Age-related decrease in the effect of parathyroid hormone-related protein on cytosolic free calcium level and tension in rat aortic smooth muscle.
Age-related changes in the effect of parathyroid hormone-related protein (PTHrP) on the cytosolic free calcium level ([Ca2+]i) and on the tension in rat aortic smooth muscle were investigated. The possible involvement of cAMP, a second messenger of PTHrP, in such changes was also investigated. Spiral aortic strip preparations without endothelium from 8-weeks, 6-months, and 24-months old rats were treated with fura 2/AM, and the fluorescence ratio R340/380, an index of [Ca2+]i was measured. Simultaneously, the tension of the preparations was measured. PTHrP-(1-34) and dibutyryl cAMP produced concentration-dependent decreases in the tension and in R340/380 in aortas precontracted with phenylephrine (10(-7) M). These effects were significantly lower in the aortas of 24-months old rats than in the vessels of 8-weeks and 6-months old rats. The effects were similar in the aortas of 8-weeks and 6-months old rats. PTHrP-(1-34) concentration-dependently increased cAMP production in vascular smooth muscle cells (VSMCs) from 8-weeks old rats. However, the increase in cAMP production was significantly lower in cultured VSMCs from 6-months and 24-months old rats than in cells from 8-weeks old rats. These results suggest that the reduced cAMP production stimulated by PTHrP and the reduced effects of cAMP with aging might contribute to the age-related changes in the decreases in tension and [Ca2+]i in response to PTHrP in the rat aorta.
Ishikawa
M
M
Department of Geriatrics, Faculty of Medicine, University of Tokyo, Japan.
Ouchi
Y
Y
Akishita
M
M
Kozaki
K
K
Toba
K
K
Namiki
A
A
Yamaguchi
T
T
Ito
H
H
Orimo
H
H
D000367:Age Factors; D000375:Aging; D000818:Animals; D001011:Aorta / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D000242:Cyclic AMP; D002118:Calcium