Thomas M. Glenn

Role of Lysosomes in the Pathogenesis of Splanchnic Ischemia Shock in Cats

Splanchnic arterial occlusion (SAO) for 2 hours followed by release of the occlusion in cats produced a lethal shock state characterized by cardiovascular collapse. Release of the occlusion resulted in a 45% fall in mean arterial blood pressure within 15 minutes; postrelease survival of these animals was 46 minutes. The plasma of cats with SAO shock exhibited a 3- to 4-fold increase in activities of the lysosomal enzymes β-glucuronidase and cathepsin, accompanied by accumulation of a myocardial depressant factor. Plasma from cats treated with methylprednisolone (20 mg/kg) prior to occlusion did not have significant levels of myocardial depressant factor nor significant increases in plasma lysosomal enzyme activity. Furthermore, the fall in mean arterial blood pressure in steroid-treated animals was significantly smaller when the occlusion was released and postrelease survival time was significantly longer. Pancreatic lysosomes from cats with SAO exhibited a marked increase in fragility as indicated by a reduction in total lysosomal enzyme activity and an increase in the percent of free enzyme activity, compared to lysosomes from cats with sham SAO or steroid-treated cats. These data indicate that the biochemical and hemodynamic alterations present in SAO-induced shock may be related to the disruption of pancreatic lysosomes and that glucocorticoids can markedly alter the course of this shock, possibly by decreasing the sensitivity of pancreatic lysosomes to splanchnic ischemia.

Significance of Splanchnic Proteases in the Production of a Toxic Factor in Hemorrhagic Shock

The pathogenesis of circulatory shock has been previously associated with the plasma accumulation of a myocardial depressant factor (MDF). The plasma accumulation of MDF in cats subjected to hemorrhagic shock was associated with marked increases (P <0.01) in activities of plasma cathepsins A-B. The pH optima for three of the five cathepsins were in the range of 4.8−5.2, a pH range close to that found intracellularly during shock. Moreover, pancreatic and hepatic tissue from these cats exhibited significant decreases in total specific activities for these enzymes, compared with minimal changes in heart, duodenum and spleen. Decreases in total pancreatic cathepsin activities were associated with marked ultrastructural changes in pancreatic acinar cells primarily characterized by vacuolization of the lysosomes. Incubation of homogenates of splanchnic viscera of unshocked dogs revealed that significant concentrations of MDF were produced only in incubated pancreatic homogenates. Infusion of MDF in amounts half that produced by a cat pancreas into intact anesthetized cats yielded a significant circulatory depression indicated by a progressive decline in cardiac output and mean arterial blood pressure and a 54% decrease in cardiac work performance within 60 minutes. These data indicate that substantial amounts of lysosomal proteases are released during shock and that they operate in a suitable pH range to account for the production of quantities of MDF that are sufficient to induce a marked degree of cardiac depression.

Mechanism of the protective effects of prostaglandins E1 and F2α in canine endotoxin shock

Abstract Prostaglandins E 1 (PGE 1 ) and F 2α (PGF 2α ) were studied for their ability to alter the course of a standardized endotoxin shock procedure in dogs. 3 hr after the administration of E. coli endotoxin, mean arterial blood pressure (MABP) was reduced 44% and cardiac output (CO) 60%. At this time plasma activities of the lysosomal protease, cathepsin D, increased 670%, and of a myocardial depressant factor (MDF), 310%. Dogs treated with PGF 2α had consistently higher MABP and CO, while plasma cathepsin D and MDF activities were moderately elevated. In addition, post-endotoxin survival was significantly improved. PGE 1 -treated dogs exhibited a higher MABP and CO, while plasma cathepsin D and MDF activities were only slighly elevated, and survival time increased ( p 1 , but not PGF 2α markedly reduced the rate of release of proteases from isolated hepatic and pancreatic lysosomes subjected to thermal activation. An enhanced release of splanchnic proteases appears to lead to the formation of MDF, a peptide involved in the pathophysiology of endotoxin shock. Prostaglandin E 1 may protect in endotoxin shock by suppressing the release of lysosomal proteases and the subsequent formation of MDF, whereas PGF 2α may protect either by circulatory support or by some secondary mechanism for preventing the release of lysosomal enzymes.

Role of the Pancreas in the Pathogenesis of Circulatory Shock

Several toxic factors have been proposed as mediators of irreversibility in circulatory shock (6, 17, 29, 48, 57). Most, however, have not been enthusiastically received because their participation in the pathophysiology of the shock state remains unsupported by convincing evidence and no factor has been isolated. Recently, a myocardial depressant factor (MDF) has been isolated from the plasma of both experimental animals (30) and man (42) in a variety of shock states, including hemorrhagic (9, 32, 54), endotoxic (55), cardiogenic (23), bowel ischemic (20, 37), burn (2), and pancreatitis (35) shock.

