Higher molecular weight immunoreactive species of luteinizing hormone releasing hormone: possible precursors of the hormone.

Separation of extracts of sheep hypothalami on Sephadex G-25 gave three peaks exhibiting luteinizing hormone releasing hormone immunoreactivity. One peak corresponded in elution volume with luteinizing hormone releasing hormone but the others (I and II) eluted earlier, indicating that they are of higher molecular weight. Elution volumes were unaffected by 8 M urea treatment. Incubation of I and II with hypothalamic peptidases produced a small quantity of immunoreactive material eluting in the luteinizing hormone releasing hormone region. Digestion of I with trypsin resulted in a marked increase in total immunoreactivity and the production of material with the same elution volume as II. Tryptic digestion of II gave rise to a small quantity of immunoreactive peptide eluting in the luteinizing hormone releasing hormone region. The amount of I and II relative to luteinizing hormone releasing hormone was lower in the median eminence than in the supra optic chiasmatic and basal hypothalamic regions.