Functional recovery of hearts after cardioplegia and storage in University of Wisconsin and in St. Thomas' Hospital solutions

There are conflicting reports of the beneficial effects of University of Wisconsin (UW) cardioplegic solution used in heart preservation techniques. Therefore we investigated the efficacy of myocardial protection in adult rat hearts subjected to single-dose infusion (3 minutes) of nonoxygenated cardioplegic solutions (UW or St. Thomas' Hospital solution No. 2 [STH]) and stored at 4 degrees C by immersion in the same solution or in saline solution. Isolated working-heart preparations (n = 8 per group) were used to assess the prearrest (20 minutes' normothermic perfusion) and postischemic left ventricular functions. Four groups of hearts underwent 5, 8, 10, and 20 hours of cold ischemia (4 degrees C) in UW solution. Hearts stored for 8 to 20 hours showed no postischemic recovery of cardiac pump function (aortic flow, 0%), had decreased levels of myocardial high-energy phosphates, and were highly edematous (50% to 70% increased). After 5 hours of storage there was also poor recovery of aortic flow, coronary flow, and aortic pressure (55.0% +/- 19.4%, 67.1% +/- 5.1%, and 58.1% +/- 11.7%, respectively) but good recovery of adenosine triphosphate, creatine phosphate, and guanosine triphosphate (18.54 +/- 1.42, 29.99 +/- 2.05, and 1.64 +/- 0.14 mumol/gm dry weight, respectively). In contrast, hearts arrested and stored in STH solution for 5 hours rapidly established normal left ventricular functions (aortic flow, 111.5% +/- 2.5%; cardiac output, 99.1% +/- 1.2%; coronary flow, 85.0% +/- 3.4%; heart rate, 95.8% +/- 2.7%; and aortic pressure, 94.6%). A group of hearts arrested with STH solution but stored in saline solution recovered more slowly, had only partial return of function (aortic flow, 73.6% +/- 14.8%; p less than 0.01 vs STH/STH group), and had significantly greater tissue water content (8.020 +/- 0.080 vs 6.870 +/- 0.126 ml/gm dry wt; p less than 0.01). These results demonstrate the superior preservation of explanted hearts at 4 degrees C obtained by STH cardioplegic solution compared with UW solution under conditions used for transplantation.

The contribution of ischaemia to the development of microvascular incompetence in the myocardium

STUDY OBJECTIVE

The aim was to determine the contribution of ischaemia per se to the development of microvascular incompetence in the myocardium.

DESIGN

Isolated, buffer perfused rat hearts were made globally ischaemic for 0-60 min, then fixed with nitrogen bubbled glutaraldehyde and perfused with nuclear track emulsion to identify and quantify competent blood vessels in scanning and transmission electron micrographs.

SUBJECTS

Adult Male Wistar rats weighing between 275 and 350 g were used.

MEASUREMENTS AND MAIN RESULTS

Thirty or more min ischaemia significantly (p less than 0.05) reduced the density of competent capillaries in the subendocardial third of the myocardium, as did 45 or more min in the subepicardial third and 60 min in the middle third. Following 60 min ischaemia virtually all vessels in the subendocardial third were not perfusable. Severely ischaemic myocardium showed relatively normal, open, unobstructed capillaries and an absence of the endothelial, myocyte and mitochondrial swelling which have previously been attributed to ischaemia.

CONCLUSIONS

In severely ischaemic myocardium microvascular incompetence shows a transmural gradient in severity. It develops progressively, starting near the endocardium. These findings suggest that postischaemic reoxygenation may accelerate the development of microvascular incompetence.

