PLASMA-CATECHOLAMINE, RENIN-ACTIVITY, AND ACTH RESPONSES TO THE SEROTONIN RECEPTOR AGONIST DOI IN JUVENILE SPONTANEOUSLY HYPERTENSIVE RATS

Mean arterial blood pressure (MAP), heart rate (HR) and arterial plasm a levels of corticotropin (ACTH), renin activity (PRA) and catechols [ norepinephrine (NE), epinephrine (EPI), and the intraneuronal NE metab olite dihydroxyphenylglycol (DHPG)] at baseline and in response to the serotonin-1C/2 (5-HT1C/ 5-HT2) agonist 1-(2,5-dimethoxy-4-iodophenyl) 2-aminopropane (DOI, 1.0 mg/kg i.a.) in conscious, freely-moving,juven ile (4 week old) spontaneously hypertensive rats (SHR's) and age-match ed Wistar-Kyoto (WKY) normotensive control rats were measured simultan eously. Baseline levels of MAP, NE, DHPG, and EPI all were significant ly higher in the SHR's. There was a similar trend for PRA, but ACTH di d not differ between the two strains. DOI produced marked increases in levels of MAP, ACTH, EPI, and also PRA but did not affect NE or DHPG concentrations. HR decreased only in the WKY group after administratio n of DOI. The magnitudes of the EPI and ACTH responses did not differ between the rat strains. Responses of MAP and PRA were significantly l arger in SHR's. These results suggest that there is a selective hyperr esponsiveness of PRA and blood pressure to 5-HT2 receptor stimulation parallel to a deficient baroreceptor reflex in juvenile SHR's.