CIRCANNUAL VARIATIONS OF THE BLEEDING-TIME IN THE RAT

This study was carried out to determine the annual fluctuations of the tail bleeding time in the rat. Bleeding time was determined by transe ction of the tail of pentobarbital-anesthetized rats. Over a 6-year pe riod, monthly measurement of the tail bleeding time revealed highly re producible circannual fluctuations. Bleeding times were shortened in t he summer (414 +/- 18 s in July), being almost half that observed duri ng the winter span (886 +/- 32 s in January). The difference between t hese two time points was highly significant (p < 0.001). This study re ports for the first time circannual variations of the bleeding time in the rat.