Sympathetic beta-agonists and cochlear blood flow in guinea pigs.

The effects of sympathetic beta-agonists on blood pressure and cochlear blood flow were studied in 15 guinea pigs. Cochlear blood flow was measured by a laser Doppler flowmeter, Periflux PF2 (Perimed, Sweden). Small doses (0.01 and 0.1 microgram/kg) of isoproterenol elevated blood pressure, but larger doses (10 and 50 micrograms/kg) decreased blood pressure. Cochlear blood flow showed a biphasic pattern, in that there was an initial decrease with a subsequent increase. Dobutamine, a beta 1-agonist, elevated blood pressure and increased cochlear blood flow in a dose-dependent manner. Salbutamol, a beta 2-agonist, decreased blood pressure in a dose-dependent manner and induced a biphasic pattern of changes (i.e., an initial decrease with a subsequent increase). The effect of isoproterenol, which is a nonselective beta-agonist, is oriented more to a beta 2-agonist at larger doses. These different effects induced by isoproterenol are probably due to a balance of dominance between beta 1 action and beta 2 action at different doses.