Submission Number: MAR-4-21-5

Abstract Number: 189

EFFECTS OF ACUTE FEED RESTRICTION AND CENTRAL INFUSION OF RECOMBINANT OLEPTIN ON THE METABOLIC AND CENTRAL REPRODUCTIVE AXES OF MATURE COWS.

M Amstalden* ^1,2, MR Garcia* ^1,2, RL Stanko* ^1,2,3, SE Nizielski ², CD Morrison* ⁴, DH Keisler* ⁴ and GL Williams* ^1,2

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 and Wildlife Sciences, Texas A&M University - Kingsville, Kingsville, TX ³
Department of Animal Science, University of Missouri, Columbia, MO ⁴

Abstract:
Short-term feed restriction reduces leptin gene expression, circulating leptin, insulin, and IGF-I, and LH pulsatility in prepubertal heifers (Amstalden et al., Biol Reprod 2000, in press). This study tested the hypotheses that: 1) acute feed restriction would fail to alter leptin gene expression, circulating leptin, or LH secretion in moderately fat mature cows; 2) central infusion of recombinant oleptin would obviate the effects of fasting on insulin and IGF-I secretion; 3) centrally-infused leptin would stimulate GH and LH secretion. Twelve ovariectomized beef cows (body condition score 6; 1-9 scale) bearing s.c. estradiol implants were assigned randomly to one of two treatments: 1) Control; normal feed consumption (n=6) and 2) Fasted; 48 h of total feed restriction (n=6). Five cows from each group were surgically fitted with an intracerebroventricular (ICV) cannula. Blood was collected at 10-min intervals for 6 h on Day 0 and for 12 h on Day 2. Cows were infused via ICV cannulas with 200 l saline every h for 3 h at the beginning of sampling on Days 0 and 2, and with 200 g recombinant oleptin every h for 3 h during the final 6 h of sampling on Day 2. Adipose tissue was collected on the day before onset (Day 1) and at the end of feeding treatments (Day 2). Acute feed restriction decreased plasma concentrations of leptin (p < 0.001), insulin (p < 0.02) and IGF-I (p < 0.01), but did not affect LH pulse frequency or plasma concentrations of LH, glucose, or GH. Preliminary results of leptin mRNA analyses were inconclusive. Central leptin infusion increased (p < 0.01) circulating concentrations of insulin to normal levels in fasted cows without affecting controls, and increased (p < 0.01) concentrations of GH without effects on plasma IGF-I or glucose. Three cows exhibiting LH pulse frequencies of 1 or less per h had abrupt and sustained increases in mean concentrations of LH after leptin treatment. The remaining cows (n = 4), with an average pulse frequency of 1.4 0.14 pulses/h, did not respond to leptin infusion. In summary, the hypothalamic-pituitary axis of mature cows appeared less sensitive to short-term fasting than observed previously for prepubertal heifers. Marked responses of the somatotrophs and endocrine pancreas to leptin were accompanied by less consistent responses within the gonadotropic axis in this model.

Keywords: Leptin, LH, GH, IGF-I, Insulin, glucose, fasting, cows

This abstract is being presented at: 8:00 AM in session:
Nutrition and Reproduction