Protein synthesis in heterotopically transplanted rat hearts

This study examines protein synthesis in heterotopically transplanted rat hearts and several tissues of recipient rats. Donor hearts and recipient tissues synthesized many of the normally occurring proteins observed in tissues of unstressed rats. In addition, a stress-induced protein with a molecular mass of 71 kilodaltons was synthesized in donor heart, recipient heart and lung. Donor hearts incorporated more L-[35S]-methionine than did recipient hearts. Tissues of recipient rats also incorporated more label than the respective tissues of sham-recipient rats. These results suggest that ischemia, endured by the donor hearts during transplantation, induced these changes in protein synthesis.     

Stem cell characteristics of transplanted rat mammary clonogens

Rat mammary glands contain a subpopulation of clonogenic epithelial cells with large proliferation and differentiation potentials. When transplanted, the clonogens in monodispersed rat mammary epithelial cell suspensions give rise to either alveolar units (AUs) or ductal units (DUs) depending on the nature of the hormonal milieu in the graft recipient. Clonogens are also the primary cells of origin of mammary cancer following exposure to ionizing radiation or chemical carcinogens. Given the other stem cell characteristics of mammary clonogens, it would be expected that the primary AUs and DUs to which they give rise when grafted and hormonally stimulated (a) would be derived from the same clonogenic cell subpopulation, (b) would contain all of the functionally differentiated cell types of homologous parts of comparably stimulated mammary glands in situ, and (c) would also contain clonogen subpopulations capable when subtransplanted of giving rise to secondary AUs and DUs of similar cell composition. The current experiments were designed to test these expectations. The data are discussed in the context of results of previous studies with this and other experimental models. The results further support the conclusion that rat mammary clonogens are multipotent mammary stem cells.     

Model of occlusion-reperfusion arrhythmias of the transplanted heart in rats

Rats with heterotopically transplanted heart were used for modeling of occlusion-reperfusion arrhythmias. Heart transplantation was carried out by performing the anastomoses between the recipient carotid artery and jugular vein and innominate artery and pulmonary artery of the transplant respectively. The reversible ischemia of myocardium was achieved through temporal occlusion of recipient carotid artery supplying transplanted heart. The model is characterised by total denervation of the heart, the absence of pump function, total nature of myocardial ischemia during occlusion of supplying artery, high reproducibility of arrhythmias and the opportunity of repeated use of the animals.     

pH is decreased in transplanted rat pancreatic islets

Recent studies of transplanted pancreatic islets have indicated incomplete revascularization. We investigated the pH, in relation to oxygen tension (Po(2)), in endogenous islets and islets syngeneically transplanted to the renal subcapsular site of nondiabetic and streptozotocin-diabetic recipients. Tissue pH and Po(2) were measured using microelectrodes. In the endogenous islets, tissue pH was similar to that in arterial blood. In the transplanted islets, tissue pH was 0.11-0.15 pH units lower. No differences in islet graft pH were seen between nondiabetic and diabetic animals, and none if the islet grafts were investigated 1 day or 1 mo posttransplantation. The Po(2) in the endogenous islets was approximately 35 mmHg. Transplanted islets had a markedly lower tissue Po(2) both 1 day and 1 mo after transplantation. A negative correlation between the tissue Po(2) and the hydrogen ion concentration was seen in the 1-mo-old islet transplants in diabetic animals. In conclusion, decreased Po(2) in transplanted islets is associated with a decreased tissue pH, suggesting a shift toward more anaerobic glucose metabolism after transplantation.     

Regenerative capacity of transplanted cardiac muscle in the rat

The authors analyzed the regenerative ability of cardiac muscle in the rat. Normal cardiac muscle was minced into mm3 fragments and homotransplanted into a triceps surae complex cavity of a nonsibling rat. Subsequent histological examination of the cardiac regenerate revealed the presence of myofibers. These myofibers typically exhibited centrally located nuclei, a characteristic of normal cardiac muscle. However, the absence of intercalated discs and autonomous contractility prevented indentification of these fibers as cardiac.     

