Disappearance Rate of ¹³³Xenon, 4-Iodoantipyrine- ¹³¹I and ¹³¹I-from Human Skeletal Muscles and Adipose Tissue

Abstract

Lindbjerg, I. F. Disappearance Rate of ¹³³Xenon, 4-Iodo-antipyrine-¹³¹I and ¹³¹I-from Human Skeletal Muscles and Adipose Tissue. Scand. J. clin. Lab. Invest. 19, 120-128, 1967. A comparison of the disappearance of ¹³³Xe and ¹³¹I-tagged 4-iodo-antipyrine (¹³¹I-AP), simultaneously injected in human leg muscles, was performed at rest and during hyperaemia, produced by maximal muscular exercise during ischaemia.

At rest the ratio between ¹³³Xe and ¹³¹I-antipyrine removal rates in 16 legs of subjects<70 years of age averaged 0.78 (S. D. 0.10); in 8 legs of subjects ⩾ 70 years it was significantly lower, averaging 0.59 (S. D. 0.17); p<0.01. In 10 legs of subjects of all ages, the ratio was 0.68 (S. D. 0.12) at rest and 0.72 (S. D. 0.12) during hyperaemia. This difference is not significant.

In contrast, the ratio between removal rates of ¹³³Xe and ¹³¹I-increased from 0.94 at rest to 1.98 during hyperaemia, indicating a relatively slower removal of ¹³¹I-at higher blood-flows.

In subcutaneous adipose tissue the ¹³³Xe/¹³¹I-AP-removal ratio was 0.102 (S. D. 0.050).

The findings are compatible with maintenance of diffusion equilibrium between tissue and blood in respect to the lipid-soluble indicators ¹³³Xe and ¹³¹I-Ap, while the removal of free ¹³¹I-seems to be impeded at high blood-flows.

Variation of the Xe/I-AP removal ratio in muscle is probably mainly caused by varying fat content.