INHIBITORY EFFECTS OF FLUORESCEIN ISOTHIOCYANATE PHOTOACTIVATION ON LYMPHATIC PUMP ACTIVITY

The effects of photoactivation of fluorescein 5'-isothiocyanate (FITC) -dextran on lymphatic pump activity of rat mesenteric collecting vesse l were studied in vivo. Rats were anesthetized with intraperitoneal al pha-chloralose and urethane, and the mesenteries were studied by using intravital videomicroscopic techniques. The diameter of the collectin g lymph vessels were continuously monitored and lymphatic pump paramet ers (end diastolic diameter, end systolic diameter, stroke volume inde x, ejection fraction, contraction frequency, and pump flow index) were calculated. FITC-dextran (42 nmol/100 g body wt) without illumination caused no disturbance of lymphatic pump activity. Photoactivated FITC -dextran significantly increased end systolic diameter and decreased s troke volume index, ejection fraction, contraction frequency, and pump flow index. End diastolic diameter was not changed throughout the exp eriment. Superoxide dismutase (120 U/ml) and catalase (5000 U/ml) had no protective effect on photoactivated FITC-induced pump dysfunction, while histidine (singlet oxygen quencher, 10 mM) significantly prevent ed the disturbance of pump parameters. These results indicate that pho toactivation of FITC induces negative chronotropic and negative inotro pic effects in lymphatic pump activity through generation of singlet o xygen in the mesentery. (C) 1997 Academic Press.