Refractoriness of both uterus and mammary gland of the cow to prostaglandin F2 alpha administration:P clinical application.

Uterine and mammary pressure changes were simultaneously measured in lactating nonpregnant cows injected (IV) with different doses (0.1 to 32.0 mg) of prostaglandin F2 alpha (PGF2 alpha). The total work of the uterus increased up to 250% of base-line value as the dose of PGF2 alpha was increased. But, a dose-response relationship was not seen in the uterus. Partial refractoriness was developed in the uterus, and total refractoriness was developed in the mammary gland. Further challenge with oxytocin (30 U) elicited significant responses in both the uterus and the mammary gland. Because of the development of refractoriness and side effects, PGF2 alpha is not recommended as a drug to be used when mechanical evacuation (free of endocrine effect) of the uterus or mammary gland (or both) is indicated.