HIGH POTASSIUM DIETS GREATLY INCREASE GROWTH-INHIBITING AGENTS IN AORTAS OF HYPERTENSIVE RATS

High potassium diets greatly reduce intimal and medial thickening in stroke-prone spontaneously hypertensive rats (SHRSP). In vascular smooth muscle cells, transforming growth factor-beta (TGF-beta) inhibits proliferation. To test whether high potassium diets decrease aortic thickening through TGF-beta, we measured TGF-beta-like activity in medium bathing aortas from rats fed either normal potassium or high potassium diets. Five-week-old SHRSP were fed 6% high NaCl diets containing either normal (0.5%) potassium (11 rats) or high (2.1%) potassium (14 rats) for 7 weeks. Aortas were freshly excised and perfused for 3 hours with tissue culture medium at ordinary arterial pressures. TGF-beta-like activity in the acid-activated perfusing medium was assessed using the growth inhibitory action on mink lung cells. Growth inhibition was assessed by [H-3]thymidine incorporation. In the medium perfusing the outside of the aorta, the growth inhibitory rates were 2.5 times-higher in high potassium SHRSP than in normal potassium SHRSP (-49% versus -20%, p<0.03). Antibodies to TGF-beta-1 and TGF-beta-2 were added to other aliquots and did not alter the results whatsoever. Thus, the difference in growth inhibition was not due to differences in TGF-beta. The high potassium aortas released 2.5 times more growth-inhibiting agents than the normal potassium aortas. The same pattern of growth inhibition was also seen using vascular smooth muscle cells rather than mink lung cells (r=+0.818, p<0.001, n=13). The increased growth inhibition of high potassium aortas was not due to an increased release of heparin. These antiproliferative agents in high potassium aortas may partially explain why the high potassium aortas have so much less intimal and medial thickening.