To compare the inhibitory influence of the caudal ventrolateral medulla (CVLM) on rostral ventrolateral medulla (RVLM) between spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats, we studied the blood pressure responses to administration of kainic acid, an excitotoxic agent, to CVLM. Unilateral or bilateral administration of kainic acid led to an initial reduction in blood pressure in both types of rats. In SH rats, this was followed by a gradual and sustained pressor response. This biphasic response in arterial blood pressure was observed in only one-third of the WKY rats. The elevation in blood pressure was significantly greater in SH than in WKY rats. The finding suggests that the tonic inhibitory influence from CVLM to RVLM may be greater in SH than in WKY rats.