Age Determines the Magnitudes of Angiotensin II-Induced Contractions, mRNA, and Protein Expression of Angiotensin Type 1 Receptors in Rat Carotid Arteries

In this study, we hypothesized that aging alters angiotensin II (Ang II)-induced vasomotor responses and expression of vascular mRNA and protein angiotensin type 1 receptor (AT(1)R). Thus, carotid arteries were isolated from the following age groups of rats: 8 days, 29 months, 1220 months, and 2030 months, and their vasomotor responses were measured in a myograph after repeated administrations of Ang II. Vascular relative AT(1)R mRNA level was determined by quantitative reverse-transcriptase polymerase chain reaction and the AT(1)R protein density was measured by Western blot. Contractions to the first administration of Ang II increased from 8 days to 6 months and then they decreased to 30 months. In general, second administration of Ang II elicited reduced contractions, but they also increased from 8 days until 2 months and then they decreased to 30 months. Similarly the AT(1)R mRNA level increased from 8 days to 12 months and then decreased to 30 months. Similarly the AT(1)R protein density increased from 8 days until 16 months and then they decreased to 30 months. The pattern of these changes correlated with functional vasomotor data. We conclude that aging (newborn to senescence) has substantial effects on Ang II-induced vasomotor responses and AT(1)R signaling suggesting the importance of genetic programs.