The β3‐adrenoceptor was initially an attractive target for several pharmaceutical companies due to its high expression in rodent adipose tissue, where its activation resulted in decreased adiposity ...and improved metabolic outputs (such as glucose handling) in animal models of obesity and Type 2 diabetes. However, several drugs acting at the β3‐adrenoceptor failed in clinical trials. This was thought to be due to their lack of efficacy at the human receptor. Recently, mirabegron, a β3‐adrenoceptor agonist with human efficacy, was approved in North America, Europe, Japan and Australia for the treatment of overactive bladder syndrome. There are indications that mirabegron may act at other receptors/targets, but whether they have any clinical relevance is relatively unknown. Besides overactive bladder syndrome, mirabegron may have other uses such as in the treatment of heart failure or metabolic disease. This review gives an overview of the off‐target effects of mirabegron and its potential use in the treatment of other diseases.
Linked Articles
This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc
The α1A‐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 α1A‐adrenoceptor than α1A‐adrenoceptors found in other parts of the body. This has led to the lower urinary tract α1A‐adrenoceptor being subclassified as an α1L‐adrenoceptor. It was demonstrated that this pharmacologically distinct α1L‐adrenoceptor is a product of the α1A‐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‐HT1B receptor. Alternatively, the influence of breast cancer resistance protein (BCRP) efflux transporters on the pharmacology of α1A‐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
Background and Purpose
Agonists acting at GPCRs promote biased signalling via Gα or Gβγ subunits, GPCR kinases and β‐arrestins. Since the demonstration of biased agonism has implications for drug ...discovery, it is essential to consider confounding factors contributing to bias. We have examined bias at human α1A‐adrenoceptors stably expressed at low levels in CHO‐K1 cells, identifying off‐target effects at endogenous receptors that contribute to ERK1/2 phosphorylation in response to the agonist oxymetazoline.
Experimental Approach
Intracellular Ca2+ mobilization was monitored in a Flexstation® using Fluo 4‐AM. The accumulation of cAMP and ERK1/2 phosphorylation were measured using AlphaScreen® proximity assays, and mRNA expression was measured by RT‐qPCR. Ligand bias was determined using the operational model of agonism.
Key Results
Noradrenaline, phenylephrine, methoxamine and A61603 increased Ca2+ mobilization, cAMP accumulation and ERK1/2 phosphorylation. However, oxymetazoline showed low efficacy for Ca+2 mobilization, no effect on cAMP generation and high efficacy for ERK1/2 phosphorylation. The apparent functional selectivity of oxymetazoline towards ERK1/2 was related to off‐target effects at 5‐HT1B receptors endogenously expressed in CHO‐K1 cells. Phenylephrine and methoxamine showed genuine bias towards ERK1/2 phosphorylation compared to Ca2+ and cAMP pathways, whereas A61603 displayed bias towards cAMP accumulation compared to ERK1/2 phosphorylation.
Conclusion and Implications
We have shown that while adrenergic agonists display bias at human α1A‐adrenoceptors, the marked bias of oxymetazoline for ERK1/2 phosphorylation originates from off‐target effects. Commonly used cell lines express a repertoire of endogenous GPCRs that may confound studies on biased agonism at recombinant receptors.
The effects of dipyrone and acetylsalicylic acid (ASA) on male fertility are still not fully understood, mainly considering the epididymis as a putative target for their anti‐fertility effects. ...Therefore, this study aimed to investigate the effects of dipyrone and ASA on the contractions of distal cauda epididymis duct, serum testosterone levels and sperm parameters in rats. Firstly, we checked the in vitro effects of dipyrone and ASA (10–1000 μM) on the contractions of distal cauda epididymis duct by pharmacological experiments. We also evaluated the effects of in vivo treatment with dipyrone and ASA 100 mg/kg (p.o.) for 15 days on epididymal duct contractions, serum testosterone levels and sperm parameters. In vitro dipyrone or ASA decreased the epididymal duct contractions induced by phenylephrine or carbachol. We observed that in vivo treatment with both drugs decreased the daily sperm production, serum testosterone levels and sperm count through epididymis without altering the epididymal duct contractions and sperm transit time through epididymis. In conclusion, in vitro dipyrone and ASA were able to diminish the contractions of epididymal duct, whilst in vivo administration decreased the sperm count throughout epididymis as a consequence of a low sperm production caused by reduced testosterone levels.
Intrinsic Adaptation of Shr Right Atrium Reduces Heart Rate Dantas Rodrigues, Juliano Quintella; Camara, Henrique; Dantas da Silva Junior, Edilson ...
Journal of cardiovascular pharmacology,
2019-December, Letnik:
Publish Ahead of Print, Številka:
6
Journal Article
Recenzirano
ABSTRACTHypertension represents an autonomic dysfunction, characterized by increased sympathetic and decreased parasympathetic cardiovascular tone leading to resting tachycardia. Therefore, studies ...assessing hypertension-associated changes in isolated cardiac tissues were conducted under electric field stimulation to stimulate the neurons. Herein we characterize the influence of the autonomic neurotransmitter on the baseline atrial chronotropism of unpaced isolated right atria of normotensive (NWR) and spontaneously hypertensive rats (SHR). Our results revealed a resting bradycardia in tissues from SHR in comparison to normotensive rats. The release of autonomic neurotransmitters, acetylcholine or norepinephrine, still occurs in the electrically unstimulated right atrium, after excision of the sympathetic nerve, which could explain differences in basal heart rate between NWR and SHR. Nicotine and the acetylcholinesterase inhibitor physostigmine reduced the chronotropism of right atria from either NWR or SHR. Conversely, the muscarinic receptor antagonist atropine did not affect the basal chronotropism of tissues from both strains. Furthermore, tyramine increased the chronotropism of NWR and SHR atria indicating availability of the neuronal stocks of noradrenaline. Although the monoamine uptake inhibitor cocaine increased right atrium chronotropism in both strains, the basal heart rate was not affected by the β-adrenoceptor antagonist propranolol. In summary, after acute section of the sympathetic nerve, autonomic neurotransmitters are still released either in resting conditions or upon pharmacological stimulation of right atria from both strains. Nevertheless, autonomic neurotransmission does not affect resting chronotropism, nor is the responsible for reduced basal heart rate of the isolated right atrium of hypertensive rats.
