Ancrod reduces intracerebral hemorrhage quantified in vivo by magnetic resonance imaging in rats.

BACKGROUND AND PURPOSE: Promising results of experimental and clinical stroke studies suggest that ancrod may provide an efficient therapy of brain ischemia. Because ancrod has been shown to produce rapid defibrinogenation, we investigated the effects of this agent in a rat model of intracranial bleeding using noninvasive magnetic resonance imaging (MRI). METHODS: Intracranial bleeding was induced in anesthetised rats by microinfusion of collagenase into the right striatum. Ancrod was intravenously infused for a period of 30 minutes starting 30 minutes after intrastriatal collagenase infusion. The dosages of ancrod were 0.33 IU . kg(-1) . min(-1) in one group and 1 IU . kg(-1) . min(-1) in another (total dosages were 10 and 30 IU . kg(-1), respectively). Control animals received equal amounts of vehicle solution (0.9% NaCl) only. The volume of intracerebral hemorrhage (ICH) was quantified in vivo by T1-weighted spin-echo MRI in eight consecutive coronal brain planes 24 hours after collagenase infusion. RESULTS: Plasma fibrinogen was dose-dependently diminished immediately after infusion of ancrod at dosages of 0.33 or 1 IU . kg(-1) . min(-1). Total volume of ICH was significantly (P<.05) reduced by 50% from 48 (35/57) mm(3) in vehicle-treated controls (n=17) to 24 (20/37) mm(3) in rats (n=15) infused with the lower ancrod dosage (median, 25th/75th centiles). Rats (n=15) treated with the higher dosage of ancrod had 34 (27/39) mm(3) volume of ICH, which is 29% lower compared with vehicle-treated controls (P=.05). CONCLUSIONS: Adverse side effects such as aggravation of intracerebral bleeding did not occur in ancrod-infused rats despite pronounced lowering of the plasma fibrinogen level during ongoing bleeding. In contrast, significant reductions in the volumes of ICH were observed suggesting favorable influence of ancrod in the event of intracranial bleeding in rats.

Simultaneous in vivo visualization and localization of solid oral dosage forms in the rat gastrointestinal tract by magnetic resonance imaging (MRI).

PURPOSE: Bioavailability of orally administered drugs is much influenced by the behavior, performance and fate of the dosage form within the gastrointestinal (GI) tract. Therefore, MRI in vivo methods that allow for the simultaneous visualization of solid oral dosage forms and anatomical structures of the GI tract have been investigated. METHODS: Oral contrast agents containing Gd-DTPA were used to depict the lumen of the digestive organs. Solid oral dosage forms were visualized in a rat model by a 1H-MRI double contrast technique (magnetite-labelled microtablets) and a combination of 1H- and 19F-MRI (fluorine-labelled minicapsules). RESULTS: Simultaneous visualization of solid oral dosage forms and the GI environment in the rat was possible using MRI. Microtablets could reproducibly be monitored in the rat stomach and in the intestines using a 1H-MRI double contrast technique. Fluorine-labelled minicapsules were detectable in the rat stomach by a combination of 1H- and 19F-MRI in vivo. CONCLUSIONS: The in vivo 1H-MRI double contrast technique described allows solid oral dosage forms in the rat GI tract to be depicted. Solid dosage forms can easily be labelled by incorporating trace amounts of non-toxic iron oxide (magnetite) particles. 1H-MRI is a promising tool for observing such pharmaceutical dosage forms in humans. Combined 1H- and 19F-MRI offer a means of unambiguously localizing solid oral dosage forms in more distal parts of the GI tract. Studies correlating MRI examinations with drug plasma levels could provide valuable information for the development of pharmaceutical dosage forms.

MRI study on delayed ancrod therapy of focal cerebral ischaemia in rats.

