Reduced α1-Adrenergic Receptor-Mediated Inositide Hydrolysis in Cardiac Atria of Senescent Rats

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Abstract
We investigated the effect of age on epinephrine stimulation of phosphoinositide hydrolysis in atrial slices prepared from F-344 female rats. Three age groups were chosed for study: young adults (aged 6 months), mature adults (aged 15 months), and senescent animals (aged 25 months). Tissue slices were labeled with [3H]myoinositol and epinephrine-stimulated hydrolysis measured in the presence of LiCl. Epinephrine caused a dose-dependent increase in phosphoinositide hydrolysis in each age group. This increase was blocked by prazosin, suggesting that .alpha.1-adrenergic receptors are involved. In animals aged 6 months, epinephrine caused a maximal increase in hydrolysis of 2.8-fold over basal. The maximal response was reduced at 15 months (2.52-fold increase, p < 0.05) and at 25 months (2.02-fold increase, p < 0.01). The potency for epinephrine stimulation of phosphoinositide hydrolysis was unchanged with age. The data indicate that .alpha.1-mediated phosphoinositide hydrolysis in atria is reduced with age.

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