Effect of the oestral cycle on respiratory mechanics in the rat

Aim: To assess the effect of the oestral cycle on the respiratory mechanics of the rat. Methods: We measured the main mechanical respiratory parameters, namely respiratory system and lung resistances and compliances, by the end-inflation occlusion method on two populations of female rats, during proestrous– oestrous and metaoestrous–diestrous phases. Results: Inflation–deflation loops of the lungs were found to be statistically higher in rats during metaoestrous–diestrous phase. No other statistically significant difference was found in the measured mechanical respiratory parameters. Conclusion: Our results suggest that the naturally occurring fluctuations in serum sexual hormone levels during the sexual cycle influence the lung’s hysteresis but do not influence the respiratory system and lung resistances or static compliances. A possible effect of female sexual hormones on surfactant activity is also suggested