Vasodilator action of the isopropyl ester of palmitoyl carnitine in the rat coronary circulation and mesenteric vascular bed

Propionyl-L-carnitine dilates human subcutaneous arteries through an endothelium-dependent mechanism

PURPOSE

The vasoactive effects of propionyl-L-carnitine (PLC) on human arteries, including endothelial and smooth muscle cell influences, were studied.

METHODS

Small (less than 200 microm) subcutaneous fat arteries (n = 19), obtained from human patients undergoing vascular surgery, were dissected and mounted in an arteriograph system that allowed measurement of lumen diameter and control of transmural pressure. To investigate the role of the endothelium, arteries were compared intact, intact and in the presence of either 0.3 mmol/L nitro-L-arginine (an inhibitor of nitric oxide synthesis) or 10 micromol/L indomethacin (an inhibitor of prostaglandin synthesis), or denuded of endothelium. After a 1-hour equilibration at a pressure of 50 mm Hg, arteries were precontracted 50% with an intermediate concentration of norepinephrine, and clinically relevant concentrations of PLC (0.1 to 100 micromol/L) were cumulatively added to the bath while the lumen diameter was continually measured.

RESULTS

Intact arteries dose-dependently dilated to PLC, with the half maximal dilation occurring at 2.9 +/- 1.2 micromol/L, increasing diameter 91% +/- 5% at 100 micromol/L. In contrast, PLC had significantly less effect on deendothelialized arteries, increasing diameter only 24% +/- 11% at 100 micromol/L (P <.01 vs. intact). This indicates the endothelial dependency of this compound. Blockade of nitric oxide did not inhibit this vasodilation, with the half-maximal response occurring at 8.6 +/- 7 micromol/L, increasing diameter 85% +/- 8% at 100 micromol/L ( P >.05 vs. intact). However, this vasodilation was significantly diminished in the presence of indomethacin, which dilated arteries only 53% +/- 18% at 100 micromol/L (P <.01 vs. intact; P >.05 vs. denuded).

CONCLUSION

PLC is an endothelium-dependent vasodilator, the mechanism of which is partially mediated by prostaglandin synthesis, not nitric oxide. The beneficial effects of this compound may, in part, be related to vasodilation and enhanced blood flow.

Structure-activity relationships of some novel coronary dilator derivatives of palmitoyl carnitine in the rat isolated heart

The structure-activity relationships of some novel coronary dilator derivatives of palmitoyl carnitine in the rat isolated perfused heart are described. It has been shown previously that esterification of palmitoyl carnitine changes the activity of the compound from a coronary constrictor to a coronary dilator. In this study, it was found that the ester group is not a necessary requirement for coronary dilator activity, but only the absence of the negatively charged carboxylic acid group of palmitoyl carnitine, as compounds containing an ethyl group in place of the ester group were also active coronary dilators. Furthermore, substituting the methyl groups attached to the nitrogen atom of the molecule profoundly altered coronary dilator activity. A quaternary ammonium group was a necessary requirement for potent coronary dilator activity.