Probenecid Inhibits α-Adrenergic Receptor-Mediated Vasoconstriction in the Human Leg Vasculature

Coordination of vascular smooth muscle cell tone in resistance arteries plays an essential role in the regulation of peripheral resistance and overall blood pressure. Recent observations in animals have provided evidence for a coupling between adrenoceptors and Panx1 (pannexin-1) channels in the regulation of sympathetic nervous control of peripheral vascular resistance and blood pressure; however, evidence for a functional coupling in humans is lacking. We determined Panx1 expression and effects of treatment with the pharmacological Panx1 channel inhibitor probenecid on the vasoconstrictor response to α1- and α2-adrenergic receptor stimulation in the human forearm and leg vasculature of young healthy male subjects (23±3 years). By use of immunolabeling and confocal microscopy, Panx1 channels were found to be expressed in vascular smooth muscle cells of arterioles in human leg skeletal muscle. Probenecid treatment increased (P<0.05) leg vascular conductance at baseline by ≈15% and attenuated (P<0.05) the leg vasoconstrictor response to arterial infusion of tyramine (α1- and α2-adrenergic receptor stimulation) by ≈15%, whereas the response to the α1-agonist phenylephrine was unchanged. Inhibition of α1-adrenoceptors prevented the probenecid-induced increase in baseline leg vascular conductance, but did not alter the effect of probenecid on the vascular response to tyramine. No differences with probenecid treatment were detected in the forearm. These observations provide the first line of evidence in humans for a functional role of Panx1 channels in setting resting tone via α1-adrenoceptors and in the constrictive effect of noradrenaline via α2-adrenoceptors, thereby contributing to the regulation of peripheral vascular resistance and blood pressure in humans.

Neural control of the circulation

The purpose of this brief review is to highlight key concepts about the neural control of the circulation that graduate and medical students should be expected to incorporate into their general knowledge of human physiology. The focus is largely on the sympathetic nerves, which have a dominant role in cardiovascular control due to their effects to increase cardiac rate and contractility, cause constriction of arteries and veins, cause release of adrenal catecholamines, and activate the renin-angiotensin-aldosterone system. These effects, as well as the control of sympathetic outflow by the vasomotor center in the medulla and the importance of sensory feedback in the form of peripheral reflexes, especially the baroreflexes, are discussed in the context of cardiovascular regulation.

Immunohistochemical localization of adrenergic receptors in the rat organ of corti and spiral ganglion

Alpha(1)-, beta(1)-, and beta(2)-adrenergic receptors (ARs), which mediate responses to adrenergic input, have been immunohistochemically identified within the organ of Corti and spiral ganglion with polyclonal antibodies of established specificity. Alpha(1)-AR was immunolocalized to sites overlapping supranuclear regions of inner hair cells as well as to nerve fibers approaching the base of inner hair cells, most evident in the basal cochlear turn. A similar preponderance across cochlear turns for alpha(1)-AR in afferent cell bodies in the spiral ganglion pointed to type I afferent dendrites as a possible neural source of alpha(1)-AR beneath the inner hair cell. Foci of immunoreactivity for alpha(1)-AR, putatively neural, were found overlapping supranuclear and basal sites of outer hair cells for all turns. Beta(1)- and beta(2)-ARs were immunolocalized to sites overlapping apical and basal poles of the inner and outer hair cells, putatively neural in part, with immunoreactive nerve fibers observed passing through the habenula perforata. Beta(1)- and beta(2)-ARs were also detected in the cell bodies of Deiters' and Hensen's cells. Within the spiral ganglion, beta(1)- and beta(2)-ARs were immunolocalized to afferent cell bodies, with highest expression in the basal cochlear turn, constituting one possible neural source of receptors within the organ of Corti, specifically on type I afferent dendrites. Beta(1)- and beta(2)-ARs in Hensen's and Deiters' cells would couple to Galphas, known to be present specifically in the supporting cells. Overall, adrenergic modulation of neural/supporting cell function within the organ of Corti represents a newly considered mechanism for modifying afferent signaling.

Alpha- and beta-adrenergic receptors: Ahlquist's landmark hypothesis of a single mediator with two receptors

This essay looks at the historical significance of an APS classic paper that is freely available online:

Ahlquist RP. A study of adrenotropic receptors. Am J Physiol 153: 586–600, 1948 ( http://ajplegacy.physiology.org/cgi/reprint/153/3/586 ).

Genetic variation of human adrenergic receptors: from molecular and functional properties to clinical and pharmacogenetic implications

Adrenergic receptors (ARs) are directly or indirectly involved in the control of a large panel of physiological functions and are the targets of drugs for the treatment of several common diseases including congestive heart failure, asthma or benign prostatic hyperplasia. The genotyping of human populations with diverse ethnicity has revealed that the genes encoding alpha(1A)-, alpha(1B)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)- and beta(3)-AR are polymorphic in their coding region as well as in their regulatory domains and non-coding regions. The functional consequences of these genetic variations include changes in expression at transcriptional or translational level, modification of coupling to heterotrimeric G-proteins resulting in a gain or a loss in function, and alteration of GRK-mediated receptor phosphorylation/desensitization or of agonist-promoted down-regulation. None of the mutations identified so far is per se a major risk factor for acquired or inherited disease; however, variants of alpha(2C)-AR and beta(1)-AR may act in synergy to determine the progression of heart failure and certain combinations of polymorphisms on beta(2)-AR correlate with asthmatic phenotypes or response to beta(2)-agonist therapy. Herein we summarize the present knowledge on AR gene polymorphisms, and discuss the putative consequences of variations resulting in receptor malfunction on pharmacogenomics and disease predisposition.

Changes in adrenoreceptors in the prefrontal cortex of subjects with dementia: evidence of compensatory changes

In Alzheimer's disease (AD) there is a significant loss of locus coeruleus (LC) noradrenergic neurons. However, recent work has shown the surviving noradrenergic neurons to display many compensatory changes, including axonal sprouting to the hippocampus. The prefrontal cortex (PFC) is a forebrain region that is affected in dementia, and receives innervation from the LC noradrenergic neurons. Reduced PFC function can reduce cognition and disrupt behavior. Because the PFC is an important area in AD, we determined if noradrenergic innervation from the LC noradrenergic neurons is maintained and if adrenoreceptors are altered postsynaptically. Presynaptic PFC alpha2-adrenoreceptor (AR) binding site density, as determined by 3H-RX821002, suggests that axons from surviving noradrenergic neurons in the LC are sprouting to the PFC of subjects with dementia. Changes in postsynaptic alpha1-AR in the PFC of subjects with dementia indicate normal to elevated levels of binding sites. Expression of alpha1-AR subtypes (alpha1A- and alpha1D-AR) and alpha2C-AR subtype mRNA in the PFC of subjects with dementia is similar to what was observed in the hippocampus with one exception, the expression of alpha1A-AR mRNA. The expression of the alpha1A-AR mRNA subtype is significantly reduced in specific layers of the PFC in subjects with dementia. The loss of alpha1A-, alpha1D- and alpha2C-AR mRNA subtype expression in the PFC may be attributed to neuronal loss observed in dementia. These changes in postsynaptic AR would suggest a reduced function of the PFC. Consequence of this reduced function of the PFC in dementia is still unknown but it may affect memory and behavior.

Quantitative mRNA analysis of adrenergic receptor subtypes in the intestines of healthy dairy cows and dairy cows with cecal dilatation-dislocation

OBJECTIVE

To investigate the distribution of mRNA coding for 9 adrenoceptor subtypes in the intestines of healthy dairy cows and cows with cecal dilatationdislocation (CDD).

SAMPLE POPULATION

Full-thickness specimens of the intestinal wall were obtained from the ileum, cecum, proximal loop of the ascending colon (PLAC), and external loop of the spiral colon (ELSC) of 15 cows with CDD (group 1) and 15 healthy (control) cows (group 2, specimens collected during laparotomy; group 3, specimens collected after slaughter).

PROCEDURES

Concentrations of mRNA for 9 adrenoceptor subtypes (alpha(1A), alpha(1B), alpha(1D), alpha(2AD), alpha(2B), alpha(2C), beta(1), beta(2), and beta(3)) were measured by quantitative real-time reverse transcriptase-PCR assay. Results were expressed relative to mRNA expression of a housekeeping gene.

RESULTS

Expression of mRNA for alpha(1B)-, alpha(2AD)-, alpha(2B)-, beta(1)-, and beta(2)-adrenoceptors was significantly lower in cows with CDD than in control cows. In the ileum, these receptors all had lower mRNA expression in cows with CDD than in control cows. The same effect was detected in the ELSC for mRNA for alpha(2AD)-, alpha(2B)-, beta(1)-, and beta(2)-adrenoceptors, and in the cecum and PLAC for alpha(2B)- and beta(2)-adrenoceptors. Groups did not differ significantly for alpha(1A)-adrenoceptors. The mRNA expression for alpha(1D)-, alpha(2C)-, and beta(3)-adrenoceptors was extremely low in all groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Differences in expression of mRNA coding for adrenoceptors, most pronounced in the ileum and spiral colon, between cows with CDD and control cows support the hypothesis of an implication of adrenergic mechanisms in the pathogenesis of CDD in dairy cows.

Adrenergic receptor characterization of CA1 hippocampal neurons using real time single cell RT-PCR

The CA1 region of the rat hippocampus exhibits both alpha and beta adrenergic receptor (AR) responses, however, the specific AR subtypes involved and the neuronal expression patterns for these receptors are not well understood. We have employed single cell real time RT-PCR in conjunction with cell-specific immunohistochemical markers to determine the AR expression patterns for hippocampal neurons located in CA1, a region often implicated in learning and memory processes. Cytoplasmic samples were taken from 55 individual cells located in stratum oriens, pyramidale, or radiatum and reverse transcribed. All successfully amplified pyramidal neuron samples (n = 17) expressed mRNA for the beta2AR, with four cells additionally expressing mRNA for the beta1AR subtype. Positive interneurons from stratum oriens (n = 10) and stratum radiatum (n = 8) expressed mRNA for the alpha1A and/or alpha(1B)AR (n = 9/18) only when coexpressing transcripts for somatostatin. Interneurons containing neuropeptide Y or cholecystokinin (n = 9/18) were not positive for any of the nine AR subtypes, suggesting that CA1 interneuron AR expression is limited to a subset of somatostatin-positive cells. These findings suggest that only a select number of AR subtypes are transcriptionally expressed in CA1 and that these receptors are selective to specific neuronal cell types.

GPCRsclass: a web tool for the classification of amine type of G-protein-coupled receptors

The receptors of amine subfamily are specifically major drug targets for therapy of nervous disorders and psychiatric diseases. The recognition of novel amine type of receptors and their cognate ligands is of paramount interest for pharmaceutical companies. In the past, Chou and co-workers have shown that different types of amine receptors are correlated with their amino acid composition and are predictable on its basis with considerable accuracy [Elrod and Chou (2002) Protein Eng., 15, 713–715]. This motivated us to develop a better method for the recognition of novel amine receptors and for their further classification. The method was developed on the basis of amino acid composition and dipeptide composition of proteins using support vector machine. The method was trained and tested on 167 proteins of amine subfamily of G-protein-coupled receptors (GPCRs). The method discriminated amine subfamily of GPCRs from globular proteins with Matthew's correlation coefficient of 0.98 and 0.99 using amino acid composition and dipeptide composition, respectively. In classifying different types of amine receptors using amino acid composition and dipeptide composition, the method achieved an accuracy of 89.8 and 96.4%, respectively. The performance of the method was evaluated using 5-fold cross-validation. The dipeptide composition based method predicted 67.6% of protein sequences with an accuracy of 100% with a reliability index ≥5. A web server GPCRsclass has been developed for predicting amine-binding receptors from its amino acid sequence [ and (mirror site)].

Functional adrenergic receptor polymorphisms and idiopathic orthostatic intolerance

OBJECTIVES

Idiopathic orthostatic intolerance (IOI) is a common disorder that is characterized by chronic orthostatic symptoms and substantial increases in heart rate and plasma norepinephrine concentrations that are disproportionately high while standing. Several features of the syndrome, including the tachycardia, tremulousness, and exaggerated norepinephrine have been considered potentially due to hypoactive or hyperactive states of adrenergic receptors of the sympathetic nervous system. The aim of this study was therefore to ascertain whether genotypes at eight polymorphic loci within five relevant adrenergic receptor genes (alpha2A, alpha2B, alpha2C, beta1 and beta2) influence the risk for IOI.

METHODS

We studied 80 young men in military service (20 patients with IOI and 60 age-matched controls). All participants underwent a tilt table test including monitoring of blood pressure, heart rate and plasma catecholamines, in the supine position and during 30 min of standing. Genotyping at the eight loci (alpha2ALys251, alpha2BDel301-303, alpha2CDel322-325, beta1Gly49, beta1Arg389, beta2Arg16, beta2Glu27, beta2Ile164) was performed in all participants. Chi-square tests of independence were used to test for associations between IOI and genotype. In addition, an association of the polymorphisms with haemodynamic variables (heart rate, supine and upright blood pressure) was ascertained using one-way variance analysis.

RESULTS

For the beta1Gly49 polymorphism we found a decrease in the risk of IOI among persons who were homozygous (odds ratio, 0.88; 95% confidence interval, 0.81-0.97). In addition, we found an association between beta1Gly49 and decreased heart rate in the upright position, regardless of IOI diagnosis. There were no associations with the other studied polymorphisms and IOI.

