Objective: 

Primary dysmenorrhea, also known as menstrual cramping, is believed to result from uterine muscle ischemia through vasocontriction and myometrial contraction due to excessive production of prostaglandins. The aim of this study was to investigate the effects of metamizole, commonly used for menstrual pain, on the contractility of isolated rat myometrium to determine whether it has also relaxing effect on the myometrium.

Methods: 

Myometrial strips were obtained from non-pregnant Wistar rats following decapitation and suspended under 1 gram of resting tension in a double-jacketed isolated tissue bath filled with physiological saline, continuously gassed with 95% O2–5% CO2 at pH 7. PGF2a (1 mM) was added to stimulate contractions and cumulatively added concentrations (7, 20, 30 and 50 mM) of metamizole-Na was tested on amplitude, frequency and area-under-contractile-curve (AUC) by 10 minutes intervals. Data were analysed using ANNOVA, p<0.05 being statistically significant.

Results: 

PGF2a significantly stimulated spontaneous contractions which were inhibited by metamizole in a dose-dependant manner. The mean frequency of PGF2a-induced contractions was 13.6±3.8, which was inhibited to 11.9 ±3.8 (p>0.05), 10±1.5 (p<0.05), 8±1 (p<0.01), 4.6±1.6 (p<0.001), (n=9 for each). Mean percentage inhibition of the AUC of PGF2a-induced contractions was found to be 0% (p<0.05), 16% (p<0.05), 42% (p<0.01) and 67% (p>0.001) after application of 7, 20, 30 and 50 mM metamizole, respectively (n= 9 for each).

Conclusions: 

Data from this study indicates that metamizole inhibits the PGF2a-induced contractions of rat myometrium in a dose dependent manner, but requiring higher concentrations could be achieved after conventional use.