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 pha se response to many disease stresses, whereas more chronic metabolic pertur bations may prolong the recovery period. In the present experiment the appl ication of a mild endotoxin challenge [lipopolysaccharide (LPS)] alone or a dditive to a chronic subclinical parasitic infection (Sarcocystis cruzi; LP S + PI) in calves was used as a model to investigate and define a dynamic a xis 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 d uration in PI + LPS calves than in those challenged with LPS alone. The pos t-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 s pecific) was in evidence in tissues harvested 24 h after LPS challenge. Whe re lung and Liver showed no immunostaining for inducible nitric oxide (iNOS ), iNOS immunostaining was present in the pancreas, localized to islets onl y. 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 presen t, but not differentially affected by treatment, in airway epithelium in th e lung. The number of islet cells with positive immunostaining for AM was i ncreased in LPS, PI, and PI + LPS calves. The percentages of AM-immunoposit ive 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 p ositive for pancreatic polypeptide. By triple label confocal fluorescence i mmunocytochemistry, colocalization of intense AM and iNOS immunostaining wa s confirmed in peripheral islet cells. A weaker, more diffuse iNOS signal w as also apparent in insulin-containing cells in PI + LPS. We conclude that chronic low level infection potentiates the severity of metabolic perturbat ions that arise with additive sudden onset immune challenge, as can occur w ith bacterial toxins. These metabolic disturbances are reflected in and pos sibly mediated by early onset increases in plasma tumor necrosis factor-alp ha, insulin, and AM and up-regulated iNOS activity. These acute complicatio ns rapidly progress into a more chronic state characterized by diminished i nsulin response to feeding stimulus and colocalized increases in pancreatic islet AM and iNOS. The pancreatic responses in AM and iNOS may play a majo r role in mediating prolonged disturbances in nutrient use by tissues throu gh their influences on temporal patterns of pancreatic hormone secretion du ring chronic illness.