Effects of long-term antihypertensive treatment on cerebral, thalamic and cerebellar blood flow in spontaneously hypertensive rats (SHR)

Hypertension-induced changes in monoamine receptors in the prefrontal cortex of rhesus monkeys

Hypertension affects approximately 60 million people in the United States. Recent studies have demonstrated that hypertension may produce progressive changes in the CNS. The present study is focused on reports in the literature that hypertension may significantly alter neurotransmitter systems, particularly dopamine (DA) and norepinephrine (NE). To address this, DA and norepinephrine (NE) receptor binding was assessed in the prefrontal cortex (PFC) of 15 male rhesus monkeys using on-the-slide in vitro assays for the DA1, NE alpha1 and NE alpha2 receptors as well as for the DA and NE uptake transporters. Eight monkeys underwent surgical coarctation of the mid-thoracic aorta which produced sustained, untreated hypertension as defined by a systolic pressure above 150 mm Hg. Compared with normotensive controls, chronic, untreated hypertension produced a significant decrease in DA1 and NE alpha1 receptor binding and an increase in DA uptake (DAU) receptor binding in the prefrontal cortex. While the mechanisms by which untreated hypertension alters DA and NE receptors is not known, the use of this non-human primate model should provide the means to uncover neurobiological changes that occur with untreated hypertension.

Why are strokes related to hypertension? Classic studies and hypotheses revisited

Although it seems obvious that excessive intravascular pressure is the cause of spontaneous intracerebral haemorrhage, the available evidence instead suggests that haemorrhage arises from previous ischaemic damage to the walls of small blood vessels. This interpretation unifies the aetiology of cerebral infarction and intracerebral haemorrhage. It is supported by much pathological evidence and also fits with observations on spontaneous stroke-prone hypertensive rats, which have smaller cerebral arteries than Wistar-Kyoto rats. Ischaemic damage to the brain probably occurs during spontaneous dips in aortic pressure in the presence of atheromatous arterial lesions and arteriolar narrowing by lipohyaline deposits. It may also follow long-lasting arterial spasm provoked by sudden pressure elevations. Local factors, especially unevenness of cerebral perfusion, probably determine the site of an infarct and whether it becomes haemorrhagic or not. In the long term, hypotensive drugs will lessen atheroma deposition. In the short term, they may act by reducing or preventing damaging arteriolar spasm.

Protective effect of treatment with nicardipine on cerebrovascular tree of spontaneously hypertensive rats

The effect of an eight-week treatment with the Ca2+ channel blocker nicardipine on different-sized pial arteries and intracerebral arteries was assessed in spontaneously hypertensive rats (SHR) by microanatomical techniques. Normotensive Wistar-Kyoto (WKY) rats were used as normotensive reference animals. In SHR a significant increase of systolic blood pressure (SBP) in comparison with WKY rats was noticeable. An increased thickness of tunica media and luminal narrowing were also seen in medium- and small-sized pial arteries, and in intracerebral arteries of SHR in comparison with WKY rats. The media-to-lumen ratio was also increased in medium (diameter between 150 and 50 microm) and small-sized (diameter < than 50 microm) pial and intracerebral arteries. Treatment with nicardipine significantly reduced SBP, the thickness of tunica media, media-to-lumen ratio and increased luminal area of medium- and small-sized pial arteries and of intracerebral arteries. These findings demonstrate that treatment of SHR with nicardipine induces a moderate vasodilatation of both pial and intracerebral arteries regulating cerebrovascular resistance. This property may be useful in avoiding generalized or exaggerated cerebrovascular dilatation in hypertension which could be accompanied by impaired brain perfusion.

Blood flow velocity changes in the middle cerebral artery as an index of the chronicity of hypertension

This study was designed to demonstrate cerebral hemodynamic changes related to hypertension using transcranial Doppler ultrasonography. We measured the flow velocities and the Gosling pulsatility index of the middle cerebral artery and the internal carotid artery in 94 stroke-free, hypertensive patients and 81 age- and gender-matched healthy controls. Compared with the control subjects, patients with a longer duration (> or = 5 years) of hypertension showed significantly lower flow velocities of the middle cerebral artery and a higher Gosling pulsatility index of the middle cerebral- and the internal carotid artery. These differences were not observed in patients with a shorter duration of hypertension (<5 years). In the patient group, the mean velocity of the middle cerebral artery was significantly and inversely correlated with the duration of hypertension. Decreased flow velocity with increased pulsatility observed in this study suggest that alterations in the small cerebral vessels and arterioles contribute primarily to cerebral hemodynamic changes occurring in long-standing hypertension and also suggest the possible usefulness of transcranial Doppler in monitoring the progression of cerebral atherogenesis related to hypertension.

