Alpha 1-adrenergic Receptor Density Research Articles

Novel combined topical gel of lidocaine–verapamil–nitroglycerin can dilate the radial artery and reduce radial pain during trans-radial angioplasty

IntroductionRadial approach for coronary angioplasty is accepted by many specialists in medical centers around the world. The use of radial access is associated with fewer vascular complications and the same success rate in comparison with traditional femoral access. Radial artery spasm is one of the main concerns in this method. The small size of the radial artery and high density of alpha-1 adrenergic receptors in this artery can accelerate the spasm. The objects of this study were to evaluate whether the combined topical gel of lidocaine–verapamil–nitroglycerin could dilate the radial artery and reduce patient pain and sympathetic response during radial puncture.MethodsPatients undergoing elective trans-radial angioplasty were randomized to either placebo or therapeutic gel group in single-center, double-blind study. Placebo or therapeutic gel applied 1 cm proximal to the radial styloid process. Radial artery size was measured by ultrasound. Radial pain was reported by the visual analog scale (VAS) and the sympathetic response was assessed by changes in systolic (SBP) and diastolic blood pressure (DBP) and heart rate (HR). The incidence of spasm was defined by the radial artery spasm score.Results60 patients (30 patients in each group) participated in this study. A significant increase in the size of the radial artery was observed in the group receiving therapeutic gel compared to the placebo group (mean diameter, mm: 2.95 ± 0.48 vs. 2.54 ± 0.43, p = 0.001; area, cm2: 0.07 vs. 0.05, p = 0.001). During radial puncture, the radial pain intensity was significantly decreased in patients receiving therapeutic gel (4 (1–5) vs. 2 (1–2), p = 0.003). Radial artery spasm didn’t happen in any group.ConclusionBased on our results, Pre-procedural administration of combined topical gel of verapamil-nitroglycerin-lidocaine significantly increases the size of the radial artery and effectively reduces the radial pain during radial puncture in patients undergoing trans-radial angioplasty.

Effects of Prenatal Exposure to a Low-Dose of Bisphenol A on Sex Differences in Emotional Behavior and Central Alpha2-Adrenergic Receptor Binding.

Prenatal exposure to bisphenol A (BPA) influences the development of sex differences neurologically and behaviorally across many species of vertebrates. These effects are a consequence of BPA’s estrogenic activity and its ability to act as an endocrine disrupter even, at very low doses. When exposure to BPA occurs during critical periods of development, it can interfere with the normal activity of sex steroids, impacting the fate of neurons, neural connectivity and the development of brain regions sensitive to steroid activity. Among the most sensitive behavioral targets of BPA action are behaviors that are characterized by a sexual dimorphism, especially emotion and anxiety related behaviors, such as the amount of time spent investigating a novel environment, locomotive activity and arousal. Moreover, in some species of rodents, BPA exposure affected males’ sexual behaviors. Interestingly, these behaviors are at least in part modulated by the catecholaminergic system, which has been reported to be a target of BPA action. In the present study we investigated the influence of prenatal exposure of mice to a very low single dose of BPA on emotional and sexual behaviors and on the density and binding characteristics of alpha2 adrenergic receptors. Alpha2 adrenergic receptors are widespread in the central nervous system and they can act as autoreceptors, inhibiting the release of noradrenaline and other neurotransmitters from presynaptic terminals. BPA exposure disrupted sex differences in behavioral responses to a novel environment, but did not affect male mice sexual behavior. Importantly, BPA exposure caused a change in the binding affinity of alpha2 adrenergic receptors in the locus coeruleus and medial preoptic area (mPOA) and it eliminated the sexual dimorphism in the density of the receptors in the mPOA.

