In a rat model, the relationship between the activity of PKA in human PPFs, the changes in arterial BK concentration, and the changes in blood pressure on infusion of PPF was investigated. The rat was chosen as a model because it is reported to be one of the few animals sensitive to human PKA. However, hypotensive reactions after infusion of human PKA-containing PPF were observed only in the presence of a bradykinin-potentiating peptide (BPP9a). A correlation was found between the PKA content of the rapidly infused PPF, the BK generation in the rat, and the fall in arterial blood pressure. In control experiments, infusions of BK provoKed a similar fall in blood pressure at corresponding BK levels. After neutralization of the PKA activity in the PPF with C1-esterase inhibitor, neither a rise in BK level nor a fall in blood pressure was observed on infusion. We conclude therefore that the hypotensive reactions were caused by PKA-mediated generation of BK.