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 a denyl 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), ip, 30 d) reduced the fenoldopa m (Fen) (100 mu mol.L-1)-induced increments of cAMP production from th e 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 mu mol.L-1)-induced decrements of cAMP production in the presence of S ch-23390 (Sch) from the control group of -0.38 +/- 0.18 to the DA-trea ted group of -0.11 +/- 0.08 nmol.min(-1)/g tissue with, however, compa rable percentile changes for the 2 groups. Sch blocked both Fen- and P BDA-induced increase in cAMP production, while domperidone (Dom) block ed the decreasing effects of PBDA on cAMP accumulation in the presence of Sch. CONCLUSION: Long-term application of DA produced marked ''dow n regulation'' of both DA(1) and DA(2) receptors in rat renal cortex w ith, however, the responsiveness of the remaining receptors unchanged.