Angiotensin and norepinephrine effects on isolated vascular strips from a reptile

In order to better understand the vascular effects of angiotensin II (AII) in lower vertebrates, the contractile responses of aortic strips from the freshwater turtle Pseudemys scripta elegans were studied. Circumferential strips from the left aortic arch were suspended in a tissue bath in 25 degrees C reptilian Ringer's solution at pH 7.5. Both [Asn1,Val5] AII (10(-9)-10(-5) M) and norepinephrine (NE) (10(-8)-10(-4) M) produced dose-dependent contractions. The threshold dosage for AII was between 10(-9) and 10(-8) M and for NE between 10(-8) and 10(-7) M. Pretreatment with [Sar1,Ile8] AII (10(-6) M) significantly attenuated the response to [Asn1,Val5] AII at 10(-5) M and totally blocked the response at lower AII concentration (P less than 0.01 in each case). The response to AII was unaffected by phentolamine (10(-6) M). Phentolamine abolished the response to NE at concentrations of 10(-6) M or less (P less than 0.01) and attenuated the response by 48% at 10(-5) M (P less than 0.05) and 43% at 10(-4) M (P less than 0.05) NE. The response to NE was unaffected by [Sar1,Ile8] AII. The results demonstrate that [Asn1,Val5] AII has a direct contractile effect on turtle vasculature and that two functionally distinct vascular receptor populations for AII and NE are present in the turtle. Since phentolamine did not affect the responses to AII, it also appears that angiotensin-evoked norepinephrine release from the sympathetic nerve terminals in the vessel is not involved in the angiotensin-induced contractions in this preparation.