Hemodynamics evoked by microelectrical direct stimulation in rat somatosensory cortex

The aim of this study was to estimate the timing (latency) of the increase in red blood cell (RBC) velocity and RBC concentration, and the magnitude of response in local cerebral blood flow (LCBF) for neuronal activation. We measured LCBF change during activation of the somatosensory cortex by direct microelectrical stimulation. Electrical stimuli of 5, 10 and 50 Hz of 1 ms pulse with 10-15 microA, were given for 5 s. LCBF, RBC velocity and RBC concentration were monitored by laser-Doppler flowmetry (LDF) in alpha-chloralose anesthetized rats (n = 7). LCBF, RBC velocity and RBC concentration increased nearly proportionally to stimulus frequency, i.e. neuronal activity. LCBF rose approximately 0.5 s after the onset of stimulation, and there was no significant time lag of the latencies among LCBF, RBC velocity and RBC concentration at the same stimulus frequency. We interpret these results to mean that the onset of LCBF increase on cortical activation is reflected by a rapid change in arteriole (resistance vessel) dilation and capillary volume. The data also elucidate the linear relationship between LCBF increase and cortical activity.     

Paracrine effects of transplanted myoblasts and relaxin on post-infarction heart remodelling

In the post-infarcted heart, grafting of precursor cells may partially restore heart function but the improvement is modest and the mechanisms involved remain to be elucidated. Here, we explored this issue by transplanting C2C12 myoblasts, genetically engineered to express enhanced green fluorescent protein (eGFP) or eGFP and the cardiotropic hormone relaxin (RLX) through coronary venous route to swine with experimental chronic myocardial infarction. The rationale was to deliver constant, biologically effective levels of RLX at the site of cell engraftment. One month after engraftment, histological analysis showed that C2C12 myoblasts selectively settled in the ischaemic scar and were located around blood vessels showing an activated endothelium (ICAM-1-,VCAM-positive). C2C12 myoblasts did not trans-differentiate towards a cardiac phenotype, but did induce extracellular matrix remodelling by the secretion of matrix metalloproteases (MMP) and increase microvessel density through the expression of vascular endothelial growth factor (VEGF). Relaxin-producing C2C12 myoblasts displayed greater efficacy to engraft the post-ischaemic scar and to induce extracellular matrix re-modelling and angiogenesis as compared with the control cells. By echocardiography, C2C12-engrafted swine showed improved heart contractility compared with the ungrafted controls, especially those producing RLX. We suggest that the beneficial effects of myoblast grafting on cardiac function are primarily dependent on the paracrine effects of transplanted cells on extracellular matrix remodelling and vascularization. The combined treatment with myoblast transplantation and local RLX production may be helpful in preventing deleterious cardiac remodelling and may hold therapeutic possibility for post-infarcted patients.     

Survival of dissociated adrenal chromaffin cells of rat and monkey transplanted into rat brain

Summary Adrenal chromaffin cells from adult rats and monkeys were mechanically dissociated and implanted into the striatum of adult rats by stereotaxic injection. Rat chromaffin cells survived (5%) and showed differentiation by forming processes 1 h-28 days after implantation. Monkey chromaffin cells survived for 48 h but showed very little formation of processes. The method presented allows rapid nonenzymatic dissociation and transplantation of adrenal medullary cells.     

Studies of adenosine incorporation in Langendorff rat heart and rat heart mitochondria

The acid-insoluble product isolated from well-oxygenated Langendorff rat heart after perfusion with [¹⁴C]adenosine was purified by phenol extraction and subjected to specific phosphorolysis by pure polynucleotide phosphorylase. TLC analysis of the reaction mixture showed that ADP was the only radioactive product, proving that the original substance was a polyribonucleotide. Studies of the time course of labelling and of the distribution of the acid-insoluble product between the mitochondrial and nuclear fractions showed that both are labelled even after 1 min at 25 °C, but at short times and low temperature more radioactivity is found in the mitochondria. The kinetics of adenosine incorporation resemble those expected for the labelling of hnRNA and mRNA. Isolated, respiring mitochondria incorporate adenosine and adenine nucleotides into acid insoluble form by a process dependent on oxidative phosphorylation and the adenine nucleotide translocase that is specific for adenine derivatives. The results are discussed in terms of the hypothesis that the polyribonucleotide might be a storage form of adenine nucleotides: it is concluded that the bulk of the labelled product is unlikely to play a major role in energy metabolism.