Type 1A dopamine receptor expression in the heart is not altered in spontaneously hypertensive rats

We have recently demonstrated that type 1A dopamine (D1A) receptor is expressed in the rat heart, but its function still remains unknown. In the present study, we investigated possible changes in the expression level and the distribution of the cardiac D1A receptor in the development of left ventricular hypertrophy in spontaneously hypertensive rats/Izumo strain (SHR/Izm) at the ages of 4, 8, and 20 weeks. We examined D1A receptor protein distribution by immunohistochemistry and gene expression by competitive polymerase chain reaction (competitive PCR). In SHR/Izm, compared with the age-matched Wistar Kyoto rats/ Izmo strain (WKY/Izm), blood pressure and heart/body weight ratio were significantly increased at 8 and 20 weeks. By immunohistochemistry, the D1A receptor was localized in cardiomyocytes and vascular smooth muscle cells of coronary arteries, but not in interstitial fibrotic tissue. D1A receptor distribution was not changed either by the strain or the age. Competitive PCR analysis showed that the D1A receptor mRNA level was significantly higher at 4 weeks than at 8 and 20 weeks in both strains of rats and that there was no significant difference in D1A receptor mRNA between SHR/Izm and WKY/Izm at any age ( 43.2 ± 10.4 attomol × 10−3/L v 43.1 ± 11.2 attomol × 10−3/L at 4 weeks, P = not significant, 3.9 ± 0.9 attomol × 10−3/L v 4.0 ± 1.3 attomol × 10−3/L at 8 weeks, P= not significant, 3.0 ± 1.2 attomol × 10−3/L v 1.9 ± 1.6 attomol × 10−3/L at 20 weeks, P = not significant). These results do not support the hypothesis that changes in D1A receptor expression are associated with the development of left ventricular hypertrophy in SHR.