Elsevier

Peptides

Volume 8, Issue 1, January–February 1987, Pages 113-118
Peptides

Article
Dual effects of (D-Ala2,Met5)-enkephalinamide on CRF and ACTH secretion

https://doi.org/10.1016/0196-9781(87)90173-2Get rights and content

Abstract

An intra-third ventricular administration of (D-Ala2,Met5)-enkephalinamide (DALA) did not elevate plasma ACTH and corticosterone levels in unanesthetized freely moving rats, but intra-third ventricular administration of DALA and methionine (Met)-enkephalin potentiated a mild stress (hanging for 10 or 30 sec)-induced plasma ACTH and corticosterone elevations in unanesthetized freely moving rats. DALA and Met-enkephalin seemed to stimulate CRF release from the median eminence to increase plasma ACTH, as the CRF concentration in the median eminence area was reduced after injection in these stressed rats. When hypothalamic tissues were perifused in vitro, DALA (1–100 ng/ml) reduced the release of CRF. These results suggest that the opiates seem to have a dual effect on the CRF-ACTH system depending on which action overrides the other.

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      The median eminence is rich in opioid receptors [1]. Many studies showed that met-enk has major effects on the release of many pituitary hormones including adrenocorticotropic hormone (ACTH) [9,11], growth hormone [8], prolactin [8], thyrotropin [23] and luteinizing hormone [8]. In the hypothalamus enkephalin immunoreactivity has been localized in the parvocellular neurons of the hypothalamic paraventricular nucleus which projects on to the median eminence [13], the site where hypothalamic releasing factors are secreted into the portal blood, hence the anterior pituitary gland.

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