SNP improves cerebral hemodynamics during normotension but fails to prevent sex dependent impaired cerebral autoregulation during hypotension after brain injury

Traumatic brain injury (TBI) is a leading cause of morbidity in children and boys are disproportionately represented. Hypotension is common and worsens outcome after TBI. Previous studies show that adrenomedullin, a cerebrovasodilator, prevented sex dependent impairment of autoregulation during hypotension after piglet fluid percussion brain injury (FPI). We hypothesized that this concept was generalizable and that administration of another vasodilator, sodium nitroprusside (SNP), may equally improve CBF and cerebral autoregulation in a sex dependent manner after FPI. SNP produced equivalent percent cerebrovasodilation in male and female piglets. Reductions in pial artery diameter, cortical CBF, and cerebral perfusion pressure (CPP) concomitant with elevated intracranial pressure (ICP) after FPI were greater in male compared to female piglets during normotension which was blunted by SNP. During hypotension, pial artery dilation (PAD) was impaired more in the male than the female after FPI. However, SNP did not improve hypotensive PAD after FPI in females and paradoxically caused vasoconstriction in males. SNP did not prevent reductions in CBF, CPP or autoregulatory index during combined hypotension and FPI in either sex. SNP aggravated ERK MAPK upregulation after FPI. These data indicate that despite prevention of reductions in CBF after FPI, SNP does not prevent impairment of autoregulation during hypotension after FPI. These data suggest that therapies directed at a purely hemodynamic increase in CPP will fail to improve outcome during combined TBI and hypotension.