Effects of endomorphin-2 on arterial blood pressure and pain threshold in spontaneously hypertensive rats and modification of these effects by β-funaltrexamine and nor-binaltorphimine

The effects of intracerebroventricular (icv) administration of endomorphin-2 (E2) on arterial blood pressure and pain threshold in spontaneously hypertensive rats (SHR) and modification of these effects by kappa [OP2] and mu [OP3] opioid receptors antagonists were investigated. Endomorphin-2 administrated icy in doses of 8, 16 and 32 meg produced dose-dependent analgesic and hypotensive effect. In SHR decrease in blood pressure amounted 2.667, 4.0 and 6.534 kPa, respectively. Pain threshold increased by 1.7, 3.6 and 8.9 (gX10). In Wistar Kyoto (WKY) strain, being the normotensive controls, E2 in doses of 8 and 16 meg decrease in blood pressure was less pronounced and amounted 1.200 and 1.467 kPa, respectively, whereas the pain threshold increased by 7.2 and 10.4 (gX10), respectively. Both E2 effects were antagonized by equimolar icy doses of beta -funaltrexamine (beta -FNA) Equimolar doses of nor-binaltorphimine (nor-BNI) attenuated analgesic action of E2, but were without hypotensive action produced by E2. A strong correlation between drop in blood pressure and increase in pain threshold observed in the SHR and WKY strains after icy administration of E2, indicate close interaction between systems responsible for pain perception and blood pressure control. (C) 2001 Elsevier Science Inc. All rights reserved.