Disruption of glucocorticoid receptors in the noradrenergic system leads to BDNF up-regulation and altered serotonergic transmission associated with a depressive-like phenotype in female GRDBHCre mice

Recently, we have demonstrated that conditional inactivation of glucocorticoid receptors (GRs) in the noradrenergic system, may evoke depressive-like behavior in female but not male mutant mice (GRDBHCre mice). The aim of the current study was to dissect how selective ablation of glucocorticoid signaling in the noradrenergic system influences the previously reported depressive-like phenotype and whether it might be linked to neurotrophic alterations or secondary changes in the serotonergic system. We demonstrated that selective depletion of GRs enhances brain derived neurotrophic factor (BDNF) expression in female but not male GRDBHCre mice on both the mRNA and protein levels. The possible impact of the mutation on brain noradrenergic and serotonergic systems was addressed by investigating the tissue neurotransmitter levels under basal conditions and after acute restraint stress. The findings indicated a stress-provoked differential response in tissue noradrenaline content in the GRDBHCre female but not male mutant mice. An analogous gender-specific effect was identified in the diminished content of 5-hydroxyindoleacetic acid, the main metabolite of serotonin, in the prefrontal cortex, which suggests down-regulation of this monoamine system in female GRDBHCre mice. The lack of GR also resulted in an up-regulation of alpha2-adrenergic receptor (α2-AR) density in the female but not male mutants in the locus coeruleus. We have also confirmed the utility of the investigated model in pharmacological studies, which demonstrates that the depressive-like phenotype of GRDBHCre female mice can be reversed by antidepressant treatment with desipramine or fluoxetine, with the latter drug evoking more pronounced effects. Overall, our study validates the use of female GRDBHCre mice as an interesting and novel genetic tool for the investigation of the cross-connected mechanisms of depression that is not only based on behavioral phenotypes.

Alpha2-adrenergic receptor distribution and density within the nucleus tractus solitarii of normotensive and hypertensive rats during development

The nucleus tractus solitarii (NTS), located in the brainstem, is one of the main nuclei responsible for integrating different signals in order to originate a specific and orchestrated autonomic response. Antihypertensive drugs are well known to stimulate alpha2-adrenoceptor (alpha2R) in brainstem cardiovascular regions to induce reduction in blood pressure. Because alpha2R impairment is present in several models of hypertension, the aim of the present study was to investigate the distribution and density of alpha2R binding within the NTS of Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats during development (1,15,30 and 90day-old) by an in vitro autoradiographical study. The NTS shows heterogeneous distribution of alpha2R in dorsomedial/dorsolateral, subpostremal and medial/intermediate subnuclei. Alpha2R increased from rostral to caudal dorsomedial/dorsolateral subnuclei in 30 and 90day-old SHR but not in WKY. Alpha2R decreased from rostral to caudal subpostremal subnucleus in 15, 30 and 90day-old SHR but not in WKY. Medial/intermediate subnuclei did not show any changes in alpha2R according to NTS levels. Furthermore, alpha2R are decreased in SHR as compared with WKY in all NTS subnuclei and in different ages. Surprisingly, alpha2R impairment was also found in pre-hypertensive stages, specifically in subpostremal subnucleus of 15day-old rats. Finally, alpha2R decrease from 1 to 90day-old rats in all subnuclei analyzed. This decrease is different between strains in rostral dorsomedial/dorsolateral and caudal subpostremal subnuclei within the NTS. In summary, our results highlight the importance of alpha2R distribution within the NTS regarding the neural control of blood pressure and the development of hypertension.

PATHOPHYSIOLOGY OF DEPRESSION: DO WE HAVE ANY SOLID EVIDENCE OF INTEREST TO CLINICIANS?

Due to the clinical and etiological heterogeneity of major depressive disorder, it has been difficult to elucidate its pathophysiology. Current neurobiological theories with the most valid empirical foundation and the highest clinical relevance are reviewed with respect to their strengths and weaknesses. The selected theories are based on studies investigating psychosocial stress and stress hormones, neurotransmitters such as serotonin, norepinephrine, dopamine, glutamate and gamma-aminobutyric acid (GABA), neurocircuitry, neurotrophic factors, and circadian rhythms. Because all theories of depression apply to only some types of depressed patients but not others, and because depressive pathophysiology may vary considerably across the course of illness, the current extant knowledge argues against a unified hypothesis of depression. As a consequence, antidepressant treatments, including psychological and biological approaches, should be tailored for individual patients and disease states. Individual depression hypotheses based on neurobiological knowledge are discussed in terms of their interest to both clinicians in daily practice and clinical researchers developing novel therapies.

