Reduction of proteinuria by adrenalectomy and its restoration by glucocorticoids in rats bearing functioning pituitary tumor

Intense proteinuria in rats bearing a functioning pituitary tumor MtT SA5 was considered to be evoked by overproduction of albumin due to elevated serum growth hormone (GH). The present study revealed a striking reduction of proteinuria by bilateral adrenalectomy. Supplementation for about 6 weeks with glucocorticoids to adrenalectomized tumor-bearing rats again induced marked proteinuria, but supplementation with mineralocorticoids failed to augment proteinuria. An analysis of systemic blood pressure and renal blood flow did not yield any conclusive result. In spite of an assumption that glucocorticoids enhance GH production of the tumor based on the presence of glucocorticoid receptor in the tumor tissue, no difference was found in serum GH levels between glucocorticoid- and mineralocorticoid-supplemented adrenalectomized rats. The mechanism remains to be clarified, but modification of glomerular permeability or a change in glomerular hydraulic pressure by glucocorticoids might be considered.