Serotonin as a modulator of skeletal muscle oxygenation: effects of ketanserin and ritanserin on oxygen pressure distributions.

Hyperoxemia induces disturbances in tissue oxygenation. The purpose of this study was to examine the influence of serotonin (5-HT) on skeletal muscle oxygenation during hyperoxemia. Two highly selective and pure 5-HT2 receptor antagonists with different T1/2, ketanserin (90 min). and ritanserin (40 h), were employed during measurements of skeletal muscle oxygenation, blood gases and hemoglobin oxygenation in a rabbit model. Surface oxygen pressure measurements were performed on the medial vastus muscle using an MDO oxygen electrode. The results are presented as oxygen pressures distributions (OPD's). Ketanserin was used in one group of 7 rabbits (K-group), and ritanserin in another 7 (R-group). Normal near-Gaussian OPD shapes during normoxemia (paO2 11 kPa) changed to abnormal (scattered) shapes during hyperoxemia (paO2 approx. 50 kPa). After injection of ketanserin (0.07 mg.kg-1 bw) or ritanserin (0.035 mg.kg-1 bw) OPD shapes normalized in 13/14 cases. In the K-group, after ninety minutes, OPD shapes had rescattered and were not completely normalized after an additional half dose of ketanserin (0.035 mg/kg-1 bw). In the R-group, OPD shapes remained normal without additional ritanserin administration. There was poor correlation between normalization of muscle tissue oxygenation and venous pO2 (PvO2) or avDO2. Hyperoxemia-induced disturbance in OPD shape was normalized both by ketanserin and ritanserin in a fashion possibly related to the T1/2 time of the respective 5-HT2 receptor antagonist. These results suggest that serotonin modulates skeletal muscle oxygenation.