Possible involvement of alpha‐2A adrenergic receptors in attention deficit hyperactivity disorder: Radioligand binding and polymorphism studies

Neuropharmacological and genetic association studies have implicated norepinephrine and adrenergic receptors in the pathogenesis of ADHD. The purpose of this study was to compare genetic association studies of three polymorphisms of the alpha-2A adrenergic receptor gene (ADRA2A) with radioligand binding studies of the alpha-2A adrenergic receptor protein in platelets from a sample of children without or with ADHD. The pediatric subjects ranged from 6 to 18 years of age. A thorough clinical assessment of each child resulted in one of the following DSM-IV ADHD diagnoses: inattentive, hyperactive/impulsive, combined, or no ADHD. No significant linkage was found between the ADRA2A polymorphisms (MspI, HhaI, and DraI) and any of the phenotypes tested. Association analysis, however, did detect significant linkage disequilibrium for the DraI polymorphism. Association was also evaluated considering the three ADRA2A single nucleotide polymorphisms as haplotypes. The HhaI-DraI and the MspI-HhaI-DraI haplotypes were significantly associated with ADHD. The platelet alpha-2 adrenergic receptor density did not differ between children without or with ADHD. The affinity of the receptor for the radioligand however, differed significantly between those without and with ADHD. In addition, there were some significant correlations between binding parameters and severity of ADHD in this well-characterized clinical population, and significant association was found between these measures of receptor function and MspI and DraI polymorphisms. Thus, both the genetic and the binding studies indicate that the alpha-2 adrenergic receptor may play a role in ADHD.

The effect of combined treatment with imipramine and amantadine on the behavioral reactivity of central ??1-adrenergic system in rats

The problem of drug-resistant depression implies a strong need for alternative antidepressant therapies. Recently, it has been shown that joint administration of a tricyclic antidepressant, imipramine (IMI), with amantadine (AMA), a drug already approved for clinical use in the treatment of other diseases, induces a stronger 'antidepressant' effect in the forced swimming test in rats than treatment with either drug given separately. Combined treatment with IMI and AMA also induces up-regulation of dopamine D2 and D3 receptors in the rat brain, and appears to be effective in the treatment of patients with drug-resistant unipolar depression. In the present study, we examined the effect of IMI (5 or 10 mg/kg p.o.) and AMA (10 mg/kg p.o.) given separately or jointly, either as a single dose or repeatedly (twice daily for 14 days) on the development of adaptive changes in the behavioral reactivity of the central alpha1-adrenergic system. Following repeated administration of the higher dose of IMI together with AMA, we observed an increase in clonidine-induced aggression in mice, and significant enhancement of D-amphetamine-induced locomotor hyperactivity, as well as phenylephrine-induced exploratory behavior, in rats. In binding studies using [3H]prazosin, no changes in the density (Bmax) or affinity (Kd) of alpha1-adrenergic receptors were observed in rat brain cortex. However, competition analysis allowed us to observe an increase in the affinity of alpha1-adrenergic receptors (Ki) for an agonist (phenylephrine) upon repeated treatment with IMI, given alone or in combination with AMA. AMA appears to act through several pharmacological mechanisms, none of which has been identified as the chief mode of action. In the light of data obtained in the present study, one can supplement the postulated mechanisms of antidepressant action of AMA by adaptive changes in the reactivity of alpha1-adrenergic receptors, which develop upon repeated combined treatment with IMI.

Comparison of opioid and alpha-2 adrenergic receptor location and density in the horse and dog using radioligand binding

As a result of the observed behavioral differences between dogs and horses in response to opioid and α-2 adrenergic agonists, we tested the hypothesis that the distribution, density, and subtype of opiate and α-2 adrenergic receptors within the central nervous system (CNS) are significantly different between the horse and the dog. Brain tissue was obtained following euthanasia as a secondary use of tissue from three dogs (3 years of age) at 126 days post-surgery and from three horses (2–5 years of age) at 72 days post-surgery. Animals were opioid- and α-2 agonist-free at the time of euthanasia. The brains were removed, sectioned coronally into 1 cm slabs, frozen in methylbutane cooled by liquid nitrogen, and stored at −70.5 °C. Receptor autoradiography was performed using established techniques. [3H]DAMGO, [3H]U-69593, and [3H]RX821002 were used for μ-opiate, κ-opiate, and α-2 adrenergic binding assays, respectively. Binding densities (fmol mg−1 protein binding) were not affected by differences in brain size. Species differences were analyzed separately for each major brain region by Repeated Measures anova for subregions followed by Fisher's protected LSD. p < 0.05 was considered significant. Only significant differences were reported. There was higher binding of μ-opiate receptors in the frontal cortex, left somatosensory cortex, colliculus (mid-brain), and granule cell layer of the cerebellum of the horse than that of the dog. There was higher binding to κ-opiate receptors in the frontal cortex of the dogs compared to the horses, whereas binding to κ-opiate receptors in the cerebellum was higher in horses. Binding to α-2 adrenergic receptors in the mid-brain was significantly higher in the dog than the horse. There was higher binding in the dorsomedial and dorsolateral periaqueductal grey matter of the dog as compared to the horse. These results suggest a neuroanatomical basis for the differences in opioid and α-2 adrenergic pharmacodynamics observed between horses and dogs.

