AGT and Cognitive impairment: One such compound is angiotensin IV (Ang IV, Val–Tyr–Ile–His–Pro–Phe, Fig. 1), a hexapeptide fragment of the renin–angiotensin system that improves performance in rodent models of cognitive impairment as was first demonstrated by Braszko et al. in 1988.8–11Ang IV was initially thought to act via a distinct AT4 receptor but subsequent research identified this target as a zinc-dependent aminopeptidase with broad physiological roles.