Serum concentrations of luteinizing hormone, growth hormone, testosterone, estradiol, and leptin in boars treated with n-methyl-D,L-aspartate

Three experiments were conducted to determine the effects of n-methyl-D,L-aspartate (NMA), an agonist of the excitatory amino acid glutamate, on secretion of hormones in boars. In Exp. 1, boars (185.0 + .3 d of age; mean +/- SE) received i.v. injections of either 0, 1.25, 2.5, 5, or 10 mg of NMA/kg BW. There were no effects of NMA (P >.1) on secretion of LH and testosterone. Treatment with NMA, however, increased (P <.01) circulating GH concentrations in a dose-dependent manner. In Exp. 2, boars (401 d of age) received an i.v. challenge of NMA at a dose of 10 mg/kg BW or .9% saline. Treatment with NMA, but not saline (P >.1), increased serum concentrations of LH (P <.01), GH (P <.01), and testosterone (P <.06). In Exp. 3, boars that were 152, 221, or 336 d of age were treated i.v. with NMA(10 mg/kg BW). Across ages, treatment with NMA increased circulating concentrations of LH (P <.07) and testosterone (P <.01). However, NMA increased (P <.01) mean GH concentrations in only the oldest boars. Treatment with NMA had no effect (P <.1) on circulating concentrations of estradiol or leptin; however, estradiol concentrations increased (P <.03) with age. In summary, NMA increased secretion of LH, GH, and testosterone in boars. However, endocrine responses to treatment with NMA may be influenced by age of the animal. Finally, NMA did not influence circulating concentrations of estradiol or leptin.