Tocopherol inhibits the relaxing effect of terbutaline in the respiratory and reproductive tracts of the rat: the role of the oxidative stress index.

AIMS: Reactive oxygen species play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (tocopherol) can reduce the effect of terbutaline in beta-2-adrenergic receptor (ß2-AR)-regulated smooth muscles. MAIN METHODS: Contractility of the tissues from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats was investigated in an isolated organ bath. The tracheal and uterine ß2-AR expressions were increased by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The accumulation of cyclic-AMP (cAMP), and the total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio of TOS and TAS. KEY FINDINGS: Terbutaline (10(-10)-10(-5)M) decreased the contractions in the nontreated and the P4-pretreated myometria, but tocopherol (10(-7)M) did not alter these actions. Terbutaline (10(-6)M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while tocopherol 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 tocopherol reduced these effects. The changes in the intracellular cAMP levels of the tissues were in harmony with the isolated organ results. The OSI was highest in the trachea and lowest in the pregnant myometrium. SIGNIFICANCE: A higher OSI is linked to a higher tocopherol sensitivity of beta-mimetic-induced relaxation. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen, while their tocolytic effect may remain unchanged during parallel tocopherol administration.

Nociceptin inhibits uterine contractions in term-pregnant rats by signaling through multiple pathways.

The actions of the endogenous peptide nociceptin (PNOC; previously abbreviated as N/OFQ) on the myometrium have not been investigated previously. Our aim was to study the presence and functional role of PNOC in the modulation of uterine contractility in pregnant rats at term. The presence of PNOC and its receptors (OPRL1; previously called NOP) in the uterus were detected by radioimmunoassay and radioligand-binding experiments. The PNOC-stimulated G protein activation was assessed by a [(35)S]GTPgammaS-binding technique. The effects of PNOC in uterine rings precontracted with KCl or oxytocin were also tested in vitro. Uterine levels of cAMP were measured by enzyme immunoassay. The K(+) channel blockers tetraethylammonium and paxilline were used to study the role of K(+) channels in mediating the uterine effects of PNOC. Both PNOC and OPRL1 were present in the uterus. PNOC revealed a maximum contraction inhibition of approximately 30%, which was increased to 40% by naloxone. Naloxone and pertussis toxin significantly attenuated the G protein-stimulating effect of PNOC. The uterine cAMP levels were elevated by PNOC and naloxone and after preincubation with pertussis toxin. Tetraethylammonium and paxilline reduced the contraction-inhibiting effect of PNOC and naloxone to approximately 10% and 15%, respectively. We presume that PNOC plays a role in regulating uterine contractility at term. Its effect is mediated partly by stimulatory heterotrimeric G (G(s)) proteins coupled to OPRL1 receptors and elevated cAMP levels, and also by Ca(2+)-dependent K(+) channels. Our results demonstrate a novel action and signaling pathway for PNOC that might be a potential drug target.

[Influence of adrenergic denervation on uterine contractility of pregnant rats in vitro]. / Az adrenerg denerváció hatása terhes patkány uterusz kontraktilitására in vitro.

The aim of the present study was to investigate the functional changes in the sympathetic nerves in the rat myometrium during pregnancy by electric field stimulation (EFS) in vitro. In our experiments the contractility of the rat myometrium were registered at 5, 10, 15, 18, 20, 22 (term) day of pregnancy, in non pregnant rats and in 6-OH-dopamine pretreated rats. The parameters of EFS were the following: pulse width 0.6 ms, frequency range of nerve stimulation 1-70 Hz, supramaximal voltage 40 V. We concluded that low pulse width and low frequency stimulation is selective for adrenergic nerves. We found that during pregnancy a gradual drop-out of low frequency induced uterine smooth muscle contraction appears. It is surprising that very low frequency stimulation has no effect on the 5th day of pregnancy although the same frequency stimulation causes contraction on the 10th day. By the 22nd day of pregnancy the rat uterus shows the same responsiveness to nerve stimulation as it is detected in 6-OH-dopamine pretreated non pregnant rats. The adrenergic denervation of the pregnant uterus does not mean that it loses the ability to respond to cathecholamines since non-synaptic adrenergic receptors exist in the late pregnant rat uterus.