Dopamine receptors in the developing sheep kidney.

These studies were designed to characterize dopamine receptor density and affinity in kidneys removed from sheep of varying ages (fetal, newborn, and adult) using radioligand binding methods. Three different radioligands were used: the specific dopamine-1 antagonist 3H-SCH 23390, the dopamine-1/dopamine-2 antagonist 3H-haloperidol, and the dopamine-2 antagonist 3H-spiroperidol. The specific binding of 3H-haloperidol and 3H-spiroperidol was saturable with time and ligand concentration, being indicative of dopamine receptors. The specific binding of the dopamine-1 selective radioligand 3H-SCH 23390 was also saturable with time but displayed several points of saturation with increasing ligand concentration. The specific binding of 3H-haloperidol, which had a low affinity and is indicative of dopamine-1 receptors, showed no age-related changes in maximum receptor density or affinity. On the other hand, the maximum receptor density of dopamine-2 receptors measured by 3H-spiroperidol decreased with age. The observations that renal dopamine-1 receptor density or affinity do not change with maturation are in agreement with our previous studies that showed no age-related changes in dopamine-receptor-mediated renal vasodilatation in sheep. The significance of the decrease in renal dopamine-2 receptor density with age remains to be determined.