low for muscarinic receptors in the desert rat but equal for benzodiazepine receptors in both species. Since there are more alpha-adrenergic, muscarinic and benzodiazepine receptors in the desert rat, this species should be of value in screening compounds active at these sites.

Concerning the assays for autonomic nerve receptors. Effects of incubation temperature and time on alterations in the number of receptors

Alterations in autonomic nerve receptors play an important role in various pathological conditions, including bronchial asthma. Nevertheless, receptor assay conditions such as incubation temperature and incubation time are not consistent among various investigators. This study was designed to clarify the effects of incubation temperature and time on alterations in the number of autonomic nerve receptors. Guinea pig lung membranes were divided into five groups which were incubated under different incubation temperatures and over different incubation times. After incubation, the following experiments were performed. Beta-, alpha-1-adrenergic, and muscarinic acetylcholine receptor assays were performed by direct binding technique using L-3H-dihydroalprenolol, 3H-bunazosin, and L-3H-quinuclidinyl benzilate, respectively. Elevation of incubation temperature and prolongation of incubation time caused a significant decrease in the number of beta-adrenergic receptors and an increase in the number of alpha-1-adrenergic receptors. The number of muscarinic acetylcholine receptors did not change significantly in spite of changes in incubation temperature and time. Adenylate cyclase activity was measured by following the synthesis of cyclic adenosine monophosphate from nonradioactive adenosine triphosphate. Isoproterenol-stimulated adenylate cyclase activity decreased significantly in correspondence with the elevation of incubation temperature and prolongation of the incubation time. Contents of free fatty acids in lung membranes were measured by high-performance liquid chromatography. Free fatty acid contents increased significantly in accordance with elevation of incubation temperature and prolongation of incubation time which reflected on the degradation of membrane phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)