UPTAKE AND PROCESSING OF PROLACTIN BY ALTERNATIVE PATHWAYS IN RAT-LIVER

The uptake and subcellular processing of radiolabeled prolactin was studied in male and female rats. Analytical subcellular fractionation of liver homogenates from rats injected with 125I-prolactin showed that in female rats the prolactin was primarily internalized to low density (1.12 g .cntdot. cm-3) membranes. Approximately 10-15% of the total label was found in high density membranes, similar in distribution to lysosomal marker enzymes. In the normal male rat, prolactin was internalized solely to lysosomal type membranes. In male rats treated with estrogen, the distribution of prolactin was very similar to that seen in the female, indicating that internalization to low density membrane is dependent on the presence of prolactin receptors. Gel exclusion chromatography showed that the prolactin internalized to the lysosomal membranes was extensively degraded while that associated with the low density membrane remained intact. Use of digitonin, to establish the identity of the low density membrane gave inconclusive results, but suggested that the prolactin was associated with membrane bearing NADH pyrophosphatase rather than the classical Golgi marker, galactosyltransferase.