Sabra rats as a model to differentiate between Na+ and GTP regulation of alpha 2-adrenoceptor densities.

Sodium ions and guanyl nucleotides play an important role in increasing alpha 2-adrenoceptor densities in cerebral and renal cortex of normotensive rats. The in vitro effect of Na+ and GTP was investigated on cerebral and renal alpha-adrenoceptors in hypertensive (SBH, salt-sensitive) and normotensive (SBN, salt-resistant) Sabra rats. In SBH and SBN rats, guanyl nucleotides increased cerebral and renal high-affinity alpha 2-adrenoceptor densities. Sodium ions, in contrast, markedly increased cerebral and renal high affinity alpha 2-adrenoceptor densities only in SBH rats. Under these conditions, alpha 1-adrenoceptor densities were unchanged. Thus, although Na+ and GTP both increase alpha 2-adrenoceptor densities, these agents appear to mediate their regulatory effects via different membrane components. Moreover, the absence of sodium regulation of alpha 2-adrenoceptors in SBN rats may be responsible for the resistance to salt-induced hypertension.