The GFR is depressed by 40 to 50% once the natriuresis induced by thiazides exceeds 35 mmol/h. This effect is termed tubuloglomerular feedback (TGR). Loop diuretics do not affect the GFR and the RPF as they block the TGR. Therefore their effect is not limited by the reduction of GFR. Hence thiazides being self-limited were earlier called low ceiling diuretics and loop diuretics were called ''high ceiling'' diuretics.