Role of Vitamin E in uterine responsiveness to acetylcholine and histamine in strips from hyperthyroid rats
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The influence of hyperthyroidism on uterine responsiveness to acetylcholine (ACh) and histamine and the effect of vitamin E treatment were assessed in non-pregnant albino rats. Twenty-four rats were initially, equally divided into euthyroid and hyperthyroid groups. One week later, euthyroid group was further re-grouped into non-treated (Group Eu) and vitamin E-treated (Group Eu-VE), and hyperthyroid group was also re-grouped into non-treated (Group H) and vitamin Etreated (Group H+VE), each of 6 rats, for another week. Experimental hyperthryoidism was induced by daily intraperitoneal injection of triiodo- L-thyronine. At the end of the experiment, isometric spontaneous contractions of isolated uterine strips, hung in standard organ baths, and the contractile response to ACh and histamine were recorded. The average strength (aSC), average duration (aDC) and frequency (FC) of contraction as well as the percent (%) change of each parameter, from its initial spontaneous value, in response to ACh and histamine were calculated. In all groups, a stimulatory effect of ACh on uterine contractility was observed, with a significant increase in aSC and PC and a significant shortening of aDC compared to those of the spontaneous contractions initially obtained. Histamine showed an inhibitory effect on uterine contractility in all groups, where aSC was significantly reduced compared to that of the initial spontaneous contractions; aDC and FC were insignificantly changed. Group Eu-VE shoed a non-significant variation in aSC, aDC and FC of the spontaneous uterine contractions and in the % changes of aSC, ADC and FC in response to ACh and histamine when compared with those in group Eu. In group H, spontaneous contractions showed a significantly more aSC and aDC and a significantly less FC compared to those in group Eu; a reduced uterine responsiveness was evident by a significant decrease in the % changes of aSC, aDC and FC in response to ACh and only of aSC in response to histamine. In Group H+VE, spontaneous contractions showed non-significant changes in aSC, aDC and FC in comparison to those in Group H, but an enhanced uterine responsiveness was evident by significantly more % changes of aSC, aDC and FC in response to ACh, and only of aSC in response to histamine. Compared to Group Eu, Group H+VE showed an insignificant variation in the % changes of aSC and aDC, but that of FC was still significantly less, in response to ACh; the % changes of all the previously mentioned parameters were statistically insignificant in response to histamine. It can be concluded that decreased uterine responsiveness to ACh and histamine is characteristic of hyperthyroidism in rats. Vitamin E treatment of hyperthyroid rats, possibly by reducing the burden of associated oxidative stress, resulted in an improvement of the uterine contractile response to both the stimulatory effect of ACh and the inhibitory effect of histamine.