Etude comparative de la fonction cardiaque chez le rat transgenique hypertendu, chez le rat spontanement hypertendu et chez le rat normotendu [A comparative study of cardiac function in transgenic hypertensive rats, in spontaneously hypertensive rats and in normotensive rats]

Left ventricular hypertrophy (LVH) entails numerous functional and molecular changes that ultimately lead to cardiac insufficiency. The renin-angiotensin system and adrenergic receptor signalling pathway have both been implicated in LVH progression and interactions between these factors may precipitate contractile dysfunction. We therefore investigated cardiac function in hypertensive rats transgenic for the human renin and angiotensinogen genes (TGR) having a genetic activation of the renin-angiotensin system, stroke-prone spontaneously hypertensive rats (SHR) and normotensive controls (CTR) aged 6 weeks. The isolated perfused heart model was used and the effect of isoproterenol (0.1-1000 nmol/L on cardiac function was studied. Cardiac protein and gene expression was studied by Western blot and RNase protection assay. TGR had 75 mmHg higher blood pressure and a 24% higher cardiac/body weight ratio than CTR; blood pressure in SHR was 17 mmHg higher without heart wheight difference (p<0.05). Basal Pmax, +dP/dt and -dP/dt were higher in TGR and SHR compared with CTR hearts. Isoproterenol stimulated these parameters by a maximum factor 6-8 in CTR and SHR but had almost no effect in TGR (p<0.05). Basal CF per g heart weight was similar in all experimental groups. Isoproterenol produced a significantly smaller vasodilation in TGR compared with CTR or SHR. β1 and β2 receptor and Gsα proteins were similar in TGR, SHR and CTR. Giα was increased in TGR hearts (p<0.05). Converting enzyme and atrial natriuretic factor mRNA expression was increased (p