Plasma catecholamines and alpha- and beta-adrenoceptors in circulating blood cells in patients on continuous ambulatory peritoneal dialysis

Autonomic system dysfunction could be the cause of postural hypotension seen in patients on continuous ambulatory peritoneal dialysis (CAPD). To verify this hypothesis, we examined the alpha 2- and beta 2-adrenoceptors on blood cells after 1/2 h in the resting supine position with the peritoneal cavity filled for 2-3 h, as well as the response of plasma norepinephrine (NE), heart rate (HR) and mean arterial blood pressure (MAP) to 10 min of standing. Supine free and particularly conjugated NE levels were significantly higher in all uremic patients compared with controls. The postural test induced similar increases of MAP and HR in 8 diabetic, 11 nondiabetic patients and 23 controls, whereas 4 diabetic patients became hypotensive. Orthostasis caused a mean free NE increment of only 0.5 nmol/l in the latter patient group with mean NE responses of 1.45-1.65 nmol/l in the former 3 groups. The densities of platelet alpha 2-adrenoceptors (assessed by [3H] yohimbine binding) and of mononuclear leucocyte (MNL) beta 2-adrenoceptors determined by (-) (125I) iodocyanopindolol binding amounted to 160 +/- 50 and 1600 +/- 520 binding sites/cell, respectively, in controls and were unchanged in patients without postural hypotension. The 4 diabetic patients suffering from postural hypotension showed numerically higher beta 2-receptor numbers (2080 binding sites/cell), significantly increased alpha 2-receptor densities (280 binding sites/cell, p less than 0.05) and significantly increased MNL isoproterenol-stimulated adenylate cyclase activities (38 vs 24 pmol cAMP/10(6) MNL/10 min in controls, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in brain biogenic monoamines and monoamine oxidase

In experiments on 2-, 10- and 22-month old rats, it was found that essential age-related changes occurred in the brain level of biogenic monoamines (BMA) and in the monoamine oxidase (MAO) activity. In 22-month old rats the levels of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) markedly declined in most of the brain structures studied. 5-HT significantly decreased in the frontal cortex, striatum and hypothalamus. DA decreased in the cerebral cortex and striatum and NA in the cerebral cortex. However, the NA level in the striatum of 22-month old rats was increased as compared to that in 2-month old rats. In most cases we observed significant differences (a decrease mainly) also in the level of BMA in 22-month old rats as compared to 10-month old rats. The differences, if any, in the BMA levels between 10- and 2-month old rats were less pronounced. The level of 5-hydroxyindole acetic acid (5-HIAA) in the cerebral cortex and striatum of 22-month old rats was significantly higher as compared to that in 2-month old rats. The MAO-T and MAO-A activities in the brain structures studied were significantly higher in 22-month old rats as compared to those in 2-month old rats. The possibility that the age-related changes in brain neurotransmission might be an important element in the neurochemical basis of some behavioral changes in advanced age is considered.

Ontogenesis of autonomic receptors and AChE activity in the rat vas deferens

The study was undertaken to obtain some information about the development of the autonomic receptors and the AChE activity in the rat vas deferens. The results suggest that the adrenoceptors were fully developed at birth. The M1-ACh receptors were developed before the M2-ACh receptors. The AChE activity developed before the ACh muscarinic receptors of the rat vas deferens.

Effects of electroconvulsive shock on noradrenergic and serotonergic receptors in rat brain

It is likely that both noradrenalin and serotonin neurotransmission are important in the pathophysiology of depression and to its treatment. In particular, certain receptors for these neurotransmitters are altered by repeated treatment with both antidepressant drugs and electroconvulsive shock. This paper reviews the effects of electroconvulsive shock on alpha-1-adrenergic, beta-adrenergic, and serotonin-2 receptors in rat brain, and compares these effects to those produced by anti-depressant drugs. The similarities and differences in the effects of antidepressant drugs and electroconvulsive shock in rat brain may provide clues for the development of more effective treatments for depression and could single out targets for future investigation of the pathophysiology of depression in patients when safe methods are developed.

The distribution of adrenergic receptors in cerebral blood vessels: an autoradiographic study

The first morphological evidence of the existence of adrenergic receptors (alpha 1, alpha 2 and beta) within the vascular walls of the central nervous system were presented using the in vitro receptor autoradiographic technique. In the rat pial arteries all three types of adrenergic receptors were demonstrated, whereas the human pial arteries failed to show significant autoradiographic grains of alpha 1 type of adrenergic receptors indicating a considerable inter-species difference in the distribution of adrenergic receptors. alpha 2 and beta receptors in human pial arteries were found not only in the arterial smooth muscle layers but also in the endothelial layers. This suggests a possibility that circulating sympathomimetic agents play some role in controlling the tone or permeability of vascular walls within the central nervous system. A distinct distribution of alpha 1 receptors in cortical layer IV where the vascular plexus was richest may suggest a relation of alpha 1 receptors and blood flow of brain parenchyma.

Post-partum depression and the effect of nomifensine treatment

The purpose of this study was to examine the difference in certain hormonal and biochemical parameters in post-partum depressed women and age and status matched post-partum, non-depressed controls and study the effect of 6 weeks treatment with nomifensine on these parameters in the depressed group. The parameters examined were: plasma oestradiol, progesterone and prolactin concentrations, platelet 3H-serotonin uptake and alpha-2adrenoceptor density and lymphocyte beta-adrenoceptor densities. There was a significant decrease in platelet serotonin uptake rate in the depressed pre-treatment group as compared to controls. Six weeks treatment with nomifensine normalized the rate of uptake in the depressed group. Lymphocyte beta-adrenoceptor density was increased in the untreated depressed group as compared to the control group. This difference was also eliminated by 6 weeks of nomifensine treatment. Both plasma prolactin levels and platelet alpha-adrenoceptor density were decreased in the depressed group following 6 weeks treatment with nomifensine. There was no difference between the untreated depressed and control groups in any of the other parameters studied.

