Plasma levels of estradiol and plasma protein binding of sex steroids in dogs. An investigation with special reference to development of hip dysplasia in growing individuals.

Peripheral plasma levels of estradiol were determined in 39 dogs of three breeds (Greyhound, German Shepherd, Golden Retriever). Blood samples were collected weekly from 3 weeks up to 17--21 weeks of age. The pups from all three breeds had mean levels of estradiol varying between 4--8 pg/ml. The lowest levels were found in pups which developed hip dysplasia. There was a significant difference (0.01 less than p less than 0.005) between the estradiol levels of German Shepherd pups with normal and dysplastic hip joints. In female Greyhounds, the peripheral plasma levels of estradiol were examined from 17 weeks of age through the first heat. No increase of the estradiol level was seen with increasing age. The ability of dog plasma to bind dihydrotestosterone (DHT) and estradiol was examined in three dogs. It was found that there are at least three types of binding components for DHT: one with high affinity and extremely low capacity, which is heat labile, another which is also heat labile but has a high capacity and low affinity, and a third which appears to be albumin. Estrogen administration to the three dogs lowered the binding of DHT. It was concluded that it is most unlikely that hyperestrogenism is an etiologic factor in canine hip dysplasia. Unphysiologically high doses of estradiol have been used for experimental induction of hip dysplasia. There is a possibility that the levels of plasma proteins, which bind steroids, could be of importance for the etiology of hip dysplasia. A low plasma level of estradiol could be biologically highly significant if there is a low level of a specific binding protein.