Serotonin response increases with age in rat coronary resistance arteries

The effect of aging on morphological and mechanical characteristics and the serotonin reactivity of ring preparations of coronary resistance arteries isolated from a specific part of the left coronary artery were studied in male Wistar rats at 6 weeks, 3 months, and 2 years of age. The media to lumen ratio of the coronary vessels was unaffected by aging, although the effective lumen diameter increased from 176 micron at 6 weeks to 212 micron at 2 years of age. The maximal active tension development, active pressure, and active media stress generation of the vessels were also unaffected by aging. At all ages the spontaneous calcium dependent intrinsic tone was similar, equal to 13% of maximal agonist induced tension development. Serotonin induced a concentration dependent contraction at all ages. Maximal vessel response to serotonin increased with age from 0.38 N.m-1 to 1.45 N.m-1 at 6 weeks and 2 years of age respectively. Serotonin sensitivity was higher in the older rats than in the younger rats. Tachyphylaxis to serotonin developed only in vessels from 6 week old rats. The results confirm that the morphology and mechanics of resistance arteries remain stable over a large age range but that the vascular reactivity to specific agents, such as serotonin, may change over that period. The results also indicate that the coronary blood flow may be seriously affected by serotonin induced vasoconstriction with increasing age in rats.