The therapeutic window for efficient post-treatment of focal cerebral ischaemia with the fibrinogen lowering agent ancrod was studied by magnetic resonance imaging (MRI) in spontaneously hypertensive rats (SHR). Ancrod or vehicle solution (0.9% NaCl) were i.v. infused (0.12 IU/kg per min) via implanted mini pumps starting 0.5, 1.5, 3 or 6 h after permanent proximal middle cerebral artery occlusion and lasting until brain mapping by multislice T2-weighted magnetic resonance imaging in vivo 24 h after middle cerebral artery occlusion. Plasma fibrinogen concentrations were measured before middle cerebral artery occlusion, before pump implantation and after magnetic resonance imaging. Total brain lesion volumes as determined by magnetic resonance imaging 24 h after middle cerebral artery occlusion were 131 +/- 36 (188 +/- 28)*, 151 +/- 39 (194 +/- 39)*, 147 +/- 44 (207 +/- 33)* and 209 +/- 60 (214 +/- 42) mm3 in rats with 0.5, 1.5, 3 and 6 h, respectively, delay of ancrod treatment (means +/- S.D., 8-11 animals/group, corresponding control groups in parentheses, *P < 0.05). Continuous i.v. ancrod infusions reduced plasma fibrinogen levels significantly (P < 0.05) in all ancrod-treated groups as compared to vehicle-treated controls until the end of the experiments 24 h after middle cerebral artery occlusion. In conclusion, significant cerebroprotection was achieved even when the onset of ancrod therapy for lowering of the plasma fibrinogen level was delayed for up to 3 h. To the best of our knowledge no drug efficacy has been reported so far with a therapeutic window of 3 h after permanent middle cerebral artery occlusion in spontaneously hypertensive rats suggesting that ancrod may provide an efficient therapy of acute human stroke.

Magnetic resonance imaging study on the effect of levemopamil on the size of intracerebral hemorrhage in rats.

BACKGROUND AND PURPOSE: Beneficial effects of calcium antagonists in cerebral ischemia and trauma have been attributed in part to improved cerebral blood flow. Enhancement of cerebral blood flow, however, could aggravate the pathological situation if brain injury is associated with intracerebral hemorrhage. In this study we used high-field magnetic resonance imaging in an animal model of intracerebral hemorrhage to determine noninvasively the effect of the calcium and serotonin antagonist levemopamil [international nonproprietary name for (S)-emopamil] when infused in a dose (6 mg/kg) that is known to increase cerebral blood flow. METHODS: Intracerebral hemorrhage was induced in rats by stereotaxic microinfusion of collagenase into the caudate putamen. Two series of experiments were performed. (1) Levemopamil was intravenously infused 30 minutes after intracerebral infusion of collagenase (0.05 U), which represents the time of intracranial bleeding. Another group of animals was given heparin (55 IU.kg-1.min-1) to evaluate the capability of this animal model to demonstrate drug-induced worsening of intracerebral hemorrhage. (2) The effects of hyperacute infusion of levemopamil (30 minutes after infusion of 0.5 U of collagenase) were compared with those of a 2-hour delayed administration. In both experimental settings, the extent of intracerebral hemorrhage was determined by T1-weighted magnetic resonance images (spin-echo; repetition time, 400 milliseconds; echo time, 23 milliseconds) taken in vivo in a coronal and a transverse brain plane 24 hours after collagenase infusion. RESULTS: (1) Hemorrhagic brain areas measured 10.1 +/- 2.9 mm2, 8.5 +/- 2.1 mm2, and 18.8 +/- 2.5 mm2 in the coronal brain plane (10 mm anterior to the interaural line) of control, levemopamil-, and heparin-infused rats, respectively (8 animals per group, mean +/- SD). In the transverse brain plane (6 mm dorsal to the interaural line) the hemorrhagic area was 11.5 +/- 3.6 mm2, 9.7 +/- 2.4 mm2, and 19.9 +/- 3.3 mm2 in control, levemopamil-, and heparin-infused rats, respectively. (2) Animals with 2-hour delayed levemopamil infusion displayed intracerebral hemorrhage similar in size to that of control rats. (3) Neither small nor large hemorrhagic lesions were increased by levemopamil. CONCLUSIONS: Aggravation of intracerebral hemorrhage was not observed by magnetic resonance imaging in levemopamil-infused animals. However, infusion of heparin caused a significant (P < .05), almost twofold increase in the size of intracerebral hemorrhage. These results justify clinical trials with levemopamil in cerebral disorders such as stroke, brain trauma, and peritumoral brain edema, which may be accompanied by intracerebral hemorrhage from the beginning or where transition to intracerebral hemorrhage may occur.

Oedema reduction by levemopamil in focal cerebral ischaemia of spontaneously hypertensive rats studied by magnetic resonance imaging.

