Attenuation of ischemic and postischemic damage to brain metabolism and circulation by a novel Ca2+ channel antagonist, NC-1100, in spontaneously hypertensive rats

Arterial hypertension and brain damage--evidence from animal models (review)

Hypertension is an important risk factor for cerebrovascular disease including stroke and has also a role in the development of vascular cognitive impairment (VCI) and vascular dementia (VaD). Research on pathophysiology and treatment of hypertensive brain damage may benefit from the availability of animal models. This paper has reviewed the main animal models of hypertension in which brain damage is documented. Spontaneously hypertensive rats (SHR) represent the animal model more largely used. In these rats cerebrovascular changes, brain atrophy, loss of nerve cells in cerebrocortical areas, and glial reaction were documented. Several changes observed in SHR are similar to those found by in vivo imaging studies in essential hypertensives. It is documented that brain gets benefit from lowering abnormally elevated blood pressure and that reduction of hypertension protects brain from stroke and probably reduces the incidence of VaD. The influence of anti-hypertensive treatment on brain structure and function in animal models of hypertension is reviewed. Among classes of drugs investigated, dihydropyridine-type Ca2+ antagonists were those with a most documented protective effect on hypertensive brain damage. Limits and perspectives in the use of animal models for assessing brain damage caused by hypertension and protection from it are discussed.

Calcium antagonist isradipine reduces metabolic alterations in acute cerebral ischemia in spontaneously hypertensive rats

The present study was designed to examine the effect of a calcium antagonist isradipine (PN200-110: PN) on local cerebral blood flow and brain tissue metabolism after 1-hour supratentorial ischemia induced by bilateral carotid artery ligation (BCL) in spontaneously hypertensive rats (SHR). PN, dissolved in ethanol plus polyethylene glycol 400, diluted with saline to make the final concentration of 0.25mg/ml and 2.5mg/ml, was administered subcutaneously either 30 min prior to BCL or just after the induction of incomplete cerebral ischemia (n = 7 in each group). Vehicle injection was served as a control group (n = 7). Cerebral blood flow in the parietal cortex (CBF) and the cerebellar cortex (CeBF) was measured by hydrogen clearance technique, and the supra- and infratentorial metabolites of the brain frozen in situ were determined by the enzymatic method. Blood pressure was lowered, but CBF was increased by PN administration in pre-BCL treatment study. After 1 hour of BCL, CBF decreased to around 10% or less of the resting value, being insignificant among the groups. Brain adenosine triphosphate was better preserved in PN-administered groups. The increase in lactate level tended to reduce dose dependently by PN treatment. PN also reduced the metabolic alterations in brain tissue with significance, even when administered just after the induction of forebrain ischemia. It is considered that pre- as well as post-BCL administration of PN is beneficial to attenuate the metabolic alterations in incomplete forebrain ischemia in SHR.

Ca2+ channel antagonists and neuroprotection from cerebral ischemia

Stroke is the third leading cause of death and the main disabling neurologic disease. The finding in experimental studies that neuronal death does not occur immediately after ischemic injury has encouraged the development of neuroprotective agents. Various Ca2+ channel antagonists, that is, L-type-selective or non-selective derivatives from classical Ca2+ channel antagonists, have been examined for their ability of neuroprotection through improvement of cerebral blood circulation or inhibition of Ca2+ overload induced by excessive glutamate release. Although some of the antagonists showed efficient neuroprotection in animal models, systemic hypotension limited the utility of these drugs, and none of the compounds showed beneficial effects in treatments for acute ischemic stroke in clinical trials. Drugs other than Ca2+ channel antagonists developed on the basis of the glutamate-Ca2+ overload hypothesis were shown also to lack clinical benefit. Recently, some mechanisms have been proposed to interpret neuronal death in relation to hyperexcitability or apoptosis after ischemic insult. In these hypotheses, activation of the Ca2+ channel types selectively expressed in neuronal tissues is proposed as a critical step of the pathways toward neurodegeneration. Thus, it is increasingly recognized that developing highly selective compounds for neuronal Ca2+ channels is not only important for treatment of stroke but also for elucidation of mechanisms that underlie neurodegeneration.