[¹²⁵I] Glucagon Binding by Liver Membranes from Young and Adult Rats

We have previously shown that adipocytes from adult (between four and five months old) rats have reduced glucagon binding and glucagon-stimulated lipolytic activity when compared with cells from young (1.5 months old) animals. In the present study we measured specific [¹²⁵I] glucagon binding by purified liver plasma membranes isolated from young and adult rats. When expressed on the basis of membrane protein content, 5'-nucleotidase activity, or specific [¹²⁵I] insulin binding, the extent of [¹²⁵I]glucagon binding by liver membranes was not influenced by aging. Furthermore, the degree of [¹²⁵I] glucagon degradation was the same in both membrane preparations. These data describe a unique condition in which glucagon binding and hormone sensitivity diminish in one tissue but remain unaltered in another.