The effect of low dose octreotide administration on renal function and on gene expression of IGF-I axis components in experimental diabetes mellitus

Transcriptional profiling of the megabladder mouse: a unique model of bladder dysmorphogenesis

Recent studies in our lab identified a mutant mouse model of obstructive nephropathy designated mgb for megabladder. Homozygotic mgb mice (mgb-/-) develop lower urinary tract obstruction in utero due to a lack of bladder smooth muscle differentiation. This defect is the result of a random transgene insertion/translocation into chromosomes 11 and 16. Transcriptional profiling identified a significantly over-expressed cluster of gene products located on the translocated fragment of chromosome 16 including urotensin II-related peptide (Urp), which was shown to be preferentially over-expressed in developing mgb-/- bladders. Pathway analysis of mgb microarray data indicated dysregulation of at least 60 gene products associated with smooth muscle development. In conclusion, the results of this study indicate that the molecular pathways controlling normal smooth muscle development are severely altered in mgb-/- bladders, and provide the first evidence that Urp may play a critical role in bladder smooth muscle development.

Expression of somatostatin receptors 1 and 2 in the adult mouse kidney

Systemic infusion of somatostatin in humans and rodents alters renal glomerular filtration rate, solute transport, and water clearance. Among the five different G-protein-coupled somatostatin receptors (SSTRs), SSTR1 is expressed in human kidney collecting ducts and SSTR2 is expressed in rat and human collecting ducts and glomeruli. Our laboratory recently localized SSTRs 3, 4, and 5 to mouse kidney proximal tubules. Our aim was to characterize the expression of somatostatin receptors 1 and 2 in mouse kidneys. We detected mRNA for somatostatin receptors 1 and 2 in the mouse kidney by reverse transcriptase-polymerase chain reaction (RT-PCR), with confirmation by Southern blotting. In contrast to the data in human kidneys, we localized SSTR1 proteins to mouse proximal tubules and glomerular podocytes. Similar to the reports in human and rat kidneys, we detected SSTR2 proteins in the murine glomerulus and collecting duct; we were further able to identify the specific SSTR2-positive cells as podocytes and principal cells, respectively. Thus, taken with our previously published results, the kidney expresses all five somatostatin receptors. Furthermore, the expression of the SSTRs in the mouse kidney correlates well with the known actions of somatostatin in the kidney.

Effects of amino acids and glucagon on renal hemodynamics in type 1 diabetes

Increased dietary protein and circulating amino acids raise glomerular filtration rate (GFR) and pressure. In diabetes, this glomerular hyperfiltration response is augmented. The purpose of this study was to determine whether glucagon mediates the augmented GFR response to amino acids in diabetes and whether the responses to amino acids and glucagon depend on prostaglandins. Patients with type 1 diabetes mellitus (n = 12) and normal control subjects (n = 12) were studied in a series of six experiments, each on different occasions. Baseline GFR was not significantly increased, but filtration fraction was higher in diabetes. In response to amino acid infusion, GFR increased more and filtration fraction was greater among those with diabetes. Their augmented GFR response to amino acids was not inhibited by octreotide or indomethacin. Participants with diabetes also had enhanced GFR and renal plasma flow responses to glucagon infusion, both of which were inhibited by indomethacin. Glomerular hyperfiltration responses induced by amino acids or glucagon occur by divergent pathways in diabetes; only the response to glucagon is prostaglandin dependent.