A functional basis for classification of alpha-adrenergic receptors

Antidiarrheal and antioxidant activities of Ajuga iva (L.) leave extract

We studied the effect of Ajuga iva leaves extract (AIE) on the intestinal absorption, motricity and its antioxidant capacity against diarrhea. Wistar rats were divided and received either: castor oil (CO), CO and loperamide or CO and different doses of AIE. AIE prevented dose-dependently CO-induced diarrhea. AIE at 800 mg/kg showed inhibition efficiency on defecation and diarrhea. The pro-oxidant effect of the CO in the small intestine was inhibited significantly in presence of AIE: increasing glutathione peroxidase (GPx) activity and lowering oxygen free radicals (OH°, O2°-), carbonyl protein and malondialdehyde (MDA) levels. However, co-administration of AIE in castor oil-exposed groups significantly increased the intestinal contents of calcium and magnesium. AIE exhibits significant anti-diarrheal activity, related in part to its antioxidant properties. Our investigation also provides experimental evidence for the traditional use of this medicinal plant in the treatment of diarrhea.

Localization and neurochemical identity of alpha1-adrenergic receptor-containing elements in the mouse locus coeruleus

The locus coeruleus (LC) is the major source for norepinephrine (NE) in the brain and projects to areas involved in learning and memory, reward, arousal, attention, and autonomic functions related to stress. There are three types of adrenergic receptors that respond to NE: alpha1-, alpha2-, and beta-adrenergic receptors. Previous behavioral studies have shown the alpha1-adrenergic receptor (α1AR) to be present in the LC, however, with conflicting results. For example, it was shown that α1ARs in the LC are involved in some of the motivational effects of stimulation of the medial forebrain bundle, which was reduced by α1AR antagonist terazosin. Another study showed that during novelty-induced behavioral activation, the α1AR antagonist prazosin reduced c-fos expression in brain regions known to contain motoric α1ARs, except for the LC, where c-fos expression was enhanced. Despite new research delineating more specific connectivity of the neurons in the LC, and some roles of the adrenergic receptors, the α1ARs have not been localized at the subcellular level. Therefore, in order to gain a greater understanding of the aforementioned studies, we used immunohistochemistry at the electron microscopic (EM) level to determine which neuronal or glial elements in the LC express the α1AR. We hypothesized, based on previous work in the ventral periaqueductal gray area, that the α1AR would be found mainly presynaptically in axon terminals, and possibly in glial elements. Single labeling immunohistochemistry at the EM revealed that about 40% of labeled elements that contained the α1AR were glial elements, while approximately 50% of the labeled neuronal elements were axon terminals or small unmyelinated axons in the LC. Double labeling immunohistochemistry found the α1AR expressed in GFAP-labeled astrocytes, in both GABAergic and glutamatergic axon terminals, and in a portion of the α1AR dendrites, colocalized with tyrosine hydroxylase (TH, a marker for noradrenergic neurons). This study sheds light on the neuroanatomical framework underlying the effects of NE and pharmaceuticals acting directly or indirectly on α1ARs in the LC.

Spinal Transection Switches the Effect of Metabotropic Glutamate Receptor Subtype 7 from the Facilitation to Inhibition of Ejaculation

Metabotropic glutamate receptor subtype 7 (mGluR7) is a member of the group III mGluRs, which localize to presynaptic active zones of the central nervous system. We previously reported that mGluR7 knockout (KO) mice exhibit ejaculatory disorders, although they have normal sexual motivation. We hypothesized that mGluR7 regulates ejaculation by potentiating the excitability of the neural circuit in the lumbosacral spinal cord, because administration of the mGluR7-selective antagonist into that region inhibits drug-induced ejaculation. In the present study, to elucidate the mechanism of impaired ejaculation in mGluR7 KO mice, we eliminated the influence of the brain by spinal transection (spinalization). Unexpectedly, sexual responses of male mGluR7 KO mice were stronger than those of wild-type mice after spinalization. Histological examination indicated that mGluR7 controls sympathetic neurons as well as parasympathetic neurons. In view of the complexity of its synaptic regulation, mGluR7 might control ejaculation by multi-level and multi-modal mechanisms. Our study provides insight into the mechanism of ejaculation as well as a strategy for future therapies to treat ejaculatory disorders in humans.

Inter-Kingdom Signaling of Stress Hormones: Sensing, Transport and Modulation of Bacterial Physiology

Prokaryotes and eukaryotes have coexisted for millions of years. The hormonal communication between microorganisms and their hosts, dubbed inter-kingdom signaling, is a recent field of research. Eukaryotic signals such as hormones, neurotransmitters or immune system molecules have been shown to modulate bacterial physiology. Among them, catecholamines hormones epinephrine/norepinephrine, released during stress and physical effort, or used therapeutically as inotropes have been described to affect bacterial behaviors (i.e., motility, biofilm formation, virulence) of various Gram-negative bacteria (e.g., Escherichia coli, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa, Vibrio sp.). More recently, these molecules were also shown to influence the physiology of some Gram-positive bacteria like Enterococcus faecalis. In E. coli and S. enterica, the stress-associated mammalian hormones epinephrine and norepinephrine trigger a signaling cascade by interacting with the QseC histidine sensor kinase protein. No catecholamine sensors have been well described yet in other bacteria. This review aims to provide an up to date report on catecholamine sensors in eukaryotes and prokaryotes, their transport, and known effects on bacteria.

Pain Perception and Management: Where do We Stand?

BACKGROUND

Pain is often flammable, sharp and sometimes described as an electrical shock. It can be categorized in three different ways as nociceptive, neuropathic and inflammatory. Nociceptive pain always originates in specific situations such as in trauma. Neuropathic pain results in nerve damage. In inflammatory pain, inflammatory mediators are involved in the sensitization of nociceptors. It is important to control the pain as it affects the individual physically, mentally, and socially.

OBJECTIVE

Recognizing pain physiopathology and pain pathways, defining the relationship between receptor and transmitter is critical in developing new treatment strategies. In this review, current information on the definitions, classifications, and physiological and chemical mechanisms involved in pain are reviewed.

METHODS

Various search engines were used to gather related articles/information. Only peer-reviewed journals were considered. Additional, books/chapters of standard publishers were also included in the article.

RESULTS

With a better understanding of the physiological and chemical mechanisms that play a role in pain, significant improvements have been made in pain treatment. Various oral or intravenous drugs, local injection treatments, physical and occupational therapy, electrical stimulation, alternative medicine applications, psychological support, and surgical applications are routinely performed in the treatment, dependent upon the type, severity and cause of the pain.

