Hormonal control of pancreatic β-cell development in the fetus during late gestation remains unclear. In fetal sheep hypothyroidism causes an increase in pancreatic β-cell mass in association with increased plasma insulin and leptin concentrations. This study investigated the effects of triiodothyronine (T3), insulin and leptin on proliferation rates in fetal ovine pancreatic β-cells in vitro.
All procedures were approved by the Animal Care and Use Committee at the University of Arizona. Pancreatic islets were isolated from twin sheep foetuses (n=9) after euthanasia between 133 and 142 days of gestation (term ~145 days). Islets were cultured for 48 h with increasing concentrations of T3, insulin and leptin. Proliferating cells were identified by the incorporation of nuclear 5-ethynyl-2′-deoxyuride (EdU) added to the media for the final 24 h and expressed as a percentage of the total insulin-positive cells determined by immunocytochemistry. A minimum of 200 EdU-insulin positive cells were counted for each treatment. Data (mean±S.E.M.) were assessed by one-way ANOVA followed by Tukeys post hoc test.
Pancreatic β-cell proliferation in vitro was inhibited by all concentrations of T3 (0 ng/ml: 7±0.5%; 0.1 ng/ml: 5±0.4%; 1 ng/ml: 3±0.3%; 10 ng/ml: 2±0.2%; P<0.05) and increased by insulin at 10 ng/ml only (0 ng/ml: 5±0.4%; 0.1 ng/ml: 5±0.5%; 1 ng/ml: 6±0.5%; 10 ng/ml: 10±0.9%; P<0.05). Leptin induced a biphasic response whereby proliferation was suppressed at the lowest concentration and increased at the highest concentration (0 ng/ml: 7±0.5%; 0.1 ng/ml: 4±0.5%; 1 ng/ml: 5±0.5%; 10 ng/ml: 10±0.9%; P<0.05).
Proliferation of β-cells isolated from the ovine fetal pancreas is sensitive to physiological concentrations of T3, insulin and leptin. Changes in these hormones may be responsible for the increased β-cell mass observed in the hypothyroid sheep fetus and may have consequences for pancreatic function in later life.
This work was supported the Nigel Groome Studentship and the Society for Endocrinology Practical Skills Grant.