RESUMO
The induced shielding cone is one of the most characteristic aspects of aromatic species. Herein, we explore its behavior under different orientations of the applied magnetic field by evaluating the overall and dissected π- and σ-electron contributions. Our results shed light onto the orientation dependence behavior of the shielding cone, unraveling a characteristic pattern upon rotation of the aromatic ring. This pattern decreases the long range of the magnetic response, such that it resembles the behavior under constant molecular tumbling in solution.
RESUMO
In immature rat uterus histamine (10(-6) mol.l-1) potentiates by 25%, the carbachol (2 x 10(-6) mol.l-1) induced uterine contractions. This potentiation is abolished by mepyramine (6 x 10(-9) mol.l-1), an H1-receptor antagonist. Higher concentrations of histamine, up to 10(-4) mol.l-1, did not exert any inhibitory effect on carbachol-induced uterine contractions. In mature rat uterus carbachol-induced contractions are inhibited by histamine by about 25%. This inhibitory effect of histamine is significantly enhanced by mepyramine by about 50%. Inhibitory effects of higher concentrations of histamine, up to 10(-4) mol.l-1, are not enhanced by mepyramine. Cimetidine (4 x 10(-4) mol.l-1), an H2-receptor antagonist, abolished the inhibitory effects of histamine on carbachol-induced uterine contractions. In conclusion, in immature rat uterus there exists only H1 histamine receptors, activation of which exert an excitatory effect. In mature rat uterus there exists both H1 and H2 histamine receptors. The relaxant effect of histamine on mature rat uterus is exerted by activation of H2-receptors which predominate.