CONCLUSION

Improved understanding of pain physiopathology will serve as the basis for future improvements in the delivery of efficacious and reliable treatments, and is likely to rely on novel technological innovations.

The Fish Pigment Cell: An Alternative Model in Biomedical Research

Receptor-mediated pigment aggregation within pigment cells (chromatophores) of an isolated fish scale is an ideal model system for functional receptor studies. The superficial layer of the scale contains both dermal chromatophores and postganglionic sympathetic nerves. By means of stimulation of the nerves, or by addition of appropriate receptor agonists, it is possible to elicit pigment aggregation within the chromatophores. A single fish can contribute hundreds of scales, various pharmacological and biochemical experiments are easily carried out and the physiological response, i.e. pigment aggregation, is readily evaluated by the aid of a light microscope or a simple scale photometer.

A denervation model, based on isolated scales, permits studies of factors involved in the sensitivity change, which typically takes place after experimental or pathological denervation.

By using isolated fish scales it is quite simple to illustrate many biomedically important concepts, like receptor theory and nerve-effector cell communication. This makes the scale a very useful preparation in biomedical education.

Adrenergic Signaling in Circadian Control of Immunity

Circadian rhythms govern a multitude of physiologic processes, both on a cell-intrinsic level and systemically, through the coordinated function of multi-organ biosystems. One such system-the adrenergic system-relies on the catecholamine neurotransmitters, adrenaline and noradrenaline, to carry out a range of biological functions. Production of these catecholamines is under dual regulation by both neural components of the sympathetic nervous system and hormonal mechanisms involving the hypothalamus-pituitary-adrenal axis. Importantly, both neural and hormonal arms receive input from the body's central clock, giving rise to the observed rhythmic variations in catecholamine levels in blood and peripheral tissues. Oscillations in catecholamine signals have the potential to influence various cellular targets expressing adrenergic receptors, including cells of the immune system. This review will focus on ways in which the body's central master clock regulates the adrenergic system to generate circadian rhythms in adrenaline and noradrenaline, and will summarize the existing literature linking circadian control of the adrenergic system to immunologic outcomes. A better understanding of the complex, multi-system pathways involved in the control of adrenergic signals may provide immunologists with new insight into mechanisms of immune regulation and precipitate the discovery of new therapeutics.

α 2-Adrenoceptors: Challenges and Opportunities-Enlightenment from the Kidney

It was indeed a Don Quixote-like pursuit of the mechanism of essential hypertension when we serendipitously discovered α₂-adrenoceptors (α₂-ARs) in skin-lightening experiments in the frog. Now α₂-ARs lurk on the horizon involving hypertension causality, renal denervation for hypertension, injury from falling in the elderly and prazosin's mechanism of action in anxiety states such as posttraumatic stress disorder (PTSD). Our goal here is to focus on this horizon and bring into clear view the role of α₂-AR-mediated mechanisms in these seemingly unrelated conditions. Our narrative begins with an explanation of how experiments in isolated perfused kidneys led to the discovery of a sodium-retaining process, a fundamental mechanism of hypertension, mediated by α₂-ARs. In this model system and in the setting of furosemide-induced sodium excretion, α₂-AR activation inhibited adenylate cyclase, suppressed cAMP formation, and caused sodium retention. Further investigations led to the realization that renal α₂-AR expression in hypertensive animals is elevated, thus supporting a key role for kidney α₂-ARs in the pathophysiology of essential hypertension. Subsequent studies clarified the molecular pathways by which α₂-ARs activate prohypertensive biochemical systems. While investigating the role of α₁-adrenoceptors (α₁-ARs) versus α₂-ARs in renal sympathetic neurotransmission, we noted an astonishing result: in the kidney α₁-ARs suppress the postjunctional expression of α₂-ARs. Here, we describe how this finding relates to a broader understanding of the role of α₂-ARs in diverse disease states. Because of the capacity for qualitative and quantitative monitoring of α₂-AR-induced regulatory mechanisms in the kidney, we looked to the kidney and found enlightenment.

β-adrenergic receptors in the up-regulation of COX2 expression and prostaglandin production in testicular macrophages: Possible relevance to male idiopathic infertility

Catecholaminergic neuronal elements (CNE) and macrophages (MACs) are increased in testes of patients with idiopathic infertility. Now, we describe an anatomical proximity between CNE and MACs, expression of specific α- and β-adrenergic receptors (ADRs) subtypes in MACs, and a positive correlation between the number of MACs and cyclooxygenase (COX2) expression - key enzyme in prostaglandin (PG) synthesis and an inflammatory marker - in testes of infertile men. To examine a potential effect of adrenergic input on COX2 expression, we used two additional experimental models: non-testicular human MACs (THP1 cell line) and non-human testicular MACs purified from adult Syrian hamsters. We found that epinephrine and norepinephrine up-regulate COX2 expression and PGD2 production through β1-and β2-ADRs. Our results demonstrate the existence of a yet unknown link between CNE and MACs in the human testis that could trigger inflammation and tissue homeostatic dysregulation associated with pathogenesis or maintenance of infertility states.

Impairment of natriuresis and diuresis induced by intrarenal adrenoceptor mechanisms in an experimental model of cirrhosis in rats

The contribution of intrarenal alpha-2 adrenergic receptors in mediating the enhanced renal excretory responses evoked by the alpha-2-agonist xylazine was examined in a model of cirrhosis in rats. In sham-operated rats, xylazine (0.2 mg/kg, i.v.) increased diuresis and natriuresis (urine flow, control: 78 ± 12.1, 10 min: 155 ± 17, 20 min: 194 ± 19, 30 min: 146 ± 16, 40 min: 114 ± 13, 50 min: 95 ± 10.5 μl/min/g; urinary sodium excretion, control: 6.75 ± 2.08, 10 min: 7.12 ± 2.1, 20 min: 13.4 ± 4.6, 30 min: 14.6 ± 4.02, 40 min: 12.05 ± 2.35, 50 min: 12.7 ± 2.45 μeq/min/g), which was accompanied by a significant reduction in renal sympathetic nerve activity (RSNA) (control: 100, 10 min: 39.5 ± 5.8, 20 min: 53 ± 8.8, 30 min: 72 ± 7.0, 40 min: 83 ± 5.0, 50 min: 94 ± 6.1 AU). Xylazine (0.2 mg/kg) in cirrhotic animals, despite resulting in a significant reduction in RSNA (control: 100, 10 min: 73 ± 4.3*, 20 min: 70 ± 5.0*, 30 min: 76 ± 7.0*, 40 min: 85 ± 5.5*, 50 min: 92 ± 4.8* AU), was unable to increase natriuresis. A higher dose (20 mg/kg) of xylazine was not capable of increasing natriuresis and diuresis, even in the presence of a robust reduction in RSNA. Renal denervation did not alter the onset and time course of cirrhosis. The results indicated that during the development of cirrhosis, there is an adaptive process that disables the intrarenal alpha-2 adrenoceptor mechanisms that selectively promote water and urinary sodium excretion via a sympathetic renal nerve-independent mechanism. Thus, in cirrhotic rats, the diuresis/natriuresis induced by xylazine is independent on RSNA. Intrarenal and/or hormonal changes are probably involved in the impairment of xylazine-induced diuresis/natriuresis in cirrhosis.

