At1

AT1 is an abbreviation with multiple meanings in different domains. In finance, AT1 refers to Additional Tier 1 capital instruments used by banks under the Basel III framework. In physiology and pharmacology, AT1 commonly denotes the angiotensin II type 1 receptor (AT1 or AT1R), a key regulator of vascular tone and blood pressure. The term may appear in scientific literature as AGTR1 (the gene).

In financial terms, AT1 capital notes are instruments designed to absorb losses and bolster bank capital, typically perpetual or with very long maturities, and they can be written down or converted to equity on specified triggers. They rank above common equity but below traditional debt in liquidation, and they carry high yields with substantial risk. Their use and accounting treatment are guided by Basel III rules and national regulators. Critics warn about valuation, market liquidity, and potential for destabilizing effects during periods of stress.

In physiology, the AT1 receptor binds angiotensin II, activating signaling pathways that cause vasoconstriction, aldosterone release, and sympathetic activity. It is expressed in vascular smooth muscle, heart, kidney, and brain. Blocking AT1 with receptor antagonists (ARBs) or reducing Ang II production with ACE inhibitors forms a major class of antihypertensive therapies. Beyond blood pressure, AT1 signaling has roles in heart failure, fibrosis, and inflammation, and it remains an active area of biomedical research.