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452<br />

the earlier finding of a lack of effect of FB on the heart of the anesthetized SD<br />

rat,may be explained by the fact that DDA is either absent or else present in<br />

FB in such small amounts as to have no significant effect on the heart rate.<br />

VII. EFFECTS OF DA AND DDA ON ENDOTHELIAL CELL<br />

PRODUCTION OF NITRIC OXIDE<br />

As our earlier studies suggested that the relaxation of the isolated rat aorta<br />

caused by DA and DDA may be mediated through the L-arginine-NO<br />

synthase pathway and NO activation of guanylate cyclase,it was decided to<br />

study the effects of DDA on NO production by human endothelial cell<br />

cultures. NO was quantified spectrometrically by the accumulation of nitrite<br />

produced by endothelial cells cultured in F12 medium for up to 48 hr. This<br />

method has been documented by previous workers (22,23).<br />

We found that DA and DDA significantly stimulated NO production<br />

by endothelial cells in a concentration-dependent manner. This suggests<br />

another possible mechanism for their hypotensive effect.<br />

FIGURE 9 Comparison of DA, DDA, and FB by TLC.<br />

Tan and Zhang

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