Different effects of baclofen on LH and cortisol responses to naloxone in normal men.
The possible involvement of GABAergic B receptors in the control of LH and ACTH/cortisol secretion in response to naloxone was evaluated in seven normal men. Subjects were tested with naloxone (4 mg IV bolus plus 10 mg infused over 2 hr) with or without previous treatment with the gamma-aminobutyric acid (GABA)-ergic B receptor agonist, baclofen (5, 10 or 15 mg PO 30 min before naloxone). In additional experiments, six normal men were tested with 15 mg baclofen or placebo 30 min before a 2-hr infusion of normal saline. Plasma cortisol levels rose 70% in response to naloxone. The naloxone-induced cortisol rise was not modified by pretreatment with baclofen (5, 10 or 15 mg). Plasma LH concentrations rose 66% in response to naloxone. When the lowest dose of baclofen (5 mg) was administered, the LH response to naloxone remained unchanged. In contrast, 10 mg baclofen produced a significant reduction, and 15 mg baclofen completely abolished the naloxone-induced LH rise. The administration of baclofen or placebo alone did not change basal plasma levels of cortisol and LH. These data suggest that, in normal men, GABA B receptors participate in the endogenous opioidergic control of LH secretion, but not of ACTH/cortisol secretion.
Coiro
V
V
Institute of Internal Medicine, School of Medicine, University of Parma, Italy.
Volpi
R
R
Marcato
A
A
Bertoni
P
P
Cavazzini
U
U
Caffarri
G
G
Capretti
L
L
Rossi
G
G
Chiodera
P
P
D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D001418:Baclofen / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D011292:Premedication; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology; D012016:Reference Values
D011963:Receptors, GABA-A; D009270:Naloxone; D000324:Adrenocorticotropic Hormone; D007986:Luteinizing Hormone; D001418:Baclofen; D006854:Hydrocortisone