The pharmacology of α1-adrenoceptor subtypes

This review examines the functions of α₁-adrenoceptor subtypes, particularly in terms of contraction of smooth muscle. There are 3 subtypes of α₁-adrenoceptor, α_1A- α_1B- and α_1D-adrenoceptors. Evidence is presented that the postulated α_1L-adrenoceptor is simply the native α_1A-adrenoceptor at which prazosin has low potency. In most isolated tissue studies, smooth muscle contractions to exogenous agonists are mediated particularly by α_1A-, with a lesser role for α_1D-adrenoceptors, but α_1B-adrenoceptors are clearly involved in contractions of some tissues, for example, the spleen. However, nerve-evoked responses are the most crucial physiologically, so that these studies of exogenous agonists may overestimate the importance of α_1A-adrenoceptors. The major α₁-adrenoceptors involved in blood pressure control by sympathetic nerves are the α_1D- and the α_1A-adrenoceptors, mediating peripheral vasoconstrictor actions. As noradrenaline has high potency at α_1D-adrenceptors, these receptors mediate the fastest response and seem to be targets for neurally released noradrenaline especially to low frequency stimulation, with α_1A-adrenoceptors being more important at high frequencies of stimulation. This is true in rodent vas deferens and may be true in vasopressor nerves controlling peripheral resistance and tissue blood flow. The α_lA-adrenoceptor may act mainly through Ca²⁺ entry through L-type channels, whereas the α_1D-adrenoceptor may act mainly through T-type channels and exhaustable Ca²⁺ stores. α₁-Adrenoceptors may also act through non-G-protein linked second messenger systems. In many tissues, multiple subtypes of α-adrenoceptor are present, and this may be regarded as the norm rather than exception, although one receptor subtype is usually predominant.

What makes the α1A -adrenoceptor gene product assume an α1L -adrenoceptor phenotype?

The α_1A -adrenoceptor is abundantly expressed in the lower urinary tract and is the principal therapeutic target for the symptomatic treatment of lower urinary tract symptoms in men. Prazosin has a lower affinity for the lower urinary tract α_1A -adrenoceptor than α_1A -adrenoceptors found in other parts of the body. This has led to the lower urinary tract α_1A -adrenoceptor being subclassified as an α_1L -adrenoceptor. It was demonstrated that this pharmacologically distinct α_1L -adrenoceptor is a product of the α_1A -adrenoceptor gene, but the mechanism by which this altered phenotype is achieved remains a mystery. Hypotheses for this altered pharmacology include the presence of an interacting protein such as cysteine-rich with EGF-like domain (CRELD) 1 or other GPCRs such as the CXCR2 chemokine or 5-HT_1B receptor. Alternatively, the influence of breast cancer resistance protein (BCRP) efflux transporters on the pharmacology of α_1A -adrenoceptors has also been investigated. These and other hypotheses will be described and discussed in this review. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Is Tamsulosin Linked to Dementia in the Elderly?

PURPOSE OF REVIEW

Lower urinary tract symptoms (LUTS) result from age-related changes in detrusor function and prostatic growth that are driven by alterations in the ratio of circulating androgens and estrogens. Alpha-adrenergic receptor blockers are commonly used to treat LUTS because they influence urethral tone and intra-urethral pressure. Molecular cloning studies have identified three α₁-adrenergic receptor subtypes (α_1A, α_1B, and α_1D). The α_1A subtype is predominant in the human prostate but is also present in many parts of the brain that direct cognitive function. Tamsulosin is the most widely used α₁-adrenergic receptor antagonist with 12.6 million prescriptions filled in 2010 alone. When compared to the other common types of α₁-adrenergic receptor antagonists (i.e., terazosin, doxazosin, and alfuzosin), tamsulosin is 10- to 38-fold more selective for the α_1A versus the α_1B subtype.

RECENT FINDINGS

Duan et al. have recently shown that men taking tamsulosin have a higher risk of developing dementia when compared to men taking other α-adrenergic antagonists or no α-adrenergic antagonists at all (HR 1.17; 95% CI 1.14-1.21). Based upon this retrospective analysis, we believe that tamsulosin, because of its unique affinity for α_1A-adrenergic receptors, may increase the risk of developing dementia when used for an extended period of time. If these findings are confirmed, they carry significant public health implications for an aging society.

Early life stress induces long-term changes in limbic areas of a teleost fish: the role of catecholamine systems in stress coping

Early life stress (ELS) shapes the way individuals cope with future situations. Animals use cognitive flexibility to cope with their ever-changing environment and this is mainly processed in forebrain areas. We investigated the performance of juvenile gilthead seabream, previously subjected to an ELS regime. ELS fish showed overall higher brain catecholaminergic (CA) signalling and lower brain derived neurotrophic factor (bdnf) and higher cfos expression in region-specific areas. All fish showed a normal cortisol and serotonergic response to acute stress. Brain dopaminergic activity and the expression of the α_2Α adrenergic receptor were overall higher in the fish homologue to the lateral septum (Vv), suggesting that the Vv is important in CA system regulation. Interestingly, ELS prevented post-acute stress downregulation of the α_2Α receptor in the amygdala homologue (Dm3). There was a lack of post-stress response in the β₂ adrenergic receptor expression and a downregulation in bdnf in the Dm3 of ELS fish, which together indicate an allostatic overload in their stress coping ability. ELS fish showed higher neuronal activity (cfos) post-acute stress in the hippocampus homologue (Dlv) and the Dm3. Our results show clear long-term effects on limbic systems of seabream that may compromise their future coping ability to environmental challenges.

Hypertension's 3 Dilemmas and 3 Solutions: Pharmacology of the Kidney in Hypertension

The Hypertension Community has 3 conflicting dilemmas: a goal systolic pressure of 120 mm Hg or less (the SPRINT Trials), 40% of our 60,000,000 hypertensives still sustain blood pressures above 140/90 mm Hg, and our most potent antihypertensive drug minoxidil sits on the sidelines, imprisoned in the Food and Drug Administration's Black Box designation. My solutions to these dilemmas are: (1) review of the facts of our most potent antihypertensive drug minoxidil which is essentially free of toxicity, (2) treatment focus on the fundamental cause of high blood pressure, that is excess dietary sodium and, (3) prevention of, and/or reversal of, the fundamental mechanism of worsening hypertension, arteriolar hypertrophy.

