Effects of a synthetic vasopressin analogue (desmopressin) in pregnant, lactating and anoestral goats.

The effects of the long-acting synthetic vasopressin analogue desmopressin (dose 2 X 2 micrograms day-1 for two days) were investigated in pregnant, lactating and anoestral goats. Urine flow fell and urine osmolality increased in all experiments. However, pregnant goats continued to drink the same volumes of water each day with the result that the ratio of water intake/urine output increased markedly and the plasma osmolality fell. The results support the hypothesis that the regulation of water intake is changed during pregnancy and that pregnant goats have a lowered sensitivity to signals that normally inhibit water consumption. In lactating goats, milk secretion was not affected by desmopressin. The animals did not drink enough to compensate for the water losses in milk and urine, but more than was needed to cover the water losses in the urine. The plasma osmolality decreased slightly. It appears as if the mechanisms involved in the control of water balance are not sufficiently adapted to take water losses via the milk into account, if the animals are subjected to challenges. In anoestral animals, the water balance was maintained during desmopressin injections. The renal sodium excretion did not change, but the renal potassium excretion decreased in pregnant and lactating goats in response to desmopressin.