An unsaturated fat diet prevents the increased angiotensin II vascular responses in renal artery stenosis.

OBJECTIVE

The aim was to characterise angiotensin II constrictor responses in two kidney, one clip (2K1C) renal hypertensive rats fed a diet with a high unsaturated fatty acid content.

METHODS

Two diets with the same total fat (37% by energy; 17% by weight) but different unsaturated fat contents were fed to rats for a three month period. Thirty four Sprague Dawley rats were used per diet group. After one month on the diets, a group of 19 rats in each diet group was operated upon to induce 2K1C hypertension. A separate group of 15 rats within each diet group received sham operations. Systolic blood pressure was measured weekly from prior to surgery to the end of the three month feeding period. At three months, angiotensin II constrictor responses were evaluated in the isolated kidney vascular preparation and in intact anaesthetised rats fed the different diets. Phenylephrine constrictor responses were also evaluated in intact anaesthetised rats in order to exclude structural vascular changes accounting for differences in angiotensin II constrictor responses.

RESULTS

The diet high in unsaturated fats prevented the development of hypertension in 2K1C rats [systolic pressure 134(7) mm Hg at eight weeks] compared to their own preoperative blood pressures [124(3) mm Hg], and to the 2K1C rats fed the control diet [163(7) mm Hg at eight weeks]. The diet high in unsaturated fats did not alter blood pressures in sham operated rats. In isolated perfused kidneys and in anaesthetised 2K1C rats fed the control diet, angiotensin II caused a greater vascular response compared to the sham operated groups. The unsaturated fat diet prevented this effect. No differences were found in blood pressure responses to phenylephrine.

CONCLUSIONS

These data suggest that the antihypertensive effect of a high unsaturated fat diet may in part be due to a depressed responsiveness of vascular smooth muscle to endogenous angiotensin II. The effect is likely to be due to modulation of angiotensin II vascular responses by local vascular changes that cannot be accounted for by structural vascular differences.