Rodents were killed by cervical dislocation and the kidneys (with the adrenal glands still attached) were immediately removed and fixed in neutral buffered formalin for 24 h at room temperature. Sheep were humanely killed by injection with 0.75 ml (kg body weight)^-1 sodium pentobarbitone (Euthatal, Rh™ne Mérieux, 200 mg ml^-1). Archival sections of tumour nephrectomized human kidneys were obtained from St Thomas’ Hospital, London with local ethics committee approval. All procedures were carried out strictly in accordance with current legislation.

Tissue sections (8 µm thickness) were subjected to antigen retrieval 0.5 % SDS and immunohistochemistry. Expression of SGK varied considerably across the species. In the mouse and rat it was restricted to the thick ascending limb of Henle, the distal convoluted and cortical collecting tubules. In the marmot, SGK expression was significantly lower in the cortex but highly expressed in the medulla. In the adrenal gland SGK was abundantly expressed in the cortex and the highest level of expression was in the zona glomerulosa, the site normally associated with the synthesis of aldosterone. SGK immunostaining was also observed in the zona fasciculata but in lower quantities.

The immunohistochemical data indicate that the restricted expression of SGK in the kidney is not an exclusive feature of rodents, but of mammals with varied diets and different basal kidney function. In most cases the sites of SGK localization do not overlap with the classical aldosterone-sensitive targets. The abundance of SGK in the adrenal cortex suggests that it may play a physiological role in the biosynthesis and secretion of glucocorticoids and mineralocorticoids.

This study was supported by the Wellcome Trust and the Pet Plan Charitable Trust (UK).