Relative effectiveness of naloxone and MR2266 in potentiating oestrogen-stimulated luteinizing hormone surges in ovariectomized female rats.
The oestrogen-stimulated surge of luteinizing hormone (LH) can be inhibited by opiates and potentiated when endogenous opiate pathways are blocked by naloxone. Experiments were undertaken to allow an assessment to be made of the opiate receptor category predominantly responsible for inhibiting LH secretion. Thus the effects of MR2266 (primarily a mu and kappa antagonist) and naloxone (primarily a mu and delta antagonist) on LH surges were compared. At a dose of 4.5 mg/kg, administered three times in the 6 h preceding the LH surge, naloxone significantly potentiated LH release whereas this dose of MR2266 was without effect. However at the lower dose of 0.5 mg/kg, administered three times also, the size of the LH surge was significantly increased by MR2266 but not by naloxone.
D000818:Animals; D001575:Benzomorphans / Q000494:pharmacology*; D002369:Castration; D004357:Drug Synergism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D009019:Morphinans / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D001575:Benzomorphans; D009019:Morphinans; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009270:Naloxone; D004958:Estradiol; C027247:MR 2266; D007986:Luteinizing Hormone