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Immunohistochemical identification of arteriolar development using markers of smooth muscle differentiation. Evidence that capillary arterialization proceeds from terminal arterioles.
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1994
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ImmunologyVascular MalformationCytoskeletonAnatomySm MhcCellular PhysiologyTerminal ArteriolesAngiogenesisSmooth Muscle DifferentiationSkeletal MuscleArteriolar DevelopmentMechanobiologyVascular AdaptationVascular BiologyNeovascularizationDevelopmental BiologyPhysiologyArteriolar GrowthVascular AnatomyMedicine
Arteriolar growth is crucial for tissue adaptation and disease, yet the origin of new arterioles remains unknown. A novel immunohistochemical technique using antibodies against SM alpha‑actin and SM‑MHC was applied to the gracilis muscle of 4‑ and 9‑week‑old rats to map arteriolar development. Terminal arterioles lacking SM‑MHC were more frequent in younger rats, indicating incomplete maturation, while capillaries formed new arcade arterioles via SM‑alpha‑actin extensions that remained continuous with upstream vessels. The abstract is truncated at 250 words.
Arteriolar growth is an important event in the adaptation of normal tissues as well as in important pathologies, but the site of origin of new arterioles remains unknown. The network pattern of arteriolar development in skeletal muscle was detected by use of a new immunohistochemical technique that is based on the observation that fully differentiated (mature) vascular smooth muscle (SM) cells express both SM alpha-actin and the two myosin heavy chains (MHCs) SM-1 and SM-2, whereas less differentiated (immature) vascular SM cells do not express MHC. The anterior gracilis muscle microvasculatures of 4- and 9-week-old Sprague-Dawley rats were labeled with monoclonal antibodies to SM alpha-actin and to SM MHC. Whole transverse arteriole networks were observed, and terminal arterioles, defined as terminal segments labeled with SM alpha-actin, were classified on the basis of the presence or absence of SM MHC. A significantly different percentage of terminal arteriolar endings per network without SM MHC was observed in the two groups (66.1 +/- 17.3% for 4 weeks and 27.1 +/- 18.5% for 9 weeks), suggesting that arteriolar development is more nearly complete in the older animals. Sparsely distributed capillaries exhibited thin extensions of SM alpha-actin that crossed collecting venules and joined similar extensions from an adjacent transverse arteriole, effectively forming the basis for new arcade arterioles. SM alpha-actin and SM MHC labeling in terminal arterioles was always continuous with upstream arterioles. (ABSTRACT TRUNCATED AT 250 WORDS)