SUMMARY

The Hypertension Community has 3 conflicting dilemmas: a goal systolic pressure of 120 mm Hg or less (the SPRINT Trials), 40% of our 60,000,000 hypertensives still sustain blood pressures above 140/90 mm Hg, and our most potent antihypertensive drug minoxidil sits on the sidelines, imprisoned in the Food and Drug Administration's Black Box designation. My solutions to these dilemmas are: (1) review of the facts of our most potent antihypertensive drug minoxidil which is essentially free of toxicity, (2) treatment focus on the fundamental cause of high blood pressure (HBP) and excess dietary sodium and, (3) prevention of, and/or reversal of, the fundamental mechanism of worsening hypertension, arteriolar hypertrophy. My focus at UT Southwestern in Dallas was on extremely severely hypertensive patients with a quantifiable, measurable complication of HBP, progression of nephrosclerotic damage to kidneys. This model had the greatest likelihood of exposing fundamental disregulatory mechanisms in hypertensive patients (which it did) and the potential for study of the most relevant antihypertensive drug interactions to achieve optimal blood pressure control (which it did). By maintaining diastolic pressures at 80 mm Hg or less in the first National Institutes of Health-supported, long-term randomized clinical trial to save the kidneys, the bases for a fundamental blood pressure support mechanism (arteriolar hypertrophy) was illuminated but not fully described until now. This fundamental hypertensinogenic mechanism results from HBP but with time and severity, becomes its own raison d'être. I am now aged 84 years. As a result of a stroke 20 years ago, which caused permanent double vision, and because of poor blood pressure control with triple therapy, I started using minoxidil 5 mg/d along with atenolol and occasional furosemide. Now, along with some dietary salt restriction, my resting blood pressure is 110/65-125/75 and, despite >30 years history of HBP, I have no retinal arteriolar hypertrophy nor arcus senilis (Dr. Schwartz-U. of Miami) which is almost universally present at this age. Yes, prevention of, or reversal of, arteriolar hypertrophy should be a central focus of HBP treatment. I simply wish to share a bit of accumulated wisdom that might be of use to others.

Role of gastrointestinal motility inhibition and antioxidant properties of myrtle berries (Myrtus communis L.) juice in diarrhea treatment

INTRODUCTION

The myrtle (Myrtus communis) belongs to the Myrtaceae family; it is one of the central plants as part of the list of medicinal plants in the Tunisian Pharmacopoeia. Myrtle berry was used for its astringent, tonic, and antiseptic properties, to treat diarrhea, hemorrhoids, and gastrointestinal injury.

METHODS

Adult male wistar rats were used to evaluate the normal gastro-intestinal transit and gastric emptying as well as castor oil-induced diarrhea, enteropooling tests, and small intestine oxidative stress. The effect of myrtle berries juice (MBJ) (5 and 10ml/kg, bw. p.o.) was after compared to the loperamide and clonidine effects.

RESULTS

MBJ significantly and dose-dependently inhibited the intestinal motility and gastric emptying. We also found that MBJ administration induced a significant dose-dependent protection against diarrhea and intestinal fluid accumulation. Castor oil-induced intestinal hypersecretion was accompanied by an oxidative stress status in the intestine, which was attenuated by MBJ administration.

CONCLUSION

We suggest that MBJ had a potent protective effects against castor oil-induced diarrhea in part due, to its antioxidant and antisecretory properties.

A targeted genome association study examining transient receptor potential ion channels, acetylcholine receptors, and adrenergic receptors in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Background

Chronic Fatigue Syndrome, also known as Myalgic Encephalomyelitis (CFS/ME) is a debilitating condition of unknown aetiology. It is characterized by a range of physiological effects including neurological, sensory and motor disturbances. This study examined candidate genes for the above clinical manifestations to identify single nucleotide polymorphism (SNP) alleles associated with CFS/ME compared with healthy controls.

Methods

DNA was extracted and whole genome genotyping was performed using the HumanOmniExpress BeadChip array. Gene families for transient receptor potential ion channels, acetylcholine receptors, and adrenergic receptors, and acetylcholinesterase were targeted. The frequency of each SNP and their association between CFS/ME and healthy controls was examined using Fisher’s exact test, and to adjust for multiple testing, False Detection Rate (FDR) and Bonferroni corrections were applied (p < 0.05).

Results

The study included 172 participants, consisting of 95 Fukuda defined CFS/ME patients (45.8 ± 8.9; 69 % female) and 77 healthy controls (42.3 ± 10.3; 63 % female). A total of 950 SNPs were included for analysis. 60 significant SNPs were associated with CFS/ME compared with healthy controls. After applying FDR and Bonferroni corrections, SNP rs2322333 in adrenergic receptor α1 (ADRA1A) was higher in CFS/ME compared with healthy controls (45.3 % vs. 23.4 %; p = 0.059). The genotype class that was homozygous minor (AA) was substantially lower in CFS/ME compared with healthy controls (4.2 % vs. 24.7 %).

Conclusions

This study reports for the first time the identification of ADRA1A and a possible association between CFS/ME and genotype classes. Further examination of the functional role of this class of adrenergic receptors may elucidate the cause of particular clinical manifestations observed in CFS/ME.

Adrenergic and noradrenergic regulation of poultry behavior and production

Norepinephrine and epinephrine (noradrenaline and adrenaline) are integral in maintaining behavioral and physiological homeostasis during both aversive and rewarding events. They regulate the response to stressful stimuli through direct activation of adrenergic receptors in the central and sympathetic nervous systems, hormonal activity and through the interaction of the brain, gut, and microbiome. The multiple functions of these catecholamines work synergistically to prepare an individual for a "fight or flight" response. However, hyper-reactivity of this system can lead to increased fearfulness and aggression, decreased health and productivity, and a reduction in overall well-being. Behaviors, such as aggression and certain fear-related behaviors, are a serious problem in the poultry industry that can lead to injury and cannibalism. For decades, catecholamines have been used as a measure of stress in animals. However, few studies have specifically targeted the adrenergic systems as means to reduce behaviors that are damaging or maladapted to their rearing environments and improve animal well-being. This article attempts to address our current understanding of specific, adrenergic-regulated behaviors that impact chicken well-being and production.