Oxygen content of the fixative is important in the interpretation of the ultrastructure of ischaemic myocardium

Isolated rat hearts were subjected to 15, 45, or 60 minutes of global ischaemia and then fixed by perfusion at 37 degrees C with glutaraldehyde containing various amounts of oxygen. This either had been bubbled with 100% oxygen (PO2 620 mm Hg) or with 100% nitrogen (PO2 40 mm Hg) immediately before use, or it had been routinely prepared and stored exposed to atmospheric oxygen (PO2 245 mm Hg). The ultrastructure of myocytes and endothelial cells subjected to 15 minutes of ischaemia was not affected by the treatment of the fixative. However, when the tissue subjected to longer periods of ischaemia was fixed with routinely prepared or oxygen-bubbled glutaraldehyde, ultrastructural changes characteristic of reoxygenation damage were uniformly evident in both the microvasculature and myocytes. These qualitatively distinct changes included mitochondrial swelling, cell swelling, endothelial bleb formation, and narrowing of capillary lumina. These abnormalities were not observed in tissue fixed with nitrogen-bubbled glutaraldehyde. These findings indicate that deliberate steps should be taken to reduce or eliminate dissolved oxygen from the fixatives used to study ischaemic tissues. Otherwise artefactual reoxygenation damage in vitro may occur and make valid ultrastructural interpretation difficult or impossible.

Tumor-dependent increased plasma nitrate concentrations as an indication of the antitumor effect of flavone-8-acetic acid and analogues in mice

The antitumor agent flavone-8-acetic acid (FAA) is remarkable because it induces hemorrhagic necrosis, altered tumor blood flow, and cytokine synthesis. We show here that FAA and structurally related analogues increase plasma nitrite plus nitrate (NO2-/NO3-) levels in mice. Dose-dependent increases in plasma NO2-/NO3- concentrations, which reached maximum levels at 12 h, were found following administration of FAA. Furthermore, the presence of a palpable s.c. Colon 38 tumor significantly enhanced the response. Tumor-dependent increases were also observed with the active FAA analogues xanthenone-4-acetic acid, 5-methyl XAA, and 5,6-dimethyl XAA, while the inactive analogue 8-methyl XAA failed to increase plasma NO2-/NO3- concentrations substantially above basal levels. Increased plasma NO2-/NO3- levels were also observed in response to endotoxin (100 micrograms/mouse) and to recombinant human tumor necrosis factor alpha (4 to 16 micrograms/mouse). NO2-/NO3- levels may signify nitric oxide production as a result of stimulation of the L-arginine-dependent pathway in activated macrophages. The tumor dependence of the response may reflect the immunological stimulus imposed by tumor implantation. A clear relationship was found between increased plasma NO2-/NO3- levels and tumor growth delays induced by FAA and xanthenone-4-acetic acid analogues. It is suggested that nitric oxide may contribute to tumor cell death by two mechanisms, alteration of blood flow contributing to tumor ischemia and direct tumor cell killing. Plasma NO2-/NO3- concentrations may be a sensitive indication of the antitumor response to this class of compounds.

Necrosis in non-tumour tissues caused by flavone acetic acid and 5,6-dimethyl xanthenone acetic acid

Images

Relation of Helicobacter pylori to the human gastric mucosa in chronic gastritis of the antrum

The spatial relations between bacteria and the affected tissues can indicate pathogenic mechanisms. This study was undertaken to define the spatial relation of Helicobacter pylori to the human gastric mucosa. Antibodies against gastric mucus and ruthenium red were used to stabilise the glycoprotein structure of the mucus and glycocalyces in antral biopsy specimens from eight patients infected with H pylori. The location of organisms and ultrastructural features were assessed using systematic scanning and transmission electron microscopy: 92 (2)% (mean (SE] of H pylori were in the pit mucus, and 7 (3)% were in the surface mucus; 60 (12)% of H pylori were close to epithelial cells, with only 5 (2)% located near the epithelial intercellular junctions. Fine filamentous strands extended between organisms and nearby epithelial cells, with few organisms in membrane to membrane contact. H pylori were not observed between, beneath, or within cells of the gastric mucosa. The preferred location of H pylori in the gastric antrum is within the pit mucus close to the epithelial cell surface, with no evidence that they have a direct toxic effect on the mucosa.

