Objective
Traumatic brain injury (TBI) contributes to morbidity and mortality in children and boys are disproportionately represented. Hypotension is common and worsens outcome after TBI. Extracellular signal-related kinase (ERK) mitogen activated protein kinase (MAPK) is upregulated and reduces CBF after fluid percussion brain injury (FPI) in piglets. We hypothesized that increased CPP via phenylephrine (PHE) sex dependently reduces impairment of cerebral autoregulation during hypotension after FPI through modulation of ERK MAPK.
Design
Prospective, randomized animal study.
Setting
University laboratory.
Subjects
Newborn (1–5 day old) pigs.
Interventions
CBF, pial artery diameter, ICP and autoregulatory index (ARI) were determined before and after FPI in untreated, pre- and post-injury PHE (1 μg/kg/min iv) treated male and female pigs during normotension and hemorrhagic hypotension. CSF ERK MAPK was determined by ELISA.
Measurements and Main Results
Reductions in pial artery diameter, CBF, CPP and elevated ICP after FPI were greater in males, which were blunted by PHE pre- or post-FPI. During hypotension and FPI, pial artery dilation was impaired more in males. PHE decreased impairment of hypotensive pial artery dilation after FPI in females, but paradoxically caused vasoconstriction after FPI in males. Papaverine induced pial artery vasodilation was unchanged by FPI and PHE. CBF, CPP, and ARI decreased markedly during hypotension and FPI in males but less in females. PHE prevented reductions in CBF, CPP, and ARI during hypotension in females but increased reductions in males. CSF ERK MAPK was increased more in males than females after FPI. PHE blunted ERK MAPK upregulation in females, but increased ERK MAPK upregulation in males after FPI.
Conclusions
These data indicate that elevation of CPP with PHE sex dependently prevents impairment of cerebral autoregulation during hypotension after FPI through modulation of ERK MAPK. These data suggest the potential role for sex dependent mechanisms in cerebral autoregulation after pediatric TBI.
Cerebrospinal fluid (CSF) adrenomedullin (ADM) levels are increased in female, but remain unchanged in male, piglets after fluid percussion injury (FPI) of the brain. Subthreshold vascular concentrations of ADM restore impaired hypotensive pial artery dilation after FPI more in males than females. Extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) is upregulated and contributes to reductions in cerebral blood flow (CBF) after FPI. We hypothesized that ADM prevents sex-dependent impairment of autoregulation during hypotension after FPI through inhibition of ERK MAPK upregulation. FPI increased ERK MAPK more in males than in females. CBF was unchanged during hypotension in sham animals, was reduced more in males than in females after FPI during normotension, and was further reduced in males than in females during hypotension and after FPI. ADM and the ERK MAPK antagonist U 0126 prevented reductions in CBF during hypotension and FPI more in males than in females. Transcranial Doppler (TCD) blood flow velocity was unchanged during hypotension in sham animals, was decreased during hypotension and FPI in male but not in female pigs, and was ameliorated by ADM. Intracranial pressure (ICP) was increased after FPI more in male than in female animals. ADM blunted elevated ICP during FPI and hypotension in males, but not in females. ADM prevented reductions in cerebral perfusion pressure (CPP) during FPI and hypotension in males but not in females. The calculated autoregulatory index was unchanged during hypotension in sham animals, but was reduced more in males than females during hypotension and FPI. ADM prevented reductions in autoregulation during hypotension and FPI more in males than females. These data indicate that ADM prevented loss of cerebral autoregulation after FPI in a sex-dependent and ERK MAPK-dependent manner.
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