Transposition response, a cardiovascular response to change of habitat in the rat

Aortic flow and arterial pressure were observed in conscious rats by means of an electromagnetic flowmeter probe implanted around the ascending aorta and an arterial cannula inserted into the abdominal aorta through a femoral artery. When the rat was transposed to a new box from its usual one, heart rate, cardiac output and peak flow acceleration were increased but arterial pressure remained unchanged. Total peripheral resistance was decreased. This response complex of the cardiovascular system to change of habitat was designated as "transposition response." After beta adrenoceptor blockade with propranolol, transposition no longer increased heart rate, cardiac output or peak flow acceleration but markedly increased arterial pressure and total peripheral resistance. The response was essentially unchanged by atropinization or adrenalectomy. Besides cardiac excitation and adrenergic vasoconstriction, the response includes a beta adrenergic vasodilatation, which is at least in part mediated by transmitters released at the sympathetic nerve endings and presumably equivalent to the cholinergic vasodilatation in the cat and dog.