Differential changes in substance P and somatostatin in brain nuclei of rats exposed to hemorrhagic shock.

Concentrations of immunoreactive substance P ( SPir ) and immunoreactive somatostatin ( SSir ) were determined in discrete brain nuclei of normal rats and rats exposed to acute hypovolemic hypotension (8 ml/300 g body weight). SPir in the hypothalamic paraventricular nucleus (PVN) and the caudal and rostral parts of the nucleus of the tractus solitarius (NTS) were significantly reduced 2 h after hemorrhage, but no changes were found in any of the brain nuclei when examined 5 min after the same bleeding. SSir in the NTS and nucleus ambiguus (NA) were reduced by 50-60% 2 h after the hemorrhage, as compared either to intact rats or rats examined 5 min after bleeding. In the forebrain, significantly lower concentrations of SSir were found in the nucleus supraopticus at both 5 min and 2 h after shock and in the PVN of rats 2 h after shock. These data suggest a role for SPir and SSir in central adaptation to hypovolemic hypotension and further indicate that functions regulated by these neuropeptides might be substantially affected by shock states.