1. Altered adrenergic responsiveness of hearts and blood vessels occurs in both experimental and clinical hypertension.
2. Since salt excess aggravates both types of hypertension, we investigated β-adrenoreceptor properties in the hearts of spontaneously hypertensive and normotensive rats drinking 1% NaCl or tap water for 3 weeks.
3. Sodium loading increased heart weight in both spontaneously hypertensive and normotensive rats.
4. In spontaneously hypertensive rats excess salt attenuated the age-related decrease in β-adrenoreceptor number observed in spontaneously hypertensive and normotensive rats drinking tap water and in normotensive rats drinking 1% NaCl.
5. Unlike the normotensive rats, which did not show a relationship between β-adrenoreceptor number and blood pressure, spontaneously hypertensive rats on tap water and 1% NaCl showed a significant negative logarithmic relationship between these two variables. These data provide further evidence implicating sodium excess as an aggravating factor in this model of experimental hypertension.