The effect of treatment with the Ca2+ channel blocker and 5-HT2 receptor antagonist levemopamil (recommended INN for (S)-emopamil) on the extent of ischaemic brain oedema was studied by magnetic resonance imaging in vivo. Focal cerebral ischaemia was induced in spontaneously hypertensive rats by permanent middle cerebral artery occlusion. The treatment consisted of slow intravenous injections of an aqueous solution of levemopamil given immediately after middle cerebral artery occlusion and again 2 h and 4 h later. One group of animals (n = 17) received 3 x 2 mg/kg of levemopamil (total dose: 6 mg/kg) and another group (n = 13) received 3 x 4 mg/kg (total dose: 12 mg/kg). Saline was administered to the controls (n = 16) at corresponding times. High-resolution T2-weighted spin echo images were obtained 24 h after middle cerebral artery occlusion from two transversal brain planes (4.5 mm and 6.5 mm dorsal to the interaural line). Dose-dependent reductions of brain oedema were achieved in both brain planes. The lower dose of levemopamil reduced the extent of oedema significantly (P < 0.05) by 20 +/- 3.7% in the upper and by 21 +/- 3.8% in the lower brain plane as compared to the controls (means +/- S.E.M.). The higher dose diminished the extent of oedema in the same planes by 30 +/- 3.5% and 31 +/- 4.0%, respectively. Dose-dependent reductions of infarct size, as determined by vital tissue staining using 2,3,5-triphenyltetrazolium chloride (TTC), were observed in the levemopamil-treated groups. Body temperature was not affected by levemopamil, suggesting direct cerebroprotection by this drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusion- and T2-weighted imaging: evaluation of oedema reduction in focal cerebral ischaemia by the calcium and serotonin antagonist levemopamil.

Magnetic resonance imaging (MRI) was used to evaluate beneficial drug effects in a rat model of focal cerebral ischaemia. Extent of cerebral oedema was measured on T2-weighted images 24 hr after permanent middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats. Areas of increased signal intensity strongly correlate with histochemically determined areas of ischaemia in corresponding brain planes (r = 0.84; p < .001). In a separate cohort of animals, spatial progression of oedema formation was studied at 3, 24, 48, and 72 hr after MCAO showing a maximum extent at 48 hr. Early events in cerebral ischaemia were monitored using diffusion-weighted imaging. Effects of levemopamil [formerly (S)-emopamil], a calcium and serotonin antagonist, and the reference compound isradipine were quantified on high resolution T2-weighted spin-echo images 24 hr after MCAO. Combined pre- and posttreatment with isradipine showed a 21% inhibition of oedema progression. Application of a single dose (10 mg/kg) of levemopamil either 30 min before or 2 hr after MCAO revealed a diminution of oedematous areas by 19% and 25%, respectively. Levemopamil reduces the extent of ischaemic brain oedema in an established stroke model.

Acute effects of tumor necrosis factor alpha or lymphotoxin on global blood flow, laser Doppler flux, and bioenergetic status of subcutaneous rodent tumors.

Global blood flow (TBF), tumor vascular resistance, laser Doppler flow in superficial tumor areas, and mean arterial blood pressure were evaluated in rats bearing s.c. DS sarcomas. Measurements were performed before and after i.v. administration of rhTNF-alpha 2 or recombinant human lymphotoxin (rhLT) (1 mg/kg). Upon application of the cytokines a significant drop in TBF was found at t greater than or equal to 90 min with a stronger action following rhLT than rhTNF-alpha. At relatively constant mean arterial blood pressure values following the cytokine injection, the microcirculatory function in the tumor periphery was found to be impaired somewhat earlier than TBF, indicating that the cytokines do not preferentially act on the poorly perfused tumor center in the model chosen. This finding is inconsistent with previous histological studies on murine tumors. Acute flow changes encompassed only substantial reductions (i.e., hypoperfusion) rather than a complete ischemia. TBF was slightly increased during the first hour following rhLT whereas after rhTNF-alpha a continuous drop was observed. This differential response could not be observed during laser Doppler flowmetry. Tumor vascular resistance changes largely reflected alterations in TBF. 31P-Nuclear magnetic resonance spectroscopy on murine Meth-A fibrosarcomas revealed dose- and time-dependent decreases of ATP/Pi and phosphocreatine/Pi ratios following i.v. administration of rhTNF-alpha. From comparisons of dose-response curves rhLT appears to be more detrimental than rhTNF-alpha with respect to the bioenergetic status. The observed changes in tumor energy metabolism are similar to those described for TBF. It may therefore be concluded that most of the cytokine effects on the bioenergetic status are secondary to the inhibition of the microcirculatory function. As a major causative factor for the latter, an arterial hypotension can be excluded in the tumor model chosen.