Angiotensin antogonists as pharmacological tools

The availability of specific competitive antagonists stimulated investigation of the physiological and pathological role of angiotensin (A-II) and permitted the qualitative and quantitative characterization of numerous angiotensin receptor sites. The specific, competitive antogonists for A-II inhibit both the direct actions of A-II on isolated smooth muscle preparations and the stimulation of specific vascular receptor sites by which A-II evokes prostaglandin biosynthesis and release. Converting enzyme inhibitors a) block the action of exogenous A-I; b) lower blood pressure in conditions associated with high plasma renin levels (e.g., two-kidney renal hypertension, dehydrated diabetes insipidus rats, or in hemorrhagic shock); c) enhance responses to exogenous bradykinin (by inhibiting bradykininase); but d) do not block the effects of A-II at its receptor sites. A-II-receptor antagonists a) block the action of both A-I and A-II, b) lower blood pressure in high renin states, but c) have no effect on bradykinin degradation or action. Angiotensin receptor and synthesis antagonists have been shown to decrease the overall peripheral resistance and to reverse the renal cortical vasoconstriction during hemorrhagic shock and to prolong survival time in hemorrhaged dogs. It is our belief that angiotensin antogonists have therapeutic potential in hemorrhagic shock and would be expected (alone or in combination with alpha-andrenergic blockade) to overcome vascular shutdown and enhance organ perfusion (especially in the kidney).