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Repetitive injections of L-glutamic acid, in contrast to those of N-methyl-D,L-aspartic acid, fail to elicit sustained hypothalamic GnRH release in the prepubertal male rhesus monkey (Macaca mulatta).

Abstract：

:The purpose of the present study was to examine whether repetitive intravenous injections of L-glutamic acid (Glu), like those of N-methyl-D,L-aspartic acid (NMA), are able to elicit a sustained train of gonadotropin releasing hormone (GnRH) discharges from the hypothalamus of the prepubertal male monkey. In order to utilize pituitary luteinizing hormone (LH) secretion as a bioassay of hypothalamic GnRH release, the responsiveness of the gonadotroph of the prepubertal animals was enhanced prior to the study with a chronic intermittent intravenous infusion of the synthetic decapeptide (0.1 microgram/min for 3 min every h). Sequential intravenous injections of Glu (150 mg/kg BW) were administered at 3-hour intervals for 6 or 24 h. Although the first injection of this acidic amino acid elicited a robust discharge of GnRH, subsequent stimulation with Glu resulted in GnRH discharges with progressively decreasing magnitudes, and by the 9th injection Glu-induced GnRH release was abolished. Peak concentrations of circulating Glu following the 1st and 4th Glu injection were indistinguishable (3,959 +/- 437 vs. 4,139 +/- 72 nmol/ml, respectively). Interestingly, the failure of repetitive intravenous injections of Glu to sustain pulsatile GnRH release was not associated with a loss of responsiveness to NMA administration, nor was it accompanied by a corresponding decrement in Glu induced growth hormone (GH) discharges. As previously demonstrated, repetitive intravenous administration of NMA (2-5 mg/kg BW) every 3 h for 9 h sustained pulsatile GnRH secretion without decrement. A similar intermittent infusion of kainic acid (KA; 1 mg/kg BW every 3 h for 6 h), however, elicited a GnRH response that mimicked that observed in response to intermittent Glu treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

journal_name

Neuroendocrinology

journal_title

Neuroendocrinology

authors

Medhamurthy R,Gay VL,Plant TM

doi

10.1159/000126186

subject

Has Abstract

pub_date

1992-06-01 00:00:00

pages

660-6

issue

eissn

0028-3835

issn

1423-0194

journal_volume

pub_type

杂志文章

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Repetitive injections of L-glutamic acid, in contrast to those of N-methyl-D,L-aspartic acid, fail to elicit sustained hypothalamic GnRH release in the prepubertal male rhesus monkey (Macaca mulatta).