Hypothyroidism is an endocrine disorder. It is well known that changes in thyroid hormone level have a profound influence on intestinal smooth muscle function. Recent studies have suggested that tyrosine kinase participates in the activation of the G-protein-mediated signal transduction pathway of smooth muscle contraction. However, the effect of hypothyroidism on other smooth muscles and involvement of tyrosine kinase in any related effects on contractile responses in this pathological condition remains uncertain. Thus, the purpose of this study was to investigate whether tyrosine kinase was involved in any possible changes in contractile responses to noradrenaline (NA) and nerve stimulation in the isolated rat vas deferens removed from hypothyroid animals.
In order to inhibit tyrosine kinases, we used genistein (a tyrosine kinases inhibitor). Control and hyothyroid rats were humanely killed and segments 2 cm long were removed from the prostatic portion of the vas deferens and mounted in a 50 ml organ bath. An isometric transducer recorded contractile responses to electrical field stimulation and NA. Data are expressed as means ± S.E.M. and analysed by one-way analysis of variance (ANOVA) and values of P < 0.05 were taken as significant.
Electrically evoked contraction in hypothyroid rats was reduced to 0.83 ± 0.04 g, compared to control of 1.7 ± 0.10 g. Maximum contractile response to NA (100 µM) was reduced to 0.38 ± 0.06 g vs. control, 1.09 ± 0.1 g. Contractile response to electrical stimulation was inhibited by genistein: 21.33 ± 3.67 % vs. control, 84.33 ± 2.18 %.
These results show that the contractile responses of vas deferens to electrical stimulation and maximum responses to NA were significantly decreased in hypothyroid rats. The inhibitory effects of genistein on contractile responses of the preparations from hypothyroid rats was less than that in control rats. This phenomenon may be due to a decrease in tyrosine kinase activation in hypothyroid rats, which decreases the Ca2+ sensitivity of actomyosin.