Role of nitric oxide in the mechanism of preclamping and remote ischemic preconditioning of adipocutaneous flaps in a rat model.

Abstract

The purpose of this study was to determine whether nitric oxide (NO) plays a role in the mechanism of acute ischemic preconditioning (IP). Fifty-eight male Wistar rats were divided into seven experimental groups. An extended epigastric flap was raised in one of the control groups (C, n = 8), and a 3-hr flap ischemia was induced. Another group served as a non-ischemic control (CO, n = 8). The animals of group S (n = 9) received 500 nmol/kg of Spermine/Nitric Oxide Complex (Sper/NO) intravenously 30 min prior to ischemia. The group N+P (L-NAME + preclamping, n = 8) received 10 mg/kg Nomega-Nitro-L-Arginine Methyl Ester (L-NAME) intravenously before preclamping of the flap pedicle (10-min cycle length, 30-min reperfusion). Ten mg/kg L-NAME were administered in group N+T (L-NAME + tourniquet, n = 9) before ischemia of the right hindlimb was induced using a tourniquet for 10 min after flap elevation. Flap ischemia was induced after 30 min of limb reperfusion. A similar protocol was used in the groups N+P+S (L-NAME + preclamping+Sper/NO, n = 8) and N+T+S (L-NAME + tourniquet + Sper/NO, n = 8). In both groups Sper/NO was administered 30 min prior to flap ischemia, additionally to the protocol of the groups N+P and N+T. Mean flap necrosis area was assessed on the fifth postoperative day using a planimetry software. Average flap necrosis area was 67 +/- 16 percent in the control group C, 28 +/- 13.3 percent in the non-ischemic controls (CO), 10 +/- 5.9 percent in group S, 77.5 +/- 10.2 percent in group N+P, 76 +/- 6.9 percent in group N+T, 71.5 +/- 9.4 percent in group N+P+S, and 78 +/- 9.9 percent in group N+T+S. The animals of group S and CO demonstrated a significantly lower area of flap necrosis than all other groups ( p < 0.001). No significant difference could be shown between the groups C, N+P, N+T, N+P+S and N+T+S. Group S showed a significantly lower flap necrosis area than group CO ( p < 0.01). The data showed, that NO plays an important role in the mechanism of IP since the administration of an NO-donor previous to ischemia simulates the effect of IP, while the unspecific blocking of NO synthesis by L-NAME eliminates the protective effect of flap preconditioning by preclamping as well as by remote IP. Exogenous NO application is insufficient to provide protection once the endogenous NO synthesis is blocked.