Leptin gene expression and circulating leptin in relation to luteinizing hormone, growth hormone, insulin, and insulin-like growth factor-I in prepubertal heifers

Abstract

The present study tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and luteinizing hormone (LH) pulsatility in prepubertal heifers in association with a decrease in circulating concentrations of insulin and insulin-like growth factor-I (IGF-I). Twelve prepubertal crossbred heifers (average body weight = 315 [] 5 kg) were assigned randomly to one of two treatments in two replicates: 1) Control; normal feed consumption (n=6) and 2) Fasted; 48 h of total feed restriction (n=6). Blood samples were collected at 15-min intervals for 8 h on Days 0 and 2 of the experiment, and twice on Day 1. Subcutaneous fat samples were collected before treatment onset (Day -1) and at the end of the intensive blood sampling on Day 2. Acute feed restriction markedly reduced leptin messenger ribonucleic acid (mRNA) in adipose tissue (p < 0.01) and circulating concentrations of leptin (p < 0.05), IGF-I (p < 0.01), and insulin (p = 0.05) compared to Controls on Day 2. Moreover, the treatment x day interaction (p < 0.076) and within-day contrasts (expressed as a percentage of Day 0 values) revealed that the mean frequency of LH pulses in the fasted group declined (p < 0.01) and was lower (p < 0.06) than in Controls on Day 2. Neither mean concentrations of growth hormone (GH) nor GH secretory dynamics were affected by acute feed restriction. Fasting-mediated decreases in leptin gene expression and circulating leptin, in association with reductions in secretion of IGF-I, insulin, and LH, provide a basis for investigating leptin as a metabolic hormone that signals energy status to the central reproductive axis in cattle.