CONCLUSIONS

Our current results suggest that the beta1Gly49 polymorphism is protective for IOI. This is likely one of several common genetic loci that may represent modifiers of IOI phenotypes.

G-protein coupled receptors: SAR analyses of neurotransmitters and antagonists

BACKGROUND

From the deductive point of view, neurotransmitter receptors can be divided into categories such as cholinergic (muscarinic, nicotinic), adrenergic (alpha- and beta-), dopaminergic, serotoninergic (5-HT1 approximately 5-HT5), and histaminergic (H1 and H2). Selective agonists and antagonists of each receptor subtype can have specific useful therapeutic applications. For understanding the molecular mechanisms of action, an inductive method of analysis is useful.

OBJECTIVE

The aim of the present study is to examine the structure-activity relationships of agents acting on G-protein coupled receptors.

METHOD

Representative sets of G-PCR agonists and antagonists were identified from the literature and Medline [P.M. Walsh (2003) Physicians' Desk Reference; M.J. O'Neil (2001) The Merck Index]. The molecular weight (MW), calculated logarithm of octanol/water partition coefficient (C log P) and molar refraction (CMR), dipole moment (DM), E(lumo) (the energy of the lowest unoccupied molecular orbital, a measure of the electron affinity of a molecule and its reactivity as an electrophile), E(homo) (the energy of the highest occupied molecular orbital, related to the ionization potential of a molecule, and its reactivity as a nucleophile), and the total number of hydrogen bonds (H(b)) (donors and receptors), were chosen as molecular descriptors for SAR analyses.

RESULTS

The data suggest that not only do neurotransmitters share common structural features but their receptors belong to the same ensemble of G-protein coupled receptor with seven to eight transmembrane domains with their resultant dipoles in an antiparallel configuration. Moreover, the analysis indicates that the receptor exists in a dynamic equilibrium between the closed state and the open state. The energy needed to open the closed state is provided by the hydrolysis of GTP. A composite 3-D parameter frame setting of all the neurotransmitter agonists and antagonists are presented using MW, Hb and mu as independent variables.

CONCLUSION

It appears that all neurotransmitters examined in this study operate by a similar mechanism with the G-protein coupled receptors.

[Influence of adrenoreceptors on functions of the body]

The remarkably diverse effects of the catecholamines and similar sympathomimetic agents are directly related to an understanding of the classification and different types of adrenoreceptors. Characteristics and physiological regulatory mechanisms of the receptor result in variable response of organ systems to catecholamines stimulation. Different adrenoreceptors regulate distinct physiological processes by controlling the synthesis or release of a variety of second messengers. The goal of this review was to turn one's attention to the below mentioned aspects. There are three known subtypes of each alpha1-, alpha2- and beta-adrenoreceptor types. Structure of the adrenoreceptors, which belong to subtypes of the same receptor type, is similar and structure of the adrenoreceptors of the separate types is very different. Genetic peculiarities of the receptors may influence liability to some diseases. Acting on the adrenoreceptors may change function of many organs and may serve for the treatment of cardiovascular, respiratory tract diseases and allergic reactions. Selective acting on the adrenoreceptors of the separate subtypes may have the different effect on the organs. Great consideration is given for that property in the development of new drugs: substitution by different chemical radicals leads to increasing selectivity for the separate subtypes of the adrenoreceptors. The prolonged use of the adrenomimetics may lead to refractoriness.

Polymorphisms of adrenergic receptors: variations on a theme

Recent studies have revealed that most of the adrenergic receptor genes are polymorphic, leading to changes in the amino sequence of the encoded receptor. The variations occur in multiple functional regions of the receptors, and appear as haplotypes with other coding and noncoding polymorphisms in their genes. The consequences of such genetic variability have been explored in recombinant cell-based systems and in human studies. Adrenergic receptor polymorphisms have been shown to alter receptor binding, G-protein coupling, regulation, and expression compared with their allelic counterparts. Here, the genetic and molecular characterization of these polymorphisms is reviewed, as well as their potential impact on pharmacogenetics, disease risk, and disease modification.

Adrenergic targets for the treatment of cognitive deficits in schizophrenia

RATIONALE

The cognitive functions of the prefrontal cortex (PFC) are profoundly impaired in schizophrenic patients. Although dopamine has been the major focus of schizophrenia research, norepinephrine (NE) also has marked influences on PFC cognitive functioning.

OBJECTIVE

This review aims to identify the adrenergic receptors which may be appropriate targets for therapeutic actions in schizophrenia.

METHODS

Studies of adrenergic mechanisms influencing PFC function in animals and humans were reviewed.

RESULTS

Modest levels of NE engage postsynaptic alpha(2A)-adrenergic receptors and strengthen working memory. These beneficial effects have been observed at both the behavioral and cellular levels in animals, and have translated to the clinic in patients with PFC impairments. Thus, the alpha(2A)-adrenergic receptor is a proven molecular target. In contrast, high levels of NE released during stress impair PFC cognitive function via activation of protein kinase C intracellular signaling, a pathway increasingly associated with the etiology of schizophrenia. Blockade of alpha(1) adrenoceptors or inhibition of protein kinase C helps to protect PFC cognitive function in animals, and may have similar therapeutic actions in humans. Blockade of the alpha(2C) receptor may also be helpful in enhancing catecholamine release while blocking detrimental DA actions in striatum.

CONCLUSION

Highly selective adrenergic agents may be useful for enhancing PFC function in schizophrenic patients

Astrocytic Adrenoceptors: A Major Drug Target in Neurological and Psychiatric Disorders?

Considerable attention has recently been paid to astrocyte functions, which are briefly summarized. A large amount of data is available about adrenoceptor expression and function in astrocytes, some of it dating back to the 1970's and some of it very recent. This material is reviewed in the present paper. The brain is innervated by noradrenergic fibers extending from locus coeruleus in the brain stem, which in turn is connected to a network of adrenergic and noradrenergic nuclei in the medulla and pons, contributing to the control of (nor)adrenergic, serotonergic, dopaminergic and cholinergic function, both in the central nervous system (CNS) and in the periphery. In the CNS astrocytes constitute a major target for noradrenergic innervation, which regulates morphological plasticity, energy metabolism, membrane transport, gap junction permeability and immunological responses in these cells. Noradrenergic effects on astrocytes are essential during consolidation of episodic, long-term memory, which is reinforced by beta-adrenergic activation. Glycogenolysis and synthesis of glutamate and glutamine from glucose, both of which are metabolic processes restricted to astrocytes, occur at several time-specific stages during the consolidation. Astrocytic abnormalities are almost certainly important in the pathogenesis of multiple sclerosis and in all probability contribute essentially to inflammation and malfunction in Alzheimer's disease and to mood disturbances in affective disorders. Noradrenergic function in astrocytes is severely disturbed by chronic exposure to cocaine, which also changes astrocyte morphology. Development of drugs modifying noradrenergic receptor activity and/or down-stream signaling is advocated for treatment of several neurological/psychiatric disorders and for neuroprotection. Astrocytic preparations are suggested for study of mechanism(s) of action of antidepressant drugs and pathophysiology of mood disorders.

