Measurement of growth hormone and prolactin receptor turnover in rat liver.

To study the rate of disappearance of GH and PRL receptors in the livers of rats treated with cycloheximide, a technique has been devised for multiple sampling from the liver of each anesthetized rat. In rats treated with cycloheximide (1 or 5 mg/kg, iv), binding sites for both bovine GH and ovine PRL disappeared following first order kinetics over the 2-h sampling period. The half-time for the GH receptor was 30-40 min, equivalent to a rate constant of approximately 0.02 min-1. The half-time for the PRL receptor was 40-50 min, equivalent to a rate constant of approximately 0.015 min-1. At 0.1 mg/kg cycloheximide, slower disappearance rates were seen for both receptors, and the GH receptor showed a partial recovery. Over the same period, binding sites for insulin were unaltered at any cycloheximide dose. Assuming cycloheximide acts simply to inhibit new receptor synthesis, these rates represent the turnover time for GH and PRL receptors in rat liver.