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 α1-adrenoceptors in the livers of Fisher 344 female rats. For comparison, we also measured β-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 α1-receptors was measured by use of [3H]-prazosin and was found to be reduced 39% (P < 0.01) at 25 months compared with 6 months. The percentage of α1-receptors displayed high affinity for adrenaline was also reduced from 85.6% at 6 months to 51.6% at 25 months (P < 0.02). 3. In contrast, the density of β-receptors, which was measured with [125I]-iodocyanopindolol, was increased 104% between 6 months and 25 months. The affinity of both α1- and β-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°C or 25°C, but that the apparent affinity for agonist was artifactually reduced in studies conducted at 37°C. This effect is poorly reversible, in that reduced agonist-affinity is also observed in tisuse which has been incubated at 37°C and then cooled to 4°C before performing the binding studies. 5. It is concluded that liver α1-adrenoceptor function is reduced and β-adrenoceptor function increased in senescence.