Involvement of mu-opioid receptors in the modulation of pituitary-adrenal axis in normal and stressed rats.
The availability of the most selective, high-affinity, natural opioid agonists for mu-receptors (dermorphin-DM) and delta-receptors (deltorphin-DT) has provided the possibility for in vivo studying of the role of acute and chronic activation of mu- and delta-opioid receptors on the functional activity of the hypothalamus-pituitary-adrenocortical (HPA) axis, both in basal conditions and in response to an acute stress in adult male rats. Plasma corticosterone (CS) and beta-endorphin-like-immunoreactivity (beta-EP-LI) levels were measured by specific radioimmunoassays before and after 5 and 30 minutes from the exposure to cold (3 +/- 0.5 C) water and forcing them to swim for 10 minutes (acute cold swimming stress). Acute administration of DM, the specific mu-receptor agonist, enhanced basal and stress induced plasma levels of CS and beta-EP-LI. These effects were antagonized by pretreatment with naloxone, specific mu-opioid receptor antagonist, but not by naltrindole, a delta-opioid receptor antagonist. Long-term administration of DM did not alter resting plasma levels of CS and beta-EP-LI, but significantly reduced stress-induced increase of these hormones. Both the acute and chronic administration of the DT, highly selective delta-opioid receptors agonist, failed to modify resting and stress induced hormone levels. Our present data show that DM throughout mu-opioid receptors, but not DT, modulates the response of HPA axis to acute stress in rats, increasing or decreasing the release of CS and beta-EP-LI when acutely or chronically administered, respectively.
degli Uberti
E C
EC
Cattedra di Endocrinologia, University of Ferrara, Italy.
Petraglia
F
F
Bondanelli
M
M
Guo
A L
AL
Valentini
A
A
Salvadori
S
S
Criscuolo
M
M
Nappi
R E
RE
Genazzani
A R
AR
D000311:Adrenal Glands / Q000503:physiopathology*; D000595:Amino Acid Sequence; D000818:Animals; D003080:Cold Temperature; D003345:Corticosterone / Q000097:blood; D007031:Hypothalamus / Q000503:physiopathology; D008297:Male; D008969:Molecular Sequence Data; D009270:Naloxone / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D018847:Opioid Peptides; D010902:Pituitary Gland / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000502:physiology*; D013312:Stress, Physiological / Q000503:physiopathology*; D013550:Swimming; D001615:beta-Endorphin / Q000097:blood
D009842:Oligopeptides; D018847:Opioid Peptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; C059567:deltorphin; C030058:dermorphin; D009270:Naloxone; D001615:beta-Endorphin; D003345:Corticosterone