Foot shock induces time and region specific adrenergic receptor changes in rat brain

Rats were subjected to 1 hr or 2 hr of electric foot shock for 1 day or 7 days and adrenergic receptor binding was evaluated in the hypothalamus, brainstem and cortex. beta-Adrenergic receptor density in the hypothalamus was dramatically reduced following 1 hr of shock. Following repeated shock, alpha 2-adrenergic receptors in the cortex and brainstem were observed to increase. Cortical alpha 2-adrenergic receptors were more sensitive to stress than the alpha 2-adrenergic receptors of the brainstem, alterations in the latter only reaching statistical significance following 7 days of shock and 24 hr of recovery. alpha 1- and beta-adrenergic receptors in the brainstem and cortex were relatively resistant to stress induced changes. The significance of type of stress, duration of stress, and strain of rat for understanding the current data are discussed in the context of prior reports of stress induced receptor changes.

Autoradiographic localization of high affinity GABA, benzodiazepine, dopaminergic, adrenergic and muscarinic cholinergic receptors in the rat, monkey and human retina

High affinity gamma-aminobutyric acid, benzodiazepine, strychnine (glycine), dopamine, spirodecanone, alpha 1-adrenergic, alpha 2-adrenergic, beta-adrenergic and muscarinic cholinergic binding sites were localized by semiquantitative autoradiography in rat and, in some instances, in monkey and human retinae using [3H]muscimol, [3H]flunitrazepam, [3H]strychnine, [3H]spiperone, [3H]prazosin, [3H]para-aminoclonidine, [3H]dihydroalprenolol and [3H]quinuclidinyl benzylate, respectively. In nearly every case, the inner plexiform layer (IP) contained a high receptor density. The distribution of alpha 1 sites was unusual in that binding was concentrated in the outer plexiform layer (OP). Dopaminergic and, to a lesser extent, beta-adrenergic binding was diffusely distributed in the outer nuclear layer, the OP, the inner nuclear layer and the IP. The ganglion cell layer displayed significant benzodiazepine binding. The intraretinal distribution of pre- and postsynaptic markers of these neurotransmitters is discussed.

Inhibition of monoamine oxidase in monoaminergic neurones in the rat brain by irreversible inhibitors

The irreversible inhibition of monoamine oxidase (MAO) inside and outside monoaminergic neurones in the rat brain by the suicide inhibitors clorgyline, selegiline (l-deprenyl), pheniprazine, phenelzine, iproniazid, pargyline and the d- and l-enantiomers of tranylcypromine was determined. This was achieved by incubating crude synaptosomal preparations of hypothalamus and striatum from rats treated with the inhibitors 24 hr earlier, with low concentrations of [14C]serotonin (0.1 microM), [14C]-noradrenaline (0.25 microM) and [14C]dopamine (0.25 microM) in the absence and presence of selective uptake inhibitors (citalopram, maprotiline and amfonelic acid, respectively). It was found that all inhibitors inhibited the deamination of serotonin and noradrenaline outside the amine neurons at slightly lower doses than that within these neurones. This could at least in part be due to protection of MAO by the endogenous amines in these neurones. The deamination of dopamine was rather more strongly inhibited inside the neutrons than outside, particularly at higher doses. There was no indication that tranylcypromine or phenelzine was accumulated in the neurones by the membranous amine uptake mechanisms. The rate of the recovery of the deaminating activities inside and outside the serotonergic and noradrenergic neurones in hypothalamus after phenelzine and clorgyline inhibition was the same (50% recovery after 12-15 days), which indicates similar rate of synthesis of MAO in different cell types.

Cellular localization of adrenergic receptors in rat and human brain

The localization of adrenergic receptors in the central nervous system was studied in two physiological conditions of noradrenergic denervation, a 6-hydroxydopamine-induced lesion of the locus coeruleus in newborn rat, and a pathological related degeneration of the locus coeruleus in man, Parkinson's disease. The localization of these receptors in the synapse has been studied with the technique of subcellular fractionation by differential centrifugation. In lesioned rats, an increase in the density of alpha 1 and beta 1 receptors was observed in several brain regions, in contrast to alpha 2 receptors which were not modified. Subcellular fractionation in lesioned rats showed an increase in alpha 1 and beta 1 receptors in synaptosomal fractions. Similar results were found in parkinsonian patients: alpha 1 receptors increased in the synaptosomal fraction; beta receptors increased in synaptosomal and microsomal fractions. These results suggest that alpha 1 and beta 1 receptors may be located on non-noradrenergic nerve terminals in mammalian brain. alpha 2 and beta 2 receptors may be situated on glial cells or neuronal elements unrelated to noradrenergic input.