Regulatory effects of reboxetine treatment alone, or following paroxetine treatment, on brain noradrenergic and serotonergic systems

When patients do not respond to an initial antidepressant, one clinical approach is to switch to an agent in a different pharmacological class. However, few studies have examined the neurochemical consequences of this practice. To study this, we examined changes in binding sites in rat brain for norepinephrine (NET) and serotonin transporters (SERT), alpha1, alpha2, and beta1 adrenergic receptors after chronic administration of paroxetine (PRX), reboxetine (RBX), or PRX followed by RBX. We also examined the effects of these treatments on mRNA expression for tyrosine hydroxylase (TH). RBX treatment for 3 weeks reduced NET binding significantly, by approximately 40% in terminal field areas, and 6 weeks of RBX reduced it even more, by approximately 60%. RBX treatment for 3 and 6 weeks reduced beta1 adrenergic receptor-binding sites equally, by 50-60%. At no time did RBX treatment reduce SERT-binding sites. PRX treatment had no effect on beta1 adrenergic or NET-binding sites, but reduced SERT-binding sites by 75-80%. Neither treatment altered mRNA for TH, alpha1, or alpha2 adrenergic receptor-binding sites. When 3 weeks of RBX treatment followed 3 weeks of PRX treatment, NET-binding sites were reduced to the same extent as measured after 6 weeks of RBX treatment alone, indicating that PRX pretreatment may have 'primed' the subsequent regulatory effect of RBX on the NET. Thus, pretreatment of rats with PRX actually enhanced at least one regulatory effect of RBX treatment on the noradrenergic system, and did not interfere with any other pharmacological effect caused by RBX treatment.

Effects of partial locus coeruleus denervation and chronic mild stress on behaviour and monoamine neurochemistry in the rat

It has been proposed that lesions of the ascending noradrenergic projections render animals more vulnerable to stress. In this study, the effects of partial denervation of the locus coeruleus (LC) by DSP-4 (10 mg/kg) treatment, chronic mild stress (CMS) and their combination were examined. DSP-4 was administered to rats 1 week before the onset of CMS, which was applied for 5 weeks. In the forced swimming test, the immobility time was decreased by both DSP-4 and CMS. In the open field test, the number of defecations was increased after DSP-4 treatment plus CMS. Partial LC denervation decreased the levels of noradrenaline (NA) by 34%, increased NA turnover, and decreased the density of beta-adrenoceptors in the cerebral cortex. CMS decreased the binding affinity of beta-adrenoceptors, an effect not observed in the DSP-4 treated animals. In conclusion, 6 weeks after partial LC denervation NA turnover is increased in the cortex, and the effect of CMS on emotionality is enhanced.

Role of perivascular sympathetic nerves and regional differences in the features of sympathetic innervation of the vascular system

Maintenance of blood pressure is mostly dependent on sympathetic "tone", and the sympathetic nerve innervates the entire vascular bed, excepting the capillaries. Although norepinephrine (NE) is the principal neurotransmitter released upon sympathetic nerve stimulation, neuropeptide Y and ATP are cotransmitters in various vascular tissues. In addition, dopamine and epinephrine, as well as acetylcholine, have been shown to be sympathetic neurotransmitters in specific vasculatures. Transmitter NE release is modified by a number of endogenous substances including the transmitter itself. Chronic denervation of the preganglionic fiber induces an increase in NE release per pulse, indicating postganglionic neuronal supersensitivity. So far, three main adrenoceptor types have been shown, alpha1, alpha2 and beta, each of which is further divided into at least three subtypes, as well as the alpha1L-adrenoceptor, a phenotype of the cloned alpha1a-adrenoceptor, in the blood vessel. Thus, the response of vessels with different receptor types to a transmitter varies quantitatively and even qualitatively from one vessel to another. The remarkable diversity in the sympathetic innervation mechanism in the vascular system may play an important role in regional variations in the regulation of blood flow. The sympathetic nerve also exerts long-term trophic action on the blood vessel. In conclusion, the sympathetic nervous system plays an important role not only in the regulation of cardiovascular dynamics but in the maintenance of the vessel structure, as well.

Lipid solubility of vasodilatory vanilloid-type beta-blockers on the functional and binding activities of beta-adrenoceptor subtypes

Various vanilloid-type beta-adrenoceptor blockers were studied on guinea pig right atrium and trachea and rat colon. In addition, we also investigated their beta(1)-, beta(2)-, and beta(3)-adrenoceptor binding affinities. All these beta-adrenergic antagonists inhibited (-)isoproterenol-induced positive chronotropic effects of the right atrium and tracheal relaxation responses in a concentration-dependent manner. Some of these agents prevented the inhibition of rat colon spontaneous motility by (-)isoproterenol. Of the agents tested, we found that ferulidilol, eugenodilol, eugenolol, isoeugenolol, and ferulinolol, as well as propranolol and metoprolol, possessed beta(3)-adrenoceptor blocking activities, others were nearly without effectiveness. Furthermore, the binding characteristics of vanilloid-type beta-adrenergic antagonists were evaluated in [3H]CGP-12177, a beta(1)/beta(2)-adrenoceptor blocker and a beta(3)-adrenoceptor agonist, binding to beta(1)-, beta(2)-, and beta(3)-adrenoceptor sites in rat ventricle, lung, and interscapular brown adipose tissue (IBAT) membranes, respectively. Eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol were less potent than both propranolol and ferulidilol in competing for the beta(3)-adrenoceptor binding sites. From the results of in vitro functional and binding studies, we suggested that propranolol, ferulidilol, eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol all possessed beta(3)-adrenoceptor blocking activities. On the other hand, we also found that eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol had a low lipid solubility in comparison with propranolol and ferulidilol. In conclusion, we proposed that beta(3)-adrenoceptor antagonistic actions of these vanilloid-type beta-blockers were positively correlated with their lipid solubility.

Adrenoceptor subtype involvement in suppression of prolactin secretion by noradrenaline

In sheep, injection of noradrenaline suppresses prolactin secretion by a direct effect at the pituitary gland. The aims of this study were to use primary cultures of ovine pituitary cells to examine the receptor subtypes that mediate the inhibitory effect of noradrenaline on prolactin secretion and, by using receptor antagonists in vivo, determine whether noradrenaline acts as a prolactin release-inhibiting factor (PIF). Noradrenaline and dopamine suppressed prolactin secretion from ovine pituitary cells with ED50s of 60.9+/-46.6 and 1.5+/-1.0x10-9 mol/l, respectively (P<0.05). The in-vitro prolactin release-inhibiting effect of noradrenaline (10-7 mol/l) was not blocked by the dopamine antagonists pimozide (D2) or SCH23390 (D1) but was blocked by each of the adrenoceptor antagonists (alpha1-adrenoceptor antagonists prazosin and WB4101, the alpha2-adrenoceptor antagonist yohimbine and the beta-adrenoceptor antagonist propranolol). The response to adrenoceptor agonists was also tested in vitro. The alpha1-adrenoceptor agonists phenylephrine and cirazoline significantly suppressed prolactin. Of the alpha2-agonists, clonidine had no effect whereas oxymetazoline and p-aminoclonidine both suppressed prolactin. The beta-adrenoceptor agonist isoproterenol also suppressed prolactin while the specific beta3-antagonist BRL37344 had no effect. When the adrenoceptor antagonists were tested in vivo in ewes manipulated to be in the luteal phase, only WB4101 significantly (P<0.05) increased plasma prolactin concentrations but this response was small and only observed in one of two experiments. In summary, these experiments suggest that adrenoceptors and not dopamine receptors are responsible for the inhibitory effect of noradrenaline on prolactin secretion in vitro but do not implicate a particular adrenoceptor subtype. The in-vivo experiments do not provide convincing evidence for a role for noradrenaline as a physiologically important PIF.

Adrenoceptor subclassification: an approach to improved cardiovascular therapeutics

The subdivision of alpha adrenoceptors into the alpha 1 and alpha 2 classes was the impetus for the design of the selective alpha 1-adrenoceptor antagonists, which remain useful antihypertensives. alpha 2-Adrenoceptor agonists also have application as antihypertensive drugs, based on their ability to reduce sympathetic outflow. Likewise, subdivision of the beta adrenoceptors has lead to the development of selective beta 1-adrenoceptor antagonists as antihypertensive and selective beta 2 agonists as bronchodilators. In the past decade, both the alpha 1 and alpha 2 adrenoceptors have been further subdivided, each into three subclasses. In addition, there is strong functional evidence to suggest the presence of additional adrenoceptor subtypes, such as the "alpha 1L" adrenoceptor and "beta 4" adrenoceptor. alpha 1A (or alpha 1L)-Adrenoceptor antagonists have been evaluated for benign prostatic hyperplasia (BPH), and selective alpha 1A agonists for stress incontinence. Gene knockout experiments in mice suggest an important role for the alpha 1B adrenoceptor in the control of vascular tone. Hence, selective alpha 1B antagonists may offer a new approach toward hypertension. Although targeting of specific adrenoceptors can be used to optimize the therapeutic profile of a drug, there are also cases where blockade of multiple adrenoceptors is desirable, as with the alpha/beta-adrenoceptor antagonist carvedilol in congestive heart failure. It is possible that combination of affinities for selected adrenoceptor subtypes within a single molecule may be desirable for certain applications.

Genistein potentiates the relaxation induced by beta1- and beta2-adrenoceptor activation in rat aortic rings

In rat aortic rings, genistein, an inhibitor of tyrosine kinase, but not daidzein, an inactive analogue of genistein, potentiated the relaxation induced by isoproterenol. Atenolol, a beta1-adrenoceptor antagonist, or ICI-118,551, a beta2-adrenoceptor antagonist, inhibited the relaxation induced by isoproterenol. The potentiating effect of genistein on the relaxation induced by isoproterenol in the presence of ICI-118,551 was apparently greater than that in the presence of atenolol. In the presence of ICI-118,551, theophylline, an inhibitor of cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (cAMP-PDE), markedly inhibited the potentiating effect of genistein on the isoproterenol-induced relaxation, whereas in the presence of atenolol, theophylline only partly inhibited the potentiating effect of genistein. The relaxation induced by forskolin, an activator of adenylyl cyclase, was potentiated by genistein or theophylline. In the presence of theophylline, the relaxation induced by forskolin was not further affected by genistein. Genistein also inhibited the activities of cAMP-PDE. In the presence of atenolol, but not ICI-118,551, iberiotoxin, an inhibitor of Ca-activated K channels, inhibited the relaxation induced by isoproterenol and the potentiating effect of genistein. In the presence of atenolol, quinacrine, an inhibitor of phospholipase A2, and metyrapone, an inhibitor of P-450 enzymes, but not alpha-naphthoflavone, an inhibitor of P-450 enzymes, indomethacin, a cyclooxygenase inhibitor, or AA861, a 5-lipoxygenase inhibitor, inhibited the potentiating effect of genistein. These results suggest that the potentiation of the beta1-adrenoceptor-induced relaxation by activation of genistein may mostly be due to inhibition of cAMP-PDE activities. In addition, the potentiation of the relaxation induced by activation of beta2-adrenoceptors by genistein may be related to the inhibition of arachidonic acid metabolism and cAMP-PDE activities.

Determination of the somatodendritic alpha2-adrenoceptor subtype located in rat locus coeruleus that modulates cortical noradrenaline release in vivo

The regulation of extracellular noradrenaline levels in the cingulate cortex by somatodendritic alpha2-adrenoceptors located in the locus coeruleus was evaluated in the rat by using dual-probe microdialysis. The concentration of noradrenaline in the cingulate cortex was decreased (37%-40%) by administration into the locus coeruleus (1microM) of the agonists clonidine and UK14304 (bromoxidine), whereas it was increased by similar administration of the nonselective antagonist RX821002 (2-methoxyidazoxan) (+ 103%) and the selective alpha2A-adrenoceptor antagonist BRL44408 (2-[2H-(1-methyl-1,3-dihydroisoindole)methyl]-4,5-dihydroimidaz ole) (+ 148%). The selective alpha2B/C-adrenoceptor antagonist ARC239 (2-[2[4-(o-methoxyphenyl)piperazin-1-yl]ethyl]-4,4-dimethyl-1,3-(2 H,4H)-isoquinolimedione) did not induce changes. In the presence of BRL44408, the effects of clonidine and UK14304 were abolished, but they were not modified in the presence of ARC239. The data demonstrate that noradrenaline release in terminal areas is tonically modulated by somatodendritic alpha2A-adrenoceptors.

