Involvement of Microsomal Na⁺/K⁺ ATPase Activity in the Mechanism of Action of Dopaminergic D2 Receptors

Problem statement: Our previous research has shown that mitochondrial ATPase may have a role in the action of dopaminergic D₂ receptors. It is therefore, thought of interest to investigate the effect of bromocriptine, sulpiride or their combination on the mitochondrial and microsomal ouabain sensitive and ouabain insensitive Na⁺/K⁺-ATPase in the liver of rats. Approach: In vivo treatment was carried out to study the effects of bromocriptine mesylate 10 mg kg^-1, sulpiride 10 mg kg^-1; or bromocriptine mesylate 10 mg kg^-1 + sulpiride 10 mg kg^-1, compared to a control group, in order to measure liver Na⁺/K⁺-ATPase activity. The drugs were injected intraperitoneally daily for 14 days. Mitochondrial and microsomal fractions were obtained by the methods of Schwartz. Results: Pretreatment of rats with both bromocriptine and sulpiride given simultaneously resulted in complete abolition of stimulation caused by bromocriptine and inhibition that resulted from sulpiride on mitochondrial as well as microsomal ATPase activities. Conclusion: This study indicated that the in vivo administration of dopaminergic agonist and antagonist drugs result in a significant alteration not only in the mitochondrial ATPase enzyme activity but also in the microsomal ATPase enzyme activity. Therefore, it is quite possible that ATPase of the tow fractions play important physiological as well as pathological roles in the mechanism of action of dopaminergic receptors.