Abstract
Fluctuations of the plasma atrial natriuretic peptide (ANP) concentration were observed in normal cattle and dog. Statistical analysis using Bartlet test and two-way analysis of variance (two-way ANOVA) did not support any circadian rhythm in the pasma ANP concentration in both species. The present study indicates that the length of the sampling time is not necessary to be considered at the time of determination of the plasma ANP concentration to estimate the intra-cardiac pressure.