Extraction of active clonidine-displacing substance from bovine lung and comparison with clonidine-displacing substance extracted from other tissues

Crude methanolic clonidine-displacing substance (CDS) extracted from bovine lung competed for radioligand binding from alpha2-adrenoceptors and I2-sites present in rat brain membranes, and from I1-sites present in rat brain and kidney membranes. There was no difference in the competition of [3H]clonidine binding to alpha2-adrenoceptors present in either rat or rabbit brain membranes by the crude CDS extract and therefore either tissue could be used to estimate the number of units of CDS present in extracts. Further purification by reverse phase high performance liquid chromatography (RP-HPLC), with UV detection, of extracts obtained from bovine lung, brain and rat brain exhibited similar three-peak profiles, previously reported. Corresponding fractions competed for radioligand binding to alpha2-adrenoceptors present in rat brain membranes, eluting between 19 and 23 min, which corresponded with the middle peak of the three-peaks. Therefore, we propose the CDS-like material eluting from all these tissues to be similar. Interestingly, CDS extracted from bovine adrenal glands under the same conditions showed a similar three-peak profile, but did not repeat the displacement of binding just at 19-23 min, but at every time point after 4 min. This suggests this tissue could represent a source of CDS in this species.

Do alpha2-adrenoceptors play an integral role in the antinociceptive mechanism of action of antidepressant compounds?

Antidepressants are analgesic in the absence or presence of depression. The underlying mechanisms probably involve a complex interplay between several neurotransmitter systems and neuroreceptors. Alpha-adrenoceptors play an important role in pain processing and alpha2-adrenoceptor agonists have been used in clinical pain management so we have investigated whether alpha-adrenoceptor sub-types mediate the antinociceptive activity of antidepressants. Thus, the abdominal constriction assay in mice was used to examine the antinociceptive responses of a diverse range of antidepressants following alpha1- or alpha2-adrenoceptor antagonism. The antidepressants or monoamine reuptake inhibitors included the serotonin selective reuptake inhibitor paroxetine, the serotonin-noradrenaline reuptake inhibitor sibutramine, the resolved (+)- and (-)-enantiomers of the noradrenaline reuptake inhibitor oxaprotiline, plus the tricyclics amitriptyline and dothiepin. All these compounds have been previously shown to be antinociceptive in this paradigm. The respective alpha1- and alpha2-adrenoceptor antagonists prazosin and RX821002 ([2-(2-methoxy-1,-4-benzodioxan-2-yl)-2-imidazoline]) did not produce antinociception though at 1.0 mg kg(-1); s.c., RX821002 but not prazosin blocked clonidine antinociception. The antinociceptive activity produced by sub-maximal doses of amitriptyline, dothiepin, sibutramine, paroxetine, (+)- and (-)-oxaprotiline were all blocked by RX821002 but not by prazosin. Additionally, both morphine and aspirin antinociception was resistant to alpha1- and alpha2-adrenoceptor antagonism. Thus, alpha2- rather than alpha1-adrenoceptors may play an integral role in antidepressant antinociception irrespective of the propensity for inhibiting reuptake of not only noradrenaline but also serotonin. It is probable, however, that other differing pharmacological properties of some antidepressants, such as opioid-like activity, may complicate any empirical correlation between monoamine uptake and analgesia.

Central injection of nicotine increases hepatic and splenic interleukin 6 (IL-6) mRNA expression and plasma IL-6 levels in mice: involvement of the peripheral sympathetic nervous system

Accumulating evidence suggests that plasma levels of interleukin 6 (IL-6), a major cytokine stimulating the synthesis of acute-phase proteins, are intimately regulated by the central nervous system. Nicotine, one of the major drugs abused by humans, has been shown to affect immunological functions. In the present study, effects of intracerebroventricular (i.c.v.) injection of nicotine on plasma IL-6 levels were investigated in mice. Nicotine administered i.c.v. dose-dependently increased plasma IL-6 levels; the lowest effective dose was 0.3 ng/mouse and the maximal effect was attained with the dose of 105 ng/mouse. The nicotine (105 ng/mouse, i.c.v.)-induced plasma IL-6 levels peaked at 3 h and approached basal levels 6 h after injection. Mecamylamine, a nicotinic receptor antagonist, blocked nicotine-induced plasma IL-6 levels. Depletion of peripheral norepinephrine with 6-hydroxydopamine [100 mg/kg, intraperitoneal (i. p.)] inhibited the nicotine-induced plasma IL-6 levels by 57%, whereas central norepinephrine depletion with 6-hydroxydopamine (50 microgram/mouse, i.c.v.) had no effect. Pretreatment with prazosin (alpha1-adrenergic antagonist; 1 mg/kg, i.p.), yohimbine (alpha2-adrenergic antagonist; 1 mg/kg, i.p.), and ICI-118,551 (beta2-adrenergic antagonist; 2 mg/kg, i.p.), but not with betaxolol (beta1-adrenergic antagonist; 2 mg/kg, i.p.), inhibited nicotine-induced plasma IL-6 levels. Among the peripheral organs, including the pituitary, adrenals, heart, lung, liver, spleen, and lymph nodes, nicotine (105 ng/mouse, i.c.v.) increased IL-6 mRNA expression only in the liver and spleen, which was inhibited by peripheral norepinephrine depletion. These results suggest that stimulation of central nicotinic receptors induces plasma IL-6 levels and IL-6 mRNA expression in the liver and spleen via the peripheral sympathetic nervous system, alpha1-, alpha2-, and beta2-adrenoreceptors being involved.

Functional characterization of alpha1-adrenoceptor subtypes in longitudinal and circular muscle of human vas deferens

The alpha1-adrenoceptor subtype(s) mediating contraction to noradrenaline in longitudinal and circular muscle of human epididymal vas deferens was studied using competitive antagonists. The effects of the alkylating agents, phenoxybenzamine and chloroethylclonidine were also investigated. Noradrenaline evoked concentration-dependent contractions of longitudinal and circular muscle with comparable potencies (pD2; 5.6 and 5.5 respectively). The contractions in longitudinal and circular muscle respectively were inhibited by prazosin (pA2, 8.6 and pKB, 9.2), 5-methylurapidil (pKB, 8.7 and 9.1) and less potently by spiperone (pA2, 7.1) or BMY 7378 (pKB, 6.3 and 6.6). Contractions of the circular but not longitudinal muscle was comparatively insensitive to pretreatment with phenoxybenzamine. In contrast pretreatment with chloroethylclonidine reduced the contractions in both muscle types and also enhanced phenoxybenzamine-sensitivity in longitudinal but not circular muscle. The results suggest that contractions evoked by noradrenaline in both muscle types of human vas deferens is mediated via activation of alpha1-adrenoceptors with pharmacological profile of the alpha1A-subtype. However the involvement of alpha1A-adrenoceptor variants, such as the hypothesised alpha1L-subtype may underlie the differential effects of phenoxybenzamine in longitudinal and circular muscle. Factors contributing to chloroethylclonidine-sensitivity are discussed.

