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TL Coventry, DS Jessop, DP Finn, MD Crabb, H Kinoshita, and MS Harbuz
Endomorphin (EM)-1 and EM-2 are opioid tetrapeptides recently located in the central nervous system and immune tissues with high selectivity and affinity for the mu-opioid receptor. Intracerebroventricular (i.c.v.) administration of morphine stimulates the hypothalamo-pituitary-adrenal (HPA) axis. The present study investigated the effect of centrally administered EM-1 and EM-2 on HPA axis activation. Rats received a single i.c.v. injection of either EM-1 (0.1, 1.0, 10 microg), EM-2 (10 microg), morphine (10 microg), or vehicle (0.9% saline). Blood samples for plasma corticosterone determinations were taken immediately prior to i.c.v. administration and at various time points up to 4 h post-injection. Trunk blood, brains and pituitaries were collected at 4 h. Intracerebroventricular morphine increased plasma corticosterone levels within 30 min, whereas EM-1 and EM-2 were without effect. In addition, pre-treatment of i.c.v. EM-1 did not block the rise in corticosterone after morphine. Corticotrophin-releasing factor (CRF) mRNA and arginine vasopressin (AVP) mRNA in the paraventricular nucleus (PVN) and POMC mRNA in the anterior pituitary were found to be unaffected by either morphine or endomorphins. Since release of other opioids are elevated in response to acute stress, we exposed rats to a range of stressors to determine whether plasma EM-1 and EM-2 can be stimulated by HPA axis activation. Plasma corticosterone, ACTH and beta-endorphin were elevated following acute restraint stress, but concentrations of plasma EM-1-immunoreactivity (ir) and EM-2-ir did not change significantly. Corticosterone, ACTH and beta-endorphin were further elevated in adjuvant-induced arthritis (AA) rats by a single injection of lipopolysaccharide (LPS), but not by restraint stress. In conclusion, neither EM-1 or EM-2 appear to influence the regulation of the HPA axis. These data suggest that endomorphins may be acting on a different subset of the mu-opioid receptor than morphine. The failure to induce changes in plasma EM-ir in response to the chronic inflammatory stress of AA, the acute immunological stress of LPS, or the psychological stress of restraint, argues against an important role for endomorphins in mediating HPA axis activity.
MS Harbuz, E Korendowych, DS Jessop, AL Crown, SL Li pdfan, and Kirwan JR
A defective hypothalamo-pituitary-adrenal axis response to inflammatory cytokines may contribute to the pathophysiology of rheumatoid arthritis (RA). The purpose of this study was to define further the mechanisms responsible for this dysregulation. Six normal individuals and seven patients with active RA were recruited and given an oral dose of dexamethasone at 2300 h the evening before the study. The next day, an i.v. catheter was fitted at 1300 h. Blood samples were collected between 1400 h and 1700 h before and after infusion (at 1500 h) of corticotrophin releasing factor (CRF). Plasma was separated and stored at-20 degrees C before radioimmunoassay for ACTH, cortisol and dihydroepiandrosterone (DHEA). Before the CRF challenge, ACTH and cortisol were significantly increased and DHEA significantly decreased in the patients with RA compared with the controls. Neither ACTH nor DHEA was significantly altered after CRF infusion. Control individuals did not mount a cortisol response to infusion of CRF. Similarly, four of the patients with RA did not respond to CRF. However, in contrast to the controls, three of the patients mounted an immediate and sustained cortisol response after receiving CRF. These data reveal that three of the seven patients with RA were able to escape from dexamethasone suppression and mount a cortisol response to CRF challenge. This suggests that there may be a subpopulation of patients with RA who have impaired glucocorticoid feedback. The implications of this alteration for disease progression remain to be determined.