Sensitivity of pressor responses to central hypertonic saline is greatly enhanced even in pre-hypertensive spontaneously hypertensive rats

It has been suggested that intracerebroventricular injection of hypertonic saline mimics the effects of a high salt diet in spontaneously hypertensive rats (SHR), a genetic model of hypertension. Intracerebroventricular injection of hypertonic saline produces an increase in blood pressure and the pressor response to hypertonic saline is enhanced in adult hypertensive SHR. In this study, we examined whether the intracerebroventricular hypertonic saline-induced pressor response is enhanced even in pre-hypertensive SHR. The basal mean blood pressure was almost the same in 4-week-old SHR and age-matched Wistar Kyoto rats (WKY), whereas it was greater in 15–16-week-old SHR than in age-matched WKY. Intracerebroventricular injection of hypertonic saline (10 μl of 230 mM NaCl) produced an increase in blood pressure in both 4-week-old and 15–16-week-old SHR, whereas it did not affect blood pressure in both age-matched WKY. Intracerebroventricular injection of hypertonic saline (10 μl of 260 mM NaCl) produced an increase in blood pressure in all rats but the pressor response was greater in both 4-week-old and 15–16-week-old SHR than in respective age-matched WKY. Intracerebroventricular injection of Phe-Met-Arg-Phe amide (FMRF), an FMRF-inducible sodium channel activator, produced an increase in blood pressure in all rats but the pressor response was greater in SHR than in WKY at both ages. These findings indicate that the sensitivities of pressor responses to intracerebroventricular hypertonic saline and FMRF are enhanced not only in hypertensive but also in pre-hypertensive SHR.