CALL FOR PAPERS Cardiovascular and Cerebrovascular Aging–New Mechanisms and Insights Aging alters reactivity of microvascular resistance networks in mouse gluteus maximus muscle

Sinkler SY, Segal SS. Aging alters reactivity of microvascular resistance networks in mouse gluteus maximus muscle. Am J Physiol Heart Circ Physiol 307: H830–H839, 2014. First published July 11, 2014; doi:10.1152/ajpheart.00368.2014.—Aging occurs with enhanced sympathetic nerve activity and endothelial dysfunction; however, little is known of how successive branches of microvascular resistance networks are affected in vivo. We questioned whether vascular reactivity is altered differentially along resistance networks with advanced age. The left gluteus maximus muscle of anesthetized 4-mo-old and 24-mo-old male C57BL/6 mice (Young and Old, respectively) was exposed for intravital microscopy and superfused with physiological salt solution (3 ml/min; pH 7.4, 34°C). Spontaneous vasomotor tone increased progressively from proximal feed arteries (FA) and first-order (1A) arterioles through distal second-order (2A) and third-order (3A) arterioles and was 15% greater in 2A and 3A of Old versus Young. Vasoconstriction during elevated superfusion PO2 increased with branch order and to a greater extent in Young. Peak constrictions to phenylephrine [ 1 adrenoreceptor ( 1AR) agonist] were similar for FA and 1A of both ages and 20% greater for 2A and 3A of Young. Across arterioles (but not FA), constrictions to UK 14304 ( 2AR agonist) were depressed 30% in Old versus Young. Thus advanced age attenuated vasoconstriction to O2 throughout networks while blunting vasoconstriction to 1AR and 2AR activation in arterioles. With ACh, endothelium-dependent dilation (EDD) was 20% greater in FA of Young yet was approximately twofold greater for 2A and 3A of Old. Sodium nitroprusside evoked maximal dilations similar to ACh. Thus, with advanced age, EDD was attenuated in FA while robust in distal arterioles having enhanced vasomotor tone. We conclude that advanced age differentially alters reactivity among branches of microvascular resistance networks.