Increased Norepinephrine Release During Sympathetic Nerve Stimulation and its Inhibition by Adenosine in the Isolated Perfused Kidney of Spontaneously Hypertensive Rats

Abstract

The present study was performed to measure norepinephrine release during sympathetic nerve stimulation and determine the inhibitory action of adenosine on stimulus-induced release of norepinephrine in the isolated perfused kidney of WKY and SHR. Norepinephrine release during periarterial nerve stimulation was measured as total ³H-overflow since greater than 75% of total ³H-overflow was ³H-norepinephrine in both the WKY and SHR. A significantly greater increase in ³H-norepinephrine overflow was observed during periarterial nerve stimulation in SHR in comparison with WKY. Adenosine (0.3, 1.0, 3.0 and 10.0 μg/ml) produced dose-dependent inhibition of ³H-norepinephrine overflow elicited by periarterial nerve stimulation. However, the effect of adenosine on transmitter release was more pronounced in the SHR in that the threshold dose required to cause inhibition of stimulus-induced release of ³H-norepinephrine was smaller in the SHR. These results demonstrate that while norepinephrine release during sympathetic nerve stimulation is greater in the SHR, this finding can not be explained on the basis of a decrease in the presynaptic inhibitory action of adenosine. Therefore, the mechanism responsible for the increased release of norepinephrine in the SHR remains to be determined.

Key Words:

• Norepinephrine
• Presynaptic
• Adenosine
• SHR
• Perfused Kidney