Acute immobilization stress and intraventricular injection of CRF suppress naloxone-induced LH release in ovariectomized estrogen-primed rats.
The present study was undertaken to evaluate the role and possible interaction of the endogenous opioid peptide (EOP) and corticotropin-releasing factor (CRF) in the acute stress-induced suppression of gonadotropin secretion in ovariectomized estrogen-primed rats. An intravenous (i.v.) injection of naloxone (10 or 20 mg/kg), an EOP antagonist, significantly elevated serum luteinizing hormone (LH) levels within 10 min in non-stressed animals. The naloxone-induced LH release was completely eliminated when tested 30 min after the onset of acute immobilization. In a subsequent study, it was found that suppression of the naloxone-induced LH release occurred as early as 5 min after the stress onset, and was still evident 60 min after the end of a 30-min period of immobilization. The effect of naloxone was restored 3 h after liberation of the animal from the 30-min immobilization. An intraventricular (i.c.v.) injection of CRF (1 or 5 micrograms) also significantly suppressed, in a dose-related manner, the effect of a subsequent i.v. injection of naloxone. However, an i.c.v. injection of alpha-helical CRF(9-41) (25 or 50 micrograms), a CRF antagonist, prior to immobilization, could not interfere with the suppressive effect of stress on naloxone-induced LH release. These results suggest that both acute immobilization stress and CRF can inhibit the LH secretory activity without mediation by EOP neurons. However, the stress-related suppression may involve non-CRF mechanism(s).
Akema
T
T
Department of Physiology, St. Marianna University School of Medicine, Kawasaki, Japan.
Chiba
A
A
Shinozaki
R
R
Oshida
M
M
Kimura
F
F
Toyoda
J
J
D000704:Analysis of Variance; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D003864:Depression, Chemical; D004723:Endorphins / Q000037:antagonists & inhibitors*; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D007276:Injections, Intraventricular; D007986:Luteinizing Hormone / Q000378:metabolism*; D009270:Naloxone / Q000037:antagonists & inhibitors*; D010052:Ovariectomy; D010053:Ovary / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012149:Restraint, Physical; D012636:Secretory Rate / Q000187:drug effects; D013312:Stress, Physiological / Q000503:physiopathology*
D004723:Endorphins; D004967:Estrogens; D009270:Naloxone; D007986:Luteinizing Hormone; D003346:Corticotropin-Releasing Hormone