EFFECT OF NIFEDIPINE ON CORONARY CAPILLARY GEOMETRY IN NORMOTENSIVE AND HYPERTENSIVE RATS

The aim of this study was to describe quantitatively changes in the co ronary capillary network resulting from hypertrophy in spontaneously h ypertensive rats (SHR) and a potential effect of long-term treatment o f these animals with nifedipine. Age-matched male SHR and Wistar-Kyoto (WKY) rats were treated for 27 weeks. Four experimental groups were a nalyzed: (1) untreated SHR, (2) nifedipine-treated SHR, (3) untreated control WKY rats, and (4) nifedipine-treated WKY rats. Treatment signi ficantly decreased systolic blood pressure in SHR, although normotensi ve pressures were not reached. SHR had significantly higher cardiac we ight, which decreased in nifedipine-treated rats, but values remained above those in control animals. Morphometric evaluation revealed lower capillary density and larger capillary domain area in hearts from SHR , which were partially attenuated by treatment with nifedipine. Capill ary domain area was also significantly larger at arteriolar portions c ompared with domains supplied at venular portions. Capillary segment l ength was consistently shorter on the venular than arteriolar portion of the capillary, whereas no differences were observed between hearts from WKY rats and SHR. Treatment with nifedipine resulted in a prolong ation of segment length. Reconstruction of the three-dimensional capil lary supply unit (capillary domain area times capillary segment length ) revealed significant differences between the amount of tissue suppli ed by a capillary at its arteriolar portion than more distally, which was detectable in all experimental groups. In hypertrophic hearts from SHR this tissue volume is increased mainly because of longer intercap illary distances and larger domains, especially on arteriolar portions . The venular portions either support smaller growth of neighboring my ocytes during hypertrophy or are subjected to additional branching. Tr eatment with nifedipine results in a moderate capillary growth along t he entire pathway, as evidenced by smaller capillary domains, longer s egment lengths, and unchanged proportion of proximal and distal capill aries in tissue cross sections.