Objective: This study investigated the vasoactive responses of quiescent and pre-contracted isolated human umbilical veins and arteries to cumulative leptin.
Materials and Methods: The vasoactive response of umbilical vessels pre-contracted with U46619 (10-10M) and angioten-sin II (10-6M) to cumulative leptin (10-11-10-7M) were recorded in vitro.
Results: Leptin did not affect the artery or vein basal tonus (p=1). The leptin-elicited relaxation in U46619-contracted vessels was greater in veins than in arteries (p<0.001). Incubation with N (omega)-nitro-L-arginine methyl ester (L-NAME) (10-4M) prevented the leptin-induced relaxation of the U46619 contraction response in the artery. The Emax and pD2 values of the L-NAME-incubated veins were lower than those of the non-incubated veins (p<0.001 and p=0.001, respectively). The relaxation in angiotensin II-contracted veins was greater than that of the arteries (p<0.001). Incubation with L-NAME prevented leptin-induced relaxation in angiotensin II-contracted arteries. The Emax of leptin-induced relaxation of L-NAME-in-cubated veins was significantly lower than that of non-incubated veins (p=0.027); the pD2 was similar.
Conclusion: Leptin did not alter the resting tension of isolated umbilical vessels; however, the results indicated that leptin caused concentration-dependent relaxation in umbilical vessels pre-contracted with U46619 or angiotensin II. The maximum relaxation was greater in veins compared with arteries. Incubation with L-NAME completely inhibited leptin-induced relax-ation in arteries and resulted in a significant inhibition in veins.