[The effect of R(+) limonene on β-adrenergic signaling in smooth muscles: the significance of oxidative stress index].

Reactive oxygen intermediers (ROI) play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (limonene) can reduce the beta-mimetic effect of terbutaline in beta-2-adrenergic receptor (β2-AR)-regulated smooth muscles. Tissue samples were collected from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats. Tissue contractility was investigated in an isolated organ bath. In separate groups of animals, the tracheal and uterine β2-AR activities were upregulated by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio ofTOS and TAS. Terbutaline (10(-10) - 10(-5) M) decreased the spontaneous contractions in the nontreated and the P4-pretreated myometria. The concentration-response curves for terbutaline in the presence of 10-3 M limonene were shifted to the left, but the maximum inhibitory effect was unchanged. Terbutaline (10(-6) M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while limonene reduced this action only in the P4-treated cervices. Terbutaline (10(-9) - 10(-4) M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while limonene reduced these effects. The OSI was highest in the trachea and lowest in the pregnant myometrium. Limonene has various influence on terbutaline induced effects in certain tissues. Higher OSI value means, that the antioxidants have greater role in the beta-adrenergic signalmechanism. We assume that the significance of ROI in the signalling process of the β2-ARs are divergent in the various tissues. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen during parallel limonene administration.