Attenuated cardiovascular response to adenosine in the brain stem nuclei of spontaneously hypertensive rats.

We previously reported that adenosine has significant depressor effects in the nucleus tractus solitarii and area postrema of the rat. The purpose of this study was to determine whether the spontaneously hypertensive rat (SHR) has abnormalities in medullary sensitivity to adenosine. Male SHR and Wistar-Kyoto (WKY) rats (aged 12 to 15 weeks) were anesthetized with urethane, and blood pressure was monitored intraarterially. Stereotaxic microinjection (60 nL) of adenosine was made into the nucleus tractus solitarii and the area postrema and was confirmed histologically. Dose-related decreases in mean blood pressure and heart rate occurred in both strains tested, and this effect was completely abolished by 1,3-dipropyl- 8-p-sulfophenylxanthine (0.92 nmol), a potent adenosine receptor antagonist. However, there were significant differences between SHR and WKY rats in the magnitude of blood pressure and heart rate depression. A similar pattern of response was found in the area postrema. Thus, adenosine is a potent depressor agent in the nucleus tractus solitarii and area postrema of rats, and adenosine has significantly fewer depressor effects in SHR. These data suggest that alterations in purinergic mechanisms of central cardiovascular control exist in the SHR model.