CARDIOVASCULAR-RESPONSES IN-VIVO TO ANGIOTENSIN-II AND THE PEPTIDE ANTAGONIST SARALASIN IN RAINBOW-TROUT ONCORHYNCHUS-MYKISS

The effects of [Asn(1),Val(5)]-angiotensin II (AngII) and [Sar(1),Val( 5),Ala(8)]-angiotensin II (saralasin) on dorsal aortic blood pressure, pulse pressure and heart examined in rainbow trout lit vivo, AngII ad ministered as a single dose of 25 mu g kg(-1) induced a biphasic respo nse in blood pressure, with a significant hypertensive response during the initial 10 min, followed by a significant hypotension of 70-75 % compared with the initial blood pressure after 50 min and continuing u ntil approximately 80 min post-injection. The co-administration of Ang II (25 mu g kg(-1)) and saralasin (50 mu g kg(-1)) resulted in the sam e hypertensive response during the initial phase, but abolished the hy potensive effect of AngII. Heart rate was significantly increased in r esponse to AngII, but the administration of AngII and saralasin togeth er attenuated approximately 44%, Stimulation renin-angiotensin system using a vasodilator, sodium nitroprusside, significantly increased dri nking rate in rainbow trout fry, a response inhibited by saralasin, in dicating a role for AngII-induced hypotension in drinking, For the fir st time, a decrease in blood pressure in response to AngII in vivo has been demonstrated in fish, and this is discussed in relation to homeo stasis of blood pressure and a possible role in the control of drinkin g.