Sodium chloride preference of genetically hypertensive and normotensive rats

Preference for 0.9% saline was examined, using two-bottle preference tests over 6-7 days, in the spontaneously hypertensive rat (SHR) and normotensive Wistar Kyoto rat (WK) of the Okamoto strain, the genetically hypertensive (GHR) and normotensive rat (NT) of the Smirk strain, and the Sprague-Dawley (SD), Dark Agouti (DA), and hooded Long-Evans or Brattleboro (BB) rat. Only the SHR exhibited a sustained and marked preference for 0.9% saline on each test day. The WK, GHR, NT, and SD preferred saline in the first 24-48 h of testing but thereafter showed neither a preference for, nor aversion to, saline. The BB showed neither a preference for, nor aversion to, saline in the first 24 h of testing and thereafter showed a significant aversion to saline on each test day. Saline preference was further examined in both the SHR and WK offered a choice of water and 0.9%, 2.0, or 2.7% saline. While preference for saline decreased in both SHR and WK with increasing saline concentration, the SHR maintained a significantly greater preference for saline and greater total sodium intake than the WK at each concentration. Hydralazine (5 mg . kg-1 . day-1, po) administered to SHR, while they were offered a choice of water and 0.9% saline, significantly lowered blood pressure over a 4-day period but failed to alter their saline preference significantly. We conclude that of the seven strains of rats examined only the SHR exhibited a preference for saline in extended two-bottle preference tests. Furthermore this preference for saline appears to be maintained independently of the blood pressure of the SHR.