The ability of the kidneys to maintain a relatively constant GFR despite changes in blood pressure without the input of nervous or hormonal control is called:

Renal autoregulation.

Explanation:

Kidneys are the important organ that are involved in the process of excretion, maintains the body pH and regulates the level of salt in the body.

Renal autoregulation may be defined as ability of the kidney to maintain the constant glomerular filtration rate withou change in the blood pressure. No nervous or hormones are involved the renal autoregulation.

Thus, the answer is renal auto regulation.