Vasodepressor action of angiotensin in conscious chickens

In chronically cannulated conscious chickens, Gallus gallus, native chicken angiotensin II ([Asp1,Val5]ANG II) caused biphasic blood pressure responses, a depressor followed by a pressor response. The pressor response appears to be mediated primarily by catecholamines. The depressor responses increased with increasing doses and were accompanied by tachycardia. The onset of the depressor action of [Asp1,Val5]ANG II (2.49 +/- 0.22 s) was nearly as quick as that of acetylcholine or histamine. Replacement of aspartic acid in position 1 with sarcosine or asparagine reduced both depressor and pressor potencies, whereas there was no difference either in depressor or pressor potencies between [Asp1,Val5] and [Asp1,Ile5]ANG II. The depressor response to [Asp1,Val5]ANG II was not inhibited by atropine, a vasopressin antagonist, prostaglandin synthetase inhibitors, methysergide, or propranolol but was blocked markedly by [Sar1, Ile8]ANG II and partially by [Sar1,Thr8]ANG II. The results suggest that the vasodepressor action of ANG II is mediated by angiotensin receptors and may possibly be a direct action on the vascular smooth muscle.