Isoprenaline HCl

Isoprenaline HCl is an agonist of β-adrenergic receptor [1].

The adrenergic receptors are a class of G protein-coupled receptors that are targets of norepinephrine and epinephrine. When reacting with epinephrine, β-adrenergic receptor causes vasodilation.

In human umbilical vein endothelial cells (HUVECs), isoprenaline (100 nM) significantly increased the expression of connexins Cx43 and also increased Cx40 and Cx37. Also, isoprenaline increased the number of coupling cells. Isoprenaline enhanced the formation of branches and complex tube networks [2].

In the isolated field stimulated rat vas deferens, isoprenaline inhibited contractions with EC50 value of 45.6 nM. In tissues in which β 2-adrenoreceptors were maximally blocked by timolol, isoprenaline inhibited contractility with EC50 value of 1.5 μM [1]. In CFW mice, IPR caused the maximal proliferative response of bone marrow cells and increased erythropoietic activity. These results suggested that isoprenaline activated beta-adrenergic receptor, which then increased the proliferative and differentiation activities of hemopoietic stem cells [3].

References:
[1].  Lotti VJ, Cerino D, Kling P. Characterization of the adrenoreceptor activities of isoprenaline in the field stimulated rat vas deferens: selective supersensitivity to beta 2-mediated responses following reserpine treatment. J Auton Pharmacol, 1982, 2(3): 169-174.
[2].  Dhein S, Gaertner C, Georgieff C, et al. Effects of isoprenaline on endothelial connexins and angiogenesis in a human endothelial cell culture system. Naunyn Schmiedebergs Arch Pharmacol, 2015, 388(1): 101-108.
[3].  Lipski S. Effect of beta-adrenergic stimulation by isoprenaline on proliferation and differentation of mouse bone marrow cells in vivo. Pol J Pharmacol Pharm, 1980, 32(3): 281-287.

Nitric oxide (NO) primarily accounts for endothelium-dependent component of beta-adrenoceptor-activated smooth muscle relaxation of mouse aorta in response to isoprenaline.[Pubmed:12596888]

J Smooth Muscle Res. 2002 Oct;38(4-5):87-99.

Isoprenaline is known to produce vascular relaxation through activation of beta-adrenoceptors. In recent years, beta-adrenoceptor-activated vascular relaxation has been the focus of pharmacological study in terms of both the receptor subtypes and the intracellular signaling mechanisms which trigger smooth muscle mechanical functions. In addition, the possible contribution of the endothelium to beta-adrenoceptor-activated relaxation of vascular beds has provoked considerable discussion, with consensus still to be established. In the present study, we examined the effects of isoprenaline on isolated mouse aortic smooth muscles to determine whether the presence of the endothelium plays a substantial role in the relaxation it produces. A possible role for nitric oxide (NO) as a primary endothelium-derived factor released in response to isoprenaline was also elucidated pharmaco-mechanically. In isolated thoracic and abdominal aortae pre-contracted with phenylephrine (3 x 10(-7)-10(-6) M), isoprenaline elicited relaxation in a concentration-dependent fashion (10(-9)-10(-5) M). In endothelium-denuded preparations, isoprenaline-elicited relaxation was reduced to 40-50% of the response obtained in endothelium-intact preparations. In the preparations treated with N(G)-nitro-L-arginine methyl ester (L-NAME, 3 x 10(-4) M; an NO synthase inhibitor) or 1H-[1,2,4]-oxadiazolo[4,3-a]-quinoxalin-1-one (ODQ, 10(-5) M; a soluble guanylyl cyclase inhibitor), isoprenaline-elicited relaxation was attenuated almost to the same degree as the response in endothelium-denuded preparations. The degree of endothelium-dependency in isoprenaline-elicited relaxation was largely diminished when treated with propranolol (3 x 10(-6) M). The present findings indicate that isoprenaline substantially relaxes the mouse aorta with both endothelium-dependent and -independent mechanisms. The endothelium-dependent component seems to correspond to about 50% of the isoprenaline-elicited relaxation, and is almost entirely due to endothelium-derived NO. Activation of propranolol (3 x 10(-6) M)-inhibitable beta-adrenoceptors seems to be primarily responsible for the NO-mediated endothelium-dependent pathway in isoprenaline-elicited relaxant response of mouse aorta.

beta 2-adrenergic receptor activates extracellular signal-regulated kinases (ERKs) via the small G protein rap1 and the serine/threonine kinase B-Raf.[Pubmed:10840035]

J Biol Chem. 2000 Aug 18;275(33):25342-50.