Increased alpha 2-adrenergic receptor binding in locus coeruleus projection areas in dementia with Lewy bodies.

Clinical studies suggest involvement of brain noradrenergic systems in the pathophysiology of disruptive agitation in Alzheimer's disease (AD). This behavioral problem is even more prevalent in dementia with Lewy bodies (DLB). Here we used receptor autoradiography with [(125)I]para-iodoclonidine to estimate alpha-2 adrenergic receptor (A2R) density in locus coeruleus (LC) projection areas in postmortem brain tissue from age and gender comparable groups of DLB (n = 6), AD (n = 5) and normal (n = 7) subjects. LC neuronal loss was substantial and equivalent in DLB and AD. A2R density was greater in DLB than in normals in the deep layers of the frontal cortex. A2R density was greater in DLB than in AD in hippocampus (CA-1, CA-3 and dentate hilus) and in the granule layer of the cerebellum. Increased A2R binding in DLB is consistent with expression of presynaptic A2R on fibers from surviving LC neurons involved in reinnervation of LC projection areas. These areas develop compensatory noradrenergic hyperinnervation in a rat model of partial LC ablation. It is also consistent with upregulation of post-synaptic A2R in response to loss of LC noradrenergic innervation. Either mechanism could lower the threshold for increased agitation in response to noradrenergic outflow in these dementing disorders.

Platelet α 2 -adrenergic receptor coupling efficiency to G i protein in subjects with post-traumatic stress disorder and normal controls

Low platelet membrane alpha2-adrenergic receptor (alpha2AR) density and low basal and forskolin-stimulated cyclic adenosine monophosphate responses, which have been reported in post-traumatic stress disorder (PTSD), suggest either abnormal alpha2AR coupling to G(i) protein or dysregulation in post-receptor signal transduction mechanisms. alpha2AR density in the high- and low-conformational states, agonist affinity in both states and coupling to G(i) protein were investigated in 23 drug-free combat PTSD patients and 25 normal controls. alpha2AR coupling measures were not different between PTSD patients and controls. Total alpha2AR density was higher in PTSD patients than controls, due to a higher density of the receptor in the high-conformational state. There were no differences in agonist affinity to the receptor in either conformational state. Results rule out dysregulation in alpha2AR coupling to G(i) protein. Studies of post-receptor signal transduction mechanisms are warranted.

Effects of weight cycling on urinary catecholamines: sympathoadrenal role in refeeding hypertension.

We sought to determine whether the sympathetic nervous system plays a role in the hypertensive response to refeeding from a very low-calorie diet (VLCD). Cycles of weight loss and regain were induced in the obese spontaneously hypertensive rat (SHROB) model of genetic obese hypertension. A 12-day VLCD (1/6 of baseline calories) was alternated with 4-6 weeks of ad libitum chow refeeding for three cycles. Control SHROB ate chow ad libitum. Urine was collected for 24 h before and after each period of VLCD, and catecholamines were measured radioenzymatically. Tail cuff blood pressures and body weight were measured in parallel with urine collections. Kidneys were collected for assay of alpha2-adrenergic receptor density. VLCD induced rapid weight loss, but all the lost weight was regained during refeeding. Blood pressure fell during caloric restriction, but rose above baseline during refeeding. Urinary excretion of norepinephrine, epinephrine and dopamine changed several fold during weight cycling. Urinary catecholamines paralleled the changes in blood pressure, falling during caloric restriction and rebounding during refeeding. Dopamine showed the greatest decreases during weight loss and rises during weight regain, whereas epinephrine changed the least and norepinephrine was intermediate. Weight cycling elevated blood pressure above the initial baseline throughout the rapid weight gain phase of refeeding. The density of alpha2-adrenergic receptors was decreased in both the renal medulla and cortex of weight cycled SHROB, consistent with receptor down-regulation owing to overstimulation. The exacerbations of hypertension during weight regain in SHROB coincide with sustained activation of sympathoadrenal activity, as reflected in urinary catecholamine excretion and adrenergic receptor down regulation.

