Upregulation of renal alpha 2-adrenergic receptors is not indicative of salt-related increases in blood pressure in spontaneously hypertensive rats.

The aim of the present study was to determine if elevations in salt intake were coupled to increases in renal alpha 2-adrenergic receptors in SHR that differ in their blood pressure response to high salt diets. Salt-resistant spontaneously hypertensive rats (SHR-R), which do not increase their blood pressure in response to high salt intake, and salt-sensitive spontaneously hypertensive rats (SHR-S), which do exhibit significant elevations in blood pressure on high salt diets (3.15% NaCl), were used. Radioligand binding studies using [3H]rauwolscine were performed on 6- and 11-week-old SHR-S and Wistar-Kyoto (WKY) rats to determine the effects of age, strain, and salt intake on alpha 2-adrenergic receptor number and affinity. One week of high salt intake significantly increased blood pressure 22% in 6-week-old SHR-S and increased the blood pressure of 11-week-old SHR-S 12% without altering WKY rat controls. This treatment did not significantly increase renal alpha 2-adrenergic receptors in either SHR-S or WKY rats. SHR-S had significantly higher numbers of renal alpha 2-adrenergic receptors than WKY rats on the high salt diets. One week of high (3.15%) or low (0.05%) salt intake did not significantly alter renal alpha 2-adrenergic receptor number in 11-week-old SHR-S or WKY rats; however, blood pressure was significantly elevated in the SHR-S (175.0 +/- 3.5 versus 196.0 +/- 3.0 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)