title: Morphine decreases LH secretion in ovariectomized ewes only after steroid priming and not by direct pituitary action.
abstract: To determine whether opiates directly modulate pituitary LH secretion in vivo, morphine was administered to hypothalamo-pituitary-disconnected (HPD) ewes which were receiving exogenous pulses of GnRH. To define the steroidal background which is permissive to a morphine-induced decrease in LH secretion, ovariectomized (OVX) ewes were treated as follows in groups of four: group 1, no implant; group 2, small 17 beta-estradiol (E2) (1 cm long x 0.33 diameter) and progesterone (P) implants; group 3, medium E2 (1 cm long x 0.46 diameter) and P implants, and group 4, medium E2 implants. Jugular blood samples were taken at 10-min intervals for 9 h, during which there was a 3-hour pretreatment period, a 3-hour treatment period when the sheep were given six intravenous injections of 10 mg morphine every 30 min, and a 3-hour run-off period. Morphine inhibited the mean plasma concentrations of LH and LH pulse frequency in group 3 only, and in 2/4 ewes in this group LH secretion was abolished and did not return to a pulsatile mode during the 3-hour run-off sampling period. In a second experiment designed to test the pituitary action of morphine, OVX-HPD ewes were primed with medium E2 and P implants and were given hourly pulses of 250 ng GnRH intravenously. Jugular blood samples were taken around each GnRH pulse over an 8-hour period. The first three pulses served as a control sampling period, after which the sheep were treated with morphine (six intravenous injections of 10 mg morphine every 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Medical Research Centre, Prince Henry's Hospital, Melbourne, Australia.
authors: R J
authors: RJ
authors: Horton
authors: J Y
authors: JY
authors: Li
authors: J T
authors: JT
authors: Cummins
authors: A I
authors: AI
authors: Smith
authors: P J
authors: PJ
authors: Shen
authors: I J
authors: IJ
authors: Clarke
mesh_terms: D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007031:Hypothalamus / Q000502:physiology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000378:metabolism; D010052:Ovariectomy; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology*; D012756:Sheep
chemical_list: D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D011374:Progesterone; D004958:Estradiol; D009020:Morphine; D007986:Luteinizing Hormone