Drug and transmitter receptors in human brain. Characterization and localization of serotonin, dopamine and adrenergic receptors

The neuroreceptors in the brain are the targets of transmitters and drugs. Tritiated ligands - mostly selective antagonists - allowed to characterize the dopamine, serotonin and adrenergic receptors in human brain. Their properties were compared to those of rat brain receptors. Our results confirm the high affinity of several antagonist drugs for the corresponding binding sites in human brain. D2 dopamine receptors were identified in the striatum. S2 serotonergic receptors were located mainly in the cerebral cortex and their binding properties in solubilized form did not differ from those of the rat brain solubilized receptors. Adrenergic receptors were located either in cortical and subcortical areas. The subregional study indicates that wide variations could occur between adjacent areas of the cortex and between the different cortical layers. The subcellular distribution of several receptors revealed a main synaptosomal localization in human brain in contrast to other species. The S2 serotonergic receptors, the substance P peptide receptors and the benzodiazepine receptors were studied in the brain of Parkinsonian patients. The results were compared with those obtained in other neurological illnesses. A decrease in receptor number often corresponds to neuronal cell loss in degenerative diseases.

Adrenergic receptors in insensitive skin of spinal cord injured patients

The factors responsible for the increased susceptibility to decubitus ulcers of the insensitive skin of spinal cord injury (SCI) patients are not known. Autonomic dysfunction leading to defective vascularity is a possibility. SCI removes cerebral control of the isolated nervous system which may mimic denervation hypersensitivity of autonomic neural synapses, where an increase in number and a scattering of the receptors on the postsynaptic membrane leads to abnormal responses. Since adrenergic receptors mediate vascular tone and regulate blood flow in the skin, it would be of great interest to determine whether the number and the concentration of receptors in the insensitive skin of SCI patients is modified as a function of time since injury. To achieve this aim, alpha and beta adrenergic receptors were measured in biopsies obtained from intact skin used to surgically repair decubitus ulcers in SCI patients admitted to The Institute for Rehabilitation and Research. Receptors were identified by competitive radioligand-binding assays in whole skin homogenates. Patients were divided into two groups: patients injured less than five years ("early") and patients injured more than five years ("late"). Alpha and beta adrenergic receptors in both cervical and thoracic SCI patients decreased in density in the "late" patients. The small sample size and the inherent large errors of the assay precluded achievement of statistically significant differences. Nevertheless, a definite trend is seen: Disconnection of the adrenergic neurons from brain integration may mimic denervation and lead to abnormal vascular responses in the insensitive skin.

[Primary orthostatic hypotension]

We studied a 25-year-old man suffering from primary orthostatic hypotension whose blood pressure decreased to 65/45 mm Hg during orthostasis and to 95/70 mm Hg during ergometric exercise (50 and 100 watt), and whose heart rate responses were inadequate. Resting catecholamine levels were within the normal range and did not show any significant increase related to orthostasis or to ergometric exercise. Hypersensitivity was observed to low doses of intravenous noradrenaline and isoproterenol. Specific binding of 3H-Yohimbine to intact platelets revealed a normal number of alpha-2-adrenoreceptors in agreement with the adrenaline-induced platelet aggregation in vitro, which was, however, in contrast to hypersensitivity to noradrenaline. Specific 3H-Dihydroalprenolol binding to intact polymorphonuclear leucocytes revealed an increased beta-2-adrenoreceptor density in agreement with hypersensitivity to Isoproterenol. Prescription of Fludrocortison improved orthostatic hypotension.

A comparison of alpha 2-adrenoceptor regulation in brain and platelets

Functional responses and alpha 2-adrenoceptor radioligand binding were studied in brain and platelets of rabbits under a variety of circumstances. The effects of oestrogen treatment and maturation were studied in female rabbits and of aging and amitriptyline treatment in male rabbits. No correlation was found between changes in brain and platelets either in response or alpha 2-adrenoceptor ligand binding under any of the conditions examined.

A noninvasive procedure for in vivo assay of a lung amine endothelial receptor

Lung endothelial N-isopropyl-p-iodoamphetamine (IMP) binding sites were assessed applying principles of competitive binding assay adapted for in vivo measurements obtained by digital imaging. Data were acquired following the method published by Rahimian et al., a modification of the dual indicator dilution technique of Chinard and Crone. Iodine-123 (123I) IMP, the test cellular tracer, and technetium-99m (99mTc) dextran, the reference vascular tracer were imaged during their first pass through the superior vena cava, right heart, lungs, and left heart in West African dwarf goats. The lung fractional extraction of IMP diminished progressively from 0.96 to 0.20 as the amount of IMP in the test tracer boluses was gradually increased from 0.6 to 150 mg. This demonstrated that lung extraction of IMP is by way of a saturable binding system, presumably receptors. The dissociation constant of IMP-lung binding sites reaction was calculated by Scatchard plot and found to be 11.7 mg. The amount of IMP bound at saturation (R), was found to be 30 mg. Assuming that a single molecule of IMP bound a single receptor, the total number of free receptors was computed as the Avogadro's number times R, divided by the IMP molecular weight, and found to be 6.04 X 10(19). Using a computer model, it was determined that the 20 mg per bolus isotherm was the most sensitive for measuring the number of total free receptors (binding sites). This is the first time, to our knowledge, that noninvasive in vivo assessment of receptors in lung has been accomplished. Basically, the method used can be applied in humans and, also, to assess receptors in organs other than the lungs.

Adrenergic receptors in depression. Effects of electroconvulsive therapy

Platelet alpha 2-and lymphocyte beta 2-adrenoceptor densities, plasma noradrenaline and serum cortisol were measured before, during and one week after a course of EEG-monitored electroconvulsive therapy, in nine depressed patients. A 50% fall in Hamilton Depression Rating scores occurred after a fairly consistent total seizure time, regardless of the amount of ECT given. Platelet alpha 2-adrenoceptor densities showed a statistically significant fall after three ECTs, but were unchanged after the full course of ECT and were independent of clinical change. Lymphocyte beta 2-adrenoceptor densities were unaltered. Plasma noradrenaline concentrations were initially high, and fell with ECT in a manner paralleling clinical recovery. Plasma noradrenaline may be a more useful index of central changes during antidepressant treatment than peripheral blood cell receptor densities.

