Plasminogen activator (urokinase) causes vascularization of the cornea

The presence of a peripheral zone of (presumed intracellular) plasminogen activator in the normal rabbit cornea has suggested that activator, once released, might regulate the permeability of limbal vessels and angiogenesis, by plasmin-dependent pathways. Plasminogen activator (urokinase [UK]) in rabbit serum albumin (RSA) was injected once (20 microliter, 3.7 CTA U) into the corneal stroma, 2 mm from the limbus. Sprouts arose from the engorged circumlimbal vessels (16 of 20 corneas) beginning on the third day and grew into the cornea over the next several days. Histologically, PMNs were observed in association with growing vessels. Contralateral corneas injected with UK (in RSA) previously inactivated by 99.7% with the specific active site inhibitor, Phe-Ala-Arg-chloromethyl ketone showed minimal vessel engorgement or stromal edema and no vascularization (0 to 20 corneas). Injuries to the so-called (plasminogen activator-containing)"critical zone" of the cornea which elicit neovascularization possibly do so by causing extracellular release of endogenous plasminogen activator. Thus, in addition to initiating the destructive events of ulceration, activator might initiate increases in vessel permeability and also neovascularization, which would result in the eventual arrest of ulceration.

Induction of lymphomas in mice by busulfan and chloramphenicol

Busulfan causes long-lasting defects in the hematopoietic stem cells and in the immune system of mice. We designed studies to determine whether chloramphenicol further damaged the already defective hematopoietic stem cells of mice that were pretreated with busulfan, and we unexpectedly observed that mice given injections of the combination of busulfan and chloramphenicol developed lymphomas in relatively high incidence. The disease is invariably associated with splenomegaly and enlargement of the thymus. Leukocytosis with lymphoblasts in the peripheral blood occurred in some affected mice. The malignant cell is a lymphoblast of thymic origin. Thirteen of 37 mice which received both busulfan and chloramphenicol developed lymphomas. An additional five of the remaining 24 mice without proven lymphoma died and were not autopsied. Twelve of the 13 proven lymphomas developed within 280 days from the start of the experiment. Four of the 35 mice treated with busulfan alone developed lymphomas, and an additional five of the remaining 31 died but were not autopsied. Two of 41 mice treated with only chloramphenicol developed lymphomas. Of the mice treated with either busulfan or chloramphenicol alone that developed lymphomas, all did so more than 280 days from the start of the experiment. None of the control mice developed lymphoma. We conclude that both busulfan and chloramphenicol may induced lymphomas in mice that are not known to develop them spontaneously. The combination of both busulfan and chloramphenicol increased the frequency and accelerated the onset of the disease.

Acute transverse myelitis: incidence and etiologic considerations

There have been few population-based studies of acute transverse myelitis (ATM). Therefore, incidence and population selectivity of this disorder in different regions is not well known. Data on all Jewish patients with ATM throughout Israel were collected for the period 1955 through 1975. Based on 62 patients who satisfied rigid diagnostic criteria, the average annual incidence rate was 1.34 per million population. No significant difference in incidence was noted between European/American-born and Afro/Asian-born populations. There was no significant seasonal or annual fluctuation in frequency. In 37% of the patients, a history of infection prior to ATM was reported, more commonly among younger patients. ATM rarely evolved into multiple sclerosis. More than one-third of the patients with ATM made a good recovery; in another one-third recovery was only fair; 14 patients failed to improve and 3 died. If other population-based studies of ATM were undertaken, comparison with our results might shed further light on the causes of this disorder.

Glucose disposal and gluconeogenesis from alanine in tumor-bearing Fischer 344 rats

For the study of glucose carbon recycling and incorporation of carbon atoms from plasma glucose, [3-3H]glucose and [U-14C]alanine were injected into inbred non-tumor-bearing (NTB) and tumor-bearing (TB) male F344 rats. The glucose and alanine kinetics were determined in relation to antecedent food intake and carcass weight loss. Whereas fed NTB and TB rats appropriately experienced reduced glucose disposal with decreased food intake (0.99 vs. 0.29 mg/min -100 g(-1) compared wtih observations in starved NTB rats), starved TB rats exhibited increased glucose utilization. Both fully fed and cachectic TB groups exhibited increased isotopic carbon recycling compared to the carbon recycling of NTB control groups, whereas starved TB rats did not demonstrate increased recycling compared to the carbon recycling (27% of C-atoms recycled). These findings suggest that alterations of glucose turnover, carbon recycling, and gluconeogenesis in the fed host parallel hypophagia and weight loss, regardless of TB status.

