Effect of immunization against LHRH on isoforms of LH in the ovine pituitary.

The role of LHRH in modulating intrapituitary LH content as well as the distribution of LH among its isoforms was examined in sheep. Rams (n = 3) and wethers (n = 6) were actively immunized against an LHRH-human serum globulin conjugate. Pituitaries collected from these animals plus pituitaries from corresponding numbers of nonimmunized rams and wethers were extracted with a buffered saline solution containing protease inhibitors. Immunization markedly reduced total amounts of immunoreactive LH in the pituitary. An aliquot of each pituitary extract was desalted by flow dialysis against water and chromatofocused on a pH 10.5-7.0 gradient. Concentrations of LH in chromatofocusing fractions were determined by radioimmunoassay. LH in pituitary extracts resolved into nine peaks during chromatofocusing which were coded with letters beginning with the most basic isoform. The percentage of LH as the two most basic isoforms, A' and B, was similar (P > 0.05) in all treatment groups. Isoform H constituted a higher percentage (P < 0.05) of the LH in both castrate groups. Nonimmunized wethers had higher percentages of isoforms C, D and E (P < 0.05) and lower percentages (P < 0.05) of the acidic isoforms (coded as peak Z herein) than did other treatment groups. Thus, castration shifted the pattern of intrapituitary isohormones towards the more basic forms. Nonimmunized rams had a higher percentage (P < 0.05) of isoform G than did other groups. Isoform F, the most abundant isoform, was present as a higher percentage (P < 0.05) in immunized rams and wethers than in nonimmunized animals.(ABSTRACT TRUNCATED AT 250 WORDS)