Markers of adenosine removal in normotensive and hypertensive rat nervous tissue

Margie Castillo-Meléndez, Bevyn Jarrott, Andrew J. Lawrence

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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 K(d) and B(max) 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 K(d) for [3H]NBMPR was significantly lower in SHR than in DRY. In competition assays, NBMPR, dilazep, dipyridamole, and adenosine displaced [3H]NBMPR binding, with K(d) values of 0.21±0.04, 57.16±16.20, 1340±100, and 87 000±12 500 nmol/L, respectively, in DRY and 0.17±0.04, 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 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 tracts solitarius microinjection of adenosine in hypertensive rats.

Original languageEnglish
Pages (from-to)1026-1033
Number of pages8
JournalHypertension
Volume28
Issue number6
DOIs
Publication statusPublished - 1 Jan 1996

Keywords

  • adenosine
  • adenosine deaminase
  • autoradiography
  • immunohistochemistry
  • rats, inbred SHR
  • solitary nucleus
  • thioinosine

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