Anti-toxic action of methylprednisolone in hemorrhagic shock☆

Abstract The potential beneficial effects of the synthetic glucocorticoid, methylprednisolone, in shock were assessed in cats subjected to hemorrhagic shock. A threefold increase in survival time was obtained using methylprednisolone (20 mg/kg) which correlated with low plasma levels of a myocardial depressant factor (MDF) and of the lysosomal enzymes, β-glucuronidase and plasma cathepsin-like activity (PCLA). These data suggest that methylprednisolone exerts a protective effect in hemorrhagic shock by preventing the release of lysosomal enzymes which may be responsible for the formation of MDF, a peptide implicated in the reduction of myocardial contractility during postoligemic shock.

Mechanism of the lack of a beneficial response to inotropic drugs in hemorrhagic shock.

Lanatoside C, glucagon, and isoproterenol, three inotropic agents were found to be ineffective in prolonging survival or in improving the over‐all circulatory status of dogs in hemorrhagic shock, despite their temporary effectiveness as inotropic agents. Lanatoside C constricted the splanchnic circulation leading to lysosomal disruption, release of cathepsin D, and production of a myocardial depressant factor (MDF). Glucagon dilated the splanchnic circulation only transiently but directly disrupted splanchnic lysosomes and thus MDF was produced. Isoproterenol dilated the peripheral vasculature to such an extent that circulatory collapse ensued. Other inotropic agents may be of value in the treatment of postoligemic shock, but potentially deleterious side effects must be considered when they are administered in circulatory shock.

Cardiovascular and lysosomal actions of corticosteroids in the intact dog.

Summary Aldosterone, deoxycorticosterone acetate (DOCA), Cortisol, and methylprednisolone were studied in the vagotomized, baroreceptor denervated dog for hemodynamic actions and lysosomal stabilizing activity in the pancreas. Only aldosterone (0.001 to 0.01 mg/kg) exerted a significant positive inotropic effect. None of the other corticosteroids in doses up to 1 to 40 mg/kg had any detectable effect on mean arterial blood pressure, aortic flow, central venous pressure, or heart rate. Furthermore, the two glucocorticoids (Cortisol and methylprednisolone) significantly stabilized the pancreatic lysosomes both in vivo and in vitro, as determined by the release of β-glucuronidase; whereas neither aldosterone nor DOCA exerted a protective effect on the lysosomal preparations.

The Lysosomal Protease — Myocardial Depressant Factor System in Circulatory Shock

Circulatory shock is characterized by severe perturbations in the homeostatic regulation of cardiovascular function leading to conditions which are incompatible with life. The nature of these perturbations is not clearly understood, nor are the origins of the positive feedback loops generated by these disturbances. Despite the obvious gaps in our knowledge, certain findings have been uncovered in recent years which, in the light of new information, point to a final common pathway in the pathogenesis of circulatory shock. These findings are: 1. a marked reduction in blood flow to the splanchnic viscera very early in circulatory shock of varying etiologies (1) 2. a marked alteration in lysosomal membranes with the attendant release of lysosomal hydrolases into the plasma during many forms of shock (2) 3. a profound impairment of myocardial performance late in circulatory shock (3,4)

Functional characteristics and lysosomal integrity of the isolated perfused cat pancreas

Abstract The isolated cat pancreas perfused with a physiological salt solution plus low molecular-weight dextran functions satisfactorally for at least 2 1 2 hours. Evidence for stability and functional integrity of the preparation included measurements of vascular resistance, arterial and venous pH, PO2, and PCO2, pancreatic juice volumes and trypsin concentrations, and studies of acinar cell ultrastructure. Total specific β-glucuronidase activity of the unstimulated perfused pancreas was comparable to that seen in the intact cat pancreas. However, pancreozymin and secretin decreased the total β-glucuronidase activity of the perfused pancreas. Pancreozymin also increased the release of β-glucuronidase from lysosomal suspensions of liver and pancreas. β-Glucuronidase activity rose in the pancreatic juice, duodenal secretion, perfusate, and the bathing medium of the hormonally stimulated perfused pancreas concomitant with a decreased number of zymogen granules and lysosomes in the acinar cells. The data are consistent with the hypothesis that pancreozymin increases the fragility of pancreatic lysosomes liberating β-glucuronidase into the pancreatic duct, extracellular space, and intravascular compartment. Lysosomal enzymes released into the duct may have an auxiliary digestive function in the duodenum, and the increased extracellular lysosomal enzyme activity may play a role in the pathophysiology of pancreatitis or other pancreatic disease states in which the pancreatic lysosomes become compromised.