Prenatal metyrapone treatment modulates neonatal cerebrovascular structure, function, and vulnerability to mild hypoxic-ischemic injury

Abstract

This study explored the hypothesis that late gestational reduction of corticosteroids transforms the cerebrovasculature and modulates postnatal vulnerability to mild hypoxic-ischemic (HI) injury. Four groups of Sprague-Dawley neonates were studied: 1) Sham-Control, 2) Sham-MET, 3) HI-Control, and 4) HI-MET. Metyrapone (MET), a corticosteroid synthesis inhibitor, was administered via drinking water from gestational day 11 to term. In Shams, MET administration 1) decreased reactivity of the hypothalamic-pituitary-adrenal (HPA) axis to surgical trauma in postnatal day 9 (P9) pups by 37%, 2) promoted cerebrovascular contractile differentiation in middle cerebral arteries (MCAs), 3) decreased compliance ≤46% and increased depolarization-induced calcium mobilization in MCAs by 28%, 4) mildly increased hemispheric cerebral edema by 5%, decreased neuronal degeneration by 66%, and increased astroglial and microglial activation by 10- and 4-fold, respectively, and 5) increased righting reflex times by 29%. Regarding HI, metyrapone-induced fetal transformation 1) diminished reactivity of the HPA axis to HI-induced stress in P9/P10 pups, 2) enhanced HI-induced contractile dedifferentiation in MCAs, 3) lessened the effects of HI on MCA compliance and calcium mobilization, 4) decreased HI-induced neuronal injury but unmasked regional HI-induced depression of microglial activation, and 5) attenuated the negative effects of HI on open-field exploration but enhanced the detrimental effects of HI on negative geotaxis responses by 79%. Overall, corticosteroids during gestation appear essential for normal cerebrovascular development and glial quiescence but induce persistent changes that in neonates manifest beneficially as preservation of postischemic contractile differentiation but detrimentally as worsened ischemic cerebrovascular compliance, increased ischemic neuronal injury, and compromised neurobehavior.

Maternal Undernutrition Modulates Neonatal Rat Cerebrovascular Structure, Function, and Vulnerability to Mild Hypoxic-Ischemic Injury via Corticosteroid-Dependent and -Independent Mechanisms

“…Paired pups of each sex from every litter underwent either Sham surgery or HI surgery for all experiments. ANOVA revealed no sexual dimorphism for any of the endpoints, consistent with other studies of the neonatal cerebrovasculature [ 42 ] including our own [ 35 ]. Statistical analysis relied on pooled groups of males and females.…”

“…Consistent with previous studies [ 35 , 37 ], neonatal hypoxic ischemia significantly shifted the phenotype of cerebrovascular smooth muscle ( Figure 4 B,D). In pups programmed by MUN, mild HI insult promoted contractile differentiation, as indicated by a rightward shift in pixel distributions for αActin colocalization that was most prominent with NM-MHC, but was also significant with SM-MHC ( Figure 4 B,D).…”

“…In addition to its focus on the corticosteroid-dependent and -independent effects of MUN on baseline cerebrovascular characteristics and neurobehavior, our experimental design also examined how MUN and corticosteroids influenced cerebral responses to hypoxic ischemia, a common cardiovascular stressor in neonates. In particular, our model evaluated mild hypoxic-ischemic injury [ 35 ], which is more common clinically than the widespread hemispheric injury produced by other neonatal models of more severe hypoxic-ischemic injury [ 41 ]. Consistent with other studies of neonatal stress [ 75 , 76 ], our model of mild hypoxic ischemia increased corticosterone levels 2 h after HI injury ( Figure 2 E,F), but this effect dissipated by 24 h. MET treatment ablated the increase in corticosterone values at 2 h post-hypoxia, but had no effect at 24 h, suggesting that MUN programmed a robust but transient, MET-sensitive increase in corticosterone following mild HI injury.…”

“…Previous studies of fetal programming have identified a significant impact on vascular smooth muscle and its development [ 31 , 32 ]. Specifically, these studies have demonstrated that the phenotype of vascular smooth muscle, as indicated by differential expression of contractile proteins such as smooth muscle αactin and myosin heavy chain isoforms [ 33 , 34 ], can be potently modulated by fetal stress [ 35 , 36 ]. Correspondingly, changes in smooth muscle phenotype in response to the cardiovascular stresses imposed by hypoxia and ischemia, can alter both resting myogenic vascular tone and contractile responses induced by depolarizing stimuli, contractile agonists, and vasodilators [ 37 , 38 ].…”

“…The model employed imposed a long-term fetal stress via 50% restriction of total caloric intake as defined by an ad libitum pair-fed control pregnant dam, during the last 11 days of gestation, as previously described [ 31 , 36 ]. Also as previously described [ 35 , 36 ], our model included administration of MET at 0.5 mg/mL in the drinking water during the last 10 days of gestation to attenuate circulating levels of maternal and fetal corticosteroids. As a short-term cardiovascular stress, our model also included a mild hypoxic-ischemic challenge induced by unilateral carotid ligation at P9/P10 followed 24 h later by 90 min of exposure to 8% O 2 and harvest at P11/P12.…”