Receptor binding sites for atrial natriuretic factor are expressed by brown adipose tissue

To explore the possibility that atrial natriuretic factor (ANF) is involved in thermoregulation we used quantiative receptor autoradiography and homogenate receptor binding assays to identify ANF bindings sites in neonatal rat and sheep brown adipose tissue, respectively. Using quantitative receptor autoradiography were were able to localize high levels of specific binding sites for ¹²⁵I-rat ANF in neonatal rat brown adipose tissue. Homogenate binding assays on sheep brown fat demonstrated that the radioligand was binding to the membrane fraction and that the specific binding was not due to a lipophilic interaction between ¹²⁵I-rat ANF and brown fat. Specific binding of ¹²⁵I-rat ANF to the membranes of brown fat cells was inhibited by unlabeled rat ANF with a K₁ of 8.0×10^-9M, but not by unrelated peptides. These studies demonstrate that brown fat cells express high levels of ANF receptor binding sites in neonatal rat and sheep and suggest that ANF may play a role in thermoregulation.