Myocardial capillaries in the fetal and the neonatal rat: A morphometric analysis of the maturing myocardial capillary bed

Abstract

Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population.(ABSTRACT TRUNCATED AT 250 WORDS)

Deficiency in endothelial nitric oxide synthase impairs myocardial angiogenesis

“…The morphology of endothelial cells and myocardial capillaries gradually matures during late gestation, and by the early postnatal period there is dramatic growth of the coronary vascular bed (25). In rats, the aggregate capillary length in the ventricular myocardium doubles in the first 11 days postnatal, suggesting that the postnatal period is critical for myocardial capillary development (30).…”

Comparison between right and left ventricular myocardia during the human fetal period. Stereological evaluation

“…In stereological analysis using the disector method, we verified a reduction in the Nv (1/mm 3 ) of the LV myocyte nuclei from 703,948 (EP = 70490) to 397.304 (EP = 27362), from the second to the third gestational trimester, respectively. The mean (second + third trimesters) was around 550,626/mm 3 . However, the total number of nuclei (N) in the heart significantly increased from 2,101,152,700 (EP = 449634529) in the second trimester to 11,147,569,300 (EP = 2222847632) in the third trimester, which resulted from the increase in the heart volume throughout time (p<0.06; Mann-Whitney Rank Sum Test).…”

“…Testing the samples, we did not identify any significant difference between the two ventricular walls (p>0.05). In a former article 36 , assessing Nv nuclei and its volume (Vp) in LV during the third gestational trimester, we found the following values: Nv = 397,304 (1/mm 3 ) and Vp = 97.66 µm 3 . In the present study, the values of RV for Nv and Vp were, respectively, 399,675.48 (1/mm 3 ) and 174.06 µm 3 .…”

“…In a former article 36 , assessing Nv nuclei and its volume (Vp) in LV during the third gestational trimester, we found the following values: Nv = 397,304 (1/mm 3 ) and Vp = 97.66 µm 3 . In the present study, the values of RV for Nv and Vp were, respectively, 399,675.48 (1/mm 3 ) and 174.06 µm 3 . Testing the samples, we did not identify significant differences between the two ventricular walls (p>0.05).…”

“…The mean values found were: Vv% of 77.8% for the cardiac myocytes and 22.2% for the interstitium. Nv of the cardiac myocytes (calculated based on the number of their nuclei) was 574,000/mm 3 . The volume of the myocyte was 1412.3µm 3 .…”