Overview of the Anatomy, Physiology, and Pharmacology of the Autonomic Nervous System

Comprised of the sympathetic nervous system, parasympathetic nervous system, and enteric nervous system, the autonomic nervous system (ANS) provides the neural control of all parts of the body except for skeletal muscles. The ANS has the major responsibility to ensure that the physiological integrity of cells, tissues, and organs throughout the entire body is maintained (homeostasis) in the face of perturbations exerted by both the external and internal environments. Many commonly prescribed drugs, over-the-counter drugs, toxins, and toxicants function by altering transmission within the ANS. Autonomic dysfunction is a signature of many neurological diseases or disorders. Despite the physiological relevance of the ANS, most neuroscience textbooks offer very limited coverage of this portion of the nervous system. This review article provides both historical and current information about the anatomy, physiology, and pharmacology of the sympathetic and parasympathetic divisions of the ANS. The ultimate aim is for this article to be a valuable resource for those interested in learning the basics of these two components of the ANS and to appreciate its importance in both health and disease. Other resources should be consulted for a thorough understanding of the third division of the ANS, the enteric nervous system. © 2016 American Physiological Society. Compr Physiol 6:1239-1278, 2016.

Isoproterenol acts as a biased agonist of the alpha-1A-adrenoceptor that selectively activates the MAPK/ERK pathway

The α_1A-AR is thought to couple predominantly to the Gα_q/PLC pathway and lead to phosphoinositide hydrolysis and calcium mobilization, although certain agonists acting at this receptor have been reported to trigger activation of arachidonic acid formation and MAPK pathways. For several G protein-coupled receptors (GPCRs) agonists can manifest a bias for activation of particular effector signaling output, i.e. not all agonists of a given GPCR generate responses through utilization of the same signaling cascade(s). Previous work with Gα_q coupling-defective variants of α_1A-AR, as well as a combination of Ca²⁺ channel blockers, uncovered cross-talk between α_1A-AR and β₂-AR that leads to potentiation of a Gα_q-independent signaling cascade in response to α_1A-AR activation. We hypothesized that molecules exist that act as biased agonists to selectively activate this pathway. In this report, isoproterenol (Iso), typically viewed as β-AR-selective agonist, was examined with respect to activation of α_1A-AR. α_1A-AR selective antagonists were used to specifically block Iso evoked signaling in different cellular backgrounds and confirm its action at α_1A-AR. Iso induced signaling at α_1A-AR was further interrogated by probing steps along the Gα_q /PLC, Gα_s and MAPK/ERK pathways. In HEK-293/EBNA cells transiently transduced with α_1A-AR, and CHO_α_1A-AR stable cells, Iso evoked low potency ERK activity as well as Ca²⁺ mobilization that could be blocked by α_1A-AR selective antagonists. The kinetics of Iso induced Ca²⁺ transients differed from typical Gα_q- mediated Ca²⁺ mobilization, lacking both the fast IP₃R mediated response and the sustained phase of Ca²⁺ re-entry. Moreover, no inositol phosphate (IP) accumulation could be detected in either cell line after stimulation with Iso, but activation was accompanied by receptor internalization. Data are presented that indicate that Iso represents a novel type of α_1A-AR partial agonist with signaling bias toward MAPK/ERK signaling cascade that is likely independent of coupling to Gα_q.

Disruption of aminergic signalling reveals novel compounds with distinct inhibitory effects on mosquito reproduction, locomotor function and survival

Insecticide resistance amongst disease vectors is a growing problem and novel compounds are needed. Biogenic amines are important for neurotransmission and we have recently shown a potential role for these in mosquito fertility. Here, we dissected the relative contribution of different aminergic signalling pathways to biological processes essential for vectorial capacity such as fertility, locomotion and survival by injecting agonists and antagonists and showed that octopaminergic/tyraminergic signalling is essential for oviposition and hatching rate. We show that egg melanisation is regulated by adrenergic signalling, whose disruption causes premature melanisation specifically through the action of tyramine. In addition to this, co-injection of tyramine with DOPA, the precursor of melanin, had a strong cumulative negative effect on mosquito locomotion and survival. Dopaminergic and serotonergic antagonists such as amitriptyline and citalopram recapitulate this effect. Together these results reveal potential new target sites for the development of future mosquito sterilants and insecticides.

Effect of Clonidine (an antihypertensive drug) treatment on oxidative stress markers in the heart of spontaneously hypertensive rats

Hypertension is a risk factor for several cardiovascular diseases and oxidative stress suggested to be involved in the pathophysiology. Antihypertensive drug Clonidine action in ameliorating oxidative stress was not well studied. Therefore, this study investigate the effect of Clonidine on oxidative stress markers and nitric oxide (NO) in SHR and nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) administered SHR. Male rats were divided into four groups [SHR, SHR+Clonidine (SHR-C), SHR+L-NAME, SHR+Clonidine+L-NAME(SHRC+L-NAME)]. Rats (SHRC) were administered with Clonidine (0.5 mg kg⁻¹ day⁻¹) from 4 weeks to 28 weeks in drinking water and L-NAME (25 mg kg⁻¹ day⁻¹) from 16 weeks to 28 weeks to SHRC+L-NAME. Systolic blood pressure (SBP) was measured. At the end of 28 weeks, all rats were sacrificed and in their heart homogenate, oxidative stress parameters and NO was assessed. Clonidine treatment significantly enhanced the total antioxidant status (TAS) (P < 0.001) and reduced the thibarbituric acid reactive substances (TBARS) (P < 0.001) and protein carbonyl content (PCO) (P < 0.05). These data suggest that oxidative stress is involved in the hypertensive organ damage and Clonidine not only lowers the SBP but also ameliorated the oxidative stress in the heart of SHR and SHR+L-NAME.

Prediction of drug combinations by integrating molecular and pharmacological data

Combinatorial therapy is a promising strategy for combating complex disorders due to improved efficacy and reduced side effects. However, screening new drug combinations exhaustively is impractical considering all possible combinations between drugs. Here, we present a novel computational approach to predict drug combinations by integrating molecular and pharmacological data. Specifically, drugs are represented by a set of their properties, such as their targets or indications. By integrating several of these features, we show that feature patterns enriched in approved drug combinations are not only predictive for new drug combinations but also provide insights into mechanisms underlying combinatorial therapy. Further analysis confirmed that among our top ranked predictions of effective combinations, 69% are supported by literature, while the others represent novel potential drug combinations. We believe that our proposed approach can help to limit the search space of drug combinations and provide a new way to effectively utilize existing drugs for new purposes.

