J.F. Tomera

Neuromuscular dysfunction in burns and its relationship to burn size, hypermetabolism, and immunosuppression.

The etiology of neuromuscular (NM) dysfunction following burn injury has not been characterized. NM deficits, together with hypermetabolism and immunosuppression, are debilitating processes which play a key role in the morbidity and mortality of burned patients. This study examined the usefulness of the murine model to replicate clinically observed NM dysfunction. Systemic effects of graded increases in burn size were studied in the acute phase (3 weeks) of burn trauma. Metabolic rates, immune response to dinitrofluorobenzene (DNFB), maximum tension developed by gastrocnemius muscle, and the response of its NM junction to d-tubocurarine (dTc) were the parameters analyzed. Groups of male CF1 mice were given a 20%, 30%, and 50% total body surface area burn and compared to controls. By Day 21 postburn, all the burn groups showed elevated metabolic rates and immunosuppression to the inflammatory antigen DNFB. NM dysfunction evidenced as a significant depression of maximal tension development was observed in the 30% and 50% groups. A threefold increase in the effective dose (ED95) values of dTc was seen only in the 50% burn group. No NM junctional changes were seen in the 20% burn group. These findings are consistent with clinical observations. We conclude that the mouse is a useful model for evaluating NM dysfunction of burns.

Multiple linear regression analysis of blood pressure, hypertrophy, calcium and cadmium in hypertensive and non-hypertensive states.

High blood pressure causes heart disease and remains a major public health issue. This paper expands mathematically and mechanically on environmental heavy metal exposure and heart disease. In rabbits, mean blood pressure was measured by direct puncture of the middle ear artery. Measurements of calcium and cadmium levels were made by flame atomic absorption spectrophotometry in tissue from hypertensive and non-hypertensive rabbits. Relationships between blood pressure, hypertrophy, calcium and cadmium were tested using multiple regression analysis. Multiple linear relationships occurred showing the dependence of high blood pressure on hypertrophy, calcium and cadmium: hypertrophy on calcium, cadmium and high blood pressure; and calcium on cadmium, high blood pressure and hypertrophy. These data provide insight into the mechanism of elevated blood pressure on heavy metal and calcium accumulation, and cardiac hypertrophy.

Mediators of burn-induced neuromuscular changes in mice.

1 Muscle paresis and aberrant pharmacological responses are two important pathophysiological changes that have been observed at the neuromuscular junction following thermal injury. By use of the mouse model of 20%, 30% and 50% total body surface area (BSA) burn, we examined the significance of intracellular mediators, adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) and prostaglandin E2 (PGE2) in perturbing the physiological function of tension development and the pharmacological response to (+)‐tubocurarine (+)‐Tc at day 21 post‐burn. 2 Cyclic AMP levels increased with the size of burn. The relationship between mean cyclic AMP levels and burn size was significant (R2 = 0.96, r = 0.98). Significant (P < 0.05) reductions in tension development (g) were observed for the 30% and 50% BSA burn group compared to controls (30.3 ± 8.3 and 34.1 ± 5.9 vs 59.1 ± 1.0, respectively). Tension alterations were associated with increased cyclic AMP levels; the relationship between increased cyclic AMP levels and tension decrease was significant (R2 = 0.82, r = 0.91). The dose of (+)‐Tc required to inhibit twitch tension increased in proportion to burn size and was statistically significant in the 50% BSA burn group compared to controls (0.3320 ± 0.09 vs 0.1093 ± 0.11 mg kg−1, P < 0.05). The alterations in the effective dose of (+)‐Tc were significantly correlated to increases in cyclic AMP levels (R2 = 0.70, r = 0.83). Although PGE2 levels were elevated in the 30% and 50% burn groups, no relation was seen to either tension or (+)‐Tc doses. 3 These studies, therefore, support the hypothesis that cyclic AMP plays a significant role in physiological and pharmacological responses in skeletal muscle following thermal injury.

