Lack of an effect of morphine or naloxone on the oestrogen-induced LH surge in anoestrous ewes.
To determine whether opioid mechanisms modulate the positive feedback effect of oestrogen on LH secretion, anoestrous ewes were given a single injection of 50 micrograms oestradiol benzoate (OB), followed by infusions of morphine or naloxone. All sheep were injected i.m. with 50 micrograms OB at 00.00 h. In experiment 1, sheep were given i.v. infusions of the following: group 1, 12 ml saline/h from 09.00 to 15.00 h (n = 12); group 2, 40 mg naloxone/h from 09.00 to 12.00 h (n = 5); group 3, 40 mg naloxone/h from 10.00 to 14.00 h (n = 5); group 4, 10 mg morphine/h from 09.00 to 15.00 h (n = 5); and group 5, 20 mg morphine/h from 09.00 to 15.00 h (n = 5). Jugular blood samples were taken at 30-min intervals to monitor LH surges, which commenced 13.0 +/- 0.6 h after injection of OB in control (OB plus saline) ewes. The infusions of naloxone or morphine did not affect the timing or magnitude of the oestrogen-induced LH surge. To examine the possibility that opioidergic regulation of the LH surge occurred earlier than the infusion regimens in experiment 1, sheep were infused from the time of the OB injection (00.00 h) until 15.00 h. In this experiment (experiment 2), sheep were given i.v. infusions of the following: group 1, 4.2 ml saline/h (n = 5); group 2, 20 mg naloxone/h (n = 5); and group 3, 20 mg morphine/h (n = 5). As in experiment 1, treatment with neither the opioid agonist or antagonist was able to alter the positive feedback response of OB.(ABSTRACT TRUNCATED AT 250 WORDS)
Horton
R J
RJ
Medical Research Centre, Prince Henry's Hospital, Melbourne, Australia.
Clarke
I J
IJ
D000780:Anestrus / Q000378:metabolism*; D000818:Animals; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D004971:Estrus / Q000378:metabolism*; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D012756:Sheep; D013997:Time Factors
D009270:Naloxone; D004958:Estradiol; D009020:Morphine; D007986:Luteinizing Hormone