Involvement of alpha1-adrenoceptors subtypes in the cardiac failure in spontaneously hypertensive rats

ABSTRACT

The function of kidney deteriorates during the development of cardiac failure because of changes in renal haemodynamics and neurohormonal activity. This study aimed to examine the alpha1 adrenoceptor subtypes involved in mediating adrenergically induced renal vasoconstriction in a rat model of cardiac failure and hypertension. Spontaneously hypertensive rats [SHR] were used in the study. Cardiac failure was induced by the combined treatment of caffeine [40mg/kg] and isoprenaline [5mg/kg] for seven days. On day eight, the rats were used for acute study. The left kidney was exposed and renal blood flow [RBF] was measured with the help of electromagnetic probe. The reduction in renal blood flow induced by electrical renal nerve stimulation, intrarenal bolus doses of noradrenaline, phenylephrine or methoxamine were determined before and after administration of amlodipine, 5-methylurapidil, chloroethylclonidine and BMY 7378. Data, means +/- s.e.m were compared with 2 way ANOVA followed by Bonferroni post hoc with the significance level of 5%. The results obtained indicated that the renal vasoconstrictor responses in this model were attenuated mainly by amlodipine, 5 methylurapidil and BMY7378 but not by chloroethylclonidine. Furthermore, administration of chloroethylclonidine did not show a significant reduction in methoxamine induced renal vasoconstriction in cardiac failure SHR. This supported the view that alpha 1A- adrenoceptors are involved in renal vasculature SHR regardless of its pathophysiological state. The findings from this study further suggested that besides the alpha 1A, the alpha ID- adrenoceptors contribute to the adrenergically induced renal vasoconstrictor responses in cardiac failure SHR