Hydrolysis of rat chylomicron acylglycerols: a kinetic model

A quantitative model describing the kinetics of hydrolysis of rat chylomicron acylglycerols by bovine milk lipoprotein lipase has been developed using data from studies on rat lymph chylomicrons containing doubly labeled acylglycerols. The detailed analysis indicates that, in addition to hydrolysis from tri- to di-, di- to mono-, and monoacylglycerol to glycerol, and apparently direct hydrolysis pathway of tri- to monoacylglycerol is also present. This accounts for the transient accumulation of monoacylglycerol seen in some of the experiments. For most hydrolysis steps, a Michaelis-Menten mechanism adequately describes the rate of hydrolysis as a function of lipoprotein lipase concentration. A higher order, more complex mechanism, however, is necessary for the apparent tri- to monoacylglycerol hydrolysis pathway. A mathematical function that describes the way free fatty acid released can control the rates of hydrolysis, and how the presence of the binding sites for free fatty acid on albumin in the incubation medium can modulate this, in included. The model simultaneously satisfies the kinetics of hydrolysis for tri-, di-, and monoacylglycerol together with the kinetics of the glycerol and fatty acid moieties for a wide range of albumin and lipoprotein lipase concentrations.

Conversational SAAM--an interactive program for kinetic analysis of biological systems

CONSAM is a conventional version of the kinetic modelling program SAAM. Adjoined to the model processing capability of SAAM, CONSAM additionally affords the user creation, inspection, and alteration capabilities in model manipulation, assessment, and development. To achieve this flexibility CONSAM incorporates a text editor, a solution-saving facility, a model image-saving facility and a graphics package. Command syntax and command logic checking together with command argument defaulting help make CONSAM easy to use. The use of CONSAM in modelling a non-linear drug response to a moderately complicated dosing strategy is presented.

Detection of high erythropoietin titers in renal extracts of hypoxic rats

Previous attempts to extract erythropoietin from the kidneys have not been uniformly successful and have yielded only small amounts. Attempts were therefore made to extract erythropoietin from renal extracts prepared from the supernatant obtained after homogenizing kidneys in various liquids and centrifuging at 2300 x g. Detectable amounts of erythropoietin were recovered from kidneys of nonhypoxic male but not female rats. After exposure to hypoxia, the amounts increased to levels greater than 6.0 U/kidney from males after 8 hr of hypoxia. Erythropoietin became detectable in extracts from kidneys obtained from females after 2 hr of hypoxia and rose to levels of 0.54 U/kidney after 4 hr of hypoxia. The amount of plasma trapped in the kidneys at the time of extraction was not sufficient to account for a significant amount of this erythropoietin, and erythropoietin was not detected in extracts made from livers or spleens. Severalfold larger titers of erythropoietin were detected in renal extracts, by a simple extraction procedure, than was the case in previous attempts. The reasons for this difference are discussed.

Influence of nicotinic acid on metabolism of cholesterol and triglycerides in man

The mechanisms for the hypolipidemic action of nicotinic acid were examined in 12 patients with hyperlipidemia. Most patients were studied in the hospital on a metabolic ward. The first month was a control period followed by 1 month on nicotinic acid. During treatment with nicotinic acid, the triglycerides (TG) decreased in total plasma by an average of 52% and in very low density lipoproteins (VLDL) by 36%. Transport rates of VLDL-TG were determined by multicompartmental analysis following injection of [3H]glycerol as a precursor. Nicotinic acid decreased transport (synthesis) of VLDL-TG by an average of 21%. Kinetic modeling of the VLDL-TG data suggested that the TG reduction was due to a decrease in TG content of VLDL and hence a reduction in lipoprotein size more than number. For the whole group, plasma cholesterol fell during nicotinic acid therapy by a mean of 22%. The drug produced no detectable changes in fecal excretions of cholesterol (neutral steroids) or bile acids. However, it induced a small but significant increment in hepatic secretion of biliary cholesterol that might have led to a net loss of cholesterol from the body even though this loss could not be detected by sterol balance. Despite this increase in outputs of biliary cholesterol, there was not a significant increase in molar % cholesterol or in % saturation of gallbladder bile. Therefore, it is doubtful that nicotinic acid enhances the risk for cholesterol gallstones.

