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  • Title: Failure of naloxone to stimulate luteinizing hormone secretion during pregnancy and steroid treatment of ovariectomized beef cows.
    Author: Rund LA, Thompson FN, Byerley DJ, Kiser TE.
    Journal: Biol Reprod; 1990 Apr; 42(4):619-24. PubMed ID: 2346772.
    Abstract:
    The response of serum luteinizing hormone (LH) to naloxone, an opiate antagonist, and gonadotropin-releasing hormone (GnRH) was measured in cows in late pregnancy to assess opioid inhibition of LH. Blood samples were collected at 15-min intervals for 7 h. In a Latin Square arrangement, each cow (n = 6) received naloxone (0, 0.5, and 1.0 mg/kg BW, i.v.; 2 cows each) at Hour 2 on 3 consecutive days (9 +/- 2 days prepartum). GnRH (7 ng/kg body weight, i.v.) was administered at Hour 5 to all cows on each day. Mean serum LH concentrations (x +/- SE) before naloxone injection were similar (0.4 +/- 0.1 ng/ml), with no serum LH pulses observed during the experiment. Mean serum LH concentrations post-naloxone were similar (0.4 +/- 0.1 ng/ml) to concentrations pre-naloxone. Mean serum LH concentrations increased (p less than 0.05) following GnRH administration (7 ng/kg) and did not differ among cows receiving different dosages of naloxone (0 mg/kg, 1.44 +/- 0.20; 0.5 mg/kg, 1.0 +/- 0.1; 1.0 mg/kg, 0.9 +/- 0.1 ng/ml). In Experiment 2, LH response to naloxone and GnRH was measured in 12 ovariectomized cows on Day 19 of estrogen and progesterone treatment (5 micrograms/kg BW estrogen: 0.2 mg/kg BW progesterone) and on Days 7 and 14 after steroid treatment. On Day 19, naloxone failed to increase serum LH concentrations (Pre: 0.4 +/- 0.1; Post: 0.4 +/- 0.1 ng/ml) after 0, 0.5, or 1.0 mg/kg BW.(ABSTRACT TRUNCATED AT 250 WORDS)
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