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Renal vasoconstriction during static handgrip (HG) and orthostatic stress: The interaction between the muscle mechanoreflex and the baroreflex.
Author(s) -
Momen Afsana,
Thomas Karen,
Blaha Cheryl,
Gahremanpour Amir,
Mansoor Ather,
Leuenberger Urs A.,
Sinoway Lawrence I.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1429-b
Renal circulatory adjustments to stress contribute to blood pressure (MAP) and volume regulation. Both HG and disengagement of baroreflexes with lower body negative pressure (LBNP) can engage the sympathetic nervous system. However, the effect of simultaneous HG and LBNP on the renal circulation in humans is not known. Eighteen young healthy volunteers were studied. Beat‐to‐beat changes in renal blood flow velocity (RBV; Duplex Ultrasound), MAP (Finapres) and heart rate (ECG) were monitored during: a) 15 s HG at 30% maximum voluntary contraction (MVC); b) LBNP at −10 and −30 mmHg (each level for 5 min); and c) 15 s HG (at 30% MVC) during LBNP at both levels. Renal vascular resistance index (RVR units) was calculated by dividing MAP by RBV. The increases in RVR during HG alone (12±6%) were not different than the responses noted during combined HG and LBNP (17±6% at −10 mmHg and 25±8% at −30 mmHg). These results suggest occlusion occurs between a neural circuit engaged during HG (central command and/or the muscle mechanoreflex) and a circuit activated by LBNP. In additional experiments (n=6) similar nonalgebraic summation of RVR was seen during 15 s involuntary biceps contractions (engages only muscle reflexes) and LBNP. With respect to RVR, neural occlusion occurs between baroreflexes and the muscle mechanoreflex. Muscle mechanoreflex mediated renal vasoconstriction during short bouts of HG is not influenced by baroreflex disengagement. Supported by P01 HL077670 and M01 RR010732.