Effects of intracerebroventricular administration of opiate receptor antagonists on the suppressed pulsatile LH release during acute fasting in ovariectomized estradiol-treated rats.
The involvement of specific opiate receptors in the suppression of LH release during acute fasting in ovariectomized estradiol-treated rats was examined by intracerebroventricular (i.c.v.) administration of opiate receptor antagonists that exert a specificity directed mainly, although not absolutely, towards the delta-, kappa- or mu-opiate receptors. Fasting for 48 h significantly decreased mean plasma LH levels in estradiol-treated animals by increasing sensitivity to the negative feedback effect of estradiol. Injecting i.c.v. the mu-opiate receptor antagonist naloxone (10 or 100 nmol in 2 microliters of saline) blocked the inhibitory effect of fasting on pulsatile LH release and reinstated LH pulses. On the other hand, i.c.v. administration of the same dosages of a delta-opiate receptor antagonist ICI 174,864 or a kappa-opiate receptor antagonist WIN 44441-3 did not have any effect. These results suggest that the increased sensitivity of the LH-releasing mechanism to the negative feedback effect of estradiol during fasting involves the endogenous opioids mainly through the selective activation of the mu-opiate receptors.
Cagampang
F R
FR
Laboratory of Animal Reproduction, School of Agricultural Sciences, Nagoya University, Japan.
Maeda
K
K
D000818:Animals; D001392:Azocines / Q000008:administration & dosage; D004743:Enkephalin, Leucine / Q000008:administration & dosage / Q000031:analogs & derivatives; D004958:Estradiol; D005215:Fasting / Q000378:metabolism*; D005260:Female; D007276:Injections, Intraventricular; D007986:Luteinizing Hormone / Q000187:drug effects / Q000378:metabolism*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage*; D010052:Ovariectomy; D010507:Periodicity; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects*
D001392:Azocines; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D009270:Naloxone; D004958:Estradiol; D004743:Enkephalin, Leucine; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine; D007986:Luteinizing Hormone; C035969:quadazocine