Measurement of Growth Hormone and Prolactin Receptor Turnover in Rat Liver*

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Abstract
To study the rate of disappearance of GH [growth hormone] and PRL [prolactin] receptors in the livers of rats treated with cycloheximide, a technique was devised for multiple sampling from the liver of each anesthetized rat. In rats treated with cycloheximide (1 or 5 mg/kg i.v.), binding sites for both bovine GH and ovine PRL disappeared following 1st 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 .apprx. 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. At 0.1 mg/kg cycloheximide, slower disappearance rates were seen for both receptors; 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.