How exercise protects and strengthens your heart (1)

How exercise protects your heart: 1

Regular exercise has been shown to reduce the incidence of heart attacks and deaths from heart disease. But how does it exert these beneficial effects? Scientists have recently discovered that regular physical activity is linked with increased production of nitric oxide, presumably by the lining of the body's blood vessels. Since the hormone cyclic guanosine monophosphate (cGMP) is the major messenger of nitric oxide actions in the cardiovascular system, could cGMP levels be taken as a reflection of cardiovascular fitness?

A Venezuelan research team set out to test this hypothesis with a comparison of urinary cGMP levels in four categories of people - all men: 13 highly-trained runners (running an average of 90k per week); 10 well-trained runners (65k/week); 12 sedentary individuals and nine patients with coronary artery disease (CAD).

Baseline cGMP measurements were obtained under resting conditions in runners and sedentary subjects and at the beginning and end of a 12-week cardiac rehabilitation programme in the CAD patients. The highly-trained runners were tested before and after a 42k marathon, the well-trained runners before and after a 15k race and the sedentary subjects under resting conditions. The nine patients with CAD were tested before and after two 3-6k walks, one at the beginning and the other at the end of their rehabilitation programme. Results were as follows:

* Basal urinary excretion of cGMP was found to be unrelated to physical activity levels, with no significant differences between the groups;
* Significant and similar increases in cGMP excretion were observed in both groups of runners within one hour of completion of their races, with a rapid return to pre-exercise levels;
* Smaller increases in cGMP excretion were observed in the heart patients after exercising for 30 minutes at 80% of maximal heart rate. Exercise-induced increases in cGMP were significantly greater after completion of the rehabilitation programme than beforehand.

'We suggest,' say the researchers, 'that [nitric oxide] increases during exercise... and that the increases in cGMP levels may reflect enhanced NO production... Because of its shorter half-life, cGMP levels would return to baseline levels soon after the stimulus terminates, whereas the longer half-life, slower diffusion from tissues, and greater stability of the NO metabolites would lead to more sustained elevations in levels.'

Perhaps their most interesting finding was that cGMP levels rose in proportion with the intensity of the exercise and the fitness of the subjects: high-intensity exercise induced larger increases than low-intensity exercise; and heart patients excreted more cGMP after rehabilitation than before.

'These findings indicate,' the researchers conclude, 'that exercise conditioning (training) plays a fundamental role in determining the amount of cGMP produced during short-term exercise, with enhanced production in physically active individuals. These findings may account for at least part of the beneficial action of physical fitness on cardiovascular health.'

J Cardiovasc Pharmacol 2000 Jun;35(6):891-6

Isabel Walker

Get on the road to gold-medal form and smash your competition.
Try Peak Performance today for just $1.97.

Tagged in Exercise & Physiology
Privacy Policy [opens in new window]
Please Login or Register to post a reply here.