Characterization of rat pituitary luteinizing hormone charge microheterogeneity in male and female rats using chromatofocusing: effects of castration.

Chromatofocusing was used to characterize the isohormones of rat (r) LH present in extracts of pituitaries of intact and castrate, male and female rats. In each case, at least seven rLH isohormones were observed: one in the void volume of the column [isohormone I, isoelectric point (pI) greater than 9.8], five in the pH range of 9.25-8.97 (isohormones II-VI), and one which was bound to the column but could be eluted with 1.0 M NaCl (isohormone VII, pI less than 7.0). The distribution of immunoreactive rLH among the isohormones was affected by castration in both sexes but was not significantly different in intact males vs. proestrous female rats. Compared to castrates of both sexes, intact male and female rats possessed a larger percentage of immunoreactive rLH as isohormone I. All seven isohormones possessed significant LH biological activity. The bioactivity-immunoactivity (B/I) ratios of rLH isohormones from castrate female rats were significantly greater than those of intact and castrate male rats. The Bio-Index (the amount of biologically active rLH) of isohormones II-VI was markedly increased as a result of castration in both sexes. Changes in B/I ratios and amounts of immunoreactive rLH were not due to the cross-reactivity of rFSH, rTSH, and rPRL in the rLH RIA. Thus, in addition to altering the amount of rLH in the pituitary, castration also alters the pattern of rLH isohormones in the pituitary, yielding a dramatic increase in the isohormones with pI values in the range of 9.06-9.25.