Pb. Lieberman et al., THE ROLE OF ENDOGENOUS OPIOIDS IN THE LUTEINIZING-HORMONE SURGE IN RATS - STUDIES WITH CLOCINNAMOX, A LONG-LASTING OPIOID RECEPTOR ANTAGONIST, European journal of pharmacology, 352(1), 1998, pp. 73-79
Endogenous opioid peptides have been demonstrated to regulate luteiniz
ing hormone (LH) secretion in a variety of species. Studies in rodents
suggest a role of opioid peptide systems in controlling the timing of
the LH surge, which is entrained to the circadian rhythm. The current
studies utilize clocinnamox, a novel long-lasting opioid receptor ant
agonist that is capable of occupying mu-opioid receptors for periods o
f one week or more, to examine the role of endogenous opioid systems o
n the LH surge. Administration of clocinnamox lorocinamoylamino)-7,8-d
ihydro-N-cyclopropylmethyl normophineone mesylate]) on the morning of
proestrus advanced the LH surge by several hours. Despite the blockade
of opioid receptors and analgesia for more than one week, administrat
ion of clocinnamox on the evening of diestrus II had no effect on the
timing of the LH surge bur significantly increased plasma LH levels th
roughout the day of proestrus. These data suggest that removal of opio
id tone is unlikely to be the critical signal controlling the initiati
on of the LH surge in rodents, although it does appear to be permissiv
e for the surge. Furthermore, the mu-opioid receptor appears to be the
receptor involved in the regulation of the LH surge. (C) 1998 Elsevie
r Science B.V. All rights reserved.