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We have reported that a reduction in renal production of 20-HETE contributes to development of hypertension in Dahl salt-sensitive (SS) rats. The present study examined whether 20-HETE production is also reduced in the cerebral vasculature of SS rats and whether this impairs the myogenic response and autoregulation of cerebral blood flow (CBF). The production of 20-HETE, the myogenic response of middle cerebral arteries (MCA), and autoregulation of CBF were compared in SS, SS-5(BN) rats and a newly generated CYP4A1 transgenic rat. 20-HETE production was 6-fold higher in cerebral arteries of CYP4A1 and SS-5(BN) than in SS rats. The diameter of the MCA decreased to 70 ± 3% to 65 ± 6% in CYP4A1 and SS-5(BN) rats when pressure was increased from 40 to 140 mmHg. In contrast, the myogenic response of MCA isolated from SS rats did not constrict. Administration of a 20-HETE synthesis inhibitor, HET0016, abolished the myogenic response of MCA in CYP4A1 and SS-5(BN) rats but had no effect in SS rats. Autoregulation of CBF was impaired in SS rats compared with CYP4A1 and SS-5(BN) rats. Blood-brain barrier leakage was 5-fold higher in the brain of SS rats than in SS-5(BN) and SS.CYP4A1 rats. These findings indicate that a genetic deficiency in the formation of 20-HETE contributes to an impaired myogenic response in MCA and autoregulation of CBF in SS rats and this may contribute to vascular remodeling and cerebral injury following the onset of hypertension., (Copyright © 2015 the American Physiological Society.)

Myogenic responses by resistance vessels are a key component of autoregulation in brain, thus playing a crucial role in regulating cerebral blood flow and protecting the blood-brain barrier against potentially detrimental elevations in blood pressure. Although cerebrovascular disease is often accompanied by alterations in myogenic responses, mechanisms that control these changes are poorly understood. Peroxisome proliferator-activated receptor γ has emerged as a regulator of vascular tone. We hypothesized that interference with peroxisome proliferator-activated receptor γ in smooth muscle would augment myogenic responses in cerebral arteries. We studied transgenic mice expressing a dominant-negative mutation in peroxisome proliferator-activated receptor γ selectively in smooth muscle (S-P467L) and nontransgenic littermates. Myogenic tone in middle cerebral arteries from S-P467L was elevated 3-fold when compared with nontransgenic littermates. Rho kinase is thought to play a major role in cerebrovascular disease. The Rho kinase inhibitor, Y-27632, abolished augmented myogenic tone in middle cerebral arteries from S-P467L mice. CN-03, which modifies RhoA making it constitutively active, elevated myogenic tone to ≈60% in both strains, via a Y-27632-dependent mechanism. Large conductance Ca(2+)-activated K(+) channels (BKCa) modulate myogenic tone. Inhibitors of BKCa caused greater constriction in middle cerebral arteries from nontransgenic littermates when compared with S-P467L. Expression of RhoA or Rho kinase-I/II protein was similar in cerebral arteries from S-P467L mice. Overall, the data suggest that peroxisome proliferator-activated receptor γ in smooth muscle normally inhibits Rho kinase and promotes BKCa function, thus influencing myogenic tone in resistance arteries in brain. These findings have implications for mechanisms that underlie large- and small-vessel disease in brain, as well as regulation of cerebral blood flow., (© 2014 American Heart Association, Inc.)

Although the use of antenatal glucocorticoids has resulted in decreased neonatal morbidity/mortality, recent animal studies have raised concerns regarding adverse effects of these medications on postnatal cardiovascular function. We hypothesized that antenatal betamethasone (Beta) exposure alters cerebral vascular reactivity in adult female sheep. We observed that K-induced constriction was comparable in middle cerebral artery (MCA) from Beta-exposed animals and age-matched controls. Pressure-induced constriction was significantly attenuated in MCA from Beta-exposed compared with control sheep. Inhibition of NOS significantly augmented pressure-induced constriction in MCA from both Beta-exposed and control sheep, whereas cyclooxygenase (COX) inhibition augmented pressure-induced constriction only in MCA from Beta-exposed sheep. Furthermore, NOS and COX inhibition significantly attenuated bradykinin (BK)-induced dilation in MCA from both Beta-exposed and control sheep. However, there seemed to be a greater contribution of both NOS and COX to BK-induced dilation in Beta-exposed compared with control MCA. Our findings demonstrate that fetal exposure to a clinically relevant course of Beta alters cerebral vascular tone and reactivity in adult female sheep.

Background/aims: In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries., Methods: In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca(2+)] ([Ca(2+)](SMC)) changes were recorded., Results: In the absence of L-NAME, asynchronous propagating Ca(2+) waves were recorded that were sensitive to block with ryanodine, but not nifedipine. L-NAME stimulated pronounced vasomotion and synchronous Ca(2+) oscillations with close temporal coupling between membrane potential, tone and [Ca(2+)](SMC). If nifedipine was applied together with L-NAME, [Ca(2+)](SMC) decreased and synchronous Ca(2+) oscillations were lost, but asynchronous propagating Ca(2+) waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either L-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK(Ca) channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca(2+) channels (VGCC), which was independent of both voltage and sGC., Conclusion: NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone., (Copyright 2009 S. Karger AG, Basel.)

Ca(2+) sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure-induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) required to sustain this view is not currently available. Here, we determined whether Ca(2+) sensitization pathways involving Rho kinase (ROK)- and PKC-dependent phosphorylation of MYPT1 and CPI-17, respectively, contribute to the myogenic response of rat middle cerebral arteries. ROK inhibitors (Y27632, 0.03-10 micromol l(-1); H1152, 0.001-0.3 micromol l(-1)) and PKC inhibitors (GF109203X, 3 micromol l(-1); Gö6976; 10 micromol l(-1)) suppressed myogenic vasoconstriction between 40 and 120 mmHg. An improved, highly sensitive 3-step Western blot method was developed for detection and quantification of MYPT1 and CPI-17 phosphorylation. Increasing pressure from 10 to 60 or 100 mmHg significantly increased phosphorylation of MYPT1 at threonine-855 (T855) and myosin light chain (LC(20)). Phosphorylation of MYPT1 at threonine-697 (T697) and CPI-17 were not affected by pressure. Pressure-evoked elevations in MYPT1-T855 and LC(20) phosphorylation were reduced by H1152, but MYPT1-T697 phosphorylation was unaffected. Inhibition of PKC with GF109203X did not affect MYPT1 or LC(20) phosphorylation at 100 mmHg. Our findings provide the first direct, biochemical evidence that a Ca(2+) sensitization pathway involving ROK-dependent phosphorylation of MYPT1 at T855 (but not T697) and subsequent augmentation of LC(20) phosphorylation contributes to myogenic control of arterial diameter in the cerebral vasculature. In contrast, suppression of the myogenic response by PKC inhibitors cannot be attributed to block of Ca(2+) sensitization mediated by CPI-17 or MYPT1 phosphorylation.