EFFECTS OF DIETARY FISH OIL ON RB+ EFFLUX FROM AORTA OF STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

The effect of fish oil on potassium efflux and basal tension in aortas from stroke prone spontaneously hypertensive rats (SHRSP) was evaluated. Four-week-old male Wistar-Kyoto rats (WKY) and SHRSP were divided into two groups: one received a 5% corn oil diet, the other a 5% menhaden oil diet. After 15 weeks, mean systolic blood pressure (mm Hg) was reduced in SHRSP-fish (202 +/- 5) compared to SHRSP-corn (227 +/- 4). Systolic pressure of WKY-fish (146 +/- 3) was not different from WKY-corn (151 +/- 4). Potassium efflux was evaluated with the isotope Rb-86. Basal Rb-86 efflux from aorta of SHRSP-corn was elevated compared to WKY-corn. Diltiazem or sodium nitroprusside decreased Rb-86 efflux and basal tension in SHRSP. Basal Rb-86 efflux, tension, and the magnitude of this diltiazem- or nitroprusside-induced inhibition were decreased in SHRSP-fish. At maximal diltiazem or nitroprusside concentration, Rb-86 efflux from both SHRSP dietary groups was similar but still greater than control aorta. The IC50 values for diltiazem or nitroprusside effects on Rb-86 efflux and tension were not altered by diet in SHRSP. Qualitatively similar changes in basal Rb-86 efflux and tension were noted in WKY-fish compared to WKY-corn. These experiments demonstrate that dietary fish oil supplementation decreased calcium-sensitive Rb-86 efflux and basal tension in vascular smooth muscle and suggest that these changes may contribute to the concomitant antihypertensive effect of dietary fish oil in SHRSP.