Modulation by monoamines of somatostatin-sensitive adenylate cyclase on neuronal and glial cells from the mouse brain in primary cultures

Primary cultures of mouse embryonic neuronal or glial cells from the cerebral cortex, striatum, and mesencephalon were used to identify and determine the cellular localization of somatostatin receptors coupled to an adenylate cyclase. Somatostatin inhibited basal adenylate cyclase activity on neuronal but not on glial crude membranes in the three structures examined. The somatostatin-inhibitory effect on neuronal crude membranes was still observed in the presence of (-)-isoproterenol, 3,4-dihydroxyphenylethylamine (dopamine, DA), or 5-hydroxytryptamine (5-HT, serotonin) used at a concentration (10(-5) M) inducing maximal adenylate cyclase activation. In addition, in most cases biogenic amines modified the pattern of the somatostatin-inhibitory effect, triggering either an increase in the peptide apparent affinity for its receptors or an increase in the maximal reduction of adenylate cyclase activity or both. However, 5-HT did not modify the somatostatin-inhibitory response on striatal and cortical neuronal crude membranes. The changes in somatostatin-inhibitory responses were interpreted as a colocalization of the amine and the peptide receptors on subtypes of neuronal cell populations. Finally, somatostatin was shown to inhibit adenylate cyclase activity following its activation by (-)-isoproterenol on glial crude membranes of the striatum and the mesencephalon but not on those of the cerebral cortex.

Electrophysiological assay and characterization of central adrenoceptors: techniques and neuropharmacology

Several single unit electrophysiological studies that have investigated central adrenoceptors are reviewed. The techniques and paradigms employed to electrophysiologically assay such adrenoceptors are discussed. Several regions of the brain, e.g., the nucleus locus coeruleus, the dorsal raphe nucleus, the lateral geniculate nucleus, and the cerebellar Purkinje neurons, are examined in detail, with reference to the nature of the adrenoceptor(s) located on these neurons. From the studies reviewed, it can be concluded that single unit electrophysiological recordings provide a valuable and powerful assay for adrenoceptors. Modification of this technique to study adrenoceptors from awake (behaving) or chronically treated animals is likely to result in significant advances in our understanding of mechanisms contributing to neuroreceptor plasticity.

Adrenergic receptor characteristics of cardiac myocytes cultured in serum-free medium: comparison with serum-supplemented medium

Neonatal rat ventricular myocytes cultured in serum-free medium coexpress both alpha 1 and beta 1 receptors as determined by radioligand binding studies. In cells exposed to serum for 48 hr surface area increased 3.69 fold, but the maximum number of binding sites ([125I]-iodocynanopindolol) only increased 1.5 fold from 12956 +/- 7579 to 19676 +/- 5181 sites/cell (n = 5, p less than .05) yielding a value of 2.48 sites/um2 for cells grown in serum-supplemented medium compared with 6.96 sites/um2 for cells grown in serum-free medium. Thus serum-induced hypertrophy is associated with a decrease in beta 1 receptor density relative to cell size; however, adenylate cyclase response is unaffected. This cell culture system constitutes an excellent model for studying interventions that may influence the regulation of cardiac myocyte hypertrophy by nonhemodynamic factors, particularly through the adrenergic receptor system.

Rapid reciprocal changes in adrenergic receptors in intact isolated hepatocytes during primary cell culture

In hepatocytes freshly isolated from adult female rat livers, catecholamine-stimulated glycogenolysis is mediated predominantly by alpha 1-adrenergic receptors, and to only a minimal extent by beta 2 receptors. Primary cell culture of these hepatocytes results in a switch in the adrenergic control of glycogenolysis from an alpha 1 to a predominant beta 2 type of response. To investigate whether this switch is due to an alteration in the plasma membrane receptor composition, we characterized alpha 1 and beta 2-adrenergic receptors in both freshly isolated and cultured hepatocytes, using radioligand-binding techniques. Binding of the selective alpha 1-adrenergic antagonist [3H]prazosin and the beta-adrenergic antagonist [125I]pindolol to intact freshly isolated hepatocytes was of high affinity, saturable, and of appropriate specificity for an alpha 1- and beta 2-adrenergic receptor, respectively. Equilibrium binding studies evaluated by a computer-assisted curve-fitting procedure indicated interaction with a single class of high affinity sites for radiolabeled prazosin (KD = 126 +/- 10 pM; Bmax = 93,000 +/- 5,500 sites/cell) and pindolol (KD = 66 +/- 6 pM; Bmax = 2,000 +/- 700 sites/cell). In intact hepatocytes and in membranes prepared from these hepatocytes, competitive inhibition curves revealed the coexistence of two different sites with high and low affinities for agonists at both alpha 1- and beta 2-adrenergic receptors. When isolated hepatocytes were kept in monolayer cell culture for up to 72 hr, the switch in adrenergic control of glycogenolysis (phosphorylase a activation) from an alpha to a beta pathway was confirmed and was associated with a progressive decrease in the number of alpha 1 receptors and an increase in beta 2-adrenergic receptor density, without marked change in the affinity of agonists or antagonists. To investigate the mechanism(s) of this reciprocal change, a number of perturbations were examined including alterations in the composition of the culture medium and the influence of various hormones and inhibitors of cellular function. De novo protein synthesis is implicated in both receptor alterations as the inhibitors cycloheximide and actinomycin D prevented the increase in beta- and attenuated the decrease in alpha-adrenergic sites. The other perturbations were without effect. Thus, these studies provide evidence for a coupling of the functional alteration in glycogenolysis to changes at the receptor level per se. The mechanism underlying the reciprocal changes in hepatocyte adrenergic receptors during culture remains undefined.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of adrenoceptors and dopamine receptors mediating vascular responses in the superior mesenteric arterial bed of the rat

