MAMMARY ARTERY - DIFFERENCE IN STRUCTURE SINCE BIRTH AS COMPARED WITHCORONARY, AND RENAL-ARTERY

A light microscopy study was made of the structure of the left coronar y, internal mammary, and renal arteries (LCA, IMA, RA) in 11 newborns after autopsy (mean age 22 +/- 22.6 days). Their intima and media thic knesses were measured. The mean intima/media ratios were: LCA 0.0745 /- 0.0621; IMA 0.0837 +/- 0.0603, RA 0.0699 +/- 0.0616. The only signi ficant difference was between the media thicknesses of the LCA and the IMA (P=0.023). The media was thinnest in the IMA, thickest in the LCA . A previous study pointed out in adults, on the other hand, the intim a thickness and the intima/media ratio are significantly different in the LCA as compared with the IMA and the RA. The ratio of only the neo natal LCA is significantly different from that of the adult (P=0.005). Media thickness in newborns and intima thickness in the adult are res ponsible for these differences in the ratio. The conclusion is drawn t hat the different structures present at birth are altered in function by the stress these arteries are subjected to and, more specifically, in direct proportion to increases in peripheral resistance. Another fa ctor is the greater freedom of nutrition and metabolic exchange offere d by the thin media of the IMA. This, indeed, may help to explain the relative immunity to atherosclerosis that has led to the use of this a rtery in bypass surgery.