Anterior pituitary function in female dogs with spontaneous mammary tumors: I. Growth hormone

It has been hypothesized that growth hormone (GH) plays a major role in the pathogenesis of canine mammary tumor disease. In order to test this hypothesis, plasma GH levels were measured at rest and during dynamic function tests in dogs with benign or malignant proliferative mammary lesions and in control dogs. Both in control dogs and in dogs with benign disease, basal GH levels were found to be elevated during both metestrus and progestin treatment, as compared to anestrus. Dogs with benign or malignant disease did not have higher basal GH levels than control dogs matched for the effect of endogenous or exogenous progestin exposure. The GH response to glucose or thyrotropin releasing hormone (TRH) did not vary significantly with progestin exposure, nor between the 3 groups of animals. The stimulatory effect of clonidine upon GH secretion was reduced in dogs with benign or malignant disease as compared to controls matched for the effect of progestin exposure. These findings indicate that mammary tumor disease in the dog is associated with a disturbance in the regulation of GH release.