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1 Division of Cardiology, Pennsylvania State University College of Medicine, Hershey, PA, USA
2 Division of Cardiology, Pennsylvania State University College of Medicine, Hershey, PA, USA; Lebanon VA Medical Center, Lebanon, PA, USA
* To whom correspondence should be addressed. E-mail: lsinoway{at}psu.edu.
During exercise, activation of the sympathetic nervous system causes reflex renal vasoconstriction. The effects of aging on this reflex are poorly understood. This study evaluated the effects of age on renal vasoconstrictor responses to handgrip. Seven older (65 ± 9 yr) and 9 younger (25 ± 2 yr) subjects were studied. Beat-by-beat analyses of changes in renal blood flow velocity (RBV; duplex ultrasound) were performed during two handgrip paradigms. Arterial blood pressure (BP) and heart rate (HR) were also measured and an index of renal vascular resistance (RVR) was calculated (BP / RBV). In protocol 1, fatiguing handgrip [40% of maximal voluntary contraction (MVC)] caused a greater increase in RVR in the older subjects (old 90% ± 15 increase, young 52% ± 4 increase; P = .03). During post-handgrip circulatory arrest (PHG-CA; isolates muscle metaboreflex), the increases in RVR were only ~1/2 of the increase seen at endgrip. In protocol 2, 15-s bouts of handgrip at graded intensities led to increases in RVR in both subject groups. This effect was not seen until the 50% MVC workload (P < .05). The RVR responses occurred early and were greater in the older than in the younger subjects at 50% MVC (32 ± 6% vs. 16 ± 5%; P = .02) and at 70% MVC (39 ± 11% vs. 24 ± 8%; P = .02). Static exercise induced renal vasoconstriction is enhanced with aging. Since the characteristics of this response suggest a predominant role for mechanoreceptor engagement, we hypothesize that mechanoreceptor responses are augmented with aging.
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