Many epidemiologic studies have disclosed that restricted fetal growth has been associated with an increased risk of insulin resistance in adulthood. We studied the relationship of intracellular magnesium ([Mg 2ϩ ] i ) in cord blood platelets to adipocytokine and birth size. The subjects were 20 infants with small for gestational age (SGA) and 45 infants with appropriate for gestational age (AGA). By using a fluorescent probe, we examined [Mg 2ϩ ] i of platelets in the cord blood. Cord plasma insulin, IGF-I, ghrelin, adiponectin, plasminogen activator inhibitor-1 (PAI-1), and leptin levels were determined with the use of ELISA. Mean [Mg 2ϩ ] i was lower in the SGA than in the AGA groups (p Ͻ 0.001). Adiponectin and IGF-I were also lower in the SGA than in the AGA, whereas PAI-1 was higher in the SGA. [Mg 2ϩ ] i was significantly correlated with birth weight, birth length, and adiponectin. Birth weight was also correlated with cord plasma IGF-I, adiponectin, and leptin. Quantitative insulin sensitivity check index (QUICKI) was lower in the SGA group than in the AGA group. T here is no doubt that low birth weight is associated with adult disorders characterized by insulin resistance such as type 2 diabetes, hypertension, dyslipidemia, and coronary heart disease (1,2). It has been proposed that this association results from fetal programming in response to the intrauterine environment (3). Intracellular magnesium (Mg 2ϩ ) i deficiency occurs in patients with diabetes and vascular diseases (4 -6). Taken together, these experimental and epidemiologic results suggest that the correlation between Mg 2ϩ and birth weight are important determinants of insulin resistance. We and other investigators reported that insulin could regulate intracellular Mg 2ϩ ([Mg 2ϩ ] i ) in platelets (7,8). Platelets are often used in the study of cellular cation metabolism in diseases (9), because they are readily available for study and are thought to share a number of features with vascular smooth muscle cells. Human platelets have been shown to have insulin receptors with similar characteristics as those in other cells (10 ] i and birth weight (11). As the next step, we hypothesized that [Mg 2ϩ ] i may affect metabolic hormones and insulin resistance in infants. We studied the correlation among [Mg 2ϩ ] i , adipokines in cord blood and insulin resistance index.
SUBJECTS AND METHODSThe study group consisted of 65 singleton subjects with gestational ages ranging from 33 to 41 wk, and birth weights ranging from 1332 to 4030 g. Most of these subjects had been previously recruited for an observational study of [Mg 2ϩ ] i (11). Gestational age was measured by dating the last menstrual period at the time of registration. None of the subjects were treated with medications, including magnesium, and did not show any evidence of endocrine malfunction or recent use of drugs that might potentially alter electrolyte balance. All the mothers were Japanese with no remarkable past medical histories, and they manifested no abno...