Regulation of Prolactin Secretion in Canine Pituitary-Dependent Hyperadrenocorticism

In 15 dogs with pituitary-dependent hyperadrenocorticism (PDH) the basal prolactin concentrations (means of 6 determinations; range 2.8-24.7 μg/l) were significantly higher than those of 23 healthy control dogs (0.9-10.5 μg/l), In five dogs with hyperadrenocorticism due to adrenocortical tumour (ATH) the prolactin concentrations were also significantly elevated, but still significantly lower than the values of the dogs with PDH. The prolactin concentrations of the dogs with PDH responded supranormally to TRH-stimulation, whereas in the dogs with ATH the response was not significantly different from the results in the control dogs. Following bromocriptine administration the plasma prolactin concentrations of the dogs with PDH decreased considerably but remained higher than the values obtained in the control dogs and the dogs with ATH. It is concluded that PDH in the dog is associated with a disturbance in the regulation of prolactin secretion, that is not secondary to hypercortisolism per se.