BETA-ADRENERGIC-RECEPTOR ACTIVITY OF CEREBRAL MICROVESSELS IS REDUCED IN AGED RATS

The effect of age on beta- (beta) adrenergic receptor number (B(max)) and adenylate cyclase (AC) activity was determined in microvessels isolated from male F-344 rats at 3, 18, and 24 months of age. Scatchard analysis of [I-125]iodocyanopindolol (ICYP) binding indicated reduced Bmax (fmol/mg) of microvessels isolated from 24 month old rats (27.2 +/- 4.9) compared with 3 month old (50.4 +/- 5.2) and 18 month old rats (p < 0.01) (61.4 +/- 7.6). The basal AC activity (pmol cAMP/mg) in 24 month old rats (32.0 +/- 6.7) and in 18 month old rats (30.4 +/- 2.1) were significantly reduced compared to the basal activity in the young (50.1 +/- 4.2). The net isoproterenol or NaF stimulated AC activity in 24 month old rats (zero and 15.6 +/- 8.5 respectively) was also reduced compared to young rats (10.1 +/- 3.9 and 166.0 +/- 21.2 respectively). It is concluded that aging is associated with reduced isoproterenol stimulated AC activity of cerebral microvessels. This reduction is the product of reduced beta-adrenergic receptor number and reduced activity of AC in aged rat cerebral microvessels.