Expression of alpha 1 adrenergic receptor subtype mRNAs in the rat cardiovascular system with aging

Alpha 1 adrenoreceptors mediate inotropic and chronotropic responses in the heart and vaso-constriction in blood vessels. Pharmacological studies using selective antagonists for subtypes of alpha 1 receptor suggest that different receptor subtypes may mediate different physiological effects. Prior studies have demonstrated that alpha 1-mediated cardiac responses are altered in aging and that alpha 1 receptor number declines with age in the rat heart. The distribution of alpha 1 receptor subtypes in cardiac tissue and subtype-specific changes with aging, however, have not been established. Using R Nase protection assays and in situ hybridization techniques, we have detected message for alpha 1B, alpha 1A, and alpha 1D in all four chambers of the rat heart and in multiple blood vessels. We found no significant changes in alpha 1 receptor subtype mRNA levels in hearts from young (4 months) and old (25 months) Sprague-Dawley rats. Also, there was expression of these three subtypes in all blood vessels assayed. We conclude that transcriptional regulation of alpha 1 adrenoreceptor subtypes does not account for age-related changes in cardiac alpha-adrenergic responsiveness.