The use of vascularised spheroids to investigate the action of flavone acetic acid on tumour blood vessels

EMT6 multicellular spheroids were introduced into the peritoneal cavities of mice and allowed to become vascularised, resulting in solid spherical tumours. The necrotic cores of the initially avascular spheroids were replaced by vascularised tumour tissue but the outer zones of the spheroids failed to become vascularised. The presence of both vascular and avascular components in each spheroid allowed the role of the vasculature in the antitumour action of flavone acetic acid (FAA) to be determined. Eighteen hours after treatment with FAA 0.8 mmol kg-1, the vascularised core became necrotic and haemorrhagic, while the outer avascular zone remained viable. Tumour cells which were infiltrating superficial sub-mesothelial fat did not become necrotic despite the presence of numerous thrombi in associated vessels. Injection of two fluorescent vascular markers, the first (Hoechst 33342) together with FAA, and the second (10-nonyl acridine orange) 4 h later, demonstrated that there is a marked loss of blood flow in the spheroids. These results provide further evidence that FAA kills blood vessel-dependent tumour cells by interrupting the tumour blood supply.

Sulphinpyrazone reduces endocardial injury and mural thrombosis

STUDY OBJECTIVE

The aim of the study was to investigate the effectiveness of sulphinpyrazone, a drug which stabilises endothelial cell membranes, in reducing endocardial injury and mural thrombosis produced by lactic acid in the left ventricle.

DESIGN

The left ventricular endocardium of isolated beating rat hearts, perfused via the aorta with oxygenated Krebs-Henseleit buffer, was exposed for up to 4 h to additional lactic acid (pH 6.4), with and without sulphinpyrazone (100 ng x ml-1). After flushing with buffer, passage of 10 ml blood, and further flushing, the hearts were fixed by coronary perfusion and the endocardium examined by scanning electron microscopy.

EXPERIMENTAL MATERIAL

Hearts from 48 male albino Wistar rats, weight 270-380 g, were used.

MAIN RESULTS

Morphometric analysis of the surface of the papillary muscles showed that lactic acid caused membrane injury in endothelial cells, up to 30% of which exfoliated. However when sulphinpyrazone was present, endothelial cell damage was reduced and there was up to 75% reduction in the area of exposed basal lamina or connective tissue. This was associated with a corresponding reduction in the extent of platelet adhesion (79%) and thrombus formation (94%).

CONCLUSIONS

The results show that sulphinpyrazone has the potential to reduce the risk of mural thrombosis following endocardial injury.

L-aspartate improves the functional recovery of explanted hearts stored in St. Thomas' Hospital cardioplegic solution at 4 degrees C

Explanted rat hearts were subjected to cardioplegic arrest by 3 minutes' perfusion with oxygenated St. Thomas' Hospital solution no. 2 and then were stored by immersion in the same solution at 4 degrees C. Prearrest and postischemic left ventricular functions were compared by means of an isolated working heart apparatus. Hearts (n = 8 per group) arrested and stored for up to 8 hours all resumed the spontaneous rhythm of contraction during reperfusion for 30 minutes at 37 degrees C. There was good recovery of aortic flow rate (105% +/- 3%) against a pressure of 100 cm H2O, of heart rate (102% +/- 2%), and of aortic pressure (86% +/- 5% of prearrest values). Hearts stored for 10 and 20 hours showed poor or no postischemic recovery of cardiac pump function (aortic flow, 16% +/- 11% and 0%, respectively). Enrichment of St. Thomas' Hospital solution with L-glutamate (20 mmol/L) also failed to improve functional recovery of hearts subjected to 10 hours of storage, but hearts treated with St. Thomas' Hospital solution containing L-aspartate (20 mmol/L) or L-aspartate plus L-glutamate (20 mmol/L each) reestablished aortic flow rates of 99% +/- 5% and 93% +/- 4%, respectively. These results indicate that the addition of L-aspartate to St. Thomas' Hospital solution improves the functional recovery and extends the safe preservation of explanted hearts stored at 4 degrees C.

The nature and progression of injury in the organ of Corti during ischemia

This study has defined the nature and sequence of ultrastructural changes in the organ of Corti following severe, total cochlear ischemia. Afferent nerve endings of IHC became swollen within 15 min and eventually ruptured. Outer hair cells were swollen within 30 min and showed alterations to mitochondria, endoplasmic reticulum and the nucleus whereas IHC remained unchanged for up to 60 min. Both efferent and afferent nerve endings of OHC were unaltered until after 60 min ischemia. Regardless of the type, cells in the base of the cochlea developed abnormalities more rapidly than those in the apical turns. These results imply a differential susceptibility to ischemic damage both among the different cell types and along the organ of Corti.

