Regional blood flow in genetically obese (ob/ob) mice

Abstract

1. Radioactively labelled microspheres have been used to measure changes in regional blood flow of lean and genetically obese (ob/ob) mice during the nonshivering thermogenesis (NST) induced by noradrenaline (NA). 2. Without NA the distribution of the cardiac output was similar in both phenotypes, with the muscular carcass and the splanchnic organs each taking approximately 30% of the output, the kidneys about 15%, the skin + white adipose tissue about 10%, and the heart 4%. Brown adipose tissue (BAT) received only 1–2% of the cardiac output. 3. The effect of NA on the total cardiac output was similar in lean and obese animals. During maximum NST the lean mice showed an increase in blood flow to most tissues, but BAT was particularly responsive with an almost 40-fold increase. The ob/ob mice responded to NA with similar changes in regional blood flow. However, in BAT the increase in flow was only half that of lean animals. 4. It is calculated from the changes in blood flow and from measurements of the arteriovenous difference in oxygen concentration across interscapular BAT that in lean mice BAT is directly responsible for at least 44% of the increase in metabolic rate effected by NA. 5. It is similarly calculated that the reduced NST and consequent lower energy expenditure of the obese mutant is entirely due to lower metabolic activity in its BAT.