Cardiovascular effects of microinjection of corticoids and antagonists into the rostral ventrolateral medulla in rats.

Experiments were performed on Wistar or Sprague-Dawley rats of both sexes. Microinjection of corticosterone (10 or 40 ng/0.1 microliter/site) into the rostral ventrolateral medulla (rVLM) caused an increase in systolic blood pressure (SBP), heart rate (HR) and pressor response induced by stimulation of the dorsal periaqueductal grey (dPAG) in the midbrain. Microinjection of aldosterone (10 or 40 ng/0.1 microliter/site) into the rVLM had similar effects showing a higher level and longer period than that of corticosterone. All these effects were dose-dependent. Microinjection of glucocorticoid antagonist RU 38486 (40 ng/0.1 microliter/site) or mineralocorticoid antagonist spironolactone (40 ng/0.1 microliter/site) caused a decrease in SBP, HR and the pressor response induced by stimulation of the dPAG. The inhibitory effects of spironolactone were more apparent. These results suggest that both corticoids could exert central modulatory effects on the resting cardiovascular activities and facilitate the pressor response during a defense reaction, and the rVLM is an essential area for the location of the central modulation. These effects may play an important role in the incidence and development of hypertension induced by stress.