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.
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Geriatric Research, Education and Clinical Center, DVA Medical Center, Gainesville, FL 32602.
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D000375:Aging / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D009278:Naphazoline / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D011942:Receptors, Adrenergic, alpha / Q000145:classification / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D013696:Temperature
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D009278:Naphazoline; D011224:Prazosin