Outcomes and quality of life issues in the pharmacological management of benign prostatic hyperplasia (BPH)

BACKGROUND

Benign prostatic hyperplasia (BPH) is a common disease of the aging male population. BPH treatment includes a variety of pharmacological and surgical interventions. The goal of this paper is to review the natural history of BPH, outcomes of pharmacological management, effects on quality of life (QoL), future pharmacotherapies, and associated patient-focused perspectives.

MATERIALS AND METHODS

Medline searches for the keywords benign prostatic hyperplasia, BPH, alpha blockers, 5 alpha-reductase, and quality of life were performed. Relevant literature was reviewed and analyzed.

RESULTS

Alpha blockers, 5 alpha-reductase inhibitors, and phytotherapy are the three categories of pharmaceutical interventions currently available for BPH. Various clinical trials have shown that alpha blockers and 5 alpha-reductase inhibitors are safe, efficacious, and improve QoL in patients with BPH. The evidence for phytotherapeutics is not as convincing. The current armamentarium of pharmaceutical interventions are encompassed in these three classes of medications. New pharmacotherapies based on novel mechanisms are on the horizon.

CONCLUSION

There are a variety of safe and efficacious medical therapies available for the management of BPH and it is important for the practicing physician to have an understanding of these pharmacotherapies and their potential impact on the patient. There is not enough evidence to make a recommendation regarding phytotherapy use. New classes of drugs for BPH will likely find their way into routine use.

α2C-adrenoceptor modulators: a patent review

INTRODUCTION

α2-Adrenoceptors (α2-ARs) are membrane proteins belonging to the superfamily of GPCRs. Detailed studies have shown three different subtypes, namely α2A, α2B and α2C. Although numerous α2-AR ligands exist, only a small set of compounds have shown even a degree of selectivity among the three α2-AR subtypes. Moreover, these compounds suffer from binding to receptor sites outside the α2-AR subfamily. Efforts made to understand the biological significance of each α2-AR subtype have greatly been assisted by genetically engineered mice. The main results obtained suggest that α2C-AR stimulation may represent a therapeutic strategy to get an analgesic response with reduced sedative effects and undesirable changes in blood pressure due to α2A-AR activation.

AREAS COVERED

This review summarizes the patent literature about the development of α2C-AR modulators from 2000 to early 2010 and their therapeutic effects evoked by the interaction with this receptor subtype.

EXPERT OPINION

Over 90 patents have been deposited in the last 10 years regarding different methods of α2C-AR modulation (use of agonists or antagonists, nucleic acids and polypeptides) for diagnosis, prognosis and treatment of disorders involving this receptor. Nevertheless, despite the numerous published patents, ligands highly selective for the α2C-AR subtype, which continues to be enigmatic, are lacking.

Adrenergic receptors. Methods of determination and mechanisms of regulation

The radioligand binding technique has been proven useful in the study of altered responsiveness after exposure to adrenergic agents. A reduction in receptor number has generally been reported after interventions serving to increase the stimulatory input to the receptors prior to assay. Conversely a decrease in receptor stimulation has been demonstrated to induce an elevation in receptor density. These phenomena have been described for alpha- as well as for beta-adrenoceptors in various tissues under a variety of experimental conditions such as prolonged agonist exposure, chronic receptor blockade, denervation and interference with catecholamine turnover. A number of clinically relevant cardiovascular experimental models have been characterized by altered adrenoceptor densities, possibly reflecting a compensatory resetting of sympathetic tone in response to an aberrant haemodynamic pattern. The mechanisms underlying receptor density changes as those discussed have been suggested to involve an internalization process which may involve phospholipase and transglutaminase activation in the cell membrane.

Intravenous naphazoline intoxication

Nine pale perspiring drug addicts with drowsiness, nausea, headache, normal blood pressure and marked sinus bradycardia with premature ventricular beats were seen at the Casualty Department soon after alleged i.v. cocaine administration. Eight were treated with atropine, as the bradycardia suggested intoxication with a parasympathomimetic compound. Seven were discharged in good condition after a few hours' observation. One patient developed a blood pressure of 150/120 mmHg after atropine. Subsequently, a hemiparesis was found and an intracerebral haematoma was evaluated at surgery. Another patient was admitted forthwith to the CCU. He did not receive any medication and recovered within two days. Urinalysis of these two patients disclosed contents of naphazoline, a powerful alpha-adrenergic agent. Samples of the alleged cocaine contained 97% naphazoline HCl. A conscious rabbit was injected with naphazoline and thereafter with atropine. I.v. naphazoline doubled mean arterial pressure (MAP) and reduced heart rate (HR) from 167 to 30 beats/min. Atropine doubled HR, but caused a marked rise in MAP, too, stressing the adverse effects of atropine in these cases. When confronted with patients after alleged cocaine abuse, the role of substitute drugs, especially alpha-adrenergic compounds, should be considered as this should influence the therapeutic approach.

Adrenergic receptors: classification, ligand binding and molecular properties

The interaction of catecholamines and drugs with adrenergic receptors leads to a set of biochemical reactions which ultimately results in a physiological response. A brief review is given of the classification of adrenergic receptors into subtypes and the use of ligand binding techniques for the identification and characterization of these receptors. Recent advances in the biochemistry of adrenergic receptors are reviewed with special reference to the interaction of the beta and alpha 2-receptors with guanine nucleotide regulatory proteins and adenylate cyclase. The role of calcium and phosphoinositides in the function of the alpha 1-receptor is also discussed.

Differences in postsynaptic alpha-adrenoceptor populations between isolated cat urethra and various other isolated tissues

This study was undertaken with the aim of determining whether the postsynaptic alpha-adrenergic receptor population of the cat urethra differed from that of other isolated tissues (rabbit aorta and rat vas deferens) and if so the possibility of selectively affect these receptors. For this purpose the substances 2-methylammonio-1-(spiro[cyclopentane-1,1'-indene]-3'-yl)ethanol (KABI 2023), noradrenaline (NA) and dopamine (DA) were used. KABI 2023 and NA acted as full agonists on all three tissues investigated. DA was a full agonist on the vas deferens but was almost inactive on urethra. The contractile response of urethra to KABI 2023 was of an alpha-adrenergic nature, as it could be blocked with phentolamine. Compared with NA, KABI 2023 showed a 10 times higher selectivity for the receptors of urethra than for those of aorta. Affinity constants (log KB) for phentolamine and haloperidol with use of the various agonists were estimated. The affinity of phentolamine was found to be significantly different when using NA and KABI 2023 as agonists on the urethra but not on the aorta. Corresponding findings were obtained with haloperidol. On the vas deferens a greater difference in log KB values than that on the urethra was found. On the basis of the results, it is suggested that the population of postsynaptic alpha-adrenoceptors in the urethra (cat) differs from that in the aorta (rabbit). On the vas deferens a heterogenicity of postsynaptic receptors seem to exist which makes the interpretation of the results more difficult on this organ. In the presence of phentolamine and haloperidol the maximum responses to NA were potentiated on the aorta and vas deferens, but not on the urethra. Investigations to evaluate this difference are now in progress.

