The specific aims of the project are: 1) to characterize the distribution of IGF I and IGF II receptors in kidney: 2) to characterize the mechanism(s) by which IGF I and IGF II """"""""signals"""""""" are transmitted across the plasma membranes of IGF-sensitive renal cells; 3) to determine whether synthesis of IGF I and/or IGF II occurs in kidney, and if so, where, and whether such synthesis is growth-hormone dependent; and 4) to determine whether insulin-like growth factors play a role in growth hormone-induced renal hypertrophy and/or the compensatory contralateral renal hypertrophy that follows unilateral nephrectomy. To these ends cells and membranes isolated from canine and rat kidney will be utilized. Binding 125I-IGF I and 125I-IGF II to several types of membranes and isolated cells from different parts of the nephron (glomeruli, proximal tubular segments, and isolated segments of papillary collecting duct) will be measured using centrifugation and affinity crosslinking techniques. It will be determined whether IGF I and/or IGF II activate(s) phospholipase C in isolated proximal tubular basolateral membranes. Binding of 125I-growth hormone to isolated membranes, glomeruli, proximal tubular segments, and isolated segments of papillary collecting duct will be measured using centrifugation and affinity crosslinking techniques. The distribution of IGF I and IGF II within kidneys from normal rats, hypophysectomized rats, hypophysectomized rats administered growth hormone, and in hypertrophied kidneys from rats that have undergone unilateral nephrectomy will be characterized using immunocytochemical techniques. It will be determined whether IGF I and/or IGF II is synthesized one or more type of renal cell by measuring radioimmunoassayable IGF I or II in media originating from cells incubated with growth hormone in vitro. Levels of IGF I and IGF II mRNA in isolated glomeruli, proximal tubular segments and segments of papillary collecting duct from rat kidney and in whole kidneys from each of the groups of rats described above will be measured using 32P-labeled mRNA probes and solution hybridization technique. These studies will characterize the growth hormone-IGF axis in kidney. Experimental findings will elucidate the role of this axis in control of renal growth under physiological and pathophysiological conditions.
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