Abstract 357 Poster Session I, Saturday, 5/1 (poster 152)

Intrauterine growth retardation (IUGR) has been linked to the development of diabetes later in life. In an animal model of IUGR we have previously shown that IUGR newborns exhibit β-cell dysfunction, insulin resistance, and eventually develop diabetes (by 15-18 weeks of age). In the early stages of diabetes, although the insulin secretory process is not normal, the β-cell can supply enough insulin to prevent hyperglycemia. Overt diabetes occurs when compensatory changes in β-cell mass and function do not occur. It is not known whether this lack of compensation is due to inadequate expansion or increased loss of β-cells. The aim of this study was to determine whether the lack of expansion and eventual reduction in β-cell mass are caused by decreased proliferation or increased apoptosis in the IUGR rat. We ligated maternal uterine arteries in pregnant rats (n=25) on day 19 of gestation (term = 21.5 d). Sham operated pregnant rats served as controls (n=25). Studies were carried out before the development of diabetes (1, 7, &10 weeks) and after the development of diabetes (18 weeks). β-cell mass and replication rates were quantified by the use of BrdU and point counting. β-cell mass did not differ between IUGR and control animals at 1, 7, and 10 weeks, however, by 18 weeks of age β-cell mass in IUGR animals was one-third that of controls (p<0.05). At 1 week, β-cell replication rates were similar in IUGR and control rats. However, by 7, 10, and 18 weeks of age, β-cell replication rates in IUGR were 30-50% of controls (p<0.05). mRNA levels (measured by RT-PCR using rhodopsin as an internal standard) of PDX-1, a crucial gene regulating β-cell proliferation, were significantly lower in IUGR rats at all ages (10-50% of control values, p<0.05). Apoptosis of β-cells was determined by colocalization using immunostaining for propidium iodide and insulin in sections of pancreas. At 1 and 7 weeks of age low levels of apoptosis were detected in IUGR and control pancreas. However, by 10 weeks of age, apoptotic rates were 4-fold higher in IUGR animals compared to controls (p<0.05). Levels of two proteins that affect apoptosis in the pancreas were measured: Bcl-2 (which inhibits apoptosis) and Bax (which promotes apoptosis). Islet mRNA levels of Bcl-2 were significantly reduced in IUGR animals at all ages (20-30% of controls, p <0.05). In contrast, Bax mRNA levels were similar in IUGR and controls until 18 weeks of age when Bax levels were 5-fold higher in IUGR pancreas (p<0.05). We speculate that the altered intrauterine milieu in IUGR permanently changes expression of PDX-1, Bcl-2, and Bax, which lead to decreased proliferation and increased apoptosis of β-cells. β-cell compensation for secretory defects and insulin resistance is thus prevented, which leads to the eventual development of diabetes.