Leptin mRNA expression and serum leptin concentrations as influenced by age, weight, and estradiol in pigs

Two experiments (EXP) were conducted to determine the roles of age, weight and estradiol (E) treatment on serum leptin concentrations and leptin gene expression. In EXP I, jugular blood samples were collected from gilts at 42 to 49 (n = 8), 105 to 112 (n = 8) and 140 to 154 (n = 8) d of age. Serum l eptin concentrations increased (P < 0.05) with age and averaged 0.66, 2.7, and 3.0 ng/ml (pooled SE 0.21) for the 42- to 49-, 105- to 112-, and 140- t o 154-d-old gilts, respectively. In EXP II, RNase protection assays were us ed to assess leptin mRNA in adipose tissue of ovariectomized gilts at 90 (n = 12), 150 (n = 11) or 210 (n = 12) d of age. Six pigs from each age group received estradiol (E) osmotic pump implants and the remaining animals rec eived vehicle control implants (C; Day 0). On Day 7, back fat and blood sam ples were collected. Estradiol treatment resulted in greater (P < 0.05) ser um E levels in E (9 +/- 1 pg/ml) than C (3 +/- 1 pg/ml) pigs. Serum leptin concentrations were not affected by age, nor E treatment. Leptin mRNA expre ssion was not increased by age in C pigs nor by E in 90- and 150-d-old pigs . However, by 210 d of age, leptin mRNA expression was 2.5-fold greater (P < 0.01) in E-treated pigs compared to C animals. Serum insulin concentratio ns were similar between treatments for 210-d-old pigs. However, insulin con centrations were greater (P < 0.05) in E than C pigs at 90 d and greater in C than E animals at 150 d. Plasma glucose and serum insulin-like growth fa ctor-I concentrations were not influenced by treatment. These results demon strate that serum leptin concentrations increased with age and E-induced le ptin mRNA expression is age- and weight-dependent. (C) Elsevier Science Inc . 1999.