Receptors involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery

1. We have investigated the neurotransmitters and receptor subtypes involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery. 2. A dense sympathetic innervation was demonstrated using catecholamine histochemistry and antibodies against the synaptic vesicle protein synaptophysin. 3. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated very strong expression of the alpha1A-adrenergic, neuropeptide Y (NPY) Y1, P2X1- and P2X4-purinergic receptors, moderate expression of the alpha2B-adrenergic receptor and the purinergic P2X5- and P2X7-receptors and weak expression of the alpha1B-, alpha1D-, alpha2A- and alpha2C-adrenergic receptors and the P2X2- and P2X3-purinergic receptors. NPY2 and P2X6 receptor expression was absent. 4. Electrical field stimulation (10 Hz, 10 s) produced contractions which were abolished by tetrodotoxin (10(-6) M) and/or guanethidine (GE, 5 x 10(-6) M) and a combination of benextramine (10(-5) M) and alpha,beta-methylene ATP, (alpha,beta-mATP, 3 x 10(-6) M) or PPADS (10(-5) M). Selective alpah1-adrenergic receptor antagonists showed the potency order of prazosin > WB-4101 > 5-methyl-urapidil > BMY 7378. Yohimbine (10(-8) M, 10(-7) M), alpha,beta-mATP (3 x 10(-6) M) and PPADS (10(-5) M) each enhanced the response to nerve stimulation. 5. Some experiments demonstrated a slow neurogenic contraction which was abolished by GE or the selective NPY1 receptor antagonist 1229U91 (6 x 10(-7) M). 6. We conclude that nerve-mediated vasoconstriction results from the activation of postsynaptic alpha,beta-adrenergic and P2X-purinergic receptors and under some conditions, NPY1 receptors. Neurotransmitter release is modulated by presynaptic alpha2-adrenergic receptors and possibly also P2X-purinoceptors. The major postsynaptic subtypes involved were well predicted by mRNA expression as measured by RT-PCR, suggesting that this technique may be a useful adjunct to studies aimed at identifying functional receptor subtypes.

Functional characterization of post-junctional adrenergic receptor subtypes in bovine intra-mammary arteries

We examined the functional role of adrenergic receptor subtypes (ARs) in bovine intra-mammary arteries (IMAs), 1.5-2.5 mm internal diameter. Norepinephrine (NE) and phenylephrine (PE) produced concentration-dependent increases in tone in segments maintained at a previously determined optimal basal tension in vitro. The sensitivity of the tissue to NE and PE, based on -log molar ED50s was 6.87 +/- 0.17 and 7.05 +/- 0.35, respectively. In addition a Schild analysis yielded antagonist affinities for the receptor mediating contractile responses to NE (pA2 value) of 10.46 +/- 0.85 for prazosin and 6.29 +/- 0.18 for yohimbine. These data indicate a dominance of functional alpha 1 (alpha(1)) over alpha 2 (alpha(2))-ARS in this tissue. Based on the inhibitory effects of chloroethylclonidine (CEC) on PE responses and the further reduction in sensitivity when nifedipine was added to the CEC, also in the presence of PE, we conclude that there is more than one alpha(1)-AR subtype, with a predominant role for alpha(1B)-ARs in phenylephrine responses. Stimulation of beta (beta)-ARs, resulted in relatively small reductions in tone (the highest magnitude of response was 25.94 +/- 6.46% of the papaverine maximum at 3 x 10(-6) M isoproterenol); in addition, propranolol did not significantly alter tissue sensitivity to NE. Additional characterization of functional autonomic receptor populations in this circulatory bed will form a basis for future studies on circulatory dynamics in the mammary gland.

[Adrenergic receptors and alpha 2 agonists--1) Molecular biological study of adrenoceptors]

Molecular biological studies have established classification of adrenergic receptors 40 years after Prof Ahlquist first classified them into alpha and beta. They are now classified into 9 subtypes consisting of 400 to 480 amino acids. They belong to a super-family of G-protein coupled receptors. Based on the amino acid sequence, the topography of adrenoceptors is depicted as a snake model twisting itself back and forth through the membrane 7 times.

[Adrenergic receptors--nomenclature and classification of the types and subtypes]

The purpose of this review is to present current knowledge regarding adrenergic receptors and their subtypes. These receptors belong to the superfamily of structures with seven transmembrane domains. They are coupled with G-regulatory proteins. Similarly to other membrane receptors, their division is based on three criteria: structural, transductional, and operational. At present, adrenergic receptors are divided into three main groups, depicted as alpha 1, alpha 2 a beta receptors. Receptors alpha 1 and alpha 2 are further divided into additional 4 subtypes, which are marked with upper case subscripts A-D. Receptors beta are subdivided into three types, marked with subscripts 1-3. Classification of adrenergic receptors can be considered as a prototype for classification of other membrane receptors. The significance of all known receptors subtypes is not yet known. Multiple subtypes of adrenergic and also other receptor types exist simultaneously not only in one tissue but also frequently in a single cell where they can exert both synergistic as well as antagonistic effects. The discovery of functions and interactions of individual receptor subtypes represents a big challenge for future studies. Introduction of new selective agonists and antagonists not only helps to classify various receptor subtypes but it also has a big therapeutic potential.

[Progress in adrenoceptor research]

According to pharmacological characteristics and molecular cloning, adrenoceptor is divided into 3 types, and each type contains at least 3 subtypes. The molecular structure of adrenoceptor fits common model of G protein coupled receptors on membrane surface. The structure-function relationship has been basically elucidated by mutation techniques. The ligand binding characteristics are decided by the structures in transmembrane domains, while the G protein coupling sites are in the third intracellular loop. There are extensive crosstalks among the subtypes of adrenoceptor. According to the mechanisms, the crosstalks can be divided into 4 types.

The role of adrenoceptor-mediated signals in the modulation of lymphocyte function

Adrenoceptors are heterotrimeric glycoproteins that bind specific endogenous ligands, such as the sympathetic neurotransmitter norepinephrine and the neurohormone epinephrine. Ligand binding to an adrenoceptor expressed on the cell surface initiates a cascade of biochemical and molecular responses inside the cell that lead to a change in cellular activity. Initially, the stimulation of an adrenoceptor directly activates G proteins that stimulate enzymes to induce the production of second messengers. The cascade continues as the second messengers activate serine/threonine protein kinases, resulting in either an inhibition or enhancement of cellular activity. The resulting changes in cellular activity are mediated by changes in gene expression that are induced by the phosphorylation of specific transcription factors. Adrenoceptor subtypes are expressed by both T and B lymphocytes. The aim of this review is to summarize and discuss the results from the many studies that have examined the role of adrenoceptor-mediated intracellular signals in the modulation of lymphocyte function. Another aim of this review is to discuss how these studies have advanced our understanding of the mechanisms by which the sympathetic nervous system transmits information to both T and B lymphocytes to maintain immune homeostasis.

