The evaluation of an isotope clearance technique in the dermis of pig skin: A correlation of functional and morphological parameters

A dermal isotope clearance technique has been assessed in pig skin. Following an intradermal injection, the tracer (^99mTc) is cleared from this site by both a fast and a slow exponent (biexponential clearance). From a comparison of age-related changes in the clearance parameters with the thickness and vascular density of the dermis, it is proposed that the two clearance exponents are related to two distinct vascular networks within the dermis: the fast exponent results from clearance by the vessels of the superficial papillary dermis while the slow exponent denotes clearance by the vessels of the reticular dermis. This evidence is further supported by changing the depth of injection; clearance rates are not affected by injection depth, but after a “deep” injection a greater proportion of isotope is removed by the slow exponent (clearance from the reticular dermis). It is concluded that the clearance of ^99mTc pertechnetate not only measures the clearance capacity of the blood flow but also relates to the number of vessels present per unit volume of the tissue under investigation. These findings may lead to a clearer understanding of isotope clearance parameters in other normal tissues.