Early follow-up of patients with the Medtronic Intact porcine valve. A new cardiac bioprosthesis

A new-generation porcine valve fixed in glutaraldehyde at zero pressure and mounted on an acetal copolymer flexible stent was inserted in 97 patients between August 1983 and October 1986. The mean age of the patients was 51 years (range 10 to 76) and eight were under the age of 20 years. There were 57 mitral, 33 aortic, and 10 tricuspid valve replacements. Concomitant coronary artery bypass grafting was performed in 9% of patients, 40% underwent multiple valve operations, and in 40% the procedure was a reoperation. Mean follow-up was 26 months (range 12 to 49) and was 99% complete. There were no examples of primary tissue failure, and only to reoperations have been undertaken for infective endocarditis alone. The early mortality rate was 8.2% and the late mortality rate, 12.1%. Four late deaths were valve related (two caused by infective endocarditis and two by embolism). The actuarial 3-year survival rate was 70%, freedom from infective endocarditis 879%, freedom from embolism 87%, freedom from reoperation 90%, and freedom from valve-related complications 77%. All but three surviving patients were in New York Heart Association class I or II. Doppler echocardiography, performed in 62 of 76 survivors, showed thin and mobile leaflets in all patients and trivial or mild regurgitation in four (6%). The mean gradient across the Medtronic Intact valves (Medtronic Blood Systems Inc., Minneapolis, Minn.) in the aortic position was 17 +/- 5.2 mm Hg, in the mitral position 3.8 +/- 1.33 mm Hg, and in the tricuspid position 4.1 +/- 1.14 mm Hg. We conclude that early results with the Intact valve are encouraging.

Uneven host tissue ongrowth and tissue detachment in stent mounted heart valve allografts and xenografts

Following explanation from the mitral position because of primary tissue failure, 30 human antibiotic sterilised stent mounted aortic valve allografts and 28 glutaraldehyde treated porcine xenografts were examined for evidence of tissue detachment from the stents. These grafts had been in situ for 34 to 166 months. Graft detachment had occurred from one or two stent posts with displacement of the commissures and central valvular incompetence in 12 (67%) of 18 allografts supported on rigid stainless steel stents, in six (50%) of 12 allografts mounted on flexible acetal copolymer stents, but in only one (4%) of 28 xenografts mounted on polypropylene stents. In regions of detachment the aortic remnant of the graft was infiltrated by components of blood and phagocytic cells which had removed not only fibrin but also graft tissue. Detachment did not occur from stent posts where the graft margin had become coated by collagenous host tissue. This intimal fibrous sheath appeared not only to strengthen the attachment of the graft but also to limit the entry of fibrin and phagocytes into the graft tissue.

Blood flow failure as a major determinant in the antitumor action of flavone acetic acid

Some investigators have suggested that the marked activity of flavone acetic acid (FAA) against advanced solid tumors in mice results from an indirect effect. This study indicates that the critical effect of FAA is irreversible inhibition of tumor blood flow. Perfusion of sc Colon 38 tumors, assessed with H33342 as a fluorescent stain for functional blood vessels, was reduced to 50% of controls within 3 hours of an ip injection of 1.2 mmol of FAA/kg and was completely inhibited by 24 hours. A double-label fluorescence technique demonstrated a significant decrease in blood flow in both sc Colon 38 and im EMT-6/Ak tumors as early as 15 minutes after iv treatment with 1.2 mmol of FAA/kg, with progressively enlarging zones of perfusion failure. The rate of cell death in totally ischemic EMT-6 tumors was shown to be sufficiently rapid to represent a major component of the observed antitumor effect of FAA if the flavonoid acts via inhibition of blood flow. Further, avascular EMT-6/Ak multicellular spheroids growing in the mouse peritoneum are relatively resistant to killing by FAA administered iv or ip, despite extensive infiltration with host immune cells. These results indicate that inhibition of tumor blood flow by FAA is a necessary component of its antitumor activity against solid tumors.

