Opioid action on luteinizing hormone secretion in newborn pigs: paradoxical effect of naloxone.
German Landrace piglets, 6-7 days of age, received either saline (9 males, 8 females), 0.5 mg naloxone/kg body weight (7 males, 7 females), 2.0 mg naloxone/kg (7 males, 8 females) or 0.5 mg DADLE (potent leu-enkephalin analog)/kg (7 males, 7 females) through a catheter inserted into the jugular vein 2-4 days previously. Male or female piglets were allocated randomly, within litter, to the different experimental groups. Blood samples were withdrawn for a period of 240 min at 10-min intervals for the first 60 min following injection and at 20-min intervals for the rest of the test period. Piglets were separated from their mother via a detachable wall and were allowed to suckle every 50 min. DADLE failed to alter plasma levels of LH in both males and females. Naloxone induced a significant (P less than 0.01) decrease in LH concentrations in females 10 to 60 min after injection (saline: 2.3 +/- 0.2 ng/ml plasma (SEM); 0.5 mg naloxone/kg: 1.0 +/- 0.2 ng/ml plasma and 2 mg naloxone/kg 1.2 +/- 0.4 ng/ml plasma). In males low doses of naloxone reduced plasma LH levels 10 to 40 min after injection (saline: 2.0 +/- 0.3 ng/ml plasma and 0.5 ng naloxone/kg: 1.1 +/- 0.3 ng/ml), whereas a decrease in plasma LH levels occurred 80 to 140 min after injection of high doses of naloxone (saline: 2.1 +/- 0.2 ng/ml and 2 mg naloxone/kg: 1.0 +/- 0.2 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)
Prunier
A
A
Research Unit Endocrinology and Neuroendocrinology, Institute of Animal Husbandry and Animal Behaviour (FAL), Neustadt, Federal Republicof Germany.
Ellendorff
F
F
Parvizi
N
N
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004958:Estradiol / Q000097:blood; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011374:Progesterone / Q000097:blood; D013552:Swine; D013739:Testosterone / Q000097:blood
D004723:Endorphins; D009270:Naloxone; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone