in the latter preparation , the negative chronotropic action of clonidine was reversed by an intravenous injection of phentolamine , whereas in the former experimental situation it was antagonized only by an intravenous plus an intravertebral artery injection of phentolamine.2 in dogs with denervated hearts the tachycardia produced by electrical stimulation of the cardioaccelerator nerve was accompanied by a rise in noradrenaline overflowing into the coronary sinus plasma .
C1372752
negative chronotropic
C0009014
clonidine