Leptin gene expression, circulating leptin, and luteinizing hormone pulsatility are acutely responsive to short-term fasting in prepubertal heifers: relationships to circulating insulin and insulin-like growth factor I(1).
In the present study, we tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and 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 (mean +/- SD = 315 +/- 5 kg body weight) 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 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) as compared with 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 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 hormone signaling energy status to the central reproductive axis in cattle.
Amstalden
M
M
Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, Beeville, Texas 78102, USA.
Garcia
M R
MR
Williams
S W
SW
Stanko
R L
RL
Nizielski
S E
SE
Morrison
C D
CD
Keisler
D H
DH
Williams
G L
GL
D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002417:Cattle; D005215:Fasting; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020738:Leptin / Q000097:blood / Q000235:genetics*; D007986:Luteinizing Hormone / Q000097:blood*; D012741:Sexual Maturation / Q000502:physiology*
D007328:Insulin; D020738:Leptin; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D013006:Growth Hormone