Cerebral blood flow and metabolism in hypertensive patients with cerebral infarction

The authors investigated, by positron emission tomography, the effect of long-standing hypertension on cerebral blood flow (CBF) and oxygen metabolism in patients with chronic atherothrombotic brain infarction. In the nonbrain infarct (non-BI) group (n = 13, mean age: sixty-two years), the regional CBF (rCBF) was decreased significantly with a rise in the mean arterial blood pressure (MABP) in the cerebral cortexes (r = -0.575) and the deep gray matter (r = -0.451), whereas the regional cerebral metabolic rate for oxygen (rCMRO2) remained unchanged. In the brain infarct (BI) group (n = 22, mean age: fifty-eight years), however, the rCBF as well as the rCMRO2 were reduced even in the normotensive patients and thus did not correlate with the MABP. These results suggest that long-standing hypertension per se causes a reduction in the rCBF but not in the oxygen metabolism with a compensatory increase in the oxygen extraction fraction. On the other hand, patients with brain infarction, even normotensives, show a diffuse decrease in cerebral circulation and metabolism, which is probably due to the more severe sclerotic changes that take place in the cerebral vessels.

Long-term changes in cerebral blood flow according to different types of ischemic stroke

Recurrence of ischemic stroke may be related to chronic hemodynamic failure of the brain. Long-term changes in cerebral blood flow (CBF) remain undetermined for each ischemic stroke subtype. We performed the present study to clarify this issue. The study group consisted of 77 unilateral, hemispheric, ischemic stroke patients who had a single stroke episode; atherothrombotic stroke in 34, cardioembolic in 26 and lacunar in 17. We measured baseline CBF in the affected and unaffected hemispheres 1.0-3.4 months after stroke onset, then repeated the measurements 10 months to 10 years later (mean 43.7 months), with the xenon-133 inhalation method. We analyzed changes in CBF in relation to other clinical characteristics. CBF in the affected hemisphere changed differently among the stroke subtypes (P < 0.01); increased in the atherothrombotic group, particularly within 40 months of stroke; remained unchanged in the cardioembolic group; and decreased in the lacunar group, especially later than 40 months of stroke. In the atherothrombotic group, CBF increased in hypertensive patients but decreased in normotensives (7.9 +/- 2.4% and -3.6 +/- 3.9%, respectively; P < 0.05). Present results suggest that long-term changes in CBF depend on ischemic stroke subtype. Development of collateral circulation may occur after several years in atherothrombotic stroke patients. The findings raise doubts about the significance of chronic hemodynamic failure as a cause of stroke recurrence.

Differential cerebrovascular responsiveness in spontaneously hypertensive rats following antihypertensive treatment with clonidine and verapamil

Numerous studies have been reported examining the effects of antihypertensive treatment on peripheral vascular responsiveness in spontaneously hypertensive rats (SHR). This study was conducted to determine the effects of chronic treatment with 2 antihypertensive agents on cerebrovascular responsiveness in male SHR and Wistar-Kyoto (WKY) rats. SHR and WKY (3-4 weeks old) received either placebo, clonidine (CLON, 10 mg pellet) or verapamil (VER, 5 mg pellet). Vascular reactivity studies on the basilar artery, using standard smooth muscle bath techniques, were conducted following 6 weeks of treatment. Both CLON and VER significantly attenuated the rise in blood pressure in SHR. Basilar artery responsiveness to KCl, serotonin (5-HT), and calcium were significantly increased whereas responses to acetylcholine (ACH), isoproterenol (ISO) and sodium nitroprusside (SNP) were significantly reduced in SHR compared to WKY. CLON had no effect on basilar artery responsiveness to either the contractile or relaxation agents in SHR. However, although responses to KCl, 5-HT and calcium were not affected by VER in SHR, VER significantly increased the responses to ACH, ISO and SNP. Neither CLON nor VER treatment affected basilar artery responsiveness to any of the agents in WKY. These data demonstrate that, even though CLON and VER have similar antihypertensive effects, differential effects of the 2 agents on cerebrovascular responsiveness in the SHR are apparent. This would suggest that the vascular effects of VER and CLON are dependent upon the mechanism of action of the agents and not simply due to prevention of the elevation in blood pressure.