The renal kallikrein-kinin system (KKS) has long been implicated in local blood pressure control and natriuresis but identification of potential regulators of the KKS are poorly defined. Animal studies have shown that arginine vasopressin (AVP) is capable of increasing urinary kallikrein and kinin excretion and it has been suggested that intra-renal kinin participates in a negative feedback with AVP. In addition, the localization of cortical dopamine (DA) receptors at sites close to KKS components, raises the possibility that local vasodilatation and natriuresis produced by DA may be partially mediated by the KKS. Since humoral agents in vivo may affect KKS activity secondary to neuronal or haemodynamic changes, the effect of AVP or DA on kallikrein and kinin release from collagenase dispersed rat (female Wistar-Kyoto) and human renal cortical cells was examined using an in vitro column superfusion technique. Superfusion was carried out at 37°C in parallel superfusion columns and 5 min eluate fractions were collected. To accurately measure kallikrein release a highly specific and sensitive kininogenase assay was developed, which involved the incubation of samples with single source human kininogen substrate. Kinins generated in kininogenase assays and kinins directly released into the superfusate were quantitated in an optimized and validated radioimmunoassay utilizing a monoclonal antibody. In subsequent experiments it was shown that stable basal kinin release from rat and human renal cortical cells was attained after approximately 60 min superfusion, and remained constant for a further 4 h. Increasing concentrations of AVP stimulated kallikrein and kinin release in a similar manner from both rat and human renal cortical cells. Further experiments using rat renal cells demonstrated that AVP and the vasopressin V₂ agonist, dDAVP, produced comparable stimulation of kallikrein and kinin responses, compatible with AVP-evoked stimulation of specific V₂ receptors. DA also stimulated kallikrein and kinin release from rat renal cortical cells, with similar kinin responses to DA over the same concentration range using human tissue. In rat renal cortical cells the dopamine DA₁ receptor antagonist, SCH-233390, significantly reduced DA-stimulated kallikrein release although kinin release was not affected. The DA₂ receptor antagonist, (-) sulpiride, did not alter DA-evoked kallikrein or kinin release. These results suggest that DA enhances kallikrein release through the selective activation of DA₁ receptors. Thus, AVP and DA are capable of directly regulating KKS activity through the activation of specific receptors on kallikrein-containing renal cortical cells. These studies provide support for the involvement of the KKS in the intra-renal actions of these endogenous hormones.