The nature of the adrenoceptors and dopamine receptors mediating vascular responses in the in-situ blood perfused superior mesenteric arterial bed of the rat have been studied. alpha 1-Adrenoceptor agonists produced vasoconstriction but alpha 2-agonists had no significant effect on vascular resistance. The vasoconstrictor effects of noradrenaline were antagonized by low doses of prazosin (26 nmol kg-1 i.v.). Isoprenaline and salbutamol produced vasodilation when the vasculature was preconstricted with arginine vasopressin. The responses to isoprenaline were potently antagonized by propranolol (1.69 mumol kg-1 i.v.) and weakly but significantly reduced by practolol (3.75 mumol kg-1 i.v.) whereas the responses to salbutamol were unaffected by the same dose of practolol. After preconstriction of the vasculature and alpha-adrenoceptor blockade, dopamine and apomorphine produced dilator responses with both compounds producing the same maximal response and apomorphine being 1.8 times more potent than dopamine. The dopamine responses were present after the animals had been pithed and were resistant to spiperone (506 nmol kg-1 i.v.) but were antagonized by cis-alpha-flupenthixol (460 nmol kg-1 i.v.). These results suggest that this vascular bed possesses vasoconstrictor alpha 1- but not alpha 2-adrenoceptors, vasodilator beta 1- and beta 2-adrenoceptors and vasodilator dopamine receptors which appear similar to the D1-type found centrally.

Biochemical alterations in cardiac hypertrophy

In both two-kidney, one clip renal hypertensive rats (RHR) and spontaneously hypertensive rats (SHR) with myocardial hypertrophy, inotropic responsiveness to adenylate cyclase mediated agonists, such as isoproterenol and glucagon is decreased, as is the responsiveness to phenylephrine acting via alpha 1 adrenergic receptors. However, defects in the excitation response pathway differ in the two hypertensive models. In SHR beta-adrenergic receptors are decreased, alpha 1 receptors increased, cyclase activity is unchanged but c-AMP stimulated protein kinase is decreased. In RHR beta-receptors are increased, alpha 1 receptors decreased, adenylate cyclase activity decreased due to decreased nucleotide regulatory protein activity, and microsomal cAMP stimulated protein kinase is increased. We conclude that, although functional changes in hypertensive cardiac hypertrophy are similar, the underlying biochemical alterations are different. The shift in balance between alpha- and beta-adrenergic pathways may be a compensatory mechanism and play a role in the pathophysiology of cardiac hypertrophy.

Effects of urapidil on blood pressure and adrenoceptors in various animal models

The interaction with alpha- and beta-adrenoceptors, and the antihypertensive and hypotensive effects of urapidil were studied in various animal models. Urapidil reduced the mean arterial pressure (MAP) of conscious normotensive and spontaneously hypertensive rates after oral administration. Urapidil antagonized alpha 1- and alpha 2-adrenoceptor-mediated vasoconstriction in pithed rats, elicited by cirazoline and B-HT 920, respectively. Urapidil itself caused pressor responses of limited magnitude at high doses in pithed rats, which were not blocked by yohimbine, prazosin or ketanserin. Urapidil displayed partial beta 1-adrenoceptor intrinsic activity in pithed rats. Urapidil was more potent in reducing MAP after infusion via the vertebral artery as compared to infusion via the femoral artery of chloralose-anaesthetized cats. The results suggest that urapidil reduces blood pressure via blockade of peripheral vascular alpha-adrenoceptors, and beta-receptor blockade. A centrally mediated hypotension not involving alpha 2-adrenoceptors may contribute to the antihypertensive effect.

Regulation of arterial adrenoceptors during hypertension development in spontaneously hypertensive rats

Diminished beta-adrenoceptor mediated relaxation and increased reactivity to norepinephrine have been observed in the arteries of spontaneously hypertensive rats (SHR). However, some reports are conflicting, while the complexity of endothelial, neural and purely morphological factors regulating the response of whole vessels is increasingly appreciated. Thus a dissection of the complex vascular contraction mechanism into single-step events is needed. Here characterization of adrenoceptors in isolated aortic smooth muscle cells of SHR by radioligand binding techniques is reported. The density of beta-adrenoceptors was decreased at 4 (-23%), 7(-20%) and 13(-39%) weeks in SHR compared with age-matched normotensive Wistar-Kyoto rats. In both strains beta-adrenoceptor density decreased significantly with age. alpha 1-Adrenoceptors exhibited complex, though slight, changes in SHR at different ages. The alpha/beta adrenoceptor density ratio was constantly increased in SHR (11.9 versus 7.6 at 7 weeks; 19.1 versus 15.8 at 13 weeks). These findings suggest that the abnormal contractility of SHR arteries may at least partially depend on changes at the adrenoceptor level. A loss of arterial beta-adrenoceptors early in the life of SHR can be an event leading to increased peripheral resistance and elevation of blood pressure.

