- Objective To study the relationship between the sensitivity to sodium content of the diet in terms of development of hypertension and the regulation of the expression of type 1 angiotensin II receptor subtypes by such a diet Methods The expression of angiotensin II receptor subtype (AT 1A and AT 1B ) mRNAs was studied by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in the four zones of the kidneys of Sabra rats, sensitive or resistant to DOCA salt-induced hypertension (SBH/y and SBN/y, respectively). Rats were fed a high (8%) or normal (0.4%) NaCI diet As vasopressin is known to be elevated in SBH/y rats and to be involved in DOCA-salt hypertension, we studied an additional group of SBH/y rats, fed a high sodium diet, enriched in water. Results With the absence of DOCA, SBH/y rats did not develop hypertension. The high sodium diet induced a greater fall in the plasma renin activity in the SBH/y (-95%) than in the SBN/y (-63%). In the cortex (C) and inner stripe (IS), the high sodium diet decreased AT 1A and AT 1B mRNAs in SBH/y and SBN/y, with a higher magnitude for SBH/y, than for SBN/y (C, -28 versus -20% ; IS, -42 versus -20%). The addition of water to the high sodium diet lessened the effect of sodium in the C and IS, although the plasma renin activity (PRA) was not altered. Conclusion A high sodium diet significantly decreases both AT 1A and AT 1B gene expression in two specific zones of the rat kidney containing the target cells of angiotensin II (C and IS). This down-regulation is organ-specific since it was observed in the kidney and adrenals, but not in the liver. Finally, SBH/y and SBN/y rats differ in the basal level of AT 1 mRNA expression in the IS, and in the ability to modulate AT 1 mRNA level under sodium intake.