Anti-diarrhoeal activity of the aqueous extract of Mezoneuron benthamianum Baill (Caesalpiniaceae)

The effect of the aqueous extract of Mezoneuron benthamianum (MB) on experimentally induced diarrhoea, intestinal propulsive movement (IPM) and intestinal fluid accumulation (enteropooling) were investigated in rats and mice. The extract (400, 800 and 1600 mg/kg, orally) produced a significant (p<0.05) and dose-dependent reduction in propulsion in the castor oil-induced intestinal transit in mice. The mean peristaltic index (%) for these doses of extract, control, (distilled water, 10 ml/kg, p.o.) and morphine, (10 mg/kg, s.c.) were 73.48, 69.34, 57.27, 89.93 and 31.56, respectively. The effect of the extract at the highest dose was significantly (p<0.05) lower than that of the standard drug. This effect was antagonised by yohimbine (1mg/kg, s.c.). In a dose-dependent manner, the extract delayed the onset of diarrhoea, produced a significant decrease in the frequency of defaecation, severity of diarrhoea and protected the mice treated with castor oil. Total diarrhoea scores were 12.0+/-0.63, 10.3+/-2.06, 8.5+/-2.15, 7.1+/-0.91 and 5.8+/-0.79 for control, extract (400, 800 and 1600 mg/kg) and morphine, respectively. The extract significantly decreased the volume (ml) of intestinal fluid secretion induced by castor oil (1.75+/-0.02 to 0.93+/-0.04) compared with 1.90+/-0.05 for control. The inhibitory effect on fluid accumulation by the extract was also attenuated by yohimbine (1.0 mg/kg). Preliminary phytochemical screening revealed the presence of flavonoids, tannins, cardiac glycosides, anthraquinones and saponins. Administration of the extract up to 2 g/kg (orally) did not produce any toxic effect in the acute toxicity studies in mice. The LD(50) of the extract when given intraperitoneally was 1021.31 mg/kg. The results obtained show that MB possesses anti-diarrhoeal activity due to its inhibitory effects on gastrointestinal propulsion and intestinal fluid accumulation. The antagonistic actions of yohimbine in the experiments suggest a role for the a(2)-adrenergic receptor system.

Cellular and subcellular localization of alpha-1 adrenoceptors in the rat visual cortex

Noradrenaline is thought to play modulatory roles in a number of physiological, behavioral, and cellular processes. Although many of these modulatory effects are mediated through alpha-1 adrenoceptors, basic knowledge of the cellular and subcellular distributions of these receptors is limited. We investigated the laminar distribution pattern of alpha-1 adrenoceptors in rat visual cortex, using immunohistochemistry at both light and electron microscopic levels. Affinity-purified anti-alpha-1 antibody was confirmed to react only with a single band of about 70-80 kDa in total proteins prepared from rat visual cortex. Alpha-1 adrenoceptors were widely distributed though all cortical layers, but relatively high in density in layers I, II/III, and V. Immunoreactivity was observed in both neuronal perikarya and processes including apical dendrites. In double-labeling experiments with anti-microtubule-associated protein 2, anti-neurofilament, anti-glial fibrillary acidic protein, anti-glutamic acid decarboxylase 65/67, anti-2-3-cyclic nucleotide 3-phosphodiesterase, and anti-tyrosine hydroxylase antibodies, alpha-1 adrenoceptors were found mainly in dendrites and somata of microtubule-associated protein 2-immunopositive neurons. About 20% of alpha-1 adrenoceptors were in GABAergic neurons. A small number of alpha-1 adrenoceptors were also distributed in axons of excitatory neurons, astrocytes, oligodendrocytes and noradrenergic fibers. Using an immunoelectron microscopic technique, numerous regions of alpha-1 adrenoceptor immunoreactivity were found in cell somata, on membranes of dendrites, and in postsynaptic regions. Moreover, a small number of immunoreaction products were also detected in axons and presynaptic sites. These findings provide the first quantitative evidence regarding the cellular and subcellular localization of alpha-1 adrenoceptor immunoreactivity in visual cortex. Moreover, the ultrastructural distribution of alpha-1 adrenoceptor immunoreactivity suggests that alpha-1 adrenoceptors are transported mainly into dendrites and that they exert effects at postsynaptic sites of neurons.

Are so many adrenergic receptor subtypes really present in domestic animal tissues? A pharmacological perspective

Adrenergic receptors (ARs) are the cellular membrane binding sites through which natural catecholamines and sympathomimetic drugs exert their physiological and pharmacological effects. In recent decades, studies to clarify the distribution and function of ARs have been performed mostly on cultured cells, laboratory animals and human target tissues, but little is known about these aspects in domestic animals. This review focuses on AR structure, classification and signalling pathways and on AR subtype distribution in target tissues of some domestic animals, namely dogs, horses and bovines. In these species, different alpha- and beta-AR subtypes have been characterized and the functions controlled by the adrenergic systems have been studied. In the dog, the role played by the adrenergic system in the pathogenesis of cardiovascular disorders and in the modulation of canine aggression has roused particular interest. In dogs affected by dilated cardiomyopathy a significant down-regulation of beta-ARs has been observed both in the heart and circulating lymphocytes. This finding confirms the involvement of the adrenergic system in the pathogenesis and progression of the disorder and suggests new therapeutic strategies. In the horse, AR distribution has been studied in the cardiac, respiratory and gastrointestinal systems as well as in digital veins and arteries. The cardiac beta-ARs in healthy horses seem to be predominantly represented by the beta(1) subtype. In this species, heart failure may increase the expression of the beta(2) subtype, rather than causing AR down-regulation. Different beta- and alpha-AR subtypes have been characterized in the smooth muscle of equine ileum. The sympathetic relaxation of equine ileum smooth muscle seems to depend mainly on beta(3)-AR subtype activation, with minor involvement of the beta(2) subtype. In the respiratory tract, regional differences have been evidenced in the functionality of beta-AR subtype. The beta(2) subtype predominates in all segments but the beta(2) subtype-mediated adenyl cyclase response is tissue-dependent, with higher activity in tracheal membranes than bronchial or pulmonary ones. Both alpha- and beta-AR subtypes are present in the genital tract of cows. Bovine ovarian and myometrial cell membranes express higher concentrations of beta(2)-ARs than the beta(1) subtype, whereas as far as alpha-ARs are concerned, a single class of alpha(1)-ARs and two distinct classes of alpha(2)-AR binding sites have been discriminated. Interestingly, it has been observed that the activation of the sympathetic system could play an important role in the pathogenesis of bovine ovarian cysts as suggested by the modifications in beta-AR levels in the hypophysis and ovary of cows affected by ovarian cysts. In this species, the phenomenon of down-regulation has been well studied in different organs of veal calves treated with clenbuterol as a "partitioning agent". Since differences exist in AR distribution among species, data obtained in laboratory animals or in human beings cannot be extrapolated to domestic animals and further investigation on AR subtypes in domestic animal tissues is necessary.

