THE STIMULATORY EFFECT OF GROWTH-HORMONE, PROLACTIN, AND PLACENTAL-LACTOGEN ON BETA-CELL PROLIFERATION IS NOT MEDIATED BY INSULIN-LIKE GROWTH FACTOR-I

The effects of GH, PRL, and placental lactogen (PL) on the proliferation of pancreatic beta-cells in vitro were studied as well as the possible effect of insulin-like growth factor-I (IGF-I) in mediating this effect. Proliferating beta-cells were identified by staining with a monoclonal antibody to bromode-oxyuridine (BrdU) after cells were incubated for 1 h in the presence of 10-mu-M BrdU. By double staining with insulin antibodies it was found that 6.3% of the beta-cells had incorporated BrdU when cultured for 7 days in the presence of 1-mu-g/ml human GH (hGH) compared to 0.6% when cultured in the absence of hGH. Similar results were obtained using rat GH. The half-maximal effect of hGH on beta-cell proliferation was observed at 10 ng/ml, and the maximal effect at 100 ng/ml. Islet cells cultured in the presence of PRL or PL caused a dose-dependent increase in beta-cell proliferation similar to that caused by hGH. GH, PRL, and PL had no effect on the proliferation of glucagonor somatostatin-producing cells. The addition of 100 ng/ml IGF-I to either control or GH-stimulated islet cells did not affect the labeling index. When GH-stimulated proliferation of beta-cells was measured in the presence of neutralizing concentrations of a rabbit IGF-I antiserum, the percentage of beta-cells incorporating BrdU was unaffected. Using Northern blot analysis, no IGF-I transcripts could be detected in RNA from GH-stimulated islets, whereas IGF-I transcripts were readily detected in RNA isolated from rat liver tissue. These data suggest that the stimulatory from rat liver tissue. These data suggest that the stimulatory effect of GH, PRL, and PL on beta-cell proliferation is not mediated by IGF-I, but, rather, is a direct mitogenic effect on the beta-cell.