A novel radioligand for imaging the AT1 angiotensin receptor with PET.

2-Butyl-5-methoxymethyl-6-(1-oxopyridin-2-yl)-3-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-3H-imidazo[4,5-b]pyridine (KR31173) was radiolabeled by coupling a tetrazole-protected hydroxy precursor with [(11)C] methyl iodide and removing the protecting group by acid hydrolysis. In mice, the highest uptake of [(11)C] KR31173 was in the adrenal glands, kidneys, and liver. Tissue to blood ratios were generally greater than 10:1. Uptake of the tracer in the adrenal glands, kidneys, lungs, and heart was blocked with a 1 mg/kg dose of KR31173 or MK-996.