Which hormone is NOT among the endocrine functions of the kidneys?

Insulin is not produced by the kidneys and is primarily secreted by the pancreas. While the kidneys play a vital role in regulating various hormones and maintaining homeostasis within the body, insulin's absence from the endocrine functions of the kidneys is notable.

On the other hand, the kidneys do produce erythropoietin, a hormone that stimulates the production of red blood cells in response to low oxygen levels. They also secrete renin, which is involved in blood pressure regulation and electrolyte balance, and are responsible for the activation of vitamin D into its active form, which helps regulate calcium levels in the body. Thus, the correct answer reflects the primary hormonal functions associated with the kidneys, clearly distinguishing them from insulin, which is not a kidney function.