Central Nervous System Blockade by Peripheral Administration of AT1 Receptor Blockers

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Abstract
After peripheral administration, AT1 receptor blockers appear to be able to enter the brain and cause AT1 receptor blockade in the central nervous system. In the current study, we investigated the effects of subcutaneous administration of embusartan versus losartan on inhibition of AT1 receptor binding in rat brain by in vitro autoradiography. At 4 hours after single doses of 5, 30, or 100 mg/kg, both losartan and embusartan decreased iodine 125I Ang II binding dose dependently in brain structures that express AT1 receptors both outside (e.g., organum vasculosum laminae terminalis) and within (e.g., paraventricular nucleus) the blood–brain barrier. At low doses, embusartan was twofold more potent than losartan inside but not outside the blood–brain barrier. After chronic treatment (30 mg/kg daily for 6 days), at 4 hours after the last dose, embusartan still caused more inhibition than losartan in the brain structures inside the blood–brain barrier. At 24 hours after the last dose, a modest, better inhibition for embusartan versus losartan remained: from 15% to 33% versus 10% to 24%, respectively. At 36 hours after the last dose, the inhibition for both blockers had almost completely disappeared inside the blood–brain barrier but persisted in, for example, the kidneys. These results demonstrate that—likely because of its high lipophilic character—embusartan appears to penetrate the blood–brain barrier more easily than losartan and therefore causes more effective AT1 receptor blockade in nuclei within the blood–brain barrier.

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