Microspheres In Rats Research Articles

Ultrastructural disposition of adriamycin-associated magnetic albumin microspheres in rats.

The ultrastructural disposition of intra-arterially administered adriamycin-associated magnetic albumin microspheres has been investigated. The rat tail was used as the target organ and demarcated into the following three parts: T1, the injection site; T2, the target site; and T3, the posttarget site. Adriamycin HCl (2.0 mg/kg) was administered via the carrier through a cannula fixed at T1. The target site, T2, was exposed to a magnetic field of 8000 G for 30 min postdosing. Animals were sacrificed at scheduled time intervals over a 72-h period, and the tissue samples from T2 were observed by light and transmission electron microscopy. Electron microscopy revealed that microspheres traverse the vascular endothelium of the target tissue as early as 2 h after dosing. Gradual loss of tissue organization and cellular components, as a function of drug exposure time, demonstrated that the pharmacodynamic characteristics of the drug are not altered by its entrapment and delivery via the magnetic microspheres. The study confirms second-order drug targeting in the target tissue of healthy animals.

Effects of traumatic brain injury on regional cerebral blood flow in rats as measured with radiolabeled microspheres.

To clarify the effect of experimental brain injury on regional CBF (rCBF), repeated rCBF measurements were performed using radiolabeled microspheres in rats subjected to fluid-percussion traumatic brain injury. Three consecutive microsphere injections in six uninjured control rats substantiated that the procedure induces no significant changes in hemodynamic variables or rCBF. Animals were subjected to left parietal fluid-percussion brain injury of moderate severity (2.1-2.4 atm) and rCBF values were determined (a) prior to injury and 15 min and 1 h following injury (n = 7); and (b) prior to injury and 30 min and 2 h following injury (n = 7). At 15 min post injury, there was a profound reduction of rCBF in all brain regions studied (p less than 0.01). Although rCBF in the hindbrain had recovered to near-normal by 30 min post injury, rCBF in both injured and contralateral (uninjured) forebrain areas remained significantly suppressed up to 1 h post injury. At 2 h post injury, recovery of rCBF to near-normal values was observed in all brain regions except the focal area of injury (left parietal cortex) where rCBF remained significantly depressed (p less than 0.01). This prolonged focal oligemia at the injury site was associated with the development of reproducible cystic necrosis in the left parietotemporal cortex at 4 weeks post injury. Our results demonstrate that acute changes in rCBF occur following experimental traumatic brain injury in rats and that rCBF remains significantly depressed up to 2 h post injury in the area circumscribing the trauma site.

Albumin microspheres as a drug delivery system for epirubicin: pharmaceutical, pharmacokinetic and biological aspects

The aim of the present work was to investigate the effectiveness of epirubicin-loaded microspheres to affect specific organ or tissue sites where tumors are present. Egg albumin microspheres were prepared using a heat denaturation method. The kinetics of in vitro release of the drug complied partially with first order ( r = 0.9894) as well as with diffusion model from a matrix ( r = 0.9982). The pharmacokinetics of epirubicin in serum, heart and lungs after a single i.v. dose of free epirubicin and epirubicin-loaded microspheres in rats could be described by the equation of the two-compartment open model. The pharmacokinetic parameters calculated suggest the possibility to improve the selective entrapment of epirubicin-loaded microspheres by the lungs. The aim of our efficacy studies was to evaluate intratumoral administration of epirubicin-loaded microspheres in mice with Ehrlich ascites carcinoma, as well as experimental metastases in 256 rats with Walker carcinoma. The difference between the mean survival time, respectively the final metastatic incidences of the animals from treated groups compared to controls and to the free-epirubicin group, were statistically significant. These findings suggest the possibility of organ targeting and of reducing unwanted side-effects, especially the cardiotoxicity, of the epirubicin-loaded microspheres in cancer chemotherapy.

Effect of naloxone on regional cerebral blood flow during endotoxin shock in conscious rats.

