Cardiorespiratory effects of topical application of endothelin-1 to the ventral surface of the rat medulla.

In urethane-anesthetized and vagotomized rats, we examined the cardiorespiratory effects of a topical application of endothelin-1 (ET-1) to the ventral surface of the medulla (VSM) and surveyed subregions of the VSM influenced by these effects. ET-1 (0.1 fmol) delivered to the S area of the VSM via a needle (i.d. of approximately 100 microns) gently pressed on the VSM had no effect on mean arterial pressure (MAP), heart rate (HR), renal sympathetic nerve activity (RSNA), phrenic nerve activity (PNA), or the burst rate of PNA. However, a dose of 1 fmol of ET-1 induced transient but significant increases in MAP, HR, RSNA, and burst rate while at a dose of 10 fmol or more, PNA also increased and simultaneously longer-lasting decreases in MAP, RSNA, and PNA followed the initial increase. The subregion of the VSM in which ET-1 most prominently elicited these effects was the S and caudal part of the M area, where topical application of 50 nmol of L-glutamate caused cardiorespiratory changes. Additionally, there was a restricted region within the caudal VSM in which ET-1 caused a decrease in PNA with an increase in burst rate. These results support our hypothesis that the VSM is crucially involved in the cardiorespiratory changes induced by centrally administered ET-1.