Effect of excessive secretion of growth hormone on tissues of the rat, with particular reference to the heart and skeletal muscle.

Rat pituitary tumours of the GH3 cell line, secreting growth hormone (GH), were induced to grow in Wistar-Furth rats and the effect of prolonged excessive secretion of GH on various organs was investigated. Total body weight of the tumour-bearing animals increased by over 100% compared with control animals and there was widespread visceromegaly affecting especially the liver, kidney, spleen and adrenals. The heart was also considerably enlarged. The effects of excessive GH on skeletal muscle were not uniform and, using a histochemical technique, it was found that the size type 1 muscle fibres was increased to the greatest extent whereas fibre type 2A was unaffected. Synthesis of DNA in the heart and skeletal muscle was also increased in tumour-bearing animals. Removal of the tumours was followed by a considerable regression in the size of most organs, although hypertrophy of the heart was affected least by a return to normal plasma levels of GH. It was concluded that animals bearing GH3 cell tumours provide a useful experimental model for the study of the tissue changes in acromegaly.