Leptin gene expression and circulating leptin in relation to luteinizing hormone, growth hormone, insulin, and insulin-like growth factor-I in prepubertal heifers
Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaves 38-55).Issued also on microfiche from Lange Micrographics.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
