Endogenous opioid peptides have a tonic inhibitory control on LH secretion, participating in the functional changes of the hypothalamic-pituitary-ovarian axis. To evaluate the activity of the endogenous opioid systems during the oestrous cycle, we measured plasma LH levels after naloxone administration (5 mg/kg, s.c.) at 09.00 and 16.00 h on all days of the cycle (two further measurements were taken at 14.00 and 18.00 h on the day of pro-oestrus) and after one dose or one week's treatment with oestradiol benzoate (OB; 0.2 micrograms/rat). Concentrations of LH were measured in the same experimental models after injection of LH-releasing hormone (LHRH; 1 microgram/kg, i.p.) or saline. Naloxone induced a significant rise in LH levels on the day of oestrus, dioestrus day-1 and dioestrus day-2; this response was blunted on the morning of pro-oestrus and absent in the afternoon and after acute and chronic OB treatment. Conversely LHRH was most effective in increasing LH levels on the day of pro-oestrus and in OB-treated rats. These results indicate that opioid mechanisms, independently of the time of day and the pituitary responsiveness, exhibit a reduced activity when preovulatory changes occur, probably as a result of increased oestrogen levels.
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|Titolo:||Oestrous cycle-related LH responsiveness to naloxone: effect of high oestrogen levels on the activity of opioid receptors.|
|Citazione:||Petraglia, F., Locatelli, V., Facchinetti, F., Bergamaschi, M., Genazzani, A.r., & Cocchi, D. (1986). Oestrous cycle-related LH responsiveness to naloxone: effect of high oestrogen levels on the activity of opioid receptors. JOURNAL OF ENDOCRINOLOGY, 108(1), 89-94.|
|Appare nelle tipologie:||1.1 Articolo in rivista|
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