OBJECTIVE: To assess the influence of elevated renal sympathetic nerve activity on renal interleukin-6 (IL-6) and interleukin-1 alpha (IL-1 alpha) production and to compare the specificity of the constitutive production of these cytokines in the spleen and kidney of the spontaneously hypertensive rat (SHR). DESIGN: In acute studies, using anaesthetized and surgically stressed rats, the renal nerves either were not stimulated or were stimulated electrically to reduce renal blood flow by 15 or 30% for 1 h. The kidneys were then extracted for analysis. For the chronic study, Wistar rats and SHR aged 9 weeks were briefly anaesthetized and kidneys and spleen extracted for cytokine measurement. METHODS: Tissue samples were subjected to reverse transcriptase and polymerase chain reaction amplification to assess levels of IL-6 and IL-1 alpha. RESULTS: Renal nerve stimulation decreased levels of IL-6 messenger RNA in the SHR kidney, from a control value of 0.677 +/- 0.043 units to 0.624 +/- 0.049 and 0.383 +/- 0.078 units during the 15 and 30% reductions in renal blood flow induced neurally. The chronic experiments showed that, although there was no difference in constitutive production of IL-1 alpha between the kidney and spleen of Wistar rats and SHR, spleen levels of IL-6 were higher in the SHR and IL-6 was expressed constitutively neither in the Wistar rat nor in the SHR kidney. CONCLUSION: These data demonstrate that renal IL-6 gene expression is low in the SHR kidney under conditions of anaesthesia and surgical stress and that it is further decreased when the kidney is subjected to adrenergic influences. These studies help to define the deficiencies and abnormalities of the SHR Immune system.