Effect of plasma from cyclophosphamide-treated mice on CFU-S in an in vivo culture system

Various studies suggest that humoral substances, capable of stimulating CFU-S proliferation, are released into the plasma in response to depletion of the CFU-S population by cytotoxic substances such as cyclophosphamide. To test this hypothesis, we placed 0.25 ml of a murine marrow cell suspension with an equal volume of plasma from either normal mice or from mice previously injected with 5 mg of cyclophosphamide into cellulose dialysis tubing. These tubes were then incubated in the peritoneal cavity of mice for 1-7 days. The CFU-S content of the tubes was then assayed. The CFu-S content of suspensions in normal mouse plasma declined to one-fourth of the initial value after 7 days, whereas those in plasma from mice that received cyclophosphamide 7 days previously were essentially unchanged in number. These data suggest that 7 days after injection of cyclophosphamide, the plasma contains a factor that either prevents death of CFU-S or stimulates them to proliferate. An alternative explanation is that normal plasma contains an inhibitor of CFU-S growth that is lacking in plasma of cyclophosphamide-treated mice.

Evidence for a role of the plasminogen activator--plasmin system in corneal ulceration

Plasminogen is present in the cornea andcan be activated to plasmin by plasminogen activator. Plasmin is able, in turn, to activate latent collagenase. This system could initiate and perpetuate the collagen degradation of corneal ulceration. This report details evidence for such a system in the cornea. Plasmin has been found to activate latent collagenase from organ cultures of ulcerating rabbit corneas and from fibroblast cultures derived from such corneas. As in the case of activation by trypsin, activation by plasmin results in the conversion of the 40,000 MW latent form to an active species of 23,000 MW. Explants of normal or alkali-burned, ulcerating corneas demonstrated plasminogen-dependent lysis of fibrin clots; frozen sections of such corneas demonstrated that lysis begins in the superficial stroma near the periphery of the cornea. Multiply freeze-thawed ulcerating corneas, but not normal corneas, showed initial lysis, not peripherally but at the ulcer region containing polymorphonuclear leukocytes. The fact that the peripheral lytic pattern existed in corneas that were obtained from eyes prefrozen in liquid nitrogen before excision of the corneas would suggest that plasminogen activator is normally contained in cells in vivo and is not made only in response to tissue injury. There was no correlation between the location of blood vessels or the presence of the corneal endothelium and the plasminogen-dependent lysis. Plasminogen activator from the ulcerating cornea and from fibroblasts was characterized by sodium dodecyl sulfate--gel electrophoresis of its cleavage products of plasminogen. The activator cleaves plasminogen into heavy- and light-chain fragments similar to those produced from plasminogen by urokinase. Plasminogen activator activity was quantitated by a new assay that restricts diffusion of the enzyme to one dimension into a narrow bore tube. The addition of plasminogen daily to cultures of ulcerating corneas resulted in earlier rises of plasminogen activator, collagenase, and collagen degradation fragments in the culture media. Although total plasminogen activator levels were not increased by the addition of plasminogen to culture, levels of both collagenase and solubilized collagen were approximately doubled. It is concluded that the plasminogen activator--plasmin system might play an important role in the destruction of stromal matrix in corneal ulceration.

The metabolism of apolipoprotein B in subjects with hypertriglyceridemia and polydisperse LDL

This research concerns the metabolism of apolipoprotein B (apoB) in hypertriglyceridemic subjects with polydisperse or heterogeneous LDL. Five subjects maintained under constant dietary control had blood samples fractionated into very low density lipoprotein (VLDL), Sf 20, Sf 10, and Sf 4 LDL, and plasma free leucine, and in three subjects VLDL was further fractionated by size. Apo B was isolated, and the masses of the plasma apo B pools were measured for these lipoproteins. Following injection of [3H]leucine as a metabolic tracer the specific activity of apo B in these lipoproteins and of plasma leucine were measured over 7 or 14 days. The kinetic data were examined using multicompartmental analysis and interpreted in terms of our previous model of apo B metabolism (1975. Federation Proc. 24: 2263.). Newly synthesized apo B, secreted as large VLDL, is metabolized by a delipidation chain yielding intermediate density lipoprotein (IDL), consisting of small VLDL and Sf 20 LDL, and eventually forms small, Sf4 LDL. LDL is metabolized in a steplike process from Sf 20 to Sf 10 and Sf 4 LDL. A second major biosynthetic input in apo B enters directly into IDL and 1/4 to 2/3 of newly synthesized apo B enters plasma by this route. Total apo B synthesis in these subjects is 5- to 10-fold greater than reported for normals. The rate of transport of VLDL apo B and IDL is slower than normal with a residence time which is increased about twofold; however, the VLDL apo B pool is enlarged 5- to 10-fold, and thus the quantity of apo B entering and leaving this pool per hour is much greater than in the normal. Two major pathways for apo B catabolism occur. Between 1/3 and 2/3 of apo B is metabolized through LDL, disappearing from plasma as Sf 4 LDL. The remainder of apo B disappears from plasma IDL directly. The four major findings in this kinetic study of apo B metabolism in hypertriglyceridemic subjects with polydisperse LDL are: 1) The marking increase in apo B synthesis; 2) the biosynthetic input of much of this apo B directly into IDL; 3) the large catabolic pathway of apo B which leaves IDL, and 4) the stepwise metabolism of LDL by which Sf 20, Sf 10 and Sf 4 LDL are generated.

