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. |
