Bovine luteinizing hormone (LH) isoforms and amounts of messenger ribonucleic acid for alpha- and LH beta-subunits in pituitaries of cows immunized against LH-releasing hormone.

Abstract

Ovariectomized beef cows were actively immunized against LHRH to test the hypothesis that decreased stimulation of gonadotropes would alter the distribution of LH isoforms and amounts of mRNA for subunits of LH in the pituitary. Eight long-term (3 yr) ovariectomized beef cows were randomly assigned to one of two treatments: immunization against LHRH conjugated to human serum globulin (n = 4) and nonimmunization (control, n = 4). Mean concentration of serum LH in cows immunized against LHRH (1.0 +/- .83 ng/ml) was less (p = 0.01) than in control cows (5.0 +/- 0.83 ng/ml). Amounts of alpha- (p = 0.13) and LH beta-subunit (p = 0.10) mRNA tended to be reduced in cows immunized against LHRH compared to control cows. However, weight of the anterior pituitary and concentrations of LH in this gland did not differ (p = 0.90) among cows from the two groups. Pituitary extracts were chromatofocused on pH 10.5-7.0 gradients, and concentrations of LH in eluent fractions were determined by RIA. Extracts of all pituitaries resolved into nine isoforms (designated A through H and Z beginning with the most basic form). Only isoform F (mid-alkaline elution, pH = 8.8) was influenced by treatment (p = 0.05). Cows immunized against LHRH had a greater relative amount of isoform F (42.1 +/- 1.4%) than controls (37.2 +/- 1.4%). In summary, immunization of cows against LHRH altered 1) circulating concentrations of LH, 2) amounts of mRNA for the subunits of LH, and 3) distribution of intrapituitary LH isoforms without changing the concentrations of LH in the anterior pituitary.