Preponderance of basic isoforms of serum luteinizing hormone (LH) is associated with the high bio/immune ratio of LH in healthy women and in women with polycystic ovarian disease.

In an attempt to correlate serum LH isoform distribution with its bio/immuno ratio, follicular phase blood samples from four normally cycling women and four patients with polycystic ovarian disease (PCOD) were studied. Chromatofocusing of peripheral serum samples across a pH gradient of 9.5-4.5 yielded a broad area of LH immunoreactivity comprising several peaks in the pH range of 7.2-9.0, and six other major peaks at pH values of 9.4, 6.8, 6.4, 5.1, 4.7 and less than 4.0. In addition, the bioactive and immunoreactive levels of LH were measured in the unfractionated serum samples. In three out of four PCOD patients and one healthy woman, the majority of LH species (approximately 70%) were distributed at a pI value greater than 7.0. All of them had a high bio/immuno ratio (greater than 2.0) and an elevated bioactive level of serum LH (greater than 40 IU/l). Conversely, fewer alkaline pI isoforms of LH were found in the other three normal women and one PCOD patient, who had low levels of the bio/immuno ratio of LH (less than 2.0) and bioactive LH (less than 40 IU/l). A significant (P less than 0.05) direct correlation was observed between the bio/immuno ratio of serum LH and the proportion of alkaline LH eluted. In conclusion, as demonstrated previously in the pituitary, the bio/immuno ratio of serum LH also correlates well with the charge distribution of LH isoforms. The results indicate that an altered isoform distribution with more basic LH forms is associated with a high biological activity of serum LH.