Nicotinic acid and the endogenous production of carbon monoxide.

The endogenous production of carbon monoxide (VCO) has been followed with the aid of a rebreathing system for 3 hours in four healthy volunteers after i.v. injection of 50 mg nicotinic acid (NA). After an initial slight decrease for 15-30 min in the CO hemoglobin per cent saturation (COHb), a rapid increase was registered for 120 min, whereafter the VCO returned to the normal preinjection level. The amount of "extra" CO produced varied between 4.1 and 2.2 ml, corresponding to 2.9 and 1.6 g Hb or 182 and 98 mumol heme,respectively. These figures are 3-5 times higher than those reported in the literature, calculated from increases in serum iron, bilirubin and COHb (without the use of a rebreathing system). When related to the total body heme (TBH) estimated with the CO dilution technique, the amount of "extra" heme metabolized after NA corresponded to 0.30% (range 0.26-0.32) of the TBH (a fourth of the total daily heme turnover or a third of the daily HB heme catabolism.