Dopamine-derived N 6 -substituents, compared to N 6 -(2-phenylethyl), in truncated (N)-methanocarba (bicyclo[3.1.0]hexyl) adenosines favored high A 3 adenosine receptor (AR) affinity/selectivity, e.g., C2-phenylethynyl analogue 15 (MRS7591, K i = 10.9/17.8 nM, at human/mouse A 3 AR). 15 was a partial agonist in vitro (hA 3 AR, cAMP inhibition, 31% E max ; mA 3 AR, [ 35 S]GTP-γ-S binding, 16% E max ) and in vivo and also antagonized hA 3 AR in vitro. Distal H-bonding substitutions of the N 6 -(2-phenylethyl) moiety particularly enhanced mA 3 AR affinity by polar interactions with the extracellular loops, predicted using docking and molecular dynamics simulation with newly constructed mA 3 AR and hA 3 AR homology models. These hybrid models were based on an inactive antagonistbound hA 1 AR structure for the upper part of TM2 and an agonistbound hA 2A AR structure for the remaining TM portions. These species-independent A 3 AR-selective nucleosides are low efficacy partial agonists and novel, nuanced modulators of the A 3 AR, a drug target of growing interest.

Hypertension and mineralocorticoid receptor activation cause cerebral parenchymal arteriole remodeling; this can limit cerebral perfusion and contribute to cognitive dysfunction. We utilized a mouse model of angiotensin II-induced hypertension to test the hypothesis that mineralocorticoid receptor activation impairs both TRPV4-mediated dilation of cerebral parenchymal arterioles and cognitive function. 16-18-week-old male C57bl/6 mice were treated with angiotensin II (800ng/kg/min) ± the mineralocorticoid receptor antagonist, eplerenone (100mg/kg/day) for 4 weeks; sham mice served as controls. Data are presented as mean ± SEM; n=5-14 per group. Eplerenone prevented the increased parenchymal arteriole myogenic tone and impaired carbachol-induced (10-10mol/L) dilation observed during hypertension. The carbachol-induced dilation was endothelium-derived hyperpolarization mediated because it could not be blocked by L-NAME (10mol/L) and indomethacin (10mol/L). We used GSK2193874 (10mol/L) to confirm that in all groups this dilation was dependent on TRPV4 activation. Dilation in response to the TRPV4 agonist GSK1016790A (10-10mol/L) was also reduced in the hypertensive mice and this defect was corrected by eplerenone. In the hypertensive and eplerenone treated animals, TRPV4 inhibition reduced myogenic tone, an effect that was not observed in arterioles from control animals. Eplerenone treatment also improved cognitive function and reduced microglia density in the hypertensive mice. These data suggest that the mineralocorticoid receptor is a potential therapeutic target to improve cerebrovascular function and cognition during hypertension.

The brain is highly susceptible to injury caused by hypertension because the increased blood pressure causes artery remodeling that can limit cerebral perfusion. Mineralocorticoid receptor antagonism prevents hypertensive cerebral artery remodeling, but the vascular cell types involved have not been defined. In the periphery, the endothelial mineralocorticoid receptor mediates hypertension-induced vascular injury, but cerebral and peripheral arteries are anatomically distinct; thus these findings cannot be extrapolated to the brain. The parenchymal arterioles determine cerebrovascular resistance. Determining the effects of hypertension and mineralocorticoid receptor signaling on these arterioles could lead to a better understanding of cerebral small vessel disease. We hypothesized that endothelial mineralocorticoid receptor signaling mediates inward cerebral artery remodeling and reduced cerebral perfusion during angiotensin-II hypertension. The biomechanics of the parenchymal arterioles and posterior cerebral arteries were studied in male C57Bl/6 and endothelial cell specific mineralocorticoid receptor knockout mice and their appropriate controls using pressure myography. Angiotensin-II increased plasma aldosterone and decreased cerebral perfusion in C57Bl/6 and mineralocorticoid receptor-intact littermates. Endothelial cell mineralocorticoid receptor deletion improved cerebral perfusion in angiotensin-II treated mice. Angiotensin-II hypertension resulted in inward hypotrophic remodeling; this was prevented by mineralocorticoid receptor antagonism and endothelial mineralocorticoid receptor deletion. Our studies suggest that endothelial cell mineralocorticoid receptor mediates hypertensive remodeling in the cerebral microcirculation and large pial arteries. Angiotensin II-induced inward remodeling of cerebral arteries and arterioles was associated with a reduction in cerebral perfusion that could worsen the outcome of stroke or contribute to vascular dementia.

Matin N, Fisher C, Jackson WF, Dorrance AM. Bilateral common carotid artery stenosis in normotensive rats impairs endotheliumdependent dilation of parenchymal arterioles. Am J Physiol Heart Circ Physiol 310: H1321-H1329, 2016. First published March 11, 2016; doi:10.1152/ajpheart.00890.2015.-Chronic cerebral hypoperfusion is a risk factor for cognitive impairment. Reduced blood flow through the common carotid arteries induced by bilateral carotid artery stenosis (BCAS) is a physiologically relevant model of chronic cerebral hypoperfusion. We hypothesized that BCAS in 20-wk-old WistarKyoto (WKY) rats would impair cognitive function and lead to reduced endothelium-dependent dilation and outward remodeling in the parenchymal arterioles (PAs). After 8 wk of BCAS, both shortterm memory and spatial discrimination abilities were impaired. In vivo assessment of cerebrovascular reserve capacity showed a severe impairment after BCAS. PA endothelial function and structure were assessed by pressure myography. BCAS impaired endothelial function in PAs, as evidenced by reduced dilation to carbachol. Addition of nitric oxide synthase and cyclooxygenase inhibitors did not change carbachol-mediated dilation in either group. Inhibiting CYP epoxygenase, the enzyme that produces epoxyeicosatrienoic acid (EETs), a key determinant of endothelium-derived hyperpolarizing factor (EDHF)-mediated dilation, abolished dilation in PAs from Sham rats, but had no effect in PAs from BCAS rats. Expression of TRPV4 channels, a target for EETs, was decreased and maximal dilation to a TRPV4 agonist was attenuated after BCAS. Together these data suggest that EET-mediated dilation is impaired in PAs after BCAS. Thus impaired endothelium-dependent dilation in the PAs may be one of the contributing factors to the cognitive impairment observed after BCAS. cerebral microcirculation; vascular remodeling; endothelium-dependent dilation; parenchymal arterioles; posterior communicating artery; epoxyeicosatrienoic acid NEW & NOTEWORTHY This is the first study investigating changes in endothelium-dependent dilation in parenchymal arterioles from a model of chronic cerebral hypoperfusion. Our findings correlate changes in the dilatory pathways of arterioles with cognitive deficits observed after chronic cerebral hypoperfusion.CHRONIC CEREBRAL HYPOPERFUSION has been implicated in dementias ranging from vascular cognitive impairment (20) to Alzheimer's disease (1, 12). Animal models of chronic cerebral hypoperfusion exhibit neuronal loss, white matter lesions, and increased levels of reactive astrocytes (10,28,29). Few studies have investigated the effect of chronic cerebral hypoperfusion on the parenchymal arterioles (PAs) (27, 49). However, none have reported changes in endothelial function in PAs or studied the effects of prolonged hypoperfusion.PAs arise from the pial arteries, perfuse the parenchyma, and eventually branch into the capillaries. These capillaries are in intimate contact with neurons, astrocytes, and pericytes and together these cell types form...