Reduction of adrenergic neurotransmission with clonidine aggravates spike-wave seizures and alters activity in the cortex and the thalamus in WAG/Rij rats

The alpha-2 adrenoreceptor agonist clonidine in low dose inhibits the release of noradrenaline and aggravates absence seizures. The present study examines properties of two types of spike-wave discharges (SWD) in a genetic model of absence epilepsy, the WAG/Rij rats. After reduction of noradrenergic neurotransmission with clonidine (0.00625 mg/kg, i.p.), the electrical activity was recorded in the neocortex, the ventroposteromedial nucleus (VPM) and the reticular thalamic nucleus (RTN). Clonidine temporally reduced percentage of wakefulness but did not affect sleep. Clonidine decreased the spectral power of sleep EEG (mostly in the delta band), this effect was found in the cortex and in the VPM. Clonidine increased the incidence of SWD type I (generalized); the spectral power of SWD I was lower in the frontal cortex (mostly in 1-9 and 30-100 Hz) and in the VPM (1-5 Hz), but higher in the RTN (9-14 Hz). Local occipital SWD (type II) had a tendency to be less numerous after clonidine, they had a lower power in the 5-9 Hz band in the occipital cortex, in the VPM and in the RTN. It can be concluded that strengthening of 9-14 Hz activity in the RTN may underlie clonidine-induced aggravation of SWD I.

Haplotype-based analysis of alpha 2A, 2B, and 2C adrenergic receptor genes captures information on common functional loci at each gene

The alpha 2-adrenergic receptors (alpha2-AR) mediate physiological effects of epinephrine and norepinephrine. Three genes encode alpha2-AR subtypes carrying common functional polymorphisms (ADRA2A Asn251Lys, ADRA2B Ins/Del301-303 and ADRA2C Ins/Del322-325). We genotyped these functional markers plus a panel of single nucleotide polymorphisms evenly spaced over the gene regions to identify gene haplotype block structure. A total of 24 markers were genotyped in 96 Caucasians and 96 African Americans. ADRA2A and ADRA2B each had a single haplotype block at least 11 and 16 kb in size, respectively, in both populations. ADRA2C had one haplotype block of 10 kb in Caucasians only. For the three genes, haplotype diversity and the number of common haplotypes were highest in African Americans, but a similar number of markers (3-6) per block was sufficient to capture maximum diversity in either population. For each of the three genes, the haplotype was capable of capturing the information content of the known functional locus even when that locus was not genotyped. The alpha2-AR haplotype maps and marker panels are useful tools for genetic linkage studies to detect effects of known and unknown alpha2-AR functional loci.

Isoflurane sparing action of epidurally administered xylazine hydrochloride in anesthetized dogs

OBJECTIVE

To evaluate the influence of epidural administration of xylazine hydrochloride on the minimum alveolar concentration of isoflurane (MAC(ISAO)) and cardiopulmonary system in anesthetized dogs.

ANIMALS

6 clinically normal dogs.

PROCEDURE

Dogs were anesthetized with isoflurane in oxygen after randomly being assigned to receive 1 of the following 4 treatments: epidural administration of saline (0.9% NaCl) solution or xylazine at a dose of 0.1, 0.2, or 0.4 mg x kg(-1). Experiments were performed on 5 occasions with at least a 1-week interval between experiments; each dog received all 4 treatments. Following instrumentation, the concentration of isoflurane was maintained constant for 15 minutes at the MAC(ISO) that had been determined for each dog, and data on heart rate, arterial blood pressure, respiratory rate, tidal volume, minute volume, arterial partial pressure of oxygen, arterial partial pressure of carbon dioxide, and arterial pH were collected. The epidural treatment was administered, and 30 minutes later, data were again collected. From this point on, determination of the MAC(ISO) following epidural treatment (ie, MAC(ISO+EPI)) was initiated. Cardiopulmonary data were collected before each electrical supramaximal stimulus during MAC(ISO+EPI) determinations.

RESULTS

The mean (+/-SD) MAC(ISO) was 1.29 +/- 0.04%. The epidural administration of xylazine at doses of 0.1, 0.2, and 0.4 mg x kg(-1) decreased the MAC(ISO), respectively, by 8.4 +/- 2.4%, 21.7 +/- 4.9%, and 33.4 +/- 2.64%. Cardiopulmonary effects were limited.

CONCLUSIONS AND CLINICAL RELEVANCE

Epidural administration of xylazine decreases the MAC(ISO) in a dose-dependent manner and is associated with few cardiopulmonary effects in anesthetized dogs.

Yohimbine reverses the exhaustion of the coital reflex in spinal male rats

The possible participation of the central noradrenergic system in the expression of the ejaculatory reflex of the rat was explored by evaluating the effects of the alpha(2)-adrenoceptor antagonist, yohimbine, on the exhausted coital reflex model. Male sexually experienced Wistar rats, subjected to the coital reflex exhaustion paradigm received a single i.v. injection of yohimbine (10 microg/animal), immediately after reaching exhaustion. Enhancement of noradrenergic transmission by yohimbine provoked the immediate expression of a single ejaculatory genital motor pattern (GMP) similar to a first reflexively evoked one, but in the absence of urethral mechanical stimulation. Pre-treatment with clonidine (10 microg/animal) completely prevented the yohimbine-induced GMP, implying that its effect was exerted upon alpha(2)-adrenoceptors. Clonidine treatment per se induced the expression of a single GMP, similar to a last reflexively evoked one, that was completely blocked by pre-treatment with prazosin (1 microg/animal) indicating that it was due to the alpha(1) properties of clonidine. Administration of prazosin previous to yohimbine did not interfere with the expression of the GMP but attenuated it, suggesting the involvement of alpha(1)-adrenoceptors in the yohimbine-induced motor response. Data reveal a facilitatory influence of the noradrenergic system on ejaculatory function mediated by both alpha(1)- and alpha(2)-adrenoceptors and support the notion of yohimbine acting at a spinal level.