Desensitization of human adipose tissue to adrenaline stimulation studied by microdialysis

1. Desensitization of fat cell lipolysis to catecholamine exposure has been studied extensively in vitro but only to a small extent in human adipose tissue in vivo. 2. We measured interstitial glycerol concentrations by microdialysis in subcutaneous, abdominal adipose tissue in healthy humans during intravenous adrenaline infusion for three 35 min periods with 30 min breaks in between. Local blood flow, interstitial adrenaline and arterial glycerol concentrations were also measured. Adrenaline was infused to result in either a high, a low and a high arterial concentration (5.8, 3.1 and 5.6 nM, respectively) or a low, a high and a low concentration (2.5, 4.6 and 2.6 nM, respectively) in order to examine both desensitization and the dose dependency of adipose tissue lipolysis to adrenaline. 3. Adipose tissue lipolysis was calculated and was found to vary directly with arterial adrenaline concentration. However, lipolytic responses to adrenaline decreased markedly during repeated stimulation at a given concentration. Further, arterial glycerol and free fatty acid concentrations varied directly with arterial. adrenaline concentrations and showed reduced responses upon repeated exposure. 4. The increase in adipose tissue blood flow in response to adrenaline was also reduced by prior adrenaline exposure, but no consistent desensitization could be demonstrated for whole-body energy expenditure, blood pressure and heart rate. 5. In the basal state, arterial plasma and interstitial adrenaline concentrations did not differ. During perturbations of arterial adrenaline concentrations, changes in interstitial concentrations were highly reproducible but smaller than changes in arterial concentrations. 6. In conclusion, in vivo adrenaline-mediated adipose tissue lipolysis and blood flow increments are desensitized by prior adrenaline exposure.