Are -Opioid Autoreceptors Involved in Blood Pressure and Pain Threshold Control in SHR?

Authors: KOLARI Ccaron S.; MAKULSKA-NOWAK H.E.; GUMU Lstrok KA S.W.

Source: Analgesia, Volume 5, Number 2, 2001 , pp. 75-81(7)

Publisher: Cognizant Communication Corporation

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Abstract:

The aim of our study was to further investigate the paradoxical effects of intracerebroventricular (ICV) administration of very low doses of opioid antagonists on pain threshold and arterial blood pressure of spontaneously hypertensive rats (SHR) with experimental inflammation. We found that low doses of ICV administered bgr -funaltrexamine (0.4 mgr g) produced paradoxical hypoalgesia. Concomitantly, significant increases in the severity of hypertension were also observed. These results seem to confirm the engagement of the mgr -opioid receptor system (OP₃) in the mechanisms of blood pressure control. Low doses of ICV administered naltrindole (0.3 mgr g) did not produce paradoxical results in either blood pressure or pain threshold. Values for these two parameters did not differ significantly from those of control SHR with experimental inflammation receiving no active treatment. Results obtained in the study suggest the involvement of the mgr receptor (OP₃) but not the dgr -opioid receptor (OP₁) in the paradoxical effects of opioid antagonists on pain threshold and blood pressure in SHR with experimental inflammation.