[Age-related and pathophysiologic significance of capillary bed rarefaction of the hypertensive vascular system]

In spontaneously hypertensive rats (SHR), in normotensive related controls (WKY), as well as in non-related controls (NR), the rarefaction of the capillary bed in the gracilis muscle has been studied. By comparing four different in vivo and in vitro techniques for estimation of the number of capillaries, a rarefaction of about 30% in SHR, was found. The precapillary arterioles revealed a reduced rarefaction by about 25.5% or 40.2% in hypertensive, as compared with normotensive control animals. Age dependency was studied in animals of 6, 12, 24 and 48 weeks with respect to the rarefaction of the capillary bed. An age-dependent reduction of capillaries was seen from 385 to 272 cap/mm2 in NR, from 346 to 276 cap/mm2 in WKY, and an age- as well as hypertension-related rarefaction was found from 285 to 213 cap/mm2 in SHR. Under antihypertensive therapy (nifedipin, 300 mg/kg b.w.) systemic pressure was reduced significantly in all three strains studied and the capillary number changed from 674 to 1051 cap/mm2 in SHR, from 806 to 864 in WKY, and from 779 to 1019 in NR. The results indicate an age-dependency of the capillary rarefaction, which may be protracted and amplified by the hypertension disease. The pathophysiological meaning may be seen in reduction of the capillary surface area during a constantly elevated effective filtration pressure. By that, the increased transvascular fluid permeability of the capillary bed is prevented, which otherwise would cause edema formation in the hypertensive system.