Kinetics of [3H]-prazosin binding to the rat cortex during aging

Kinetics (Bmax, KD, k on, k off) of [3H]-prazosin binding to the rat cortex was measured at different ages of animals (2-4, 13-15, 20-24 months old). Additionally, an agonist (phenylephrine) and an antagonist (phentolamine) inhibition of [3H]-prazosin binding was performed at two different rat ages (2-4 and 20-24 months old). The number of cortical alpha 1-adrenoceptors was significantly reduced in 20-24-month-old rats, when compared with 2-4-month ones. Association (k on) and dissociation (k off) rate constants were also reduced in the oldest group, but the dissociation constant (KD) was similar in all the age groups tested. Affinity of phenylephrine, but not of phentolamine, was reduced in the oldest group (20-24 months old). The obtained data suggest that changes in the brain alpha 1-adrenoceptors, correlated with the animal age, are connected to the number of binding sites, rate constants and the affinity of an agonist.