DECREASED DENSITY OF BETA-ADRENERGIC AND MUSCARINIC CHOLINERGIC RECEPTOR-SITES IN THE VASA NERVORUM OF AGED RATS

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague-Dawley rats of 4 and 24 months of age were used. [H-3]Dihydroalprenolol (DHA) and [H-3]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (K(d)) values (about 1.37 nM for [H-3]DHA and 0.75 nM for [H-3]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (B(max)) for [H-3]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The B(max) value for [H-3]QNB was reduced by about 50%, in the aged rats. Light microscope autoradiogaphy revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [H-3]DHA or [H-3]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum.