N-(2-Benzoxazol-2-yl-ethyl)-guanidine hydrochloride (10) was synthesized and pharmacologically tested. This compound showed high affinity for the 5-HT3 receptor (Ki= 0.77 nM) and potently triggered the von Bezold–Jarisch reflex (BJR) in rats with an ED50= 0.52 μg/kg iv and intrinsic activity next to 1 (ia= 0.94). This stimulant effect was abolished by pretreatment with the 5-HT3 receptor antagonist granisetron and was subject to a rapid ...