Diurnal variation in endogenous production of carbon monoxide. Effect of caloric restriction.

The endogenous production of carbon monoxide (VCO) and total serum bilirubin (SB) have been followed in five healthy male volunteers during one baseline day and one day with no caloric intake. VCO in the morning studies was 11.2+/-1.7 (mean +/-1 S.E.M.) on the baseline day and 10.1+/-2.3 mumol/mmol total body heme (TBH) and day on the fasting day, respectively. In studies before noon, VCO increased significantly on both days, to values of 17.8+/-1.6 and 19.6+/-2.2 mumol/mmol TBH and day, respectively. In the first study in the afternoon, VCO differed significantly between the two days, amounting to 12.1+/-3.0 and 23.7+/-3.5 on the baseline and the fasting day, respectively. The difference was still significant in the evening, when VCO was 11.6+/-3.1 and 22.1+/-4.9 mumol/mmol TBH and day. SB followed the same pattern, with mean values of 4.0+/-0.3, 4.9+/-0.3, 4.2+/-0.9 and 3.0+/-0.3 mug/ml during the baseline day and 4.5+/-0.6, 5.4+/-1.2, 7.0+/-0.5 and 8.5+/-1.0 mug/ml, respectively, during fasting day. Only insignificant amounts of conjugated bilirubin were found. The studies confirm earlier reports on the effect of caloric restriction on VCO. Since this effect is simultaneous with an increase in SB, it is concluded that the changes are secondary to an increase in total heme catabolism. They might be due to an increase in intracellular hepatic heme turnover but it cannot be excluded that starvation affects erythropoiesis and/or red cell catabolism, thereby causing an increase in VCO and SB.