Microheterogeneity of luteinizing hormone in pituitary glands from women of pre- and postmenopausal age.

Luteinizing hormone from the pituitaries of women of premenopausal (Pre-M) and postmenopausal (Post-M) age has been studied to further understand the variations in the quality of plasma LH in women of different ages. The median and range for bioactive LH was 101: 85-155 IU/mg protein and 83: 52-201 IU/mg protein for the Pre- and Post-M groups respectively. The ratios of LH bioactivity/immunoreactivity (B:I) were 1.04 +/- 0.13 (Pre-M) and 0.97 +/- 0.02 (Post-M). Broad range isoelectrophoretic profiles of the pituitary extracts revealed a heterogeneous population of coincident bioactive and immunoreactive LH peaks. Recoveries from the columns were similar in both groups and B:I values of the LH material throughout the columns were between 0.5 and 2.0 in over 90% of the fractions. Between 31.8 and 36.6% of the LH from both groups appeared between pH 7 and pH 8. The most striking difference between the two groups was that greater than 34% of the bioactive LH from the Post-M pituitaries, but less than 6% of the LH from the other group had migrated as a major discrete peak to an acidic region of pH less than 6. We conclude that although there is no difference in total LH activity in the pituitaries from the two groups, substantially more 'acidic' LH material is stored in the postmenopausal pituitaries. These observations are consistent with the recent finding of greater circulating levels of acidic LH in plasma from post-menopausal women.