Vascular responses to angiotensins in the toad. Role of the adrenergic system.
The isolated hindlimbs (vasoconstrictor) and the whole toad pressor assays were used to investigate the effects of some angiotensin II (AT II) analogues and the influence of the adrenergic system on the vascular response to AT II in the toad Bufo arenarum. Three of the analogues assayed (Leu8AT II, Sa1, Ala8AT II, Sar1, I1e8AT II) were unable to block the response to AT II, and a fourth, Ala1, Ile8AT II, potentiated it. In the case of Sar1, Ala8AT II (saralasin), this confirms previous negative findings from this laboratory on water and electrolyte transport in toad skin, probably reflecting differences between AT II receptors in mammals and amphibians. This notion is further supported by the fact that desamino AT II, and AT II analogue reported not to produce tachyphylaxis in the guinea-pig ileum, behaves like AT II when injected repeatedly in the isolated hindlimbs. Tyramine was devoid of vascular effects in this preparation. Phentolamine (which blocked the response to norepinephrine) and Ro 4-1284 (an in vitro catecholamine depleting agent) failed to alter the vasoconstrictor action of AT II. An unexpected finding was the inhibiting effect of Ro 4-1284 on the vasoconstrictor response to exogenous norepinephrine.
D000804:Angiotensin II / Q000031:analogs & derivatives; D000809:Angiotensins / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001808:Blood Vessels / Q000187:drug effects* / Q000294:innervation; D002022:Bufo arenarum; D005260:Female; D006614:Hindlimb / Q000098:blood supply; D008297:Male; D011945:Receptors, Angiotensin / Q000502:physiology; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000502:physiology*
D000809:Angiotensins; D011945:Receptors, Angiotensin; D000804:Angiotensin II