Chronic overproduction of growth hormone in cats is most often caused by a GH-producing tumour of the pituitary gland. In dogs the usual cause is quite different. In this species endogenous progestins and exogenous progestins cause excessive GH secretion that is reversible.

In October 2003 a 6.5-year-old intact female terrier with features of acromegaly was referred to small animal hospital of Tehran university. She had a visible increase in soft tissue mass, respiratory stridor, enlargement of the interdental spaces, prominent skin folds, abdominal enlargement and radiographic evidence of an increase in soft tissue mass in the oropharyngeal and pyometra. For a conclusive diagnosis was demonstrated elevation of GH levels (153.9ng/ml). Plasma Glucose level was 108 mg/dl and she had not any signs of polyuria and polydipsia. Also SAP level was high and PCV was low.

This animal was treated with progesterone to prevent estrus from 2 years ago. The history of frequent and excessive administration of a progestational drug induced acromegaly and pyometra. Progesterone withdrawal and ovariohysterectomy in this case was resulted in a reduction of plasma GH and appreciable clinical improvement. As well as E.coli was separated from uterus discharges.

It is concluded that treatment of dogs with synthetic progestins can induce the overproduction of GH in the mammary gland. This GH is biologically active, highly similar to pituitary derived GH, and originates from foci of hyperplastic ductular epithelium of the mammary gland. This results also suggested that acromegaly in this dog was caused by medroxyprogesterone acetate-evoked GH elevation.