1. The effective volume of distribution of labelled glycerol was studied in conscious young adult rabbits provided with in-dwelling cannulae in the femoral blood vessels. This could be estimated after sampling arterial blood throughout an intravenous infusion of [2-3H]glycerol. The volume was calculated by using an algebraic method of graphical area analysis over 100 min of equilibration, and is symbolized 100V e or 100V e%. It occupied 34.1 +/- 2.2% (mean +/- S.E.M.; n = 13) of the body weight. The pool of endogenous glycerol occupying this space is distinguished in the present paper by calling it the transit pool, symbolized 100Me. 2. The median time of transit of glycerol through this pool was approx. 6 min in these conscious rabbits with normal (less than 0.2 mM) blood glycerol concentrations. 3. The metabolism of glycerol was also studied in rabbits while anaesthetized with urethane or while conscious. On average, half of the change in glycerol concentration that occurred on overnight starvation could be attributed to a decrease in clearance, whereas half was due to an increase in lipolysis. 4. The correlation between the reciprocal of glycerol concentration and clearance showed that in these animals about a quarter of the variation in concentration was due to an association with clearance. The remainder of the variation was attributed to variations in the rate of glycerol formation (lipolysis). 5. The regression of glycerol turnover rate on concentration implied that turnover was positive at zero glycerol concentration. This confirms previous findings from studies on other species. The explanation offered for this phenomenon is that the well-known physiological changes induced by feeding (decreased lipolysis, increased splanchnic blood flow) may independently decrease the glycerol concentration by both decreasing its release into the blood and simultaneously increasing its clearance.
