Fairly certain this is also a typo. Constanzo 6th edition pg 301-302 discusses the positive effect of ADH on urea REcycling, not the urea cycle. It discusses urea recycling throughout the chapter and never mentions the urea cycle itself. "When ADH levels are low, as in water drinking or in central diabetes insipidus, the differential permeability effects do not occur and urea is not recycled. The positive effect of ADH on urea recycling is the second mechanism by which ADH augments the corticopapillary osmotic gradient (the first is stimulation of Na+-K+-2Cl− cotransport and the single effect of countercurrent multiplication). Thus the corticopapillary osmotic gradient is larger when ADH levels are high (e.g., water deprivation, SIADH) than when ADH levels are low (e.g., water drinking, central diabetes insipidus)."
