Raisa N. Kazi

Influence of high dietary sodium intake on the functional subtypes of α1‐adrenoceptors in the renal cortical vasculature of Wistar–Kyoto rats

1 Increased renal vascular resistance is one renal functional abnormality that contributes to hypertension, and alpha(1)-adrenoceptors play a pivotal role in modulating this renal vascular resistance. This study investigates the functional contribution of alpha(1)-adrenoceptor subtypes in the renal cortical vasculature of Wistar-Kyoto rats on a normal sodium diet (WKYNNa) compared with those given saline to drink for 6 weeks (WKYHNa). 2 The renal cortical vascular responses to the adrenergic agonists noradrenaline (NA), methoxamine (ME) and phenylephrine (PE) were measured in WKYHNa and WKYNNa rats either in the absence (the control phase) or presence of chloroethylclonidine (CEC), an alpha(1B)-adrenoceptor antagonist, 5-methylurapidil (5-MeU), an alpha(1A) antagonist, or BMY7378, an alpha(1D) antagonist. 3 Results showed a greater renal cortical vascular sensitivity to NA, PE and ME in the WKYHNa compared with WKYNNa rats (P < 0.05). Moreover, 5-MeU and BMY7378 attenuated adrenergically induced renal cortical vasoconstriction in WKYHNa and WKYNNa rats; this response was largely blunted in CEC-treated WKYHNa rats (all P < 0.05) but not in CEC-treated WKYNNa rats. 4 The data suggest that irrespective of dietary sodium content, in Wistar-Kyoto rats alpha(1A)- and alpha(1D)-subtypes are the major alpha(1)-adrenoceptors in renal cortical vasculature; however, there appears to be a functional involvement of alpha(1B)-adrenoceptors in the WKYHNa rats.

Functional Subtypes of Renal α1-Adrenoceptor in Spontaneously Hypertensive Rats with Streptozotocin-Induced Experimental Diabetic Nephropathy

Aim: This study investigated the impact of hypertension combined with diabetic nephropathy on rat renal α1-adrenoceptor subtype composition. Methods: In streptozotocin-induced diabetic spontaneously hypertensive rats (SHR), diabetic nephropathy developed as reflected by increased kidney index, plasma creatinine, albumin excretion, creatinine clearance and fractional excretion of Na+ (all p < 0.05). Renal vasoconstrictions caused by electrical stimulation of renal nerves and intrarenally administered noradrenaline (α-adrenoceptor agonist), phenylephrine (α1-adrenoceptor agonist) and methoxamine (α1A-adrenoceptor agonist) were determined in the presence and absence of intrarenally administered amlodipine (Ca2+ channel blocker), 5-methylurapidil (α1A-adrenoceptor antagonist), chloroethylclonidine (α1B-adrenoceptor antagonist) and BMY 7378 (α1D-adrenoceptor antagonist). Results: In diabetic nephropathy SHR, there was a significant (all p < 0.05) attenuation of all adrenergically induced vasoconstrictor responses in the antagonists, except chloroethylclonidine, which caused a significant (all p < 0.05) enhancement of the responses. Conclusion: The data demonstrated that there was a functional coexistence of α1A- and α1D-adrenoceptors in the renal vasculature of SHR irrespective of the presence of diabetic nephropathy. However, there was a minor contribution of pre-synaptic α-adrenoceptors to the adrenergically mediated vasoconstrictor responses in the diabetic nephropathy SHR.

Effect of renal sympathetic nerve on adrenergically and angiotensin II-induced renal vasoconstriction in normal Wistar-Kyoto rats.

Abstract Background. This study examined the effect of renal sympathetic innervation on adrenergically and angiotensin II (Ang II)-induced renal vasoconstriction in Wistar-Kyoto (WKY) rats. Methods. Forty-eight WKY rats were treated with either losartan (10 mg/kg/day p.o.) or carvedilol (5 mg/kg/day p.o.) or a combination of them (10 mg/kg/day + 5 mg/kg/day p.o.) for 7 days. On day 8, the rats were anaesthetized, and renal vasoconstrictor experiments were carried out. A group of rats was subjected to acute unilateral renal denervation during the acute study. Changes in the renal vasoconstrictor responses were determined in terms of reductions in renal blood flow caused by Ang II, noradrenaline (NA), and methoxamine (ME). Results. In normal animals, losartan decreased (P < 0.05) the renal vasoconstrictor response to Ang II but not to NA or ME. Carvedilol treatment, however, blunted (P < 0.05) the renal vasoconstrictor responses to Ang II and adrenergic agonists. Combination of losartan and carvedilol blunted (P < 0.05) the renal vasoconstrictor response to Ang II but augmented the responses to NA and ME (all P < 0.05). Interestingly, when denervated rats were treated with the same combination, there was a reduction (P < 0.05) in the renal vasoconstrictor responses to Ang II and adrenergic agonists. Conclusions. Data suggest that the renal sympathetic nerve contributes to adrenergic agonist-mediated renal vasoconstrictions in normal rats. The data further indicate an interactive relationship between renin-angiotensin and sympathetic nervous systems in modulating adrenergically and Ang II-induced renal vasoconstriction in WKY rats.

The role of A 1b -Ars in Regulations of Renal Hemodynamic and Renal Functions in Hypertensive Rats; Impact of High Dietary Sodium Intake

Background: Renal α1B-adrenoreceptors (α1-ARs) contributes to the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). The present study examined the role of α 1B -ARs in renal hemodynamic and tubular functions in SHR subjected to high-salt diet (SHRHNa) for 6 weeks. Methods: Renal cortical vasoconstriction to noradrenaline (NA), phenylephrine (PE), and methoxamine (ME) in presence and absence of chloroethylclonidine (CEC) was measured in SHRHNa and SHR on normal sodium diet (SHRNNa). Renal tubular functional responses to PE and CEC were assessed as a measure of insulin clearance. Results: SHRHNa showed no significant change in the mean arterial pressure (MAP) as compared to SHRNNa. SHRHNa expressed enhanced renal cortical vascular sensitivity to NA, PE, and ME. Furthermore, renal vasoconstrictor response to NA, PE and ME was accentuated in the presence of CEC in SHRNNa. On the other hand in SHRHNa, renal cortical vasoconstriction to NA and ME was inhibited by CEC. However tubular response to PE was inhibited by CEC in SHRNNa and remains unaffected in SHRHNa. Conclusion: Thus it is concluded that, augmented α 1 -adrenergic response to adrenergic stimuli contribute to salt-related increase in renal vascular sensitivity in SHRHNa and these changes were independent of any further increase in MAP in SHRHNa. Irrespective of dietary sodium changes, α1-ARs are involved in mediation of tubular functions like antinatriuresis and antidiuresis of SHR. In addition, α 1B -ARs are the functional subtypes that mediate renal cortical vasoconstriction in SHRHNa and tubular function in SHRNNa, while high sodium in SHR did not influence the functionality of α 1B -ARs in mediating tubular functions.