[Augmentation, by naloxone, of the frequency and amplitude of LH-RH pulses in hypothalamo-hypophyseal portal blood in the castrated ram].
The effect of naloxone administration on the LH-RH secretion in hypophyseal portal blood and LH secretion in peripheral blood was studied in four short term castrated rams (between 2 to 4 days after castration). For two animals (A and B) given a single naloxone injection, an increase of LH-RH pulse amplitude was observed (A, 22.3 to 80.5 pg/ml and B, 22.5 to 34.5 pg/ml) with only a small (nonsignificant) increase in LH-RH pulse frequency. For animals C and D given four injections of naloxone, both LH-RH pulse amplitudes and LH-RH pulse frequency were increased. Means of LH-RH pulse amplitude increase from 29.3 to 65.1 pg/ml and from 34.6 to 50.8 pg/ml for animals C and D respectively and the number of LH-RH pulses detected during the 3 hrs. before and after the first injection of naloxone were respectively 3 vs. 5 and 3 vs. 7. Whereas all LH pulses were preceded with a LH-RH pulse in animals A and B, after the multiple naloxone injections in animals C and D, a rapid LH-RH pulse frequency was associated with a sustained increment of LH secretion in peripheral blood in such a way that individual LH pulses were not clearly defined. The present report is the first documentation on naloxone increasing the release of LH-RH secretion in hypophyseal portal blood of conscious, unrestrained, short-term castrated rams. The results indicate: (1) that the opiate antagonist naloxone is able to increase both the amplitude and the frequency of LH-RH discharge by the hypothalamus and (2), when the LH-RH pulse frequency exceeds one pulse every 30 min., discrete LH secretory episodes are not observed in peripheral blood.
D000818:Animals; D007987:Gonadotropin-Releasing Hormone / Q000097:blood*; D007031:Hypothalamus / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009919:Orchiectomy; D010902:Pituitary Gland / Q000378:metabolism*; D011168:Portal System / Q000032:analysis*; D012756:Sheep; D013268:Stimulation, Chemical
D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D007986:Luteinizing Hormone
Augmentation par la naloxone de la fréquence et de l'amplitude des pulses de LH-RH dans le sang porte hypothalamo-hypophysaire chez le bélier castré.