Abstract: 91

LEPTIN GENE EXPRESSION IS ACUTELY RESPONSIVE TO SHORT-TERM FASTING IN PREPUBERTAL HEIFERS: RELATIONSHIP TO CIRCULATING LEPTIN, INSULIN-LIKE GROWTH FACTOR-1, AND LUTEINIZING HORMONE PULSATILITY.

M Amstalden¹ , MR Garcia^{1 *}, SW Williams¹ , RL Stanko¹ , 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

A role for leptin as a metabolic signal linking body energy reserves to the central reproductive axis has not been demonstrated in ruminants. We tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and LH pulsatility in prepubertal heifers. As a corollary, we monitored serum insulin-like growth factor-1 (IGF-1), which is acutely suppressed by short-term fasting and is involved in pubertal maturation. Twelve prepubertal crossbred heifers (315 ± 5 kg BW) were assigned randomly to one of two treatments in two replicates: 1) Control; normal feed consumption (n = 6); 2) Fasting; 56-h of total feed restriction (n = 6). Blood samples were collected at 15-min intervals for 8 h on Days 1 and 3 of the experiment, and twice on Day 2. Subcutaneous fat samples were collected before treatment onset (Day 0) and at the end of intensive blood sampling on Day 3. Fasting reduced leptin mRNA expression in adipose tissue by 45% (p < 0.01) on Day 3, with a similar decline (50%; p < 0.01) in serum concentrations of IGF-1. The frequency of LH pulses (2 ± 0.2 pulses/8h) did not differ between groups on Day 1. However, by Day 3, LH pulse frequency in the Fasted group had declined (p < 0.01) to 0.83 ± 0.3 vs 1.4 ± 0.3 pulses/8h in Controls (Trt × Day = p < 0.08). Neither circulating concentrations of growth hormone nor leptin were affected by fasting. These findings are consistent with our hypothesis that leptin gene expression is acutely responsive to short-term nutrient restriction in heifers. The close association of leptin gene expression with changes in serum IGF-1 and LH pulse frequency suggests that leptin may serve as a metabolic signal to the central reproductive axis in cattle. However, the lack of correspondence between leptin synthesis and serum leptin concentrations remains problematic and needs to be examined further.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.