Reduced high-affinity alpha 1-adrenoceptors in liver of senescent rats: implications of assessment at various temperatures.

1. We investigated the changes occurring as a result of aging in alpha 1-adrenoceptors in the livers of Fisher 344 females rats. For comparison, we also measured beta-adrenoceptors in this tissue. Three age groups were studied, including young adults (aged 6 months), mature adults (aged 16 months) and senescent animals (aged 25 months). 2. The density of alpha 1-receptors was measured by use of [3H]-prazosin and was found to be reduced 39% (P less than 0.01) at 25 months compared with 6 months. The percentage of alpha 1-receptors displaying high affinity for adrenaline was also reduced from 85.6% at 6 months to 51.6% at 25 months (P less than 0.02). 3. In contrast, the density of beta-receptors, which was measured with [125I]-iodocyanopindolol, was increased 104% between 6 months and 25 months. The affinity of both alpha 1- and beta-adrenoceptors for antagonists was unchanged with age. 4. We found that receptor affinity for agonists may be measured accurately in binding studies conducted at 4 degrees C or 25 degrees C, but that the apparent affinity for agonist was artifactually reduced in studies conducted at 37 degrees C. This effect is poorly reversible, in that reduced agonist-affinity is also observed in tissue which has been incubated at 37 degrees C and then cooled to 4 degrees C before performing the binding studies. 5. It is concluded that liver alpha 1-adrenoceptor function is reduced and beta-adrenoceptor function increased in senescence.