Peripheral plasma met-enkephalin levels in ovulatory and anovulatory human menstrual cycles

To test the hypothesis that met-enkephalin has a role in human ovulation and that plasma levels may differ between ovulatory and anovulatory ovarian cycles. This is a descriptive study comparing levels of plasma met-enkephalin, gonadotropins, and ovarian steroids in 12 ultrasonically confirmed ovulatory cycles and 12 anovulatory cycles. The study took place in the infertility clinic of a large teaching hospital receiving primary and tertiary referrals of both private and public sector patients. All patients (n = 16) had infertility ≥ 3 years and normal findings on previous investigation including evidence of ovulation. Ovarian cycles were defined using transabdominal ultrasound scanning. Biochemical analyses were by radioimmunoassay. The differences between plasma met-enkephalin levels in the two groups of cycles were compared. Met-enkephalin levels are significantly higher in ovulatory cycles with a significant peak in the 2 postovulatory days (Duncan’s multiple range test; P < 0.05). Human ovulation is associated with cyclic elevation of plasma met-enkephalin. Further studies are required to elucidate causality.