Involvement of the central noradrenergic system in opioid modulation of luteinizing hormone and prolactin secretion in the pig.
The role of norepinephrine (NE) in the progesterone (P)-dependent endogenous opioid peptide (EOP) suppression of LH and prolactin (PRL) secretion in the pig was studied. Fifteen ovariectomized gilts treated with P (0.85 mg/kg b.w. i.m.) twice daily for 10 days were assigned, 5 gilts each, to the following treatment groups: 1) control, 2) AIMAX (N-methyl-N1[1-methyl-2-propenyl]1,2 hydrazinedicarbothioamide), and 3) anti-GnRH serum. On day 4 of P treatment, AIMAX (125 mg per 1.8 kg feed/day), previously shown to be an NE synthesis inhibitor, was fed daily for 7 days to group 2. On the last day of P treatment, group 3 gilts received an i.v. injection of anti-GnRH serum at 0800 h while Group 1 animals received an i.v. injection of serum collected from hypophysectomized gilts. Jugular blood samples were collected every 15 min for 9 h starting at 1000 h. All gilts received two injections of naloxone (NAL; 1 mg/kg b.w., i.v.) at 1400 h and 1600 h and an injection of a GnRH analogue (D-[Ala6-desGly-NH10]-ethylamide; 5 micrograms/pig, i.v.) at 1800 h. Pretreatment serum LH concentrations were lower (p < 0.05) in AIMAX-treated gilts (0.19 +/- 0.09 ng/ml) than in controls (0.53 +/- 0.09 ng/ml), but were similar to those in GnRH antiserum-treated gilts (0.32 +/- 0.09 ng/ml). NAL increased (p < 0.001) serum LH concentrations in control animals and averaged 1.6 +/- 0.2 ng/ml the first h. AIMAX and anti-GnRH serum blocked the NAL-induced LH secretion. Serum PRL concentrations averaged 6.0 +/- 0.1 ng/ml for all groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Chang
W J
WJ
Animal and Dairy Science Department, University of Georgia, Athens 30602.
Barb
C R
CR
Kraeling
R R
RR
Rampacek
G B
GB
Leshin
L S
LS
D000818:Animals; D004723:Endorphins / Q000502:physiology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors; D007986:Luteinizing Hormone / Q000378:metabolism*; D008693:Methallibure / Q000494:pharmacology; D009638:Norepinephrine / Q000502:physiology*; D010052:Ovariectomy; D010053:Ovary / Q000502:physiology; D011374:Progesterone / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism*; D013552:Swine
D004723:Endorphins; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D011388:Prolactin; D007986:Luteinizing Hormone; D008693:Methallibure; D009638:Norepinephrine