Maintenance of cerebral blood flow (CBF) is vital during cardiovascular shock. Since opioids have been implicated in the pathophysiology of endotoxin shock and have been shown to alter cerebral perfusion patterns, we determined whether opioids were responsible for any of the changes in regional CBF observed during endotoxin shock and whether the use of naloxone might impair or aid in the maintenance of CBF. When blood flow (BF) is studied with microspheres in rats, the left ventricle of the heart is often cannulated via the right carotid artery. Questions have arisen concerning the potential adverse effects of this method on CBF in the hemisphere ipsilateral to the ligated artery. We measured right and left regional CBF by use of this route of cannulation. Twenty-four hours after cannulations were performed, flow measurements were made using radiolabeled microspheres in conscious unrestrained male Sprague-Dawley rats (300-400 g) before and 10, 30 and 60 min after challenging with 10 mg/kg Escherichia coli endotoxin (etx) or saline. Naloxone (2 mg/kg) or saline was given as a treatment 25 min post-etx. We found no significant differences between right and left cortical, midbrain, or cerebellar BF at any time in any treatment group. After etx, the whole brain received a large share of the depressed cardiac output. Thus global CBF was not significantly reduced below its pre-etx value, an effect unaltered by naloxone. Regionally, BF was reduced to cerebellum and midbrain by 30 min post-etx. Naloxone prevented this depression. No region was affected to a greater or lesser degree than others.(ABSTRACT TRUNCATED AT 250 WORDS)

Method of measuring deposition of unlabeled monodisperse microspheres in rat lungs

A system to simultaneously measure the total deposition of four different sizes of monodisperse microspheres in normal and damaged lungs of rats was developed and tested. The system reproducibly measured the deposition of microspheres in control rats, and the procedure was shown to be sufficiently sensitive to measure ozone-induced changes in deposition rates. Rats exposed to 1.2 ppm ozone 6 h/d for 2 consecutive days showed greater deposition of the 1.09-micron-, 2.02-micron-, and 2.99-micron- but not of the 0.48-micron-diameter microspheres when compared to controls. After 8 consecutive days of exposure to the same concentration of ozone, there were no differences in deposition rates between control and ozone-exposed rats. Respiratory physiology and lung histopathology data provided evidence that subtle changes in the airway architecture and/or aerodynamics were likely to be responsible for the differential deposition rates as a function of the duration of ozone exposure.

Simple methods for determining the accuracy of tumor blood flow measurements using radioactive microspheres in rats

Two simple methods are presented which allow positive identification of the accuracy and precision of the microsphere technique and a quick verification of sphere entrapment in tumor vessels. A known flow of Ringer's solution from a motor-driven syringe is perfused through the rat's isolated systemic circulation from left ventricle to right atrium and collected in a funnel. Using this preparation, total blood flow in rats measured with radioactive microspheres injected into the left ventricle was 97% of actual flow. The coefficient of variation (standard deviation/mean) of the microsphere measurements was 0.22. In the same preparation, nonentrapment of microspheres in subcutaneous tumor nodules grown on a hind limb could be measured from the difference in counts collected in venous effluent before and after placement of a tourniquet proximal to the tumor. For example, in two types of transplantable carcinoma, we found nonentrapment of less than 0.1% of the injected microspheres. Such a shunt would correspond to less than 10% of microspheres entering a typical tumor nodule and, in turn, less than 10% underestimation of true flow to the tumor. These two techniques may be helpful to other investigators in testing the accuracy of microsphere methods in various small animal tumor models.

Importance of injection site for coronary blood flow determinations by microspheres in rats.

Because coronary blood flow (CBF) determinations require that blood and microspheres be uniformly mixed in the root of the aorta, we developed a technique of left-atrial (LA) catheterization in rats and compared the variability of results obtained by LA injection and left-ventricular (LV) injection as regards systemic [cardiac output (CO)], proximal (coronary), and distal (renal, cerebral) flows in anesthetized animals. CBF values averaged 410 +/- 224 and 358 +/- 99 (SD) ml.min-1.100 g-1 from LV and LA injection, respectively, or 5.7 +/- 2.9 and 4.9 +/- 1.3 (SD) %CO. The variability with LA injection was significantly lower than with LV injection as shown by the marked differences in standard deviations obtained with the two methods (224 vs. 99 ml.min-1.100 g-1 or 2.9 vs. 1.3 %CO, P greater than 0.01). In contrast, no significant difference in variability was found for either CO or more distal regional flows. These results indicate that LV injections might be adequate for systemic flow and regional flows to relatively distal beds but that accurate measurements of CBF require LA injection of microspheres.

