Abstract: 515

LEPTIN AND PUBERTAL DEVELOPMENT IN HEIFERS: RELATIONSHIP OF ob GENE EXPRESSION TO CIRCULATING LEPTIN AS MEASURED BY HETEROLOGOUS RADIOIMMUNOASSAY.

MR Garcia^{1 *}, M Amstalden¹ , SW Williams² , CD Johnson² , SE Nizielski² , DH Keisler^{3 *}, GL Williams^{1 *}
Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, Beeville, TX ¹
Department of Animal Science, Texas A&M University, College Station, TX ²
Department of Animal Science, University of Missouri, Columbia, MO ³

The role of leptin in regulating the onset of puberty in cattle has not been determined. We characterized the patterns of leptin gene expression, and circulating leptin and IGF-1 in heifers during pubertal development. Crossbred beef heifers (7- 9 mo. of age) with an average body weight (BW) of 231.4 ± 3.6 kg and an average body condition score (BCS) of 5.1 ± 0.1 (1-9 scale) were utilized. Blood samples were collected twice weekly for analysis of serum leptin, IGF-1 and progesterone, to confirm the onset of puberty, by RIA. The heterologous leptin RIA was validated by confirming parallelism of inhibition curves of diluted bovine serum with RIA standards, and by quantitative recovery of ovine leptin (Gertler et al., FEBS Letters, 422:137-140; 1998). Subcutaneous adipose tissue was collected every three weeks for Northern analysis using riboprobes prepared from a 350 bp ovine cDNA (GenBank accession #U62123). Heifers gained an average of 119.2 ± 5 kg and 1.1 ± 0.1 BCS units until puberty was confirmed at 14-18 mo. of age. Multiple regression analysis relating week relative to puberty (WKRP) to leptin mRNA, serum leptin and IGF-1, BCS and BW, revealed that BW accounted for most of the variation (R₂ = 0.77; p < 0.001). However, leptin concentrations averaged 6 ± 0.1 ng/ml from -20 to -11 weeks before puberty, then declined 43% (p < 0.001) to a nadir of 3.4 ± 0.1 ng/ml until the pubertal ovulation. Leptin concentrations then increased (p < 0.001) to 4.9 ± 0.6 ng/ml. No consistent differences in leptin mRNA expression or circulating concentrations of IGF-1 were observed during pubertal development; however, serum leptin and leptin mRNA were inversely correlated (R₂ = -0.5; p < 0.003). Although mechanisms are as yet undetermined, these observations suggest that leptin may contribute to pubertal maturation.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.