Beta-adrenoceptor responsiveness of splenic macrophages in normotensive and hypertensive rats

The aim of the present study was to investigate putative mechanisms implicated in the impaired phagocytic response of spontaneously hypertensive rats (SHR)1. The effect of in vitro treatment with isoproterenol (ISO), a β-adrenergic drug, on phagocytosis and respiratory burst by splenic macrophages (SpM0) from normotensive Wistar-Kyoto rats (WKY) and SHR with established hypertension, respectively, was evaluated. Furthermore, the relaxant effect of ISO was determined in phenilephrine-precontracted thoracic aorta strips from SHR compared with age-matched WKY rats. Results indicate that exposure of rat SpM0 to ISO generate a significant and dose-dependent reduction of phagocytosis and oxidative burst which was antagonized, almost completely, by the β-adrenergic antagonist propranolol (PRO). Unlike normotensive, in hypertensive rats treatment with ISO fail to modulate phagocytosis and respiratory burst activity by SpM0. At vascular level, aortic relaxation by ISO was reduced in SHR when compared to WKY rats. These findings suggest that SHR exhibit changes not only in vascular, but also in macrophage β-adrenoceptor-mediated responses. It is postulable that sympathetic overactivity could be responsible for impaired phagocytic functions and β-receptor alterations observed in SHR.