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Stimulation of brain Na⁺ channels by FMRFamide in Dahl SS and SR rats

Hypertension Unit, University of Ottawa Heart Institute, Ottawa, Ontario, Canada K1Y 4W7

Submitted 19 May 2003 ; accepted in final form 8 July 2003

Stimulation of brain Na⁺ channels by Phe-Met-Arg-Phe-NH₂ (FMRFamide) increases sympathetic nerve activity and blood pressure (BP) in Wistar rats. Blockade of brain ouabain-like compounds (OLC) by specific antibody Fab fragments prevents these responses to intracerebroventricular FMRFamide. In the present study, we evaluated the effects of high-salt intake on brain FMRFamide levels and the responses of BP and brain OLC to intracerebroventricular infusion of FMRFamide in Dahl salt-sensitive (SS) and salt-resistant (SR) rats. FMRFamide and OLC content was measured with the use of RIA and ELISA, respectively. A high-salt diet (1,370 µmol Na⁺/g) for 2 wk significantly increased BP in Dahl SS but not in SR rats. On a regular salt diet, Dahl SS and SR rats showed similar FMRFamide levels in the whole hypothalamus, pons and medulla, and spinal cord. A high-salt diet for 2 wk did not affect FMRFamide levels in these tissues in both Dahl SS and SR rats. In Dahl SS but not in SR rats, chronic intracerebroventricular infusion of FMRFamide (200 nmol · kg^–1 · day^–1) for 2 wk significantly increased BP (mean arterial pressure: 116 ± 5 vs. 100 ± 2 mmHg; P < 0.01). Chronic intracerebroventricular infusion of FMRFamide significantly increased hypothalamic and pituitary OLC in Dahl SS but not SR rats. These results indicate that Dahl SS rats exhibit enhanced central responses to FMRFamide. In Dahl SS but not in SR rats on a high-salt diet, enhanced Na⁺ entry through FMRFamide-activated brain Na⁺ channels may increase brain OLC release, thereby leading to hypertension.

ouabain-like compounds; blood pressure; salt-sensitive and salt-resistant rats

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