Preservation studies on canine kidneys recovered from the deep frozen state by microwave thawing

Uniform heating of frozen canine kidneys (-79 to 23 ± 10°C) has been achieved using a microwave heating system at 2450 MHz. The kidneys contained the cryoprotective agent dimethyl sulfoxide; Uniform cooling was obtained at 1°C/min, with fluorocarbon perfusion down to -40°C. Slow environmental cooling was used from -40 to -79°C, the temperature at which the organs were stored for periods up to several days. After microwave thawing at rates between 2 and 4°C/s, temperature differences were ≤10°C, provided the initial perfusion of the kidney had been complete and uniform. For comparative purposes, these microwave heating rates were also applied to organs immediately after perfusion cooling to +4°C. Microfil injection and histological studies of thawed and reimplanted kidneys have shown some preserved capillary blood vessels, but, as yet, frozen-thawed kidneys have not functioned. Viability tests-oxygen and para-amino-hippurate (PAH) uptake-- have been performed on kidney slices recovered from -79 or -196°C by the same method. As yet PAH uptake has not survived kidney slice thawing, although light microscopic structure of these slices is well preserved. The work describes a complete System for the uniform deep freezing and thawing of whole organs, a system in which all the variables can be controlled, and from which viability studies can be established.