Intact luteinizing hormone, LHβ, and LHβ core fragment in urine of menstruating women.

Background: We examined different molecular forms of luteinizing hormone (LH) in urine samples taken during periovulatory days with the aim of revealing different forms of LH immunoreactivity (LH-ir) in normally menstruating women.

Methods: Serum and first-morning-voided urine serum samples were obtained from six healthy, 22 to 38 years old, regularly menstruating women during their periovulatory days based on their previous menstrual cycles. The day of the LH surge was determined on the basis of serum LH concentrations and confirmed by an at least two-fold increase in urinary concentrations of intact LH on consecutive days. Different molecular forms of LH-ir were identified by gel filtration of first-morning-voided urine samples obtained from regularly menstruating women on periovulatory days.

Results: Different forms of LH immunoreactivity (LH-ir) were distinguished as intact LH, its free beta-subunit (LHβ), and the core fragment of LHβ (LHβcf) according to their molecular sizes. The latter two are also called non-intact LH. Intact LH was the dominating form on the day before and on the day of LH surge while LHβcf was the major form of LH immunoreactivity after the LH surge for the following 5-7 days. LHβ was detected on the day of the LH surge as well as on the following day.

Conclusions: These results indicate that LH is degraded in the kidneys and excreted as LHβ, and mainly as LHβcf for 7 days following the LH peak.