Disintegration and reorganization of fibrin networks during tissue-type plasminogen activator-induced clot lysis.

In this study, we investigated tissue-type plasminogen activator (tPA)-induced lysis of glutamic acid (glu)-plasminogen-containing or lysine (lys)-plasminogen-containing thrombin-induced fibrin clots. We measured clot development and plasmin-mediated clot disintegration by thromboelastography, and used scanning electron microscopy (SEM) to document the structural changes taking place during clot formation and lysis. These events occurred in three overlapping stages, which were initiated by the addition of thrombin, resulting first in fibrin polymerization and clot network organization (Stage I). Autolytic plasmin cleavage of glu-plasminogen at lys-77 generates lys-plasminogen, exposing lysine binding sites in its kringle domains. The presence of lys-plasminogen within the thrombin-induced fibrin clot enhanced network reorganization to form thicker fibers as well as globular complexes containing fibrin and lys-plasminogen having a greater level of turbidity and a higher elastic modulus (G) than occurred with thrombin alone. Lys-plasminogen or glu-plasminogen that had been incorporated into the fibrin clot was activated to plasmin by tPA admixed with the thrombin, and led directly to clot disintegration (Stage II) concomitant with fibrin network reorganization. The onset of Stage III (clot dissolution) was signaled by a sustained secondary rise in turbidity that was due to the combined effects of lys-plasminogen presence or its conversion from glu-plasminogen, plus clot network reorganization. SEM images documented dynamic structural changes in the lysing fibrin network and showed that the secondary turbidity rise was due to extensive reorganization of severed fibrils and fibers to form wide, occasionally branched fibers. These degraded structures contributed little, if anything, to the structural integrity of the residual clot, and eventually collapsed completely during the course of progressive clot dissolution. These results provide new perspectives on the major structural events that occur in the fibrin clot matrix during fibrinolysis.

Characterization of a mouse model for thrombomodulin deficiency.

Mutations in the gene encoding thrombomodulin (TM), a thrombin regulator, are suspected risk factors for venous and arterial thrombotic disease. We have previously described the generation of TM(Pro/Pro) mice carrying a TM gene mutation that disrupts the TM-dependent activation of protein C. Here, it is shown that inbred C57BL/6J TM(Pro/Pro) mice exhibit a hypercoagulable state and an increased susceptibility to thrombosis and sepsis. Platelet thrombus growth after FeCl(3)-induced acute endothelial injury was accelerated in mutant mice. Vascular stasis after permanent ligation of the carotid artery precipitated thrombosis in mutant but not in normal mice. Mutant mice showed increased mortality after exposure to high doses of endotoxin and demonstrated altered cytokine production in response to low-dose endotoxin. The severity of the hypercoagulable state and chronic microvascular thrombosis caused by the TM(Pro) mutation is profoundly influenced by mouse strain-specific genetic differences between C57BL/6 and 129SvPas mice. These data demonstrate that in mice, TM is a physiologically relevant regulator of platelet- and coagulation-driven large-vessel thrombosis and modifies the response to endotoxin-induced inflammation. The phenotypic penetrance of the TM(Pro) mutation is determined by as-yet-uncharacterized genetic modifiers of thrombosis other than TM.

The structure and biological features of fibrinogen and fibrin.

Fibrinogen and fibrin play important, overlapping roles in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, and neoplasia. These events are regulated to a large extent by fibrin formation itself and by complementary interactions between specific binding sites on fibrin(ogen) and extrinsic molecules including proenzymes, clotting factors, enzyme inhibitors, and cell receptors. Fibrinogen is comprised of two sets of three polypeptide chains termed A alpha, B beta, and gamma, that are joined by disulfide bridging within the N-terminal E domain. The molecules are elongated 45-nm structures consisting of two outer D domains, each connected to a central E domain by a coiled-coil segment. These domains contain constitutive binding sites that participate in fibrinogen conversion to fibrin, fibrin assembly, crosslinking, and platelet interactions (e.g., thrombin substrate, Da, Db, gamma XL, D:D, alpha C, gamma A chain platelet receptor) as well as sites that are available after fibrinopeptide cleavage (e.g., E domain low affinity non-substrate thrombin binding site); or that become exposed as a consequence of the polymerization process (e.g., tPA-dependent plasminogen activation). A constitutive plasma factor XIII binding site and a high affinity non-substrate thrombin binding site are located on variant gamma' chains that comprise a minor proportion of the gamma chain population. Initiation of fibrin assembly by thrombin-mediated cleavage of fibrinopeptide A from A alpha chains exposes two EA polymerization sites, and subsequent fibrinopeptide B cleavage exposes two EB polymerization sites that can also interact with platelets, fibroblasts, and endothelial cells. Fibrin generation leads to end-to-middle intermolecular Da to EA associations, resulting in linear double-stranded fibrils and equilaterally branched trimolecular fibril junctions. Side-to-side fibril convergence results in bilateral network branches and multistranded thick fiber cables. Concomitantly, factor XIII or thrombin-activated factor XIIIa introduce intermolecular covalent epsilon-(gamma glutamyl)lysine bonds into these polymers, first creating gamma dimers between properly aligned C-terminal gamma XL sites, which are positioned transversely between the two strands of each fibrin fibril. Later, crosslinks form mainly between complementary sites on alpha chains (forming alpha-polymers), and even more slowly among gamma dimers to create higher order crosslinked gamma trimers and tetramers, to complete the mature network structure.

