The calibre of the foramen of Panizza in Crocodylus porosus is variable and under adrenergic control

The foramen of Panizza is located within the outflow tract of the crocodili an heart, between the left and right aortas. It has been suggested that the foremen of Panizza has a variable calibre, which could explain the profoun d changes in the distribution of flows and pressure profiles recorded in th e right and left aortas. We investigated this possibility using a modified in-situ perfused heart preparation in combination with isolated strip prepa rations from the outflow tract. In the perfused heart preparation, bolus in jections of adrenaline increased the resistance in the foramen of Panizza, indicating a decrease in its diameter. Isolated strip preparations from the outflow tract showed a concentration-dependent increase in tension in resp onse to adrenaline, while vasoactive intestinal polypeptide caused a relaxa tion in adrenaline pre-contracted strip preparations. We propose that an in crease in the diameter of the foremen of Panizza may be important during pu lmonary to systemic shunts to allow blood to flow from the left to right ao rta (reverse foramen flow) in order to supply the carotid and coronary arte ries. During non-shunting conditions, a constricted foramen may prevent exc ess flow from the right to left aorta during diastole.