title: Markers of adenosine removal in normotensive and hypertensive rat nervous tissue.
abstract: Adenosine mechanisms are altered in brain stem nuclei associated with cardiovascular control in spontaneously hypertensive rats (SHR). Therefore, in the present study we used a number of techniques to compare the binding of the adenosine transport inhibitor [3H]nitrobenzylthioinosine ([3H]NBMPR) as well as adenosine deaminase immunoreactivity (ADA-IR) in brain stems and nodose ganglia of SHR and age-matched normotensive Donryu rats (DRY). Saturation binding revealed a single class of [3H]NBMPR binding sites in the dorsal brain stem of both strains, with Kd and Bmax values of 65 +/- 9 pmol/L and 282 +/- 31 fmol/mg protein, respectively, in SHR and 129 +/- 2 pmol/L and 217 +/- 23 fmol/mg protein in DRY. The Kd for [3H]NBMPR was significantly lower in SHR than in DRY. In competition assays, NBMPR, dilazep, dipyridamole, and adenosine displaced [3H]NBMPR binding, with Kd values of 0.21 +/- 0.04, 57.16 +/- 16.20, 1340 +/- 100, and 87000 +/- 12500 nmol/L, respectively, in DRY and 0.17 +/- 0.04, 28.24 +/- 3.60, 621 +/- 100, and 32000 +/- 6820 in SHR. Kd values for all displacers were lower in SHR; however, only values for dipyridamole and adenosine reached statistical significance. Autoradiography of adenosine transport sites with [3H]NBMPR revealed that unilateral nodose ganglionectomy reduced [3H]NBMPR binding on the denervated side of the nucleus tractus solitarius by 20.6 +/- 1.1% in DRY and 18.7 +/- 2.3% in SHR. The density of [3H]NBMPR binding in nodose ganglia was significantly lower in SHR (0.99 +/- 0.06 Bq/mm2) than in DRY (1.25 +/- 0.08). Immunohistochemical studies demonstrated ADA-IR in the dorsal vagal complex, associated with both nerve cells and fibers. Measurement of ADA-IR in the dorsal vagal complex with an 125I-labeled secondary antibody revealed a significantly higher level of ADA-IR in SHR (122%) than in DRY. In the nodose ganglia, ADA-IR was associated with a population of vagal perikarya. The present study helps provide a molecular explanation for the previously reported impaired cardiovascular responses to intra-nucleus tractus solitarius microinjection of adenosine in hypertensive rats.
authors.affiliation: Department of Pharmacology, Monash University, Clayton, Victoria, Australia. casmel@monash.med.edu.au
authors.forename: M
authors.initials: M
authors.lastname: Castillo-Meléndez
authors.forename: B
authors.initials: B
authors.lastname: Jarrott
authors.forename: A J
authors.initials: AJ
authors.lastname: Lawrence
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001933:Brain Stem / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D013045:Species Specificity; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D013868:Thioinosine; D000243:Adenosine Deaminase; C001789:4-nitrobenzylthioinosine; D000241:Adenosine