Age- and exercise-related sympathetic activity in untrained volunteers, trained athletes and patients with impaired left-ventricular contractility

To study the influence of training, aging and left-ventricular contractility on the sympathetic nervous system, responses of plasma catecholamines and density of adrenoreceptors on intact blood cells were evaluated in 21 dynamically trained subjects, 8 statically trained weight lifters, 15 healthy young and 15 old control subjects, and 55 post-infarction patients. Plasma catecholamines are indicators of the overall sympathetic tone, while the density of adrenoreceptors is a cellular indicator of the sensitivity to catecholamines. Static and dynamic training result in lower catecholamine response at identical work loads during incremental ergometric tests. Higher density of beta 2 receptors on intact leucocytes and higher sensitivity to isoproterenol are seen in the dynamically trained test subjects. Higher density of alpha 2 receptors on intact thrombocytes is found in the weight lifters. Despite the training-dependent control of the sympathetic activity bradycardia occurs only in endurance-trained subjects, indicating an additionally increased vagal control. The exercise-related tachycardia of the weight lifters, on the other hand, points to an insufficient vagal control of the cardiac sinus rate. Decrease of physical fitness, as related to aging, a deficit in physical training and impaired left-ventricular contractility are connected with a higher sympathetic activity at identical work loads and a lower beta-receptor density on intact blood cells and, in cardiac patients, on myocardial cells as well (Bristow et al. 1982). Changes in the sympathetic system may amplify the age- and disease-dependent decrease of the cardiac function.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholamines and their receptors in blood: evidence for alterations in schizophrenia

The simultaneous determination of serum catecholamine (CA) and their receptors in blood cells offers the possibility of evaluating disturbances of the dopamine (DA) and noradrenaline (NA) neuronal systems in man. High-affinity binding sites for 3H-yohimbine in platelets, 3H-DHA in granulocytes, and 3H-spiperone in lymphocytes from healthy control persons, unmedicated (n = 28), and medicated (n = 8) schizophrenics, and from an unmedicated psychiatric control group (n = 14) were investigated. Furthermore, the actual concentration of the circulating CA was determined with HPLC-ECD. In unmedicated schizophrenics, as compared with controls, specific binding of 3H-spiperone to lymphocytes was markedly elevated in capacity and less in affinity. For beta 2 receptors a significant decrease was found in capacity with no change in affinity. The changes in alpha 2 receptors, viz. a slight decrease in capacity, were less distinct. The concentrations of circulating CA ranged from normal values to a more than threefold increase in NA and DA, whereas adrenaline (A) concentrations were nearly unchanged. No overall change in these data was found in the medicated schizophrenic patients. 3H-Spiperone binding was characteristically increased only in schizophrenics, but did not rise above control data in the nonschizophrenic psychiatric control group. Preliminary family studies suggest that this model could be valuable as a vulnerability marker.

Sympathetic activity and cardiac adrenergic receptors in one-kidney, one clip hypertension in rats

The activity of the sympathetic nervous system, as measured by levels of plasma and cardiac catecholamines and catecholamine metabolites and the function of cardiac alpha- and beta-adrenergic receptors, was evaluated at 3 days and 4 weeks after induction of one-kidney, one clip hypertension (1K1C) in the rat. At 3 days, the plasma level of norepinephrine (NE) was lower in the 1K1C group than the control group (p less than 0.01), whereas epinephrine (E) and the metabolites dihydroxymandelic acid (DOMA), dihydroxyphenylglycol (DOPEG), and normetanephrine (NMN) were similar in both groups. In addition, cardiac content of catecholamines, their metabolites, and adrenergic receptors were similar in both groups. At 4 weeks, plasma levels of NE and DOPEG were lower (p less than 0.01), whereas levels of DOMA and NMN were higher (p less than 0.02 and p less than 0.001, respectively) in the 1K1C group than the control group. Cardiac content of NE (p less than 0.01), and DOPEG (p less than 0.05) was significantly lower, whereas DOMA and NMN were significantly higher (p less than 0.01) in the 1K1C group as compared to controls. In addition, cardiac density of both alpha- and beta-adrenergic receptors was reduced in the 1K1C group, whereas receptor affinities were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

[Development of the sympatoadrenergic function in the fetus and the newborn infant]

An analysis of the available data concerning the events bringing to the completion of the adrenergic function in early life shows the existence of an early response making the detection of MOPEG-SO4 levels in the urine--the foetus and in the new-born. This response isn't the same in the adult and in the infant as in the latter the number of receptors is lower, the prevalent mediator is NA and the receptorial subtype is almost entirely beta. The effector system, on the contrary, is as fully developed in the infant as it's in the adult. Maybe it will be possible in the future to evaluate--through non-invasive methods such as the detection of MOPEG-SO4 levels in the urine--the degree of development of the central simpatoadrenergic system in order to exactly work out perinatal asphyxia and brains congenital injuries.

Distribution of adrenergic receptors does not explain regional differences in blood flow in the pregnant rabbit uterus

The increase in uterine blood flow during pregnancy is maximal at the placental implantation site, but the mechanisms of this increase are poorly understood. Adrenergic receptor activation may influence blood flow both directly and indirectly. We therefore asked whether distribution of myometrial adrenergic receptors within the rabbit uterus could explain the increased blood flow to smooth muscle under the placenta. alpha-Adrenergic and beta-adrenergic receptor concentrations and affinities were measured in myometrium from under the placenta and compared to myometrium between placentas and distant from the placentas. There were no differences in receptor concentrations or affinities in different parts of the uterus. We therefore conclude that the distribution of adrenergic receptors in the pregnant rabbit uterus cannot explain the preferential blood flow to myometrium at the placental implantation site.