Fibrinogen naples I (B beta A68T) nonsubstrate thrombin-binding capacities.

Fibrinogen Naples I (Bbeta A68T) is characterized by defective thrombin binding and fibrinopeptide cleavage at the fibrinogen substrate site in the E domain. We evaluated the fibrinogen of three homozygotic members of this kindred (II.1, II.2, II.3) who have displayed thrombophilic phenotypes and two heterozygotic subjects (I.1, I.2) who were asymptomatic. Electron microscopy of Naples I fibrin networks showed relatively wide fiber bundles, probably due to slowed fibrin assembly secondary to delayed fibrinopeptide release. We evaluated 125I-thrombin binding to the fibrin from subjects I.1, I.2, II.1, and II.2 by Scatchard analysis with emphasis on the high-affinity site in the D domain of fibrin(ogen) molecules containing a gamma chain variant termed gamma'. Homozygotic subjects II.1 and II.2 showed virtually absent low-affinity binding, consistent with the Bbeta A68T mutation, whereas heterozygotes I.1 and I.2 showed only moderately reduced low-affinity binding. The homozygotes also showed impaired high-affinity thrombin binding, whereas that of the heterozygotes was nearly the same as normal. Genomic sequencing of the gamma' coding sequence (I.2, II.2), ELISA measurements of two gamma' chain epitopes (L2B, gamma'409-412, and IF10, gamma'417-427) (I.2, II.1, II.2, II.3), and mass spectrometry of Naples I fibrinogen (II.2) showed no differences from normal, thus indicating that there were no abnormal structural modifications of the gamma' chain residues in Naples I fibrinogen. However, thrombin reportedly utilizes both of its available exosites for binding to high- and low-affinity sites on normal fibrin, suggesting that binding is cooperative. Thus, reduced high-affinity thrombin binding to homozygotic Naples I fibrin may be related to the absence of low-affinity binding sites.

The amino acid sequence in fibrin responsible for high affinity thrombin binding.

Human fibrin has a low affinity thrombin binding site in its E domain and a high affinity binding site in the carboxy-terminal region of its variant gamma' chain (gamma'408-427). Comparison of the gamma' amino acid sequence (VRPEHPAETEYDSLYPEDDL) with other protein sequences known to bind to thrombin exosites such as those in GPIbalpha, the platelet thrombin receptor, thrombomodulin, and hirudin suggests no homology or consensus sequences, but Glu and Asp enrichment are common to all. Tyrosine sulfation in these sequences enhances thrombin exosite binding, but this has not been uniformly investigated. The fibrinogen gamma' chain mass determined by electrospray ionization mass spectrometry, was 50,549 Da, a value 151 Da greater than predicted from its amino acid/carbohydrate sequence. Since each sulfate group increases mass by 80 Da, this indicates that both tyrosines at 418 and 422 are sulfated. A series of overlapping gamma' peptides was prepared for evaluation of their inhibition of 125I-labeled PPACK-thrombin binding to fibrin. gamma'414-427 was as effective an inhibitor as gamma'408-427 and its binding affinity was dependent on all carboxy-terminal residues. Mono Tyr-sulfated peptides were prepared by substituting non-sulfatable Phe for Tyr at gamma'418 or 422. Sulfation at either Tyr residue increased binding competition compared with non-sulfated peptides, but was less effective than doubly sulfated peptides, which had 4 to 8-fold greater affinity. The reverse gamma' peptide or the forward sequence with repositioned Tyr residues did not compete well for thrombin binding, indicating that the positions of charged residues are important for thrombin binding affinity.

Protransglutaminase (factor XIII) mediated crosslinking of fibrinogen and fibrin.

Plasma factor XIII (plasma protransglutaminase) circulates as an A2B2 tetramer bound to the gamma' variant chains