The intima of human coronary arteries

Intimal thickness relative to that of the media (r) was measured in coronary and internal mammary arteries from 300 human subjects. Whereas this ratio remained low (less than 0.17) in the mammary arteries, coronary arteries showed progressive intimal thickening (r = 4.10 by 60 years). The intimal surfaces of 70 pairs of arteries were compared by light, transmission, and scanning electron microscopy. The mammary arteries had a continuous endothelial lining, but the coronary arteries showed incomplete coverage of the thickened intima. In affected vessels the endothelial cells showed loss of attachment to adjacent cells and to the underlying tissue. It was concluded that the progressive intimal thickening of the human coronary artery, which develops early in life and is associated with defects in the internal elastic lamina, is also associated with endothelial cell separation and detachment, with the formation of denuded areas on the intimal surface.

Endocardial injury and the pathogenesis of mural thrombosis in the left ventricle

To define the interactions between blood and endocardium damaged by lactic acid, the left ventricles of 48 isolated continuously perfused and beating hearts were exposed for 0-4 hours to Krebs Henseleit buffer (KHB) with or without 33 mumol.ml-1 of lactic acid (pH 6.4). After excising its apex, the left ventricle was flushed with KHB, followed by 10 ml of lightly heparinised blood, and then by a further 10 ml of KHB. Lactic acid caused endothelial cell membrane rupture, intercellular separation, and exfoliation with exposure of the basal lamina and underlying connective tissue. Whereas multilayered platelet aggregations formed on exposed basal lamina, fibrin deposition and incorporation of blood cells were only observed in the larger thrombi which formed on exposed collagen. These findings indicate that a metabolite which accumulates in ischaemic myocardium can cause endocardial injury which would predispose to the mural thrombosis which can complicate myocardial infarction.

Endocardial damage induced by lactate, lowered pH and lactic acid in non-ischemic beating hearts

The left ventricular lumen of isolated perfused beating hearts was perfused for up to 8 h with either Krebs Henseleit buffer (KHB, pH 7.4), KHB including 33 mumol/ml of lactic acid at pH 7.4 or 6.4, or with KHB including hydrochloric acid to reduce the pH to 6.4. Scanning and transmission electron microscopy showed that whereas control hearts maintained an intact endocardium, those groups exposed to increased concentrations of lactate, hydrogen ions or both, developed endothelial cell separation and exfoliation with exposure first of basal lamina and then of endocardial collagen. The underlying myocytes also showed evidence of irreversible cell injury. The extent and severity of damage was greater in hearts exposed to lactic acid than to either lactate or lowered pH alone. These findings suggest that the increased concentrations of metabolites which accumulate in developing myocardial infarcts can diffuse through and damage the endocardium in ways which are likely to predispose in vivo to the development of mural thrombosis.

Differences between heart valve allografts and xenografts in the incidence and initiation of dystrophic calcification

Following surgical removal because of primary tissue failure, 30 antibiotic-sterilized human aortic valve allografts and 27 glutaraldehyde-treated porcine aortic valve xenografts were examined for macroscopic and microscopic evidence of dystrophic calcification. These grafts had been mounted on stents and used for from 34 to 166 months to replace diseased mitral valves. After explantation the grafts were carefully examined then prepared for light microscopy, for transmission electron microscopy and for energy dispersive X-ray microanalysis. Gross calcification occurred significantly (p = 0.002) more frequently in xenografts (89%), and was more extensive than in allografts (53%). Calcification usually appeared as nodular excrescences on the cusps, although occasionally it formed plates within them. This reduced tissue pliability and was usually associated with either valvular stenosis or regurgitation. The calcified deposits contained calcium and phosphate in ratios approaching those of hydroxyapatite. In xenograft valves the smallest discrete deposits of calcification were spherical and usually associated with membranous debris of porcine donor fibroblasts, but allografts did not contain donor cell remnants and early calcification was linearly arranged along collagen fibres.

