Renal alpha 2-adrenoceptors in New Zealand genetically hypertensive rats

1. Renal alpha 1- and alpha 2-adrenoceptors were characterized in the New Zealand strain of genetically hypertensive (GH) rat and the Otago random-bred albino normotensive (NT) control rat at 4 and 12 weeks of age with [3H]-prazosin and [3H]-rauwolscine. 2. At 4 weeks of age, the density of alpha-adrenoceptors in NT and GH rats was similar to both the alpha 1- (193 +/- 11 vs 163 +/- 14 fmol mg-1 protein) and alpha 2- (347 +/- 34 vs 319 +/- 41 fmol mg-1 protein) adrenoceptor. At 12 weeks of age, GH rats had a greater density of renal alpha 1- (152 +/- 27 vs 238 +/- 17 fmol mg-1 protein) and alpha 2- (175 +/- 42 vs 350 +/- 23 fmol mg-1 protein) adrenoceptors compared to the NT rats. 3. Pre-incubation of kidneys from GH rats (12 weeks of age) with 1 and 10 microM clonidine decreased the density of receptors identified by unlabelled clonidine displacement of [3H]-rauwolscine to 77% and 56% of control. Pre-incubation with adrenaline, 2,6 dimethylclonidine or phenylephrine failed to alter binding. 4. Pre-incubation of kidneys from NT rats (12 weeks) or young GH rats (4 weeks) with 10 microM clonidine failed to alter displacement of [3H]-rauwolscine by unlabelled clonidine. 5. These studies demonstrate that in another strain of hypertensive rat, the GH rat, alpha 2-adrenoceptor density is increased as compared to the normotensive control at 12 but not 4 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)