Metabolic effects of kinins: historical and recent developments

In 1928, Frey and co-workers discovered kallikrein in human urine and described its prolonged hypotensive effect in the dog. Four years later, the same authors first reported a blood glucose-lowering effect of orally administered kallikrein in diabetic patients. However, the observed blood glucose-lowering effect of kallikrein appeared to fade with repeated administration, and therefore its possible metabolic role was not further investigated and fell into disregard. One decade ago, experimental data yielded indirect evidence that the regulation of local skeletal muscle blood flow and glucose uptake during work was mediated by proteolytically cleaved kinins. Further experiments demonstrated that in insulin-resistant states such as postoperative stress and type II diabetes, reduced muscular insulin sensitivity was increased and partly restored by continuous low-dose infusion of synthetic bradykinin. Recent work showing that tissue kallikrein is present in a number of different tissue sites, including skeletal muscle and our own observation of local kinin overflow after muscle work in healthy subjects, but not in type II diabetics, support the concept of a skeletal muscle kallikrein-kinin system (KKS) that is locally activated upon contraction. Moreover, in isolated perfused rat heart preparations, favorable effects of kinins on myocardial glucose uptake, oxidation, and glycolytic flux have been reported. Most interestingly, cardioprotective effects of kinins have been observed and attributed to improved energy and substrate metabolism in ischemic hearts. Taken together, these data gave rise to the concept that tissue KKS might be involved in the local modulation of skeletal muscle and myocardial tissue blood flow and substrate metabolism, and that activation of the KKS is defective in insulin-resistant states.