Human amniotic fluid stimulates DNA synthesis of rat pancreatic islets

Collagenase isolated pancreatic islets from newborn Lewis rats were used to study the effect of human amniotic fluid (HAF) on DNA synthesis measured as incorporation of 3H-thymidine into islet DNA and as estimation of labeling index. We investigated individual samples of HAF obtained from pregnant women between the 28th and 39th week of gestation. Since there were no significant differences of HAF obtained from different gestational weeks on islet DNA synthesis, the following experiments were carried out with pooled HAF. When islets were cultured for 2 days in TCM 199 containing 10 mmol/l glucose the addition of 50% HAF resulted in a significantly increased DNA synthesis in comparison to islets cultured in TCM 199 supplemented to 50% with Hank's balanced salt solution (HANK). When extending the culture period from 2 to 4 days the stimulatory effect of 50% HAF was well preserved. Islets cultured in HANK are characterized by a declined DNA-content, which was prevented in the presence of HAF. There was a good correlation between incorporation of 3H-thymidine and the percentage of labeled nuclei, estimated on hematoxylin/eosin-stained autoradiograms of islets cultured for 4 days either in TCM 199 alone, in the presence of 50% HANK or 50% HAF, indicating that the measured incorporation of labeled thymidine into islet DNA was representative for islet replication.