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Biology of Reproduction 59, 1124-1130 (1998)
©Copyright 1998 Society for the Study of Reproduction, Inc.

Excitatory Amino Acid Regulation of Gonadotropin Secretion in Prepubertal Heifer Calves1

Ali Honaramooza, Ramesh K. Chandolia3,a, Andrew P. Bearda, , and Norman C. Rawlings2,a

a Department of Veterinary Physiological Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5B4

The mechanisms controlling the pulsatile release of gonadotropins in prepubertal heifers are not completely understood. We examined the role of excitatory amino acid neurotransmitters, via activation of N-methyl-D-aspartate (NMDA) receptors, in the control of pulsatile LH and FSH release during prepubertal development in heifers. Hereford heifer calves received 4.7 mg/kg of N-methyl-D,L-aspartic acid (NMA), a potent NMDA receptor agonist (n = 5, i.v.), or saline (n = 5, i.v.), as single doses, at 4, 8, 12, 24, 36, and 48 wk of age. Blood samples were collected every 15 min, for 1 h before and 9 h after injection, on the days of treatment. Injection of NMA resulted in an acute release of LH (p < 0.001) in 0, 3, 3, 4, 5, and 5 calves (p < 0.01) and of FSH (p < 0.001) in 0, 1, 2, 4, 3, and 2 calves at 4, 8, 12, 24, 36, and 48 wk of age, respectively. The peak response of LH and FSH release to NMA was at 15 min posttreatment, and these peak responses were highest at 36 wk of age (p < 0.05). We suggest that neuroexcitatory amino acids, through NMDA receptors, are involved in prepubertal development of LH and FSH secretion in heifer calves.

1 This study was supported by a Natural Sciences and Engineering Research Council Grant to N.C.R. Portions were presented at the 29th annual meeting of the Society for the Study of Reproduction, London, Ontario, Canada, July 27–30, 1996. A.H. was supported by the Iranian Ministry of Culture and Higher Education.

2 Correspondence: Norman C. Rawlings, Department of Veterinary Physiological Sciences, Western College of Veterinary Medicine, 52 Campus Drive, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5B4, Canada. FAX: 306 966 7376; rawlings{at}sask.usask.ca

3 Current address: Department of Dairy and Poultry Sciences, P.O. Box 110920, University of Florida, Gainesville, FL 32611–0920.




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