EFFECTS OF NOREPINEPHRINE, DOPAMINE AND POTASSIUM ON TENSION AND CA-45 FLUXES IN CANINE AND RABBIT RENAL-ARTERIES

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  • 1 January 1978
    • journal article
    • research article
    • Vol. 207  (2) , 364-371
Abstract
The actions and interactions of 3 vasoconstrictors, norepinephrine (NE), dopamine (DA) and elevated K+ on contractile responses and associated 45Ca movements were investigated in isolated rabbit and canine renal arteries (RA). Dose-response curves indicate that NE is 39 .times. more potent than DA in canine RA and 122 .times. more potent in rabbit RA. Prior exposure to 80 mM K+ did not prevent contractile responses to NE or DA, but K+-induced responses did not occur after exposure to NE or DA. Responses to NE persisted after maximum DA-induced contractions but only a small response to DA was observed after a maximum NE-induced contraction. After 30-60 min in either a 0-Ca or a O-Ca plus 0.05 mM EDTA solution, contractile responses were differentially inhibited (K+ > DA > NE). Efflux of 45Ca into a O-Ca plus EDTA solution was qualitatively similar in canine and rabbit RA. Addition of K+, DA or NE decreased the rate of 45Ca efflux in both RA; phentolamine abolished the NE-induced decrease, partially inhibited the DA-induced decrease and had no effect on the K+-induced decrease. The decrease in 45Ca efflux may reflect an inward shift of 45Ca from membrane binding sites. The mechanisms by which this effect is obtained appear to differ for K+, DA and NE. The differing actions of NE and DA cannot be explained solely by variations in potency at a single type of receptor.