Studies on the absorption of desmosine and isodesmosine

Intestinal absorption of desmosine and isodesmosine was investigated in several animal species. Hamsters given desmosine injections intraperitoneally excreted 70% of the injected dose in the urine. When desmosines or elastin were given via gastric intubation, desmosines failed to appear in the urine, indicating a lack of desmosine absorption. Additional studies with everted hamster intestine in vitro showed that norleucine was actively transported from the mucosal to the serosal side but that desmosines and lysinonorleucine were not transported. Intestinal slice experiments with hamster, rabbit, and dog intestine indicated desmosines only in the extracellular space and not absorbed by the mucosal cells. These studies strongly suggest that desmosines are not absorbed via the gastrointestinal tract. The importance of this study rests with the conclusion that desmosines recovered in the urine must represent the degradation products of elastin destruction in the tissue. Newly synthesized elastin cannot interfre, since elastin precursor molecules do not contain desmosines. Thus quantitation of urinary desmosines may be of clinical value as a method of evaluating elastin catabolism.