Sympathetic nerve activity and peripheral vasodilator capacity in young and older men.

Am J Physiol Heart Circ Physiol. 2014 Mar;306(6):H904-9. doi: 10.1152/ajpheart.00181.2013. Epub 2014 Jan 10. Hart EC, Wallin BG, Barnes JN, Joyner MJ, Charkoudian N. In this paper, they looked at the fact that high MuscleSNA in young men can be cancelled out by a decreased vasoconstriction response to adrenergic stimuli and a lower cardiac output, where older people with increased SNA tend to have higher blood pressure. What they found was that younger men with high MSNA have decreased responses to intra-arterial vasodilators, but older men do not. Their conclusion was that young men can regulate their blood pressure better than older men, who showed no relationship between MSNA and the effect of vasodilators. They point out that since older men tend to have higher basal MSNA, they may not be able to regulate their blood pressure as well. Mechanistically, this makes sense in older men since fast firing nerves can't fire much faster and their downstream effect is already near its maximum. However, I don't know why this doesn't hold true for younger men, other than how they say that other vasoconstrictor mechanisms may come in to play. -DH