Transfer of carbon atoms among circulating glucose, alanine, and lactate in pancreatectomized dogs

The rates of transfer of carbon atoms (mg C . kg body wt-1 . min-1) among plasma glucose, alanine, and lactate have been calculated in pancreatectomized dogs from the tracer concentration versus time curves in the plasma after an intravenous injection of either [2,3-3H]- and [U-14C]alanine or [3-3H]- and [U-14C]glucose. The calculations were based on an integrated kinetic model derived earlier from experimental data. In comparison to normal dogs, in insulin-deprived pancreatectomized dogs, the rate of turnover of glucose (mg C . kg-1 . min-1) is increased about twofold, but the turnover rates of lactate and alanine are not changed significantly. About twice as much carbon is transferred from lactate to glucose, whereas the transfer of carbon from alanine is increased by 47%. Carbon transfer to glucose from unidentified sources is also doubled. In conclusion, in the pancreatectomized dog, gluconeogenesis is increased not by an increased production of alanine and lactate but by an increased diversion of their carbon atoms to glucose at the expense of other pathways.

A model for carbon kinetics among plasma alanine, lactate, and glucose

To account for the exchange of carbon atoms among alanine, lactate, and glucose in vivo, [2,3-3H]- and [U-14C]alanine or [3-3H]- and [U-14C]glucose were injected simultaneously to nonanesthetized normal dogs. The concentrations in plasma of 14C-labeled alanine, lactate, and glucose, and the injected 3H-labeled substrate were followed for 160 min after injection of the tracers. An integrated kinetic model describing the exchange of carbon atoms among substrates was developed from these data. The analysis suggests that there is a very rapid exchange of the carboxyl carbon of alanine with lactate in contrast to carbons 2 and 3. The model was used to calculate the fluxes of carbon atoms among the substrates in a steady state. In normal dogs plasma alanine and lactate contribute 14% of the carbon atoms released into the circulation as glucose.

Prostaglandin E1 binding and adenylate cyclase activation in normal and transformed fibroblasts

The binding of [3H]prostaglandin E1 to membranes of clones of normal rat kidney fibroblasts (NRK cells) has been measured. Cell lines that responded to prostaglandin E1, such as NRK and NRK transformed with Schmitt-Ruppin strain of Rous sarcoma virus (SR-NRK cells), have a high affinity prostaglandin E1 binding site. Murine-sarcoma-virus-transformed lines of NRK cells are unresponsive to prostaglandin E1 and have reduced prostaglandin E1 binding Exposure of cells to prostaglandin E1 results both in decreased prostaglandin E1 responsiveness and reduced prostaglandin E1 binding. Activation of adenylate cyclase is correlated to binding of prostaglandin E1 to receptors in both NRK and SR-NRK cell membranes. Mathematical models suggest that GTP decreases the affinity of hormone for its receptor while increasing the catalytic efficiency of adenylate cyclase, and that aggregates of occupied receptors may play an important role in the activation of adenylate cyclase.

Collagenase levels in a new model of experimental herpetic interstitial keratitis

A reproducible model of severe herpetic interstitial keratitis was developed by injecting live herpes simplex virus type 2 intrastromally into the corneas of presensitized rabbits. Herpes-infected corneas showed significantly more stromal infiltration and vascularization, iritis, conjunctivitis, and epithelial disease than the control corneas injected with cell supernatant without virus. Levels of total collagenase detected in the culture media of the herpes-infected corneas were high and were similar to those observed previously in alkali-burned rabbit corneas. Unlike alkali-burned corneas, the herpes-infected corneas showed much more of the enzyme in the latent form during the first two days of culture.