The transmural progression of the no-reflow phenomenon in globally ischemic hearts

A no-reflow phenomenon (NRP) develops in hearts subjected to global ischemia and prevents reperfusion of the subendocardial myocardium upon restoration of arterial supply. In the present study the transmural progression of the NRP across the left ventricular wall in globally ischemic rat hearts was quantitatively defined by using autoradiographic nuclear track emulsion (NTE) as an indicator of microvascular competence. Rat hearts were isolated and perfused for 10 min with oxygenated Krebs-Henseleit buffer, then were made completely globally ischemic for from 0 to 60 min and were maintained at 37 degrees C. They were then fixed by perfusion with glutaraldehyde after which NTE was injected into the coronary arteries. Transverse sections through the left ventricles were examined by scanning electron microscopy using back-scattered electron imaging and the vessels in a standard transmural contiguous series of photomicrographs were classified according to whether they did or did not permit the flow of NTE. Non-ischemic control myocardium showed a mean proportion of filled vessels of 99.4 +/- 0.5% SD, and those subjected to 15 min of ischemia showed only a slight overall reduction. After 30 min of ischemia 96 +/- 3% of vessels in the subepicardial third could be reperfused, but the proportion progressively diminished across the myocardium to total no-reflow near the endocardium. From 45-60 min of ischemia the totally non-reperfusible region remained confined to the subendocardial third but there was a significant reduction in the proportion of reperfusible vessels in the subepicardial third to 40% +/- 27%. Ischemia thus progressively reduces the capacity of myocardium to be reperfused.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of glutamic acid on cardiac function and energy metabolism of rat heart during ischaemia and reperfusion

The effects of exogenous glutamate (20 mM) on myocardial energy metabolism and cardiac function during low-flow ischaemia and subsequent reperfusion were studied in isolated working rat hearts. Hearts were made severely ischaemic for 60 min by reducing the perfusion rate to 0.17 ml/min, and then reperfused for 30 min. Low-flow ischaemia resulted in a 50% reduction of myocardial ATP, a 70% reduction of both creatine phosphate (CP) and GTP, and a 250% rise in AMP. After reperfusion, CP was restored to normal levels but ATP and GTP remained significantly low. All hearts failed completely to recover cardiac pump function. The addition of glutamate to the perfusate during low-flow ischaemia had no significant effect on myocardial high-energy phosphates (HEP) but slightly increased succinate production. Subsequent reperfusion without added glutamate resulted in the recovery of 62% of pre-ischaemic aortic flow rate, as well as restoration of myocardial ATP and GTP to 70% of their control values and of creatine phosphate to supranormal levels. Reperfusion with added glutamate did not raise HEP levels any further but did increase recovery of cardiac function to 92% or more of pre-ischaemic values. Thus, by mechanism(s) which are not yet clear but which may include an increase in HEP via anaerobic succinate production, elevated levels of exogenous glutamate exert a highly beneficial effect on the post-ischaemic recovery of cardiac function.

Strategies for research: active or passive

This paper provides an introduction to a symposium on challenges for medical research held to mark the golden jubilee of the Medical Research Council of New Zealand. It provides some historical, international and national perspectives for the papers which follow and discusses the interrelationships which exist between society, health care and medical research and also between medical research workers, the institutions in which they work and the agencies which provide funds for research. The point is made that in basic research, where the final applications of the new knowledge cannot be predicted, the initiative and direction may equally well be determined by the investigators or by the institutions which support them. It is considered that the research funding agencies, however, have a major responsibility to actively encourage research in fields where specific needs for improved health care can be defined or predicted.

The intestinal and diffuse types of gastric carcinoma in Maori and non-Maori patients in Auckland

Histologic specimens of gastric carcinoma from 128 Maori, Pacific Island Polynesian, and European patients in Auckland, New Zealand, were classified into intestinal or diffuse type. The ratio of intestinal to diffuse type (ID) was lowest (0.3) in the female Maori patients and highest (1.4) in the male Maori. The higher ID ratio reflects the increased risk of gastric carcinoma in the Maori men as compared with the other groups studied.

