RAT ADIPOSE-TISSUE AMINO-ACID-METABOLISM IN-VIVO AS ASSESSED BY MICRODIALYSIS AND ARTERIOVENOUS TECHNIQUES

In fed, anesthetized rats, microdialysis demonstrated a net release of glycerol, glutamine, serine, tyrosine, and taurine and a net uptake o f glutamate, aspartate, glycine, and arginine across the inguinal adip ose depot. However, the results also indicated excessive proteolysis a ssociated with implantation of the microdialysis probe, and a novel ar teriovenous difference technique was developed. Arteriovenous differen ce across the inguinal fat pat demonstrated a net uptake of glucose an d a net release of lactate and glycerol. Starvation (48 h) resulted in higher rates of glycerol and lactate release with lower rates of gluc ose uptake. A net uptake of triacylglycerol was seen in starved-refed animals. Net glutamine, tyrosine, and taurine release was seen in fed and starved animals, but in starved-refed animals taurine and serine w ere the only amino acids showing significant release. No significant n et uptake or release of ammonia, pyruvate, or alanine was observed. Th ese experiments confirm that adipose tissue is a site of glutamine syn thesis and suggest that the principal substrates are derived from intr acellular proteolysis. The results also demonstrate the viability of a n arteriovenous difference technique for the study of adipose tissue i n the rat.