The effects of acute treatment with sibutramine on the peripheral sympathetic neurotransmission in vas deferens of young rats were still not evaluated. Therefore, we carried out this study in order ...to verify the effects of acute sibutramine treatment on the neuronal- and exogenous agonist-induced contractions of the young rat vas deferens. Young 45-day-old male Wistar rats were pretreated with sibutramine 6 mg/kg and after 4h the vas deferens was used for experiment. The acute treatment with sibutramine was able to increase the potency (pD2) of noradrenaline and phenylephrine. Moreover, the efficacy (Emax) of noradrenaline was increased while the efficacy of serotonin and nicotine were decreased. The maximum effect induced by a single concentration of tyramine was diminished in the vas deferens from treated group. Moreover, the leftward shift of the noradrenaline curves promoted by uptake blockers (cocaine and corticosterone) and β-adrenoceptor antagonist (propranolol) was reduced in the vas deferens of treated group. The initial phasic and secondary tonic components of the neuronal-evoked contractions of vas deferens from treated group at the frequencies of 2 Hz were decreased. Moreover, only the initial phasic component at 5 Hz was diminished by the acute treatment with sibutramine. In conclusion, we showed that the acute treatment with sibutramine in young rats was able to affect the peripheral sympathetic nervous system by inhibition of noradrenaline uptake and reduction of the neuronal content of this neurotransmitter, leading to an enhancement of vas deferens sensitivity to noradrenaline.
Fluoxetine and sertraline are antidepressants drugs capable to impair male fertility by decreasing the number of sperm cells in the ejaculate. However, the mechanism underlying these effects is still ...not fully understood. It is also reported that alterations in epididymis contraction induced by different drugs affect the number of sperm cells, leading to male fertility alterations. Therefore, this study aimed to investigate if both fluoxetine and sertraline could affect the rat epididymis contraction, altering the sperm transit and/or sperm count trough rat epididymis. In vitro effects of fluoxetine and sertraline (1, 3 and 10 μM) were evaluated in isolated distal cauda epididymis of rats by pharmacological experiments. The effects of long-term treatment with fluoxetine and sertraline (20 mg/kg, i.p., 21 days) were also checked on distal cauda epididymis contractions, serum testosterone levels, sperm production, sperm reserves and sperm transit time trough rat epididymis. In vitro fluoxetine and sertraline (>3 μM) impaired the contractions induced by KCl, phenylephrine or carbachol although fluoxetine 1 μM potentiate the phenylephrine-induced contractions. Long-term in vivo treatment with fluoxetine and sertraline promoted: (a) an enhancement of rat distal cauda spontaneous contractions; (b) a potentiation of phenylephrine-induced contractions; (c) a decreased in serum testosterone levels; and (d) a diminished daily sperm production, sperm reserves trough epididymis and sperm transit time in rat cauda epididymis. In conclusion, the alteration in the motor activity of epididymis could be associated to the low sperm count in this organ and accelerated transit time trough epididymal cauda of rats.
Autonomic nerves release ATP, which is processed into adenosine in the synaptic cleft. Adenosine and ATP exert a negative chronotropic effect in the heart. This study aims to evaluate adenosine and ...P2 receptors and cellular signalling in cardiac arrest produced by purines in the heart. Right atria of adult Wistar rats were used to evaluate the effects of adenosine, ATP and CPA (an adenosine A1 receptor agonist), in the presence and absence of DPCPX, an adenosine A1 receptor antagonist. Effects of adenosine A2 and A3 receptors agonists and antagonists were also investigated. Finally, involvement of calcium and potassium channels in these responses was assessed using BayK 8644 and 4-Aminopyridine. Cumulative concentration–effect curves of adenosine and CPA resulted in a negative chronotropic effect culminating in cardiac arrest at 1000μM (adenosine) and 1µM (CPA). Furthermore, ATP produced a negative chronotropic effect at 1–300µM and cardiac arrest at 1000μM in the right atrium. ATPγS (a non-hydrolysable analogue of ATP) reduced chronotropism only. The effects of adenosine, CPA and ATP were inhibited by DPCPX, a selective adenosine A1 receptor antagonist. The selective adenosine A2 and A3 receptors antagonists did not alter the chronotropic response of adenosine. 4-Aminopyridine, a blocker of potassium channels at 10mM, prevented the cardiac arrest produced by adenosine and ATP, while BayK 8644, activator of calcium channels, did not prevent cardiac arrest. Adenosine A1 receptor activation by adenosine and ATP produces cardiac arrest in the right atrium of Wistar rats predominantly through activation of potassium channels.
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