Effects of long-term application of dopamine HCl on dopamine agonist-induced cAMP production in rat renal cortex.

AIM: To study the effects of long-term application of dopamine HCl (DA) on the functional changes of dopamine receptor subtypes coupled to adenyl cyclase in rat renal cortex. METHODS: cAMP levels were measured by radioimmunoassay as an index of dopamine receptor function. RESULTS: Injection of DA (30 mg.kg-1.d-1, i.p. 30 d) reduced the fenoldopam (Fen) (100 mumol.L-1)-induced increments of cAMP production from the control group of +1.26 +/- 0.04 to the DA-treated group of +0.63 +/- 0.22 nmol.min-1/g tissue and the propyl-butyl-dopamine (PBDA) (100 mumol.L-1)-induced decrements of cAMP production in the presence of Sch-23390 (Sch) from the control group of -0.38 +/- 0.18 to the DA-treated group of -0.11 +/- 0.08 nmol.min-1/g tissue with, however, comparable percentile changes for the 2 groups. Sch blocked both Fen- and PBDA-induced increase in cAMP production, while domperidone (Dom) blocked the decreasing effects of PBDA on cAMP accumulation in the presence of Sch. CONCLUSION: Long-term application of DA produced a marked "down regulation" of both DA1 and DA2 receptors in rat renal cortex with, however, the responsiveness of the remaining receptors unchanged.