Cardiomegaly and haemodynamics in rats with a transplantable growth hormone-secreting tumour

To investigate cardiovascular changes in experimental acromegaly, a growth hormone-secreting tumour (MtT-W-15) was implanted in adult female rats. Somatic and tumour growth occurred steadily during the 8 week study period, as did an increase in serum growth hormone titre. Weight of left ventricle and right ventricle increased directly with tumour growth, both on an absolute basis and when compared with normal rats of equal body weight. Atrial weight also increased substantially. Haematocrit declined sharply at first, and more slowly later with increasing tumour weight. Haemodynamic measurements were made on these animals at two stages of tumour growth using an anaesthetised open-chest preparation. Cardiac index (per g body wt), stroke index, stroke work, left ventricle +dP/dtmax, and dF/dtmax of aortic flow were greatly elevated in rats with the largest tumours (longer duration), and to a lesser extent in those with smaller tumours (shorter duration). Systemic peripheral resistance and heart rate were depressed. Ventricular weight increased non-linearly with increases in cardiac index. Cardiac output, stroke volume, stroke work and dF/dtmax normalised per g left ventricle weight were also elevated. Splenomegaly accompanied tumour growth; however, splenectomy of tumour-bearing animals failed to prevent development of anaemia and cardiomegaly. While a direct effect of elevated growth hormone provides the best explanation for development of cardiomegaly in this model, volume work overloading due to anaemia and water retention may be a contributory cause.