Arterial hypertrophy in the fetal and neonatal spontaneously hypertensive rat

Large artery dimensions in prenatal and postnatal normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were evaluated to determine whether increased medial thickness is evident during early development. Microscopic cross-sections from perfusion-fixed aortas and carotid arteries of fetal (22-day gestation) and neonatal (5-day-old) animals were examined for numbers of laminae, luminal diameter and area, and medial thickness and area. SHR had a smaller mean body weight, and luminal diameters were the same in both strains. However, medial thickness and the numbers of laminae were significantly greater in SHR at both stages. Normalized ratios of medial thickness/luminal diameter and medial area/luminal area were also greater in SHR, indicating a disproportionate size of the arterial wall relative to the luminal space. Medial area/body weight ratios were also larger for SHR, suggesting the presence of greater medial mass per unit of body weight. The data support the view that the increased mass of the hypertensive arterial system is established in SHR as early as the fetal stage.