Vascular β-Adrenergic Receptor Adenylyl Cyclase System From Renin-Transgenic Hypertensive Rats

Abstract

Abstract-In transgenic rats harboring the mouse Ren-2 d gene [TG(mREN2)27], downregulation of the myocardial ␤-adrenergic receptor adenylyl cyclase system has been demonstrated previously. Because a reduced vasodilatory reactivity may significantly contribute to hypertension in this model of an activated tissue renin-angiotensin system, the present study investigated alterations of the vascular ␤-adrenergic receptor adenylyl cyclase system. In freshly harvested aortas from transgenic rats, the activity of adenylyl cyclase was reduced significantly (PϽ.05) in the presence of isoprenaline (10 mol/L; Ϫ28Ϯ4.5%), guanosine 5Ј-triphosphate, 5Ј-guanylylimidodiphosphate [Gpp(NH)p] (100 mol/L; Ϫ29Ϯ4.7%), and forskolin (100 mol/L) with (Ϫ42Ϯ6%) and without (Ϫ40Ϯ4.3%) MnCl 2 . Densities of ␤-adrenoceptors were similar in both strains. In situ hybridization demonstrated the expression of the transgene in aortic smooth muscle cells. These data indicate a reduced catalyst function as a major contributing factor involved in the maintenance of high blood pressure in TG(mREN2)27. However, in cultivated aortic smooth muscle cells, cAMP production after stimulation with isoprenaline, forskolin, and Gpp(NH)p in the presence or absence of MnCl 2 was not different. Affinities and densities of ␤-adrenoceptors and amounts of immunochemically detected inhibitory and stimulatory G-protein ␣-subunits were unchanged. Desensitization after incubation with 10 mol/L isoprenaline for 72 hours was identical in smooth muscle cells from both strains. Cell cultivation and isoprenaline treatment had no effect on transgene expression. We concluded that in transgenic rats the downregulation of the aortic ␤-adrenergic adenylyl cyclase system is due to humoral and hemodynamic factors present in vivo rather than to transgenicity itself. (Hypertension. 1998;31:1157-1165.) Key Words: renin-angiotensin system Ⅲ adenyl cyclase Ⅲ receptors, adrenergic Ⅲ muscle, smooth, vascular Ⅲ rats, transgenic P rimary hypertension is thought to be influenced by genetic and environmental factors. Animal models with genetic forms of hypertension can serve as tools to understand genotype-phenotype interactions in this disease. Significant genetic heterogeneity has been demonstrated in polygenic inbred rats.1 Recently, a transgenic rat model overexpressing a mouse renin gene (mouse Ren-2 d ) was generated.2 It has been characterized by fulminant hypertension and cardiac hypertrophy, low renal and plasma renin activities, and low circulating levels of angiotensin II, thus reflecting an activated tissue RAS.3,4 TG(mREN2)27-rats may represent an appropriate model for studying the impact of a single candidate gene on the development of hypertension. In hypertrophied hearts from this strain, our laboratory demonstrated desensitization of the ␤-adrenergic receptor adenylyl cyclase system, ie, downregulation of ␤ 1 -adrenoceptors, reduced expression of G i ␣-subunits, and reduced positive inotropic responses to isoprenaline. The activity of the catalyst of adenylyl cyclase was only...

Vascular smooth muscle Gqsignaling is involved in high blood pressure in both induced renal and genetic vascular smooth muscle-derived models of hypertension

“…Studies from animal models provide support for the important role of 7TMRs and GRK2 in hypertension. There is a downregulation of the aorta ␤-AR-adenylate cyclase system due to humoral and hemodynamic factors in vivo in spontaneously hypertensive (SHR) and Dahl salt-sensitive rats (45). In addition, the coupling of ␤-ARs to ATP-sensitive K ϩ channels via the heterotrimeric G protein, G s , is compromised, thereby preventing K ϩ influx and subsequent vasodilation (21).…”

Vascular Smooth Muscle Overexpression of G Protein–Coupled Receptor Kinase 5 Elevates Blood Pressure, Which Segregates With Sex and Is Dependent on G i -Mediated Signaling

“…A, Standards generated to determine cAMP levels to ensure that measurements were within linear portion of curve. B, Picomoles of cAMP in 2.5ϫ10 4 actions on the heart. Our data suggest that direct VSM ␤ 1 AR signaling inhibition, in high-BP models with elevated GRK5 expression and activity, is also partially responsible for attenuation of high BP.…”

“…4 In addition, we have also generated another line of transgenic mice with VSM-GRK2 overexpression, and these mice are hypertensive because of abnormal (uncoupled) ␤AR signaling leading to loss of dilatory control. 9 Therefore, we examined the relaxation in response to ␤AR stimulation in male thoracic and abdominal aorta, which is a typical physiological response caused by ␤AR-G s activation (Figure 4).…”

“…For example, impairment in ␤-adrenergic receptor (AR)-G s heterotrimeric signaling has been documented in patients with hypertension, and studies from animal models provide further support for the critical role of ␤ARs in hypertension. [1][2][3][4][5] Other GPCRs, such as angiotensin II (Ang II) receptors, are also essential to BP regulation. 6 Ang II receptors couple to both G q and G i , and activation of both these heterotrimeric G proteins mediates vasoconstriction.…”

β 2 -Adrenergic Receptor Gene Delivery to the Endothelium Corrects Impaired Adrenergic Vasorelaxation in Hypertension

“…Indeed, in hypertensive conditions, several reports indicate a reduction in ␤AR signaling and regulation. [5][6][7][8][9][10] If these premises hold true, improving ␤AR signaling should result in the restoration of ␤AR vasorelaxation. In fact, some interventions have been effective in correcting ␤AR signaling in hypertension, such as dietary salt restriction 7 or pharmacological treatment.…”