CHRONIC MELATONIN TREATMENT AND THE HYPOTHALAMO-PITUITARY-ADRENAL AXIS IN THE RAT - ATTENUATION OF THE SECRETORY RESPONSE TO STRESS AND EFFECTS ON HYPOTHALAMIC NEUROPEPTIDE CONTENT AND RELEASE
R. Konakchieva et al., CHRONIC MELATONIN TREATMENT AND THE HYPOTHALAMO-PITUITARY-ADRENAL AXIS IN THE RAT - ATTENUATION OF THE SECRETORY RESPONSE TO STRESS AND EFFECTS ON HYPOTHALAMIC NEUROPEPTIDE CONTENT AND RELEASE, Biology of the cell, 89(9), 1997, pp. 587-596
The pituitary-adrenal secretory response to acute and chronic stress,
suppressibility of adrenocortical secretions by exogenous glucocortico
ids, and hypothalamic content and in vitro release of the two major pe
ptidergic activators of the hypothalamo-pituitary-adrenal (HPA) axis,
corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP),
were examined in rats receiving daily melatonin (MEL) injections coinc
ident with the circadian increment of endogenous pineal and adrenocort
ical secretory activity. After 7 days of MEL administration, the rats
displayed a significant attenuation of the adrenocortical secretory re
sponse to acute and chronic stress. Chronic MEL treatment also prevent
ed the decline in adrenocorticotropic hormone (ACTH) release resulting
from chronic stress exposure. Hypothalamic CRH content was significan
tly lower in rats receiving MEL treatment, while AVP remained largely
unaltered; however, MEL administration counteracted the chronic stress
-induced decrease in hypothalamic AVP content and in vitro release. Wh
en exposed to dexamethasone in vitro, hypothalamic explants from MEL-t
reated rats responded with a stronger suppression of CRH and AVP relea
se than those originating from vehicle-injected animals. These observa
tions indicate that MEL attenuates the adrenocortical response to stre
ss and influences the biosynthesis, release and glucocorticoid respons
iveness of hypothalamic ACTH secretagogues. ((C) Elsevier, Paris).