The Influence Of a Combined Oral Contraceptive On Uterine Activity And Reactivity To Agonists In Primary Dysmenorrhea

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Abstract
The mechanisms underlying the therapeutic effect of an oral contraceptive (150 .mu.g levonorgestrel and 30 .mu.g ethinyl estradiol daily for 21 days) in primary dysmenorrhea were studied by recordings of uterine acitivity and reactivity to lysine (L) vasopressin (VP) and prostaglandin (PG) F2.alpha. on the first day of menstruation in 14 women before and after one period of oral contraceptive treatment. During the first session, when all women had moderate to severe dysmenorrhea, intra-uterine pressure recording showed an intensive uterine activity, and bolus injections of LVP (6 pmol/kg body weight; 6 subjects) or PGF2.alpha. (6 or 12 nmol/kg body weight; 4 subjects in each group) increased contractile activity and discomfort. After oral contraceptive treatment, spontaneous uterine activity, measured as total pressure area, decreased significantly (p=0.02 and p=0.03 in the VP and PG groups, respectively). The mean uterine responses to LVP and PGF2.alpha. were on average smaller after oral contraceptive treatment and the women experienced minimal discomfort after this injection. It is suggested that inhibition of uterine activity could be an important mechanism for the tharapeutic effect of gestagen-dominated oral contraceptives in primary dysmenorrhea and that reduced uterine reactivity to agonists might contribute to the effect.