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The oxytocin page does indicate that at low doses oxytocin can act as an anti-diuretic, but it also describes how higher doses can apparently result in sodium loss, making it act more like a diuretic. Am I missing something?
Another question: Should insulin count as an anti-diuretic? One function of insulin is to cause the kidneys to retain sodium, reducing how much water is lost in urine. Reducing insulin levels (e.g. low carb diet) has a diuretic effect, reducing blood pressure.