Biological and immunological characterization of human luteinizing hormone: I. Biological profile in pituitary and plasma samples after electrofocusing.

Pituitary and plasma pools from postmenopausal women and plasma pools from women at midcycle were fractionated by electrofocusing in sucrose density gradients. The biological LH activity was determined in each of the electrofocusing fractions by the use of an in vitro bioassay method. A heterogeneous profile of LH activity was found in both pituitary and plasma samples with a large proportion present within the pH range 6.5-10. In a total of 11 electrofocusing runs 7 main regions of high LH activity were found within this range with mean pI values (+/- SD) of 6.75 +/- 0.08 (n = 6), 7.33 +/- 0.08 (11), 7.80 +/- 0.09 (11), 8.23 +/- 0.10 (11), 8.81 +/- 0.04 (7), 9.17 +/- 0.05 (6) and 9.55 (2). A significantly higher proportion of LH activity was found in the midcycle plasma samples (36%) in the pH regions with mean pI values of 8.81, 9.17 and 9.55 than in postmenopausal plasma (7%) and pituitary extracts (5%). This indicates that the profile of biologically active LH in women in the fertile age is different from that present in postmenopausal women. By detailed fractionation based on narrow pH range studies and the refocusing of specific peak fractions it was shown that each of the regions studied consisted of several peaks of LH activity indicating the presence of a large number of molecular species exhibiting varying degrees of LH activity. The relative proportions of these species showed considerable differences between sources but also between samples from the same source.