G protein-coupled receptors can induce cellular proliferation by stimulating the mitogen-activated protein (MAP) kinase cascade. Heterotrimeric G proteins are composed of both alpha and betagamma subunits that can signal independently to diverse intracellular signaling pathways including those that activate MAP kinases. In this study, we examined the ability of isoproterenol, an agonist of the beta(2)-adrenergic receptor (beta(2)AR), to stimulate extracellular signal-regulated kinases (ERKs). Using HEK293 cells, which express endogenous beta(2)AR, we show that isoproterenol stimulates ERKs via beta(2)AR. This action of isoproterenol requires cAMP-dependent protein kinase and is insensitive to pertussis toxin, suggesting that Galpha(s) activation of cAMP-dependent protein kinase is required. Interestingly, beta(2)AR activates both the small G proteins Rap1 and Ras, but only Rap1 is capable of coupling to Raf isoforms. beta(2)AR inhibits the Ras-dependent activation of both Raf isoforms Raf-1 and B-Raf, whereas Rap1 activation by isoproterenol recruits and activates B-Raf. beta(2)AR activation of ERKs is not blocked by expression of RasN17, an interfering mutant of Ras, but is blocked by expression of either RapN17 or Rap1GAP1, both of which interfere with Rap1 signaling. We propose that isoproterenol can activate ERKs via Rap1 and B-Raf in these cells.

Characterization of the adrenoreceptor activities of isoprenaline in the field stimulated rat vas deferens: selective supersensitivity to beta 2-mediated responses following reserpine treatment.[Pubmed:6292228]

J Auton Pharmacol. 1982 Sep;2(3):169-74.

1 Low concentrations of isoprenaline (EC50 = 45.6 nM) inhibited contractions in the isolated field stimulated rat vas deferens. This inhibitory effect was markedly attenuated by the postjunctional beta 2-adrenoreceptor antagonist timolol, but not affected by the prejunctional alpha 2 or postjunctional alpha 1-adrenoreceptor antagonists rauwolscine and prazosin, respectively. 2 In vas deferens of rats previously treated with reserpine, the postjunctional beta 2-adrenoreceptor-mediated inhibitory response to isoprenaline was markedly potentiated. 3 High concentrations of isoprenaline (EC50 = 1.5 microM) also inhibited contractility in tissues in which postjunctional beta 2-adrenoreceptors were maximally blocked by high concentrations of timolol. This contractile inhibition produced by isoprenaline was abolished by rauwolscine but not significantly altered by prazosin or pretreatment of the rats with reserpine indicating stimulation of prejunctional alpha 2-adrenoreceptors. 4 Rauwolscine pretreatment unmasked an ability of isoprenaline (EC50 = 17.1 microM) to produce enhancement of field stimulation-induced contractions. This response was abolished by prazosin but was unaffected by timolol or reserpinization indicating an action upon postjunctional alpha 1-adrenoreceptors. 5 The data indicate isoprenaline activates adrenoreceptor mechanisms in the field stimulated rat vas deferens by a direct action not dependent upon endogenous catecholamines and with an order of activity of beta 2 much greater than alpha 2 greater than alpha 1. Pretreatment with reserpine produces rapid and selective development of supersensitivity to the postjunctional beta 2-mediated inhibitory response of isoprenaline in this preparation.

Isoprenaline hydrochloride is a non-selective beta-adrenergic receptor agonist with potent peripheral vasodilator, bronchodilator, and cardiac stimulating activities.

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