Intact luteinizing hormone (LH), LHβ, and LHβ core fragment in urine of menstruating women

Objectives: We examined different molecular forms of luteinizing hormone (LH) in samples taken during periovulatory days with the aim of revealing different forms of immunoreactivity (LH-ir) in normally menstruating women. Methods: Serum and first-morning-voided urine serum samples were obtained from healthy, 22 to 38 years old, regularly menstruating women during their periovulatory days on their previous menstrual cycles. The day of the LH surge was determined on the basis 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 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, free beta-subunit (LHI3), and the core fragment of LHI3 (LHI3cf) according to their molecular sizes. The latter two are also called non-intact LH. Intact LH was the dominating form day before and on the day of LH surge while LHI3cf was the major form of immunoreactivity after the LH surge for the following 5-7 days. LHI3 was detected on the 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 and mainly as LHI3cf for 7 days following the LH peak.