Patterns of messenger RNA expression for adrenergic receptor subtypes in the rat kidney

The distribution of mRNA for the rat alpha-1 A/D, alpha-1B, alpha-2A/D (RG20), alpha-2B (RNG), alpha-2C (RG10), beta-1 and beta-2 adrenergic receptors were studied in the rat kidney using in situ hybridization. After hybridized sections were exposed to autoradiography film or dipped in photographic emulsion and counterstained with hematoxylin and eosin, specific and selective labeling patterns characteristic for each probe in the kidney were observed. Labeling with the probe to the alpha-1A/D receptor was only observed in vessels in the renal parenchyma and in the ureter. Alpha-1B receptor mRNA was demonstrated in the outer and inner stripe of the outer medulla, corresponding to segment S3 of proximal tubules and the thick ascending limb of loop of Henle. Alpha-2A/D receptor mRNA was distributed in the inner stripe of the outer medulla and in the inner medulla, corresponding to collecting tubules, and in the ureter. The strongest signal in the kidney was obtained with the alpha-2B receptor probe, showing labelling in the outer stripe of the outer medulla with tubular rays radiating into the cortex, coinciding with segment S3 of proximal tubules. Weak labeling obtained with the alpha-2C receptor probe was present in the renal medulla. Labeling obtained with the probe to the beta-1 receptor was seen in the entire cortex and to a lesser extent also in the outer medulla. In addition, beta-1 receptor mRNA was shown in perirenal adipose tissue and in the ureter. Labeling obtained with the probe to the beta-2 receptor was demonstrated in the outer and inner stripe of the outer medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Octopamine receptor subtypes and their modes of action

Octopamine receptor subclasses were first proposed to explain differences in the pharmacological profiles of a range of physiological responses to octopamine obtained in the extensor-tibiae neuromuscular preparation of the locust. Thus, OCTOPAMINE1 receptors which inhibit an endogenous myogenic rhythm, increase intracellular calcium levels. Also OCTOPAMINE2 receptors which modulate neuromuscular transmission in this preparation, increase the level of adenylate cyclase activity. The current status of this classification is reviewed by examining the pharmacology of responses to octopamine in a range of preparations. It is concluded that the distinction between OCTOPAMINE1 and OCTOPAMINE2 receptor types is still valid, but that OCTOPAMINE2 receptors exhibit some tissue specific variations. Studies on a cloned Drosophila octopamine/tyramine (phentolamine) receptor are discussed and illustrate many of the difficulties presently encountered in making a definitive classification of octopamine receptors. These include the possibilities that single receptors may activate multiple second messenger systems and that different agonists may differentially couple the same receptor to different second messenger systems.

Adrenergic receptors, G proteins, and cell regulation: implications for aging research

Aging is associated with changes, typically blunting, in response to catecholamines and activation of the sympathetic nervous system. These changes are observed in the presence of a substantial increase in circulating catecholamines. Adrenergic receptors with their linkage to guanine nucleotide binding (G) proteins and to effector molecules provide the critical components between catecholamines and tissue response. In this article, I review recent discoveries related to the expansion of size of adrenergic receptor family and G protein superfamily and the possible implication of these discoveries for research in aging. Nine subtypes of adrenergic receptors have been identified (alpha 1A, alpha 1B, alpha 1C, alpha 2A, alpha 2B, alpha 2C, beta 1, beta 2, beta 3), and other subtypes may yet be identified by molecular cloning techniques. The functional role of all of these receptors remains ill-defined. For the heterotrimeric G proteins, at least 16 alpha, 4 beta, and 4 gamma subunits have been identified. The G alpha subunits are unique among G proteins and have been divided into four principal families, termed Gs, G(i), Gq, and G12. G proteins are multifunctional and can link to multiple effectors. Although it is probable that beta-adrenergic receptors preferentially link to Gs, alpha 1-adrenergic receptors to members of the Gq family, and alpha 2-adrenergic receptors to members of the G1 family, many unanswered questions remain as to the determinants of these linkages.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic caffeine alters the density of adenosine, adrenergic, cholinergic, GABA, and serotonin receptors and calcium channels in mouse brain

1. Chronic ingestion of caffeine by male NIH strain mice alters the density of a variety of central receptors. 2. The density of cortical A1 adenosine receptors is increased by 20%, while the density of striatal A2A adenosine receptors is unaltered. 3. The densities of cortical beta 1 and cerebellar beta 2 adrenergic receptors are reduced by ca. 25%, while the densities of cortical alpha 1 and alpha 2 adrenergic receptors are not significantly altered. Densities of striatal D1 and D2 dopaminergic receptors are unaltered. The densities of cortical 5 HT1 and 5 HT2 serotonergic receptors are increased by 26-30%. Densities of cortical muscarinic and nicotinic receptors are increased by 40-50%. The density of cortical benzodiazepine-binding sites associated with GABAA receptors is increased by 65%, and the affinity appears slightly decreased. The density of cortical MK-801 sites associated with NMDA-glutaminergic receptors appear unaltered. 4. The density of cortical nitrendipine-binding sites associated with calcium channels is increased by 18%. 5. The results indicate that chronic ingestion of caffeine equivalent to about 100 mg/kg/day in mice causes a wide range of biochemical alterations in the central nervous system.

Pharmacology and molecular biology of adrenergic receptors

The recent cloning of multiple adrenergic receptors has moved our understanding of these receptors from a conceptual one (Alquist, 1948) to one based on well-defined unique cellular proteins. The biochemical and pharmacological properties of these receptors can now be studied in detail by expression of a single subtype in cells normally devoid of adrenergic receptors. By site-directed mutagenesis, the relationship between the structures of these receptors and their function is now being elucidated for each adrenergic receptor subtype. These functions include the binding of catecholamines and other ligands, G protein coupling and functional regulation.

[Molecular structure and function of renal adrenergic receptors]

The kidney is the principal organ in the body that mediates the excretion of water and minerals, and also functions as an endocrine organ in producing hormones, enzymes (e.g., renin), and vasoactive molecules (e.g., prostaglandins). Circulating catecholamines and autonomic innervation of the kidney can influence those important functional responses as well as vascular constriction via renal adrenergic receptors. The adrenergic receptors are members of a large family of G protein-coupled receptors. Recent advance of molecular cloning has revealed a growing heterogeneity of adrenergic receptor subtypes. They share a common topographical motif consisting of seven putative transmembrane regions, where. They are thought to be essential for ligand binding. Multiple subtypes of adrenergic receptors may exist in the kidney. Defining the precise role of renal adrenergic receptors in disease states, particularly hypertension, will certainly require the application of new tools of biochemistry and molecular biology.