Dopamine D 1 and D 2 receptors in the caudate nucleus of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats

Abstract

A series of studies was carried out to characterize the binding properties of dopamine D 1 and D 2 receptors in membrane homogenates of the caudate nucleus of spontaneously hypertensive rats (SHR). Binding in SHR was studied at the age of 4 weeks when the rats were still in the prehypertensive phase, and at the age of 8 weeks, during the phase in which blood pressure is increasing dramatically; age-matched normotensive Wistar-Kyoto rats (WKY) were used as controls. Binding to dopamine D 1 receptors was studied using [ 3H]SCH 23390. Antagonist binding of dopamine D 2 receptors was performed with [ 3H]spiperone. At both ages no differences were found between SHR and WKY in affinity ( K d ) or concentration ( B max ) of dopamine D 1 and D 2 receptzrs. Binding to the high affinity state of the dopamine D 2 receptor was measured using the agonist [ 3H] N-n-propylnorapomorphine (NPA). No differences in B max or K d were found between SHR and WKY at both ages studied. indicating that the ratio between dopamine D 2 receptors in the high and in the low affinity state is not altered in spontaneous hypertension. Although the results do not reveal differences in affinities or concentrations of dopamine D 1 or D 2 receptors in the caudate nucleus between SHR and WKY, a role in the development of hypertension for the here described lack of receptor up-regulation in connection with our previous observation of lower release of dopamine in the caudate nucleus of SHR, cannot be excluded.