The vasopressin is a protein, which has a
bisulphide bond at two amino acid sequences and readily forms the channel, (42) whereas urea may not be able to form the channel-like vasopressin but, being a crystalloid particle, draws water more actively than vasopressin, thereby resulting in decreased [L.
Nevertheless, the alternatives of thiourea, thiosulphate, thiocyanate,
bisulphide, ammonia or halogens are not, except in special circumstances, really viable.