Increase in receptor binding affinity for nimodipine in the rat brain with permanent occlusion of bilateral carotid arteries

The influence of nimodipine on cerebral and general hemodynamics in rats under condition of hypokinesia

The aim of the study was to reveal the influence of nimodipine on cerebral and general hemodynamics at different periods of hypokinesia (HK). The gauging of parameters was carried out under general anesthesia before and at the third minute after intravenous injection of three doses of nimodipine (1, 3 and 10 microg/kg). The local cerebral blood flow (ICBF) was measured with laser-Doppler flowmetry probe placed on the parietal cortex. In the 15-day HK indices did not differ from the control group, only mean the arterial blood pressure (MABP) and resistance of cerebral vessels (CVR) were smaller when the highest dose was used. In the 30- and 45-day HK a statistically significant increase of ICBF and a decrease of CVR and MABP was observed. These changes were more expressed in the 45-day HK, and in the 60-day HK some stabilization of these parameter was noted. Most vividly expressed augmentation of HR, in comparison with the control is revealed at the dose of 10 microg/kg on the 30th day of HK. The deltaHR/deltaMABP ratio was decreased with augmentation of term of the HK, achieving its minimum by the 45th day. However, at the dose of 10 microg/kg in 60-day HK this ratio decreased even more. It has been concluded that HK was able to change the sensitivity to the cerebrovasoselective calcium channel blocker--nimodipine.

Neuroprotective effect and brain receptor binding of taltirelin, a novel thyrotropin-releasing hormone (TRH) analogue, in transient forebrain ischemia of C57BL/6J mice

Thyrotropin-releasing hormone (TRH) and some of its stable analogues have been shown to improve neurologic dysfunctions such as brain trauma in both animals and humans. Our previous study revealed that taltirelin, a novel orally active TRH analogue, binds to rat brain TRH receptors in vivo. The present study was undertaken to investigate whether taltirelin has neuroprotective effects in transient brain ischemia of C57BL/6J mice induced by bilateral carotid artery occlusion (2VO). Neuronal cell density in the hippocampal CA1 region of C57BL/6J mice was significantly (39.9%) decreased 1 week after 2VO-reperfusion, compared to the case of the sham group, and this reduction of hippocampal neuronal density was significantly suppressed by an intravenous (i.v.) injection of taltirelin (0.3 mg/kg). The i.v. injection of taltirelin at this dosage produced a significant increase in the dissociation constant (Kd) of specific [3H]MeTRH binding in sham and 2VO-reperfusion groups (33.6 and 51.4%, respectively) compared with the vehicle-treated group. These results indicate that the intravenously injected taltirelin bound to TRH receptors in the ischemic brain. There was little difference in the brain-to-plasma concentration ratio (Kp) of [14C]sucrose between the sham and 2VO groups of C57BL/6J mice, indicating that the tight junction of the blood-brain barrier may be intact in the ischemic brain. In conclusion, the study has shown that taltirelin may have a significant neuroprotective effect on the ischemic brain.