EFFECTS OF PROTECTION FROM PRESSURE ON RESISTANCE ARTERY MORPHOLOGY AND REACTIVITY IN SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS

The effects of regional hypotension on femoral resistance artery reactivity and morphology were investigated in spontaneously hypertensive rats (SHR) and control Wistar-Kyoto (WKY) rats. A partially constricting ligature (0.4 mm i.d.) was placed around the left external iliac artery at 5 weeks, which resulted in significantly reduced femoral mean arterial pressures distal to the ligature at 12 and 24 weeks. The femoral mean arterial pressure distal to the ligature in SHR was similar to that in WKY unprotected hind limbs. Resistance arteries (approximately 200-mu-m i.d.) were taken from unligatured and protected hind limbs and mounted in a myograph for reactivity and morphological measurements. Each experiment therefore utilized one artery distal to a ligature and one from the control hind limb. Histological examination revealed that nuclear density differed neither between strains nor between arteries from protected and unprotected femoral beds. Media thickness, media cross-sectional area, and media/lumen ratios were reduced in arteries from the hypotensive hind limb in SHR and WKY rats at 12 and 24 weeks. Arteries from the protected hind limbs of SHR were structurally indistinguishable from those from the normally perfused WKY vasculature. It is concluded that the medial content and maximal contractile responses of femoral resistance arteries from SHR and WKY rats are mainly determined by the local perfusion pressure and that normalization of perfusion pressure in SHR normalizes resistance artery structure.