We conclude that pre-term birth leads to remodelling of the myocardium that alters its final structure. This may programme for long-term cardiac vulnerability.

Quantitative assessment of myocardial development and disease requires accurate measurement of cardiomyocyte volume, nuclearity (nuclei per cell), and ploidy (genome copies per cell). Current methods require enzymatically isolating cells, which excludes the use of archived tissue, or serial sectioning. We describe a method of analysis that permits the direct simultaneous measurement of cardiomyocyte volume, nuclearity, and ploidy in thick histological sections. To demonstrate the utility of our technique, heart tissue was obtained from four species (rat, mouse, rabbit, sheep) at up to three life stages: prenatal, weaning and adulthood. Thick (40 μm) paraffin sections were stained with Wheat Germ Agglutinin-Alexa Fluor 488 to visualise cell membranes, and DAPI (4′,6-diamidino-2-phenylindole) to visualise nuclei and measure ploidy. Previous methods have been restricted to thin sections (2–10 μm) and offer an incomplete picture of cardiomyocytes. Using confocal microscopy and three-dimensional image analysis software (Imaris Version 8.2, Bitplane AG, Switzerland), cardiomyocyte volume, nuclearity, and ploidy were measured. This method of staining and analysis of cardiomyocytes enables accurate morphometric measurements in thick histological sections, thus unlocking the potential of archived tissue. Our novel time-efficient method permits the entire cardiomyocyte to be visualised directly in 3D, eliminating the need for precise alignment of serial sections.

BackgroundGlobally, ∼10% of infants are born before full term. Preterm birth exposes the heart to the demands of postnatal cardiovascular function before cardiac development is complete. Our aim was to examine, in hearts collected from infants at autopsy, the effects of preterm birth on myocardial structure and on cardiomyocyte development.Methods and resultsHeart tissue was collected at perinatal autopsies of 16 infants who died following preterm birth between 23 and 36 weeks of gestation, and survived for 1-42 days; the hearts of 37 appropriately grown stillborn infants, aged 20-40 weeks of gestation, were used for comparison. Using confocal microscopy and image analysis, cardiomyocyte proliferation, maturation, ploidy, and size were quantified, and interstitial collagen and myocardial capillarization were measured. Preterm birth resulted in a marked reduction in the proliferation of cardiomyocytes relative to age-matched stillborn infant controls (preterm vs. control P<0.0001). In contrast, preterm birth did not affect heart weight, capillarization, interstitial collagen or cardiomyocyte maturation, ploidy, and size.ConclusionsPreterm birth appears to lead to an abrupt reduction in cardiomyocyte cell division. This reduced cardiomyocyte proliferation in preterm infants may adversely impact upon the final number of cardiomyocytes which may reduce cardiac functional reserve, and impair the reparative capacity of the myocardium.

Treatment of the pregnant ewe with glucocorticoids early in pregnancy results in offspring with hypertension. This study examined whether glucocorticoids can reduce nephron formation or alter gene expression for sodium channels in the late gestation fetus. Sodium channel expression was also examined in 2-mo-old lambs, while arterial pressure and renal function was examined in adult female offspring before and during 6 wk of increased dietary salt intake. Pregnant ewes were treated with saline (SAL), dexamethasone (DEX; 0.48 mg/h) or cortisol (CORT; 5 mg/h) over days 26-28 of gestation (term = 150 days). At 140 days of gestation, glomerular number in CORT and DEX animals was 40 and 25% less, respectively, compared with SAL controls. Real-time PCR showed greater gene expression for the epithelial sodium channel (α-, β-, γ-subunits) and Na(+)-K(+)-ATPase (α-, β-, γ-subunits) in both the DEX and CORT group fetal kidneys compared with the SAL group with some of these changes persisting in 2-mo-old female offspring. In adulthood, sheep treated with dexamethasone or cortisol in utero had elevated arterial pressure and an apparent increase in single nephron glomerular filtration rate, but global renal hemodynamics and excretory function were normal and arterial pressure was not salt sensitive. Our findings show that the nephron-deficit in sheep exposed to glucocorticoids in utero is acquired before birth, so it is a potential cause, rather than a consequence, of their elevated arterial pressure in adulthood. Upregulation of sodium channels in these animals could provide a mechanistic link to sustained increases in arterial pressure in cortisol- and dexamethasone-exposed sheep, since it would be expected to promote salt and water retention during the postnatal period.

No abstract