Sodium Intake Sensitivity in Hypertensive (HT) and Normotensive (NT) Congenic, Spontaneously Hypertensive Rats (SHR)

Abstract

A congenic model of SHR was developed by mating HT female SHR (Aoki‐Okamoto strain) with NT, male Brown Norway rats (Charles River Labs, Inc.). HT female offspring then were backcrossed with the original Brown Norway male for 6 generations (F6). F6 HT and NT congenic female rats then were inter‐bred with HT and NT F6 male rats. Salt appetite related to hypertension was evaluated to determine whether HT rats (129.0 ± 5.2 mmHg) have altered sodium (Na+) intake sensitivity compared to NT controls (100.7 ± 6.2 mmHg). Rats were housed in metabolic pens and were allowed distilled water and Na+ free chow. Rats titrated Na+intake by drinking 0.9% saline (5 days), 2.0% hypertonic saline (5 days) and 0.9% saline (5 days) during the 15 day protocol. In days 1–5, Na+ intake averaged 1.98 ± 0.55 mMol in NT and 1.46 ± 0.82 mMol in HT rats (p ≥ 0.05). After offering 2.0% saline, NT rats decreased Na+ intake but that of HT rats remained unchanged. Both NT and HT rats increased water intake during 2.0% saline with that of NT rats exceeding HT rats despite NT rats decreasing Na+ intake. Both HT and NT rats had similar urinary protein excretions indicating normal kidney function in both groups. These data indicate that HT SHR/BN congenic rats have reduced sensitivity to orally ingested NaCl. This reduced sensitivity may cause HT congenic SHR to increase long term NaCl intake and predispose them to hypertension in adulthood.