The effects of ketanserin, methysergide and LY 53857 on sympathetic nerve activity.

Preganglionic sympathetic nerve activity, blood pressure, heart rate and femoral arterial conductance were recorded in anaesthetised, paralysed cats. Three 5-HT2 antagonists, ketanserin, methysergide and LY 53857, were infused separately over 1 h periods. Ketanserin caused a fall in, methysergide a rise followed by a fall and LY 53857 only a rise in preganglionic sympathetic nerve activity. The sympathoexcitation caused by both LY 53857 and methysergide was not associated with any changes in blood pressure and heart rate. The sympathoinhibition caused by ketanserin and methysergide was accompanied by a fall in blood pressure and heart rate. Both ketanserin and LY 53857 caused increases in femoral arterial conductance, while methysergide caused a transient decrease. These differences are explained on the basis that ketanserin possesses alpha 1-adrenoceptor antagonist and methysergide 5-HT receptor agonist properties. It is suggested that 5-HT2 sympathoinhibitory receptors are involved in central cardiovascular control.