Alpha-adrenergic receptors in orthostatic hypotension syndromes

Alpha-adrenergic receptor function was measured in platelets from patients with orthostatic hypotension and normotensive controls. Patients with idiopathic orthostatic hypotension (IOH) or multiple system atrophy (MSA) had more alpha-receptors than controls. Patients with IOH, but not MSA, produced less prostaglandin E1 (PGE1)-stimulated cyclic AMP (cAMP) than controls. Patients with sympathotonic orthostatic hypotension (SOH) were similar to controls in receptor number and cAMP production. The percent norepinephrine (NE) inhibition of PGE1-stimulated cAMP production was similar in patients and controls. An increase in alpha-receptor number may result from decreased peripheral NE secretion in IOH and MSA. Increased alpha-receptor number and decreased cAMP production, which accompany essential hypertension, may contribute to the supine hypertension of IOH, and an increase in alpha-receptor number may contribute to the supine hypertension of MSA. SOH patients appear to have no abnormalities of alpha-receptor function.

Reserpine-induced changes in cardiac adrenergic receptors

Using radioligand binding techniques, the effect of reserpine pretreatment on ventricular adrenergic receptors from guinea pig was studied. [3H]Prazosin and [3H]dihydroalprenolol were used to label alpha 1- and beta-adrenergic receptors, respectively. Administration of 2.5 mg/kg reserpine for 2 days caused a significant increase in the number of beta-adrenergic receptors with no effect on their affinity to respective ligands. Similar reserpine pretreatment did not affect either density or affinity of alpha 1-adrenergic receptors for ligands. The results may explain the previous report from our laboratory in which an identical reserpine pretreatment selectively enhanced the inotropic responsiveness of the working guinea pig heart to isoproterenol.

Myocardial inotropic responses and adrenoceptors in protein-deficient rats

Inotropic effects of isoprenaline, phenylephrine and calcium were studied in left atria of 5 weeks old rats fed a low (5%) or a normal (21%) protein diet for 3 weeks. Rats maintained on a low (5%) protein diet consume about half the amount of food eaten by the same rats maintained on a normal (21%) protein diet and thus suffer from protein-calorie malnutrition (PCM). Body weight did not increase in PCM, but heart weight adjusted to body weight was slightly increased compared to normal rats. Atrial resting tension and peak developed tension in response to isoprenaline, phenylephrine or calcium were not diminished by PCM. The number of alpha and beta-adrenoceptors and the receptor affinity in ventricular membranes were not reduced by PCM.

Ontogeny of rat hepatic adrenoceptors

Hepatic alpha-1, alpha-2 and beta-2 adrenoceptors were characterized during development of the rat through Scatchard analysis of [3H]prazosin, [3H]rauwolscine and [125I]pindolol binding to liver membrane preparations. Major changes in adrenoceptor numbers occur shortly before birth at weaning. The fetal rat liver is characterized by a large number of alpha-2 adrenoceptors, which falls 10-fold by birth. The number of hepatic beta-2 adrenoceptors decreases gradually during development, and is lower at all times than the number of alpha-1 and alpha-2 adrenoceptors. The developmental profile of the hepatic alpha-1 adrenoceptor is biphasic: there is a 2 to 3-fold fall in alpha-1 adrenoceptor number at birth and a 3- to 5-fold rise at weaning. While absolute numbers of alpha-1 and beta-2 adrenoceptors do not correlate precisely with reported actions of epinephrine and norepinephrine on hepatic metabolism during ontogeny, the increasing ratio of alpha-1/beta-2 hepatic adrenoceptors may contribute to the conversion from predominantly beta effects of catecholamines reported in fetal and suckling rat liver to the predominantly alpha-1 effects that are well documented in the adult male rat.

Mammalian beta-adrenergic receptors. Structural differences in beta 1 and beta 2 subtypes revealed by peptide maps

Photoaffinity labeling techniques using p-azido-m-[125I]iodobenzylcarazolol have recently demonstrated that both the beta 1- and beta 2-adrenergic receptor-binding subunits from mammalian tissues including heart, lung, and erythrocytes reside on peptides of Mr approximately equal to 62,000-64,000. In this study, a two-dimensional gel electrophoresis method for peptide mapping was used to investigate and compare the structure of beta 1 - and beta 2-adrenergic receptor subtypes. When the photoaffinity labeled Mr approximately equal to 62,000 peptides from the beta 2-adrenergic receptors of rat lung and erythrocyte are subjected to simultaneous proteolysis using Staphylococcus aureus V8 proteinase or papain, exactly the same peptide fragments are generated from each subunit. In contrast, when the Mr approximately equal to 62,000 peptide containing the beta 1-adrenergic receptor-binding subunit derived from the rat heart is proteolyzed simultaneously with the Mr approximately equal to 62,000 peptide containing the beta 2-adrenergic receptors from either lung or erythrocyte, the peptide fragments generated are distinctly different. Peptide maps of beta 1-adrenergic receptors from the myocardial tissue of different species (pig versus rat) yield slightly different maps while the maps derived from the beta 2-adrenergic receptors of hamster lung and rat lung or erythrocytes reveal no interspecies differences. These data suggest: 1) alterations in the primary structure of the beta-adrenergic receptor may be responsible for the pharmacological specificities characteristic of beta 1- and beta 2-adrenergic receptor subtypes; and 2) alterations in the primary structure of similar beta-adrenergic receptor subtypes across different species may relate to the magnitude of their phylogenetic differences.

