MARKERS OF ADENOSINE REMOVAL IN NORMOTENSIVE AND HYPERTENSIVE RAT NERVOUS-TISSUE

Adenosine mechanisms are altered in brain stem nuclei associated with cardiovascular control in spontaneously hypertensive rats (SHR). There fore, in the present study we used a number of techniques to compare t he binding of the adenosine transport inhibitor [H-3]nitrobenzylthioin osine ([H-3]KBMPR) as well as adenosine deaminase immunoreactivity (AD A-IR) in brain stems and nodose ganglia of SHR and age-matched normote nsive Donryu rats (DRY). Saturation binding revealed a single class of [H-3]NBMPR binding sites in the dorsal brain stem of both strains. wi th K-d and B-max values of 65 +/- 9 pmol/L and 282 +/- 31 fmol/mg prot ein, respectively, in SHR and 129 +/- 2 pmol/L and 217 +/- 23 fmol/mg protein in DRY. The lid for [H-3]NBMPR was significantly lower in SHR than in DRY. In competition assays, NBMPR, dilazep, dipyridamole, and adenosine displaced [H-3]NBMPR binding, with K-d values of 0.21 +/- 0. 01, 57.16 +/- 16.20, 1340 +/- 100, and 87 000 +/- 12 500 nmol/L, respe ctively, in DRY and 0.17 +/- 0.01, 28.24 +/- 3.60, 621 +/- 100, and 32 000 +/- 6820 in SHR. K-d values for all displacers were lower in SHR; however, only values for dipyridamole and adenosine reached statistic al significance. Autoradiography of adenosine transport sites with [(3 )]NBMPR revealed that unilateral nodose ganglionectomy reduced (H-3]NB MPR binding on the denervated side of the nucleus tractus solitarius b y 20.6 +/-1.1% in DRY and 18.7 +/- 2.3% in SHR. The density of [H-3]NB MPR binding in nodose ganglia was significantly lower in SHR (0.99 +/- 0.06 Bq/mm(2)) than in DRY(1.25 +/- 0.08). Immunohistochemical studie s demonstrated ADA-IR in the dorsal vagal complex associated with both nerve cells and fibers. Measurement of ADA-IR in the dorsal vagal com plex with an I-125-labeled secondary antibody revealed a significantly higher level of ADA-IR in SHR (122%) than in DRY. In the nodose gangl ia, ADA-IR was associated with a population of vagal perikarya. The pr esent study helps provide a molecular explanation for the previously r eported impaired cardiovascular responses to intra-nucleus tractus sol itarius microinjection of adenosine in hypertensive rats.