Effect of graded exercise on sympathetic vasoconstriction in normoxic and chronically hypoxic rats: a role for NO?

Wallice, Rachel (2013). Effect of graded exercise on sympathetic vasoconstriction in normoxic and chronically hypoxic rats: a role for NO? University of Birmingham. M.Res.

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Abstract

During exercise, sympathetic vasoconstriction is attenuated, a phenomenon is known as functional sympatholysis. It is not clear whether sympatholysis is graded with exercise level. Nitric oxide (NO) has been suggested to be important in mediating sympatholysis. This study tested the hypothesis that functional sympatholysis is graded with increasing levels of hind limb contraction in normoxic (N) and chronically hypoxic (CH: acclimated to 12% O2 for 3 weeks) rats. Investigations also included whether sympatholysis is still present after α-adrenoreceptor inhibition. Arterial blood pressure (ABP) and femoral blood flow (FBF) were used to calculate femoral vascular resistance (FVR = ABP/FBF) in anaesthetised N (n=11), N+phentolamine (n= 9) and CH (n=10) rats. L-NAME increased baseline FVR and enhanced sympathetic vasoconstriction. SNP restored baseline FVR and responses to pre-L-NAME levels. Sympathetic vasoconstriction was evoked during rest and graded tetanic contraction before and after administration of L-NAME then SNP. Sympatholysis occurred at every level of contraction and was graded in N and CH. In N rats vasoconstriction still occurred after phentolamine as did sympatholysis. Results suggested that the magnitude of sympatholysis was graded with initial peak of contraction rather than with force during period of sympathetic stimulation. It is proposed that sympatholysis is graded due to greater recruitment of glycolytic fibres and build-up of acidosis at higher contractions which attenuate constriction mediated by α2-adrenoreceptors. During blockade of α-adrenoreceptors it is possible NPY was released and whilst its constrictor effect was not graded it was attenuated by another mechanism during contraction. The present results show exercise induced blunting of sympathetic vasoconstriction in skeletal muscle is not mediated by NO under the conditions used in this study.

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

Supervisor(s):