Correlation Between Urinary Vasopressin and Water Content of Food in the Bottlenose Dolphin (Tursiops truncatus)

Marine mammals, including the bottlenose dolphin Tursiops truncatus, must rely on the water content of their food to achieve water balance. We have investigated the endocrine role of the antidiuretic hormone (vasopressin) in relation to food intake and water conservation. A series of seven bottlenose dolphins, maintained in a controlled environment, were sampled for blood and urine before and after the meals. Blood vasopressin levels were around 1.1 pg/ml. In urine, the hormone is one hundred fold more concentrated than in blood. Therefore we considered the urinary vasopressin content in relation to food intake. A direct relationship was detected among food intake, vasopressin and NaCl urinary concentrations. Our data indicate that urinary vasopressin levels increase after the meal and correspond to a rise in NaCl levels, a sign of urine concentration indicating that the effect of vasopressin in this species is aimed at curtailing the dispersion of food-derived water.