Ins(1,4,5)P3 receptors in cerebral arteries: changes with development and high-altitude hypoxia.

We and others have shown that adrenergic-mediated contractile responses in cerebral vessels in vitro differ with vessel segment, with developmental age, and with high-altitude, long-term hypoxia. This is associated with significant differences in alpha 1-adrenergic receptor density and norepinephrine (NE)-induced response of the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. To test the hypothesis that vessel-specific, developmental, and hypoxic-associated contractility changes are mediated, in part, by changes in Ins(1,4,5)P3-receptor [Ins(1,4,5)P3-R] density or affinity, we performed the following study. In common carotid (Com), circle of Willis, and main branch anterior, middle, and posterior cerebral arteries (MBC) from normoxic fetal (approximately 140 days), newborn (3-5 days), and adult sheep and fetal and adult sheep acclimatized to high altitude, we quantified Ins(1,4,5)P3-R with [3H]Ins(1,4,5)P3. In normoxic Com, Ins(1,4,5)P3-R density values (fmol/mg protein) in fetus, newborn, and adult were 8 +/- 53, 150 +/- 18, and 357 +/- 21, respectively (P < 0.05). In normoxic MBC cerebral arteries, the receptor density values in the three age groups were 115 +/- 15, 105 +/- 9, 99 +/- 5 fmol/mg protein, respectively. For fetal and adult Com, high-altitude, long-term hypoxemia was associated with decreases in Ins(1,4,5)P3-R density of 32 (to 58 +/- 5) and 70% (to 109 +/- 12), respectively, from control values (P < 0.01). In MBC cerebral arteries of fetus and adult, hypoxic-associated decreases in Ins(1,4,5)P3-R density from control were 80 (to 23 +/- 3) and 47% (to 53 +/- 7), respectively (P < 0.01). Ins(1,4,5)P3 binding affinity to the receptor averaged 11.8 +/- 0.5 nM and did not vary significantly as a function of vessel type, developmental age, or hypoxia. In Com, but not in MBC, Ins(1,4,5)P3-R density increased dramatically with developmental age. This suggests that differences in Ins(1,4,5)P3-R density values may account, in part, for differences in contractile responses of the two artery types in the several age groups. In response to long-term, high-altitude hypoxia, Ins(1,4,5)P3-R density values in both fetal and adult Com and MBC decreased significantly, as did their NE-induced contraction. This suggests a cellular basis for changes in cerebrovascular contractility in response to long-term hypoxia and that Ins(1,4,5)P3-R may play a role in acclimatization responses to high altitude.

High altitude-induced changes in alpha1-adrenergic receptors and Ins(1,4,5)P3 responses in cerebral arteries.

