alpha 1-adrenoceptors can mediate chronotropic responses in the rat heart

In the pithed rat, amidephrine a "selective" alpha 1-adrenoceptor agonist, evokes a positive chronotropic response. This response can be antagonized by prazosin but not by propranolol or by rauwolscine. Similarly, part of the chronotropic response to cardioaccelerator nerve stimulation is resistant to blockade by propranolol but is sensitive to prazosin or WB4101. We conclude that alpha 1-adrenoceptors can mediate a chronotropic response in the rat heart either to exogenous agonists or to the endogenous neurotransmitter noradrenaline.