Alpha adrenergic receptor subtypes in human, monkey and dog cerebral arteries

In helical strips of human and monkey cerebral arteries, norepinephrine produced a greater contraction than that in dog cerebral arteries. In monkey cerebral arteries, phenylephrine and norepinephrine produced a similar magnitude of maximum contractions, although the ED50 value of phenylephrine was approximately 5.6 times greater than that of norepinephrine. Clonidine (up to 10(-5) M) did not produce contractions. Dog cerebral arteries responded to phenylephrine in high concentrations with a greater contraction than that induced by norepinephrine and to clonidine with significant contractions. Contractions induced by norepinephrine of human and monkey cerebral arteries were attenuated by low concentrations of prazosin but were not influenced by yohimbine in concentrations up to 10(-8) M. In contrast, norepinephrine-induced contractions of dog cerebral arteries were attenuated by yohimbine but were unaffected by prazosin. It appears that norepinephrine-induced contractions are mediated by alpha-2 adrenoceptors in dog cerebral arteries and by alpha-1 receptors in human and monkey cerebral arteries as well as monkey and dog mesenteric arteries. The relative unresponsiveness of monkey and dog cerebral arteries to adrenergic nerve stimulation may not be explained by a paucity of alpha adrenoceptors in neuroeffector junction.

Differentiation of noradrenergic and dopaminergic nerves in the rat kidney: evidence against significant dopaminergic innervation

In the rat kidney catecholaminergic nerve elements were identified by fluorescence histochemistry in perivascular plexuses around corticula arteries and juxtaglomerular arterioles and in medullary vascular bundles. Fluorescence was abolished in all areas 24 h after treatment with 6-hydroxydopamine (6-OHDA; 150 mg/kg i.v.). Protection of noradrenergic endings from destruction by 6-OHDA was afforded by pretreatment with desipramine (DMI; 25 mg/kg i.p.) which restored fluorescence towards control levels. By semiquantitative analysis fluorescence was identical in juxtaglomerular regions but slightly reduced around larger vessels in (DMI + 6-OHDA)-treated rats when compared to controls. Changes in tissue noradrenaline content, but not dopamine content, paralleled the changes in nerve fluorescence. Noradrenaline content was 4.10 pmol/mg protein (s.e.m. = 0.22, n = 32) in controls and was reduced by 90% to 0.40 pmol/mg (s.e.m. = 0.05, n = 23) in 6-OHDA-treated and by 26% to 3.01 pmol/mg (s.e.m. = 0.21, n = 23) in (DMI + 6-OHDA)-treated rats. Kidney dopamine content was 0.38 pmol/mg protein (s.e.m. = 0.05, n = 32) in controls and was reduced by 55% to 0.18 pmol/mg (s.e.m. = 0.02, n = 17) in 6-OHDA-treated and by 53% to 0.17 pmol/mg (s.e.m. = 0.02, n = 23) in (DMI + 6-OHDA)-treated rats. The renin response to haemorrhage was examined in pentobarbitone sodium-anaesthetized rats as a test of functional integrity of renal nerves in the three groups. Progressive 1 ml haemorrhages (to total blood loss of 4 ml, 1.3% body weight) resulted in similar increases in plasma renin activity in controls and (DMI + 6-OHDA)-treated animals but the response was significantly attenuated in 6-OHDA-treated rats. Renal catecholaminergic nerves appear to be predominantly noradrenergic. It is doubtful if a significant intrarenal dopaminergic system exists in the rat.

Increased beta-adrenergic receptor density in an experimental model of cardiac transplantation

We examined beta-adrenergic receptor density, basal, maximal isoproterenol and fluoride-stimulated adenylate cyclase activities, and morphologic characteristics of rabbit and rat native and heterotopic isograft cardiac tissue. Four weeks after graft placement there were only subtle histologic differences between native and graft tissue. Membrane preparations from isografts of rabbits demonstrated increases in beta-receptor density (maximum [3H]DHA binding = 111 +/- 19.3 fmol/mg versus 52.4 +/- 4.9 in native hearts, p less than 0.05). In a small number of experiments, rat isografts also demonstrated a suggestive increase in beta-receptor density (69.8 +/- 7.1 fmol/mg versus 40.2 +/- 7.3 in native hearts). Isoproterenol-stimulated adenylate cyclase activity was greater in rabbit graft hearts (3.98 +/- 0.20 X basal activity) than in native tissue 2.67 +/- 0.16 X basal activity, p less than 0.05). We conclude that cardiac denervation may lead to a postsynaptic form of beta-adrenergic supersensitivity that is due to an increase in beta-receptor density.

Alpha-adrenergic receptors in platelets from patients with Raynaud's syndrome

The pathophysiologic basis for spastic Raynaud's syndrome remains undefined but may be related to altered adrenergic activity. The relationship between Raynaud's syndrome and alterations in adrenergic receptor populations was examined in the present study by evaluation of alpha 2-adrenergic receptors in platelets. Direct binding assays revealed 78 +/- 8 fm/mg protein of alpha 2-adrenergic receptors in the platelets from control subjects. Similar levels of alpha 2-adrenergic receptors were observed in patients with obstructive Raynaud's syndrome. In contrast, platelet alpha 2-adrenergic receptor levels were significantly elevated (182 +/- 15 fm/mg protein) in the platelets from patients with spastic Raynaud's syndrome. These results indicate the presence of an altered alpha 2-adrenergic receptor population in the platelets from patients with spastic Raynaud's syndrome, which may be related to the vasospasm experienced by these patients.