In response to high-altitude long-term hypoxemia, the cerebral arteries of fetal and adult sheep show decreased contractile responses to norepinephrine (NE) and other agonists. To test the hypothesis that hypoxia-induced developmental and vessel specific cerebral artery contractility changes are mediated, in part, by changes in alpha1-adrenergic receptor (alpha1-AR) density and/or NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] responses, we performed the following study. In common carotid (Com) and main branch cerebral (MBC) arteries from normoxic adult ewes and near-term fetuses and those acclimatized to high altitude (3,820 m), we quantified alpha1-AR density (maximal binding in fmol/mg protein) and affinity (dissociation constant in nM) with the alpha1-AR antagonist [3H]prazosin. In addition, we quantified NE-induced Ins(1,4,5)P3 responses in these arteries. With long-term hypoxemia, alpha1-AR density in fetal and adult Com decreased 75% (from 113 +/- 18 to 28 +/- 5 fmol/mg protein) and 66% (from 54 +/- 3 to 18 +/- 4 fmol/mg protein), respectively, from normoxic control values. alpha1-AR density of the fetal and adult MBC decreased 76% (from 47 +/- 4 to 11 +/- 1 fmol/mg protein) and 61% (from 23 +/- 3 to 9 +/- 3 fmol/mg protein), respectively, from controls. In hypoxemic adult Com, the NE-induced Ins(1,4,5)P3 response decreased 51% (from 309 +/- 38 to 151 +/- 24%) from the control value. In fetal and adult MBC, long-term hypoxemia was associated with decreases of 35% (from 345 +/- 40 to 225 +/- 30%) and 44% (from 355 +/- 55 to 199 +/- 16%), respectively, from control values. We conclude that in the adult Com and MBC vessels, acclimatization to high-altitude, long-term hypoxemia was associated with significant decreases in both alpha1-AR density values and Ins(1,4,5)P3 responses to NE. Similarly, in the fetal MBC arteries, high-altitude hypoxemia was associated with marked attenuation of both alpha1-AR density and NE-induced Ins(1,4,5)P3 responses. The magnitude of decreases in NE-induced Ins(1,4,5)P3 responses in these vessels correlated fairly well with the decreases in alpha1-AR density. These findings suggest that changes in noradrenergic receptor-second messenger coupling may play a role in altered cerebrovascular tone in association with high-altitude acclimatization and other forms of long-term hypoxia in both fetus and adult.

Developmental changes in alpha 1-adrenergic receptors, IP3 responses, and NE-induced contraction in cerebral arteries.

Cerebral arteries show significant developmental and artery-specific changes in noradrenergic-mediated contraction. To test the hypothesis that these changes result from differences in the density of alpha 1-adrenergic receptors (alpha 1-ARs) and/or norepinephrine (NE)-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3,IP3] synthesis, we quantified these variables and the NE-induced contraction in the common carotid artery (Com) and main branch cerebral arteries (MBC) from term fetal (approximately 140 gestational day) and newborn (2- to 5-day) sheep and compared them with adult values. In fetal and newborn Com, maximal contractions to NE (percent K+ maximum response) were 132 +/- 14 and 118 +/- 9%, respectively (adult = 92 +/- 7%). For fetal and newborn middle cerebral artery, these values were 34 +/- 10 and 43 +/- 7%, respectively (adult = 24 +/- 7%). alpha 1-AR density values in Com of fetal and newborn sheep were 113 +/- 18 and 106 +/- 4 fmol/mg protein, respectively (adult = 54 +/- 3 fmol/mg protein). For the MBC, density values were 47 +/- 2 and 24 +/- 3 fmol/mg protein, respectively (adult = 23 +/- 3 fmol/protein). In term fetal and newborn MBC, NE produced dose-dependent increases in Ins(1,4,5)P3, the maximal increases above basal values being 245 +/- 40 and 189 +/- 16%, respectively (adult = 254 +/- 35%). Neither fetus nor newborn Com showed significant Ins(1,4,5)P3 responses to NE. We concluded that in fetal and newborn Com and MBC, alpha 1-AR density and NE-induced Ins(1,4,5)P3 response varied as a function of developmental age and specific vessel. However, these variations did not correlate with NE-induced maximum contraction. Thus we reject the hypothesis that age-dependent and vessel-specific differences of cerebral artery adrenergic-mediated contraction are a function of alpha 1-AR density or Ins(1,4,5)P3 response. Rather, the differences would appear to result from other factors such as non-Ins(1,4,5)P3-mediated calcium activation and/or sensitivity to Ins(1,4,5)P3. The studies also suggest considerable potential for maturational modulation of pharmacomechanical coupling and homeostatic regulation of cerebrovascular tone.

Effects of long-term high-altitude hypoxemia on alpha 1-adrenergic receptors in the ovine uterine artery.

To elucidate the effects of chronic hypoxia on alpha 1-adrenergic receptor-mediated contractions of the uterine artery, we examined norepinephrine-induced contractions in tissues obtained from near-term (approximately 140 days gestation) pregnant ewes maintained near sea level (approximately 300 m) and at high altitude (3,820 m) from 30 days gestation. Compared with the sea-level controls, contractions induced by norepinephrine in main and fourth-branch uterine arteries of the high-altitude animals were significantly depressed. The norepinephrine dose-response curves were shifted to the right and the concentrations at which 50% of the maximal response was attained were increased 3.2- and 5.7-fold in the main and fourth-branch uterine arteries, respectively. The maximal responses were decreased 22 and 36% in main and fourth-branch uterine arteries, respectively. The dissociation constants of norepinephrine were increased from 0.77 to 1.53 microM and from 0.72 to 2.05 microM in main and fourth-branch uterine arteries, respectively. Radioligand binding studies with [3H]prazosin revealed a decrease in the density of alpha 1-adrenergic receptors in both vessels from high-altitude animals. We conclude that chronic hypoxia depresses alpha 1-adrenergic receptor-induced contractions of conduit- and resistance-type uterine arteries. The depressed contractility is mediated, at least in part, by decreases in alpha 1-adrenergic receptor density and agonist binding affinity.

