Epidemiologic studies have linked intrauterine growth restriction (IUGR) with an increased incidence of cardiovascular disease later in life; reduced cardiomyocyte number in IUGR hearts may underlie such prenatal programming. Our aim was to examine the effect of IUGR, as a result of maternal protein restriction, on the number of cardiomyocytes in the rat heart at birth. Rats were fed either a low-protein diet (LPD) or a normal-protein diet (NPD) during pregnancy. At birth, the offspring were killed and the hearts were immersion-fixed. The number of cardiomyocyte nuclei in the hearts were stereologically determined using an optical disector-fractionator approach. In some litters, cardiomyocytes were enzymatically isolated from freshly excised hearts and the proportion of binucleated cells was determined. Taking into account the number of binucleated cells, the nuclear counts were adjusted to estimate total cardiomyocyte number. Birth weight and heart weight were significantly reduced in the LPD offspring. This was accompanied by a significant reduction in the number of cardiomyocytes per heart in the LPD offspring compared with the NPD offspring (1.18 Ϯ 0.05 ϫ 10 7 and 1.41 Ϯ 0.06 ϫ 10 7 , respectively; p ϭ 0.001). The number of binucleated cardiomyocytes was low (~3%) and equal in both groups. In conclusion, IUGR as a result of maternal protein restriction leads to a reduction in the number of cardiomyocytes per heart. As cardiomyocyte proliferation is rare after birth, it is plausible that this reduction in cardiomyocytes may lead to compromised cardiac function later in life. Epidemiologic studies have shown a link between low birth weight, as a result of intrauterine growth restriction (IUGR), and an increased incidence of cardiovascular disease later in life (1), suggesting that maternal nutrition may affect the long-term disease profile of offspring. IUGR can result from a lack of nutrients, oxygen, or blood supply to the fetus (2). The link to cardiovascular disease later in life in IUGR infants may relate to underdevelopment of vital organs in utero. Indeed, early studies report that a reduced supply of nutrients during early life, prenatal and postnatal, interferes with the rate of cell multiplication in various organs (3) and that the effect is proportionally more deleterious in tissues with a faster rate of cell multiplication (4). Under these circumstances, growth of the brain is generally "spared" by preferential diversion of blood flow to the brain, whereas growth of other organs is usually proportional to body weight (5). For example, a reduced kidney weight in IUGR rats was shown to be associated with decreased nephron endowment (6,7). The effects of IUGR on the heart are less well defined. In IUGR rats that are exposed to maternal protein restriction, a reduced heart weight is often found (8,9). Alternatively, an increased heart weight as a result of a low-protein diet (LPD) has also been documented (10). Whether IUGR influences the number of cardiomyocytes in the heart is still unclear. If IUGR ...

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