Bicuspid aortic and pulmonary valves in the Syrian hamster.

We studied the conditions of the aortic and pulmonary valves of 153 Syrian hamsters belonging to a single family subjected to high endogamous pressure. Semilunar valves of 143 specimens were examined using a stereomicroscope, and in 5 of these cases a histologic study was also performed. The remaining 10 specimens were studied by means of scanning electron microscopy. In 77 specimens both semilunar valves were normal. The aortic valve was bicuspid and the pulmonary valve was normal in 46 animals, while a normal aortic valve and a bicuspid pulmonary valve occurred in 24. In the remaining 6 specimens both semilunar valves were bicuspid. All bicuspid semilunar valves detected herein showed the same morphotype, namely with the leaflets oriented ventrodorsally. The incidence of these anomalous valves did not significantly differ between sexes. Results of a chi 2-test substantiate that conditions of both outflow tract semilunar valves are independent traits. Thus, concurrence of a bicuspid aortic valve and a bicuspid pulmonary valve in an individual is a random event. The present findings support the assumption that bicuspid aortic and pulmonary valves have different morphogenetic origin, although factors producing a bicuspid aortic valve and those leading to a bicuspid pulmonary valve are not mutually exclusive.