What hormone cause vasoconstriction when the blood volume decrease?

When blood volume decreases, the hormone that primarily causes vasoconstriction is angiotensin II. This peptide hormone is part of the renin-angiotensin-aldosterone system (RAAS), which is activated in response to low blood pressure or decreased blood volume. Angiotensin II not only constricts blood vessels to increase blood pressure but also stimulates the release of aldosterone, promoting sodium and water retention to help restore blood volume.