T. Akema et al., ACUTE STRESS SUPPRESSES THE N-METHYL-D-ASPARTATE-INDUCED LUTEINIZING-HORMONE RELEASE IN THE OVARIECTOMIZED ESTROGEN-PRIMED RAT, Neuroendocrinology, 62(3), 1995, pp. 270-276
The effects of N-methyl-D-aspartate (NMDA) and luteinizing hormone rel
easing hormone (LH-RH) on luteinizing hormone (LH) secretion were exam
ined in ovariectomized estrogen-primed rats under nonstressed and acut
ely stressed conditions. The basal LH levels were significantly elevat
ed 15 min after the onset of acute immobilization stress, but were not
altered in emotionally stressed or nonstressed rats. Intravenous inje
ctions of 10 and 40 mg/kg NMDA significantly elevated serum LH levels
by 161 and 212%, respectively, from baseline within 10 min in nonstres
sed animals. However, the NMDA-induced LH release was significantly re
duced when tested 30 min after the onset of acute immobilization stres
s. Acute emotional stress, which did not affect the baseline LH, also
suppressed the LH release response to NMDA, suggesting that the reduce
d LH responses to NMDA in stressed animals was not due to the elevated
baseline level. Pituitary LH release responses to LHRH were not affec
ted by acute immobilization. We conclude from these results: (1) acute
immobilization stress exerts both stimulatory and inhibitory effects
on LH release, while acute emotional stress has only an inhibitory eff
ect in estrogen-primed ovariectomized rats; (2) this inhibition occurs
at the supra-pituitary level, and (3) it involves a suppression of th
e responsiveness of the hypothalamic LH-RH neuronal system to the exci
tatory amino acid input.