Influence of noradrenaline on blood flow to brown adipose tissue in rats exhibiting diet-induced thermogenesis.

1. The influence of noradrenaline on regional blood flow was determined using radioactive microspheres in rats maintained on either stock diet or a palatable cafeteria diet. 2. Cardiac output and blood flow to brain, lungs, liver and skeletal muscle were similar for rats on the two diets. 3. Blood flow to total dissectable brown adipose tissue in control and cafeteria rats represented 1 and 2% of cardiac output respectively but these values rose to 7 and 15.5% during infusion of noradrenaline. 4. Arterial oxygen content was similar for all groups but the oxygen content of venous blood draining the interscapular brown adipose tissue fell to 6 ml O2/100 ml blood in control rats and 1 ml/100 ml in cafeteria rats after noradrenaline. 5. The total oxygen consumption of brown adipose tissue was calculated and found to account for 42% of the response to noradrenaline in control rats and 74% in cafeteria animals. The increments in the oxygen consumption of other tissues were almost identical in both groups and so all the diet-induced changes in thermogenic capacity can be attributed to increases in brown adipose tissue metabolism. 6. These findings demonstrate the quantitative importance of brown adipose tissue in diet-induced thermogenesis and confirm the similarities between diet and non-shivering thermogenesis.

Systemic hemodynamic effects of microspheres in conscious rats.

The effect of increasing quantities of carbonized microspheres (15 +/- 5 micrometer diam) on systemic hemodynamics was evaluated in 21 Sprague-Dawley, 6 normotensive Wistar-Kyoto (WKY), and 8 spontaneously hypertensive (SHR) male rats. Total cumulative injections of more than 100,000 microspheres produced significant systemic hemodynamic alterations manifested by decreased oxygen consumption, cardiac output, and mean arterial pressure; and by increased heart rate, total peripheral resistance, and arterial-venous blood oxygen content difference. There were no hemodynamic alterations characteristic of any rat species, and reproducibility of three separate injections of 20,000 microspheres in each rat was excellent.

The circulation in liver tissue and experimental liver metastases before and after embolization of the liver artery.

Simultaneous measurement of cardiac output distribution with 86Rubidium and 57Cobalt-tagged microspheres in rats implanted with liver tumors by intraportal injection of sarcoma cells enables quantitation of arterial and portal tumor circulation. The portal circulation was found to be increased in small tumors as compared to the liver, but as the tumor grew there was a decrease in the portal tumor circulation. When the tumor growth became massive even the total liver circulation was reduced, as measured with 133Xenon wash-out. All the tumors had increased arterial circulation. This arterial hyperperfusion was changed into ischemia when the liver artery was occluded through embolization with degradable microspheres.

Postnatal development of cardiac output distribution measured by radioactive microspheres in rats.

Distribution of cardiac output was measured in rats, 9, 18, 25, 42 and 64 days old, by means of 85Sr-labelled microspheres 15 micrometer in diameter. The fractions of the cardiac output supplying the heart, lungs, cerebrum, hindbrain, kidney, liver, spleen, stomach, small intestine, large intestine, bones and muscles of the hindlegs and skin were estimated. The values obtained were further related to the relative weights of the respective organs. The distribution of cardiac output changed with age, the changes being most pronounced in the brain, kidney and small intestine.

Renal arteriolar obstruction without hypertension.

Selective partial occlusion of the intrarenal arteriolar bed with microspheres in rats resulted in contracted kidneys simulating those of benign nephrosclerosis in man. There was no elevation of blood pressure, renal vein plasma measured by radioimmunoassay, or juxtaglomerular indices of affected kidneys. It is unlikely that arteriolar lesions are pathogenetically related to the development of hypertension.