Changes in diaphragm polyinositol phosphates caused by a large body surface area burn

Respiratory problems are common among burn patients, and an understanding of the changes that occur in the phosphatidyl inositol signal transducing system (s.t.s.) in diaphragm muscle may identify pharmacological agents that would be useful in the treatment of these patients. This report examines changes that occur in polyinositol phosphates of diaphragm muscle due to the systemic effects of large (> 30 per cent) body surface area (per cent BSA) burns. Burn injury was applied to specific per cent BSA of the dorsal and ventral skin surfaces of mice. At postburn day 21, polyinositol phosphate levels were measured in the diaphragm by the incorporation of myo-[2-3H]inositol with separation of the phosphates by anion-exchange chromatography. All data were analysed using analysis of variance and curve fitting. In the diaphragm, levels of [3H]inositol, inositol-1,4,5 trisphosphate (IP3), inositol-1,4 bisphosphate (I1,4P2) and inositol-1 phosphate (I1P) increased with increasing burn size. Furthermore, a variety of independent relationships existed between the various phosphates in each burn group (i.e. control, 20 per cent and 50 per cent BSA burn). These data indicate that the systemic effects of burn trauma result in changes in the polyinositol phosphate part of the phosphatidyl inositol signal transducing system of diaphragm muscle.

Myocardial [3H]polyinositol phosphates and their response to burn trauma☆

Polyinositol phosphates comprise a portion of the phosphatidyl signal transducing system. The most well known is IP3 which stimulates Ca2+ release from Ca2+ sequestering organelles within cells. In this study, polyinositol phosphate changes in the heart subjected to the systemic effects of burn trauma were examined. The hypothesis was that systemic trauma induced by large body surface area (% BSA) burn may perturb the phosphatidylinositol signal transducing system. At postburn day 21 left ventricular tissues were harvested from mice with varying burn sizes (i.e. 0, 20 and 50 per cent). Levels of the polyinositol phosphates were measured by incorporation of myo-[2-3H]inositol with separation of the phosphates by anion-exchange chromatography. Analysis of variance was used for statistical evaluation. Multivariate relationships between the independent polyinositol forms (inositol, Il,4P2 and I1P) existed for control (r2 = 0.71 and 50 per cent burn groups (r2 = 0.78). Numerous interdependent relationships existed within each of the multivariate tests. These analyses confirm that several independent polyinositol phosphates contribute to changes in the second messenger IP3 in ventricular tissue subjected to the systemic effects of burn trauma. Disruption of the polyinositol phosphates may underlie either the cause, or exacerbation, of heart dysfunction and cellular damage in burn patients.

Formation of gastrocnemius [3H]polyinositol phosphates in response to burn trauma

The purpose of this report was to see if changes in polyinositol phosphates occurred with increasing percentage body surface area (% BSA) burn. Burn injury was applied to predefined areas of the dorsal and ventral skin surface of mice. After a 10-min stimulation period involving muscle twitch, polyinositol phosphate levels at 3 weeks postburn were measured by the incorporation of myo[2-3H]inositol with separation of the phosphates by anion-exchange chromatography. Analysis of variance was used for all statistical evaluations. In gastrocnemius muscle an increase (P < 0.001) occurred for levels of [3H]inositol, inositol-1, phosphate (I1P), and inositol-1,4,5-trisphosphate (I1,4,5P3) for the 50 per cent BSA burn group. However, levels of inositol-1;4,biphosphate (I1,4P2) decreased (P < 0.001). Positive correlations were found between [3H]inositol, I1P and IP3 and 50 per cent BSA burn. A negative correlation between I1,4P2 and percentage BSA burn was found. These data provide evidence that polyinositol phosphate metabolism in skeletal muscle was altered due to large burn size.

Modification of calcium flux of twitch skeletal muscle in mice subjected to 20% body surface area burn.

