The Main Effects of Oxytocin Are on the Contraction of Smooth Muscle (Mammary Gland and Uterus); the Effects OfVasopressin Are Primarily on the Conservation of Water (Antidiuresis) and Secondarily on Blood Pressure

The main effects of oxytocin involve the contraction of the myo­epithelial cells, which surround the alveoli in the mammary gland and the myometrium of the uterus (see Chapters 38 and 39).

The main activity of vasopressin belies its name because its main effect is antidiuretic, the enhancement of water retention by the kidney. As a consequence, the hormone is often called antidiuretic hormone (ADH) (Figure 33-13). Vasopressin is the most important hormone for the control of water balance. Vasopressin also has a pressor effect, which involves the con­traction of smooth muscle of the vascular system and there­fore has an effect on blood pressure. The main form of vasopressin in most species is arginine vasopressin, whereas in pigs it is lysine vasopressin, and in birds arginine vaso­tocin.