Figure 1.

Daily rhythms of serum and salivary urea concentrations in sheep. Both urea profiles showed clear diurnal rhythms: urea levels were high during the light phase and low during the dark phase of the natural light-dark cycle. Each point represents mean ± SEM. Gray bars indicate the dark phase of the natural light-dark cycle. Arrowheads indicate times of feeding. Asterisks indicate peaks of urea concentrations.