One systemic effect of burn trauma is skeletal muscle weakness. This is the result of changes in second messenger systems involving calcium (Ca2+). Kinetic analysis of Ca2+ from cellular compartments of skeletal muscle of mice that were subjected to small burn injury (20% body surface area) was performed. Muscles of the burn group showed an increased 45Ca2+ uptake maxima compared with those of time-matched control groups. Also, 45Ca2+ efflux analysis showed a lack of differentiation between electrically stimulated tissues and nonstimulated tissues that was easily observed in time-matched control groups. This lack of differentiation indicated changes in intracellular compartmentation. It can be speculated that burn trauma may have a regulatory role in the excitation-contraction coupling mechanism by altering myoplasmic levels of Ca2+ even before skeletal muscle dysfunction occurs. These findings suggest that agents capable of controlling myoplasmic Ca2+ levels may aid in alleviating chronic skeletal muscle dysfunction in patients with burns.

Multivariate and vectorial analysis of pharmacological signalling: diaphragm inositol 1,4,5-triphosphate under the duress of burn trauma

Aberrant signal transduction processes within the diaphragm contribute to the weakness of this primary muscle involved in respiration. The importance of this report emphasizes how scald burn injury manifests distant systemic effects which impact on respiration. Scald burn injury from hot water is a common type of thermal injury in three specific patient groups: young children, the elderly, and the mentally and physically handicapped. Multivariate and vectorial analyses are presented within this paper with application to the effects of burn trauma on pharmacological signal transduction systems in the diaphragm. Multivariate equations showed the dependence of IP, on three to five independent variables. The independent variables included: burn size, glycerophosphate, and other polyinositols (inositol 1,4 biphosphate (I1,4P2), inositol 1 phosphate (I1P) and inositol). Graphic illustration of the equations used vectorial analysis. The multivariate analysis gives rise to a wider class of contributing factors than those observed using standard univariate relationships. This may be useful clinically in the identification of therapeutic agents for the treatment of respiratory problems in burn patients.

Multiple linear regression analysis of hypertrophy, calcium and cadmium in hypertensive and non-hypertensive states

Heart disease remains a major public health issue. In this study we aimed to achieve a greater mathematical and mechanistic understanding of the relationship between exposure to heavy metals and heart disease. Measurements of calcium and cadmium levels were made by flame atomic absorption spectrophotometry in tissue from hypertensive and non-hypertensive rabbits. Relationships between hypertrophy, calcium and cadmium were tested using multiple regression analysis. Multiple linear relationships occurred that showed the dependence of hypertrophy on calcium and cadmium levels, and of calcium accumulation on cadmium and hypertrophy. These data provide an insight into the mechanisms of heavy metal accumulation and the development of cardiovascular hypertrophy.

Calcium accumulation in experimental hypertension

At present, the significance of calcium accumulation in the aetiology of coronary artery disease (CAD) in humans is not known, except only to exacerbate the condition. In an attempt to understand ionic disturbances in vasculature derived from cardiovascular abnormalities, soft tissues from hypertensive models were examined. The study hypothesis was to see if basic cardiovascular regulatory sites in hypertensive models accumulated greater amounts of Ca2+. Calcium levels were measured by flame atomic absorption spectrophotometry in tissue derived from two types of hypertensive rabbits. Both models of hypertension developed mean arterial pressures of at least 50 mm Hg greater than those of controls over a 5-wk period. Significant increases in calcium levels were found in left ventricle and aorta derived from both hypertensive groups compared with controls. Renal cortex and medulla were not significantly different among any of the groups. These levels corroborate the findings of others which show increased calcium levels in cardiovascular tissues in experimental hypertension in rabbits. Although there have been several studies that have shown the relationship between calcium, hypertension and CAD, this is the first study to look at calcium accumulation rather that the effects of calcium channel blockers. The link between hypertension and calcium accumulation in a number of tissues may be important in the development of CAD and other cardiac dysfunction.