NE-induced contraction, alpha 1-adrenergic receptors, and Ins(1,4,5)P3 responses in cerebral arteries.

Adrenergic-mediated responses in cerebral vessels in vitro differ with vessel segment. We performed this study to test the hypothesis that these vessel-specific cerebral artery norepinephrine (NE)-induced contractility changes are mediated in part by differences in alpha 1-adrenergic receptor (alpha 1-R) density (Bmax) or antagonist dissociation constant (KD), and/or inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] synthesis. In common carotid (Com), circle of Willis (Wil), and middle cerebral arteries (MCA) from adult sheep we measured NE-induced contractions. We also quantified alpha 1-R in these, and in anterior, middle, and posterior (AMP) cerebral arteries and cerebral microvessels (Micro). In addition, we quantified NE-induced Ins(1,4,5)P3 synthesis. pD2 values of Com and MCA were 5.2 +/- 0.1 and 6.3 +/- 0.1, respectively. In contrast, the MCA maximum response to NE compared with K+ was much lower than that of the Com. In the Com, Wil, AMP, and Micro, alpha 1-R Bmax was 54 +/- 3, < 5 +/- 2, 23 +/- 3, and 35 +/- 3 fmol/mg protein, respectively. KD averaged 0.20 +/- 0.05 nM in the several vessel groups. In Com and in AMP cerebral arteries, NE produced a rapid increase in Ins(1,4,5)P3 with a peak at 45 s, and 50% effective concentration of 5.5 +/- 0.2 microM. NE stimulated a 240% increase of Ins(1,4,5)P3 in both Com and AMP, whereas Wil showed essentially no response. The ovine MCA was more sensitive to NE than was the Com. In contrast, MCA showed a much lower maximum contractile response to NE compared with K+. Cerebral arteries (AMP) had only about half the alpha 1-R density of the Com. In AMP cerebral arteries, both the basal and NE-stimulated Ins(1,4,5)P3 values were much less than those of the Com. In MCA, the ratio of Ins(1,4,5)P3 response to alpha 1-R Bmax was much greater than in Com. These findings suggest important artery-to-artery differences in components of the cerebrovascular alpha 1-R-mediated contractile pathway. They also suggest considerable potential for modulation of pharmacomechanical coupling and homeostatic regulation of cerebrovascular tone.

Sexual dimorphism of renal alpha2-adrenergic receptor regulation in Dahl rats.

Male Dahl salt-sensitive hypertensive (S) rats develop hypertension faster than females. We measured renal alpha2-adrenergic receptor density of inbred Dahl salt-sensitive (SS/JR) and salt-resistant (SR/JR) rats, using [3H]-rauwolscine saturation binding studies. Male and female SS/JR rats were gonadectomized or sham-operated at 6 weeks of age and fed a high salt diet for 4 weeks. Additional intact SS/JR and SR/JR rats of both sexes were fed the high salt diet for a longer period of time (7 weeks instead of 4 weeks). Both blood pressure and renal alpha2-adrenergic receptor density were significantly higher in male than female SS/JR rats on high salt diet for 4 weeks. Gonadectomy did not change blood pressure nor did it change renal alpha2-adrenergic receptor density measured at the 4th week of high salt feeding in either male or female SS/JR rats. When the SS/JR rats were fed high salt diet for a longer period (for 7 weeks), blood pressure of female SS/JR reached the level of males, but the density of renal alpha2-adrenergic receptors was still significantly lower than that of males. Both renal alpha2-adrenergic receptor density and blood pressure were higher in male than female SR/JR. We conclude that higher blood pressure in male Dahl SS/JR and SR/JR rats is associated with higher renal alpha2-adrenergic receptor density compared with their female counterparts.

Effect of experimental cryptorchidism on alpha 1-adrenergic receptors of rat testis.

Alpha 1-adrenergic receptors play an important role in the transport of spermatozoa through seminiferous tubules to the efferent ducts leading to the epididymis. The density of alpha 1-adrenergic receptors in adult Sprague-Dawley rat testis before and during 14 days of experimental cryptorchidism was determined by binding assays with [3H]prazosin in membrane preparations. The number of maximal binding sites (Bmax) per milligram protein began to increase at 7 days after surgery (p < .05). The testicular weight and diameter of seminiferous tubules began to decrease at 5 days after surgery (p < .01). However, Bmax per testis did not differ before and during cryptorchidism. This study demonstrates that the density of alpha 1-adrenergic receptors in rat testis is not affected by cryptorchidism.

Sex influence on renal alpha 2-adrenergic receptor density in the spontaneously hypertensive rat.

Male spontaneously hypertensive rats (SHR) have higher blood pressure than females. We compared renal alpha 2-adrenergic receptor density among intact SHR and Wistar-Kyoto (WKY) rats of both sexes, male and female SHR gonadectomized at 4 weeks of age, and gonadectomized SHR supplemented with testosterone. Additional groups of SHR were treated with enalapril (30 mg/kg per day), an angiotensin-converting enzyme inhibitor, from 5 to 14 weeks of age. Renal alpha 2-adrenergic receptor density was higher in males than females in both SHR and WKY rats. Female SHR and WKY rats had identical low renal alpha 2-adrenergic receptor density. Castration of male SHR reduced the male-female differences in blood pressure and renal alpha 2-adrenergic receptor density by 60%. Treatment with testosterone raised blood pressure and renal alpha 2-adrenergic receptor density to the intact male levels in both gonadectomized males and females. Treatment with enalapril decreased blood pressure but not renal alpha 2-adrenergic receptor density in both male and female SHR. We conclude that (1) both renal alpha 2-adrenergic receptor density and blood pressure are influenced by sex in SHR and WKY, (2) renal alpha 2-adrenergic receptor density like blood pressure is regulated by androgens, and (3) increased renal alpha 2-adrenergic receptor density is not a consequence of high blood pressure in male SHR.

Androgen regulation of thromboxane A2/prostaglandin H2 receptor expression in human erythroleukemia cells.

Thromboxane A2 (TxA2), a platelet aggregator and vasoconstrictor, has been implicated as a potential mediator of cardiovascular diseases. Abuse of androgenic steroids has been associated with thrombotic cardiovascular diseases. Human erythroleukemia (HEL) cells, a megakaryocyte-like cell line, express functional TxA2/prostaglandin H2 (PGH2) receptors with characteristics similar to those seen in platelets. This study characterized testosterone regulation of HEL cell TxA2/PGH2 receptors. TxA2/PGH2 receptor affinity (Kd) and density (Bmax) were determined via equilibrium binding experiments using the radiolabeled TxA2 mimetic (1S-[1 alpha,2 beta(5Z),3 alpha(1E,3R*),4 alpha])-7-(3-[3-hydroxy-4-(4'- iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]heptan-2-yl)-5-he ptenoic acid (125I-labeled BOP). Testosterone (200 nM) but not estradiol increased Bmax from 108 +/- 9 fmol/mg protein to 157 +/- 9 fmol/mg protein (n = 7 experiments; P < 0.01) without any significant change in Kd. Testosterone had no significant effect on alpha 2-adrenergic receptor density. The maximum increase in intracellular free calcium induced by the TxA2 agonists I-BOP or U-46619 was significantly (P < 0.005) greater in testosterone-treated cells compared with controls. Hydroxyflutamide (1 microM), an androgen-receptor antagonist, completely blocked the effect of testosterone (P < 0.01). Dihydrotestosterone, the active metabolite of testosterone, also increased Bmax in a concentration-dependent manner and was more potent than testosterone. The effect of testosterone to increase Bmax was significantly (P < 0.01) inhibited by coincubation with cycloheximide (0.1 microgram/ml) or actinomycin D (10 ng/ml). These results indicate that androgenic steroids regulate the expression of functional TxA2/PGH2 receptors in HEL cells. These findings may have relevance to cardiovascular disease.