|Barrett, John - Benny|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/26/2001
Publication Date: 2/20/2002
Citation: Gazal, O.S., Kouakou, B., Amoah, E., Barb, C.R., Barrett, J.B., Gelaye, S. 2002. Effects of n-methyl-d, l-aspartate on lh, gh and testosterone secretion in goat bucks maintained under long or short photoperiods.. Journal of Animal Science. Interpretive Summary: Inadequate nutrition is characterized by low blood levels of pituitary hormones which are necessary for stimulation of the reproductive system (luteinizing hormone; LH) and growth (growth hormone; GH). A lack of these hormones results reduced reproductive efficiency and poor growth. The excitatory amino acids (EAA), aspartate and glutamate, are potent stimulators of LH and GH secretion in the rodent. In the ram season effected the LH response to n-methyl-aspartate (NMA), a potent agonist of EAA , treatment. The EAA act as neurotransmitters in the mammalian brain and are localized in a region that controls LH and GH release from the pituitary gland. Male goats exposed to long (LD) and short (SD) days were treated with NMA. The LH and GH response to NMA was greater in LD than SD goats. These results indicated that the EAA modulation of LH and GH secretion is dependent on day length in the goat.
Technical Abstract: Eight mature, intact bucks were used in two simultaneous 4x4 Latin Square design. Variable were photoperiod (Short Day: SD, 10 h light: 14 h dark; n = 4; vs Long Day, LD, 16 h light: 8 h dark; n = 4 treatment) and N-methyl- d, l-aspartate (excitatory amino acid agonist, NMA; 0, 1, 2 and 4 mg/kg BW, iv). Blood samples were collected 2 h before and 2 h after NMA and an addition hour after GnRH injection. NMA increased mean LH and LH pulse frequency and this effect was greater in LD goats and dose dependent. The LH response to GnRH was not affected by photoperiod. Long day reduced testosterone secretion compared to SD bucks. GH secretion was enhanced in LD animals compared SD bucks. The GH response to NMA was greater in LD bucks compared to SD bucks. Exposure of bucks to LD reduced serum testosterone concentrations compared to SD. NMA treatment increased testosterone secretion in a dose dependent manner and was similar between photoperiods. These results indicate that NMA receptors are involved in regulating LH, GH and testosterone secretion in the goat.