The effects of magnesium sulphate on the contractile activity of uterus in an animal model of preeclampsia.

PURPOSE: This study was undertaken to evaluate the effects of magnesium sulfate (MgSO4) on the contractile activity of the uterus in a pregnant rat model of preeclampsia induced by N-nitro-arginine methyl ester (L-NAME). MATERIALS AND METHODS: Twenty-eight, 160-220 gram, three to four month old female Sprague-Dawley rats were used in this study. After conception was confirmed by vaginal smears on the first day of pregnancy, the animals were allocated into four groups according to the chemicals fed in their drinking water as control (nothing administered), L-NAME (50 mg/kg L-NAME), MgSO4 (600 mg/kg MgSO4), and MgSO4 + L-NAME group (600 mg/kg MgSO4 + 50 mg/kg L-NAME). The pregnant uterus strips were isolated on the 19th day and the contractile activity of uterus was examined by applying 0, 0.1, 0.2, 0.4, 0.8, and 2.5 mIU/ml oxytocin to each group and responses are recorded accordingly. RESULTS: There were no statistically significant differences regarding fetal parameters and peak amplitudes of the oxytocin stimulated pregnant rat myometrial strips among groups. In L-NAME group at 0 and 0.1 mIU/ml oxytocin, the contraction frequency in a ten-min period was statistically lower than the control group (Z = -2.850, p = 0.004; Z = -2.902, p = 0.004, respectively). In MgSO4 group only at 0 mIU/ml oxytocin, the frequencies of the contractions in ten-min period were statistically lower than the control group (Z = -2.973,p = 0.003). In L-NAME + MgSO4 group at 0, 0.1 and 0.2 mIU/ml oxytocin concentrations the frequencies of the contractions in ten-min period were statistically lower than the control group (Z = - 4.018, p = 0.000; Z = -3.237, p = 0.001; Z = -2.902, p = 0.004, respectively). In L-NAME + MgSO4 given group at each oxytocin concentrations, the frequencies of the contractions in ten-min period were lower but not statistically different than the L-NAME group. CONCLUSION: MgSO4 has no significant effect on the amplitude of spontaneous or oxytocin induced myometrial contractions, but decreased the frequency of spontaneous contractions. At each doses of oxytocin, MgSO4 has no significant effect on the frequency of contraction in a pregnant rat model of preeclampsia induced by L-NAME.

Antinicotinic activity of some 2-aminotetralin derivatives. A structure-activity relationship study.

The antagonistic potencies of some methoxy-2-aminotetralin derivatives on nicotinic type acetylcholine receptors were compared in rat anococcygeus muscle and frog rectus abdominis muscle preparations. Stimulation of intrinsic non-adrenergic non-cholinergic (NANC) nerves with nicotine (100 mumol/l) produced a 65.7 +/- 3.2% relaxation in phenylephrine (1 mumol/l) precontracted (2.53 +/- 0.20 g) preparations (n = 17). 2-Aminotetralin derivatives inhibited the nicotine-induced relaxations in rat anococcygeus muscle in a concentration-dependent manner with the following order of potency: BDI-60 > BDI-85 > BDI-51. Preincubation of frog rectus abdominis muscles with the test compounds caused noncompetitive antagonism as reflected by significant reductions in the maximum contractions obtained with nicotine. The order of potency according to their pD2' values was BDI-60 > BDI-85 > BDI-51. All three compounds possess antagonistic action with the same order of potency on both neuronal and muscular type nicotinic acetylcholine receptors. It has been concluded that doubling the n-propyl residue on the 2-amino moiety causes an increase in the antagonistic potency on nicotonic type acetylcholine receptors, while shifting of the 8-methoxy residue to the fifth position reduces it.

Comparative study on different responses of vascular and extravascular smooth muscles mounted inside the guinea-pig trachea: effects of ovalbumin sensitization.

The difference between the responses of phenylephrine (1 microM)-precontracted vascular (endothelium-denuded rat or rabbit aortic strips) and nonvascular (rat anococcygeus muscle) smooth muscles to acetylcholine (0.1-100 microM) was investigated when they were mounted co-axially inside the tracheas isolated from normal or ovalbumin-sensitized guinea-pigs. Acetylcholine produced concentration-dependent relaxations in both types of bioassay tissues. These relaxations, previously shown to be due to the release of airway epithelium-derived relaxing factor(s), were significantly attenuated when the epithelial layer of the tracheas was removed mechanically (as confirmed by histological examination). There were no significant differences in responsiveness to acetylcholine between vascular strips mounted inside the epithelium-intact normal or sensitized tracheas. The phenylephrine-induced precontraction was significantly more pronounced in rat anococcygeus muscles mounted inside sensitized tracheas as compared to tissues mounted inside control tracheas. The acetylcholine-induced relaxations were significantly decreased but this effect disappeared when the concentration of phenylephrine was reduced to obtain a similar precontraction level as in tissues mounted inside control tracheas. The responsiveness of both vascular strips and anococcygeus muscles to acetylcholine was attenuated when they were mounted inside sensitized tracheas and incubated with ovalbumin for 20 min, which may be explained by the epithelial damage induced by ovalbumin challenge. This attenuation was absent when co-axial pairs, utilizing normal tracheas, were used. These results indicate a difference in response patterns of the rat anococcygeus muscle and vascular strips in ovalbumin-sensitized tracheas, which should be taken into consideration in co-axial bioassay studies.