Underlying disease stress augments plasma and tissue adrenomedullin (AM) responses to endotoxin:: Colocalized increases in AM and inducible nitric oxide synthase within pancreatic islets

Rapid onset metabolic impairments accompany the initiation of the acute phase response to many disease stresses, whereas more chronic metabolic perturbations may prolong the recovery period. In the present experiment the application of a mild endotoxin challenge [lipopolysaccharide (LPS)] alone or additive to a chronic subclinical parasitic infection (Sarcocystis cruzi; LPS + PI) in calves was used as a model to investigate and define a dynamic axis coordinated between adrenomedullin (AM) and nitric oxide in response to immune challenge. Plasma AM and NO2/NO3 concentration responses after LPS (0.45 mu g/kg, iv) were rapid in onset and of higher magnitude and longer duration in PI + LPS calves than in those challenged with LPS alone. The post-LPS increase in plasma insulin was significantly greater in PI + LPS than in LPS; following refeeding of calves, insulin secretion was most blunted in PI + LPS calves, consistent with the inhibitory effects of NO and AM on insulin secretion. A more chronic response to the immune challenge (organ specific) was in evidence in tissues harvested 24 h after LPS challenge. Where lung and Liver showed no immunostaining for inducible nitric oxide (iNOS), iNOS immunostaining was present in the pancreas, localized to islets only. The percentages of iNOS-immunopositive cells in islets were 1.7%, 21%, 6.7%, and 24% for control(C; saline infused), PI, LPS, and PI + LPS calves, respectively. AM immunostaining was not evident in the liver and was present, but not differentially affected by treatment, in airway epithelium in the lung. The number of islet cells with positive immunostaining for AM was increased in LPS, PI, and PI + LPS calves. The percentages of AM-immunopositive cells in islets were 8%, 27%, 20%, and 33% for C, PI, LPS, and PI + LPS, respectively. Immunostaining for AM and iNOS was colocalized with cells positive for pancreatic polypeptide. By triple label confocal fluorescence immunocytochemistry, colocalization of intense AM and iNOS immunostaining was confirmed in peripheral islet cells. A weaker, more diffuse iNOS signal was also apparent in insulin-containing cells in PI + LPS. We conclude that chronic low level infection potentiates the severity of metabolic perturbations that arise with additive sudden onset immune challenge, as can occur with bacterial toxins. These metabolic disturbances are reflected in and possibly mediated by early onset increases in plasma tumor necrosis factor-alpha, insulin, and AM and up-regulated iNOS activity. These acute complications rapidly progress into a more chronic state characterized by diminished insulin response to feeding stimulus and colocalized increases in pancreatic islet AM and iNOS. The pancreatic responses in AM and iNOS may play a major role in mediating prolonged disturbances in nutrient use by tissues through their influences on temporal patterns of pancreatic hormone secretion during chronic illness.