Stromal vascularization prevents corneal ulceration

Experiments were performed with a model of focal, thermal-induced ulceration to test the clinical impression that vascularization prevents ulceration of the corneal stroma. Slow-release polymers containing a vasoproliferase agent (tumor angiogenesis factor) were placed in corneal pockets 2 mm central to the limbus of albino rabbits. These polymers elicited blood vessel ingrowth up to the implant. Control eyes received empty polymers which caused minimal to no vessel growth. Polymers were removed, and each cornea received a focal, thermal burn placed just central to the polymer site. All control corneas ulcerated: most (79%) developed deep stromal or perforating ulcers. Only 25% of prevascularized corneas developed stromal ulcers, and none was deep or perforating. After thermal burns, vessels in both groups grew at the same linear rate toward the burned area. There was a direct relationship between the distance separating the nearest blood vessel and the burned area at the time of burning and the maximum depth of stromal ulceration. Thus prevention of or less severe stromal ulceration is correlated with the earlier presence of vessels in the burned area.

Insulin kinetics, models, and delivery schedules

Several insulin models are examined as to their responses to various insulin inputs and glucose utilization and production control. It is shown that the action of insulin on glucose utilization correlates best with model compartments having a 30--50-min delay compared with plasma, whereas glucose production control is rapid. It is further shown that whereas the predicted plasma insulin response curves are nearly the same for various models, the responses at possible sites of action (e.g., receptors or slowly exchanging tissues) can differ considerably for the different models. By determining the parameter values for the glucose-insulin system in a patient through isotope kinetics studies, it is possible to use the patient's model either as a direct algorithm for insulin delivery or as a tool for studying glucose control under various conditions and thus aid in the design of appropriate algorithms or schedules for insulin delivery.

Benign recurrent intrahepatic cholestasis: studies of bilirubin kinetics, bile acids, and cholangiography

Three patients with benign recurrent intrahepatic cholestasis are described. They had had between five and 16 attacks of cholestasis. Between attacks the liver function tests, including serum bile acids, were normal. Serial serum bilirubin and bile acid estimations during the cholestasis in one patient revealed a consistent discrepancy between the serum bilirubin and bile acid concentrations during three consecutive attacks. In the other two patients the serum concentrations of bile acids and bilirubin varied in parallel. Analysis of the individual serum bile acids did not reveal high concentrations of any 'toxic' bile acid. In one patient, plasma bromsulphthalein (BSP) curves were obtained during both remission and cholestatic periods. The 45 minute retention was slightly increased (10.8%) during remission. During the cholestasis, the 45 minute retention (25%) and the fractional extraction coefficient (Ke=0.069 min-1) were markedly abnormal. The hepatic clearance of unconjugated radiobilirubin was normal at all times in this patient, although during cholestasis, conjugated bilirubin reflexed from the liver to the plasma and was then cleared slowly with a half life of approximately 12 hours. Treatment with corticosteroids, cholestyramine, and phenobarbitone was unsatisfactory.

Kinetic modeling of insulin binding to receptors and degradation in vivo in the rabbit

In vivo metabolism of insulin, with emphasis on the distribution, binding, and degradation from receptor and nonreceptor sites, has been studied in rabbits by analyzing the kinetics of antibody-bindable, TCA-precipitable, and TCA-soluble components in plasma. Tracer amounts of 125I-and 131I-labeled high affinity (pork) and low affinity (guinea pig) insulins were injected simultaneously into rabbits in the basal state or after a large bolus of unlabeled pork insulin. In one series of experiments, a bolus of unlabeled pork insulin was given from 5 to 30 min after the tracers. Based on the kinetic curves derived in these experiments, a model is developed for insulin metabolic pathways in vivo. A number of features are contained in the model. First, some of the kinetics are caused by distribution spaces in the body and some by specific binding sites, presumably receptors. Two equilibration phases between plasma insulin and receptors can be detected. The first and major one occurs within about one minute. The second one takes about 15 or 20 min. Partial degradation of the insulin molecule can be detected rapidly by the kinetics and is associated with the rapid (1 min) receptor phase. About 27% of the labeled insulin molecules are partially degraded via this pathway. There is, also, irreversible loss of insulin from the receptors without significant return of label to plasma during the experiment. This loss could be a result of internalization of insulin by the cells. About 48% of the insulin injected follows this pathway. The remaining degradation of insulin (∼24%) takes place at other sites in the body. The results of the kinetic analysis also suggest that there are two populations of receptors. The high affinity population has an equilibrium dissociation constant equal to about 9 × 10−9 M, a value comparable to that observed in vitro (∼5 × 10−9 M). The low affinity population has an equilibrium dissociation constant about 100 times greater than that of the high affinity population; its capacity, however, is about 30 times greater. It is, further, concluded that the TCA-soluble degradation products observed in plasma could not be accounted for by the partial and irreversible degradation pathways identified in the insulin model. They could be accounted for, however, by a 5%–15% subpopulation of injected labeled TCA-precipitable molecules that decay monoexponentially from plasma.