Transmural differences in the postischemic recovery of cardiac energy metabolism

After 25 minutes of ischemia, in the isolated rat preparation, hearts fail to reestablish adequate contractile function. To determine whether this failure was associated with a transmural variation in the metabolic response of myocardial cells to reperfusion, the authors subjected hearts to 25 minutes of global ischemia with and without 5 or 20 minutes of reperfusion. After freeze-drying the left ventricular myocardium was divided into subepicardial (EPI) and subendocardial (ENDO) regions before estimating the lactate, total adenine pool metabolites, and creatine phosphate (CP) and phosphate concentrations in each region. Other groups of hearts were perfusion-fixed with glutaraldehyde then injected with nuclear track emulsion to demonstrate that a high proportion of capillaries in both the subendocardial (89%) and subepicardial (95%) myocardium transmitted perfusate after 5 minutes of reperfusion. Reperfusion removed lactate equally from each region. Thus the differences in the capacity of reperfusion of these regions to recover CP (ENDO, 100%; EPI, 168% of preischemic values), to elevate adenosine triphosphate (ATP) (ENDO, 32%; EPI, 63%), or to retain adenosine monophosphate (AMP) (ENDO, 625%; EPI, 277%) were unlikely to be due to regional differences in microvascular function. Despite the better preservation of both structure and metabolism in the subepicardium, there was, during reperfusion, a progressive loss of purine precursors from cells in both regions of the myocardium. These results suggest that the loss of ability of the myocardium to recover significant function after relatively short periods of ischemia is due to their inability, on reperfusion, to synthesise sufficient ATP from the available precursors. This capacity for resynthesis of ATP is lost more rapidly in the subendocardial than in the subepicardial myocardium.

Mechanism of resistance of noncycling mammalian cells to 4'-(9-acridinylamino)methanesulfon-m-anisidide: comparison of uptake, metabolism, and DNA breakage in log- and plateau-phase Chinese hamster fibroblast cell cultures

Resistance of noncycling cells to amsacrine (m-AMSA) has been widely reported and may limit the activity of this drug against solid tumors. The biochemical mechanism(s) for this resistance have been investigated using spontaneously transformed Chinese hamster fibroblasts (AA8 cells, a subline of Chinese hamster ovary-cells) in log- and plateau-phase spinner cultures. In early plateau phase most cells entered a growth-arrested state with a G1-G0 DNA content and showed a marked decrease in sensitivity to cytotoxicity induced by a 1-h exposure to m-AMSA or to its solid tumor-active analogue, CI-921. Studies with radiolabeled m-AMSA established that similar levels of drug were accumulated by log- and plateau-phase cells and that there was no significant drug metabolism in either of these cultures after 1 h. However, marked differences in sensitivity to m-AMSA-induced DNA breakage were observed using a fluorescence assay for DNA unwinding (Kanter P.M., and Schwartz, H.S., Mol. Pharmacol., 22: 145-151, 1982). Changes in sensitivity to DNA breakage occurred in parallel with changes in sensitivity to m-AMSA-induced cell killing. DNA breaks disappeared rapidly after drug removal (half-time approximately 4 min), suggesting that these lesions were probably mediated by DNA topoisomerase II. Resistance to m-AMSA may therefore be associated with changes in topoisomerase II activity in noncycling cells.

Back-scattered electron imaging of sections through the cochlea: a new technique for studying cochlear morphology

A new technique for studying the morphology of the cochlea is described. The development of back-scattered electron (BSE) detectors has allowed the examination of heavy-metal stained tissues by scanning electron microscopy. Comparison with light microscopy on adjacent resin sections through whole decalcified cochleae demonstrated that the back-scattered electron technique provides equal or superior clarity and resolution throughout the light microscope range of magnification, allows identification of lysosomes, mitochondria and endoplasmic reticulum, and extends useful magnification into the range previously associated only with transmission electron microscopy. Back-scattered electron imaging enables the study of sections of the undissected cochlea at high magnifications and resolution.

Preservation of mucus in situ in rat colon

Mucus, a hydrated complex consisting mainly of glycoproteins, forms a layer over the epithelial surface of the gastrointestinal tract. The usual preparative procedures for histological and scanning electron microscopic examination of the gut result in the loss or distortion of this mucus layer. Careful evaluation of two new methods reported to stabilize the mucus layer showed that acrolein vapor did not provide adequate fixation, but application of heat-inactivated antiserum raised in rabbits against rat colon mucus reliably preserved a continuous layer closely adherent to the epithelium. This stabilized layer is continuous with the mucus in the colonic crypts.