Effects of clonidine and guanethidine on peripheral sympathetic nerve function in the pithed rat.

Clonidine, in low intravenous doses, inhibited the increased heart rate of pithed rats caused by peripheral sympathetic nerve stimulation. The magnitude of this effect was greatest at low frequencies of nerve stimulation, responses to high frequencies being little affected by the drug. In contrast, guanethidine reduced cardiac responses to both low and high rates of nerve stimulation. The difference between the depressant effects of the two drugs on responses to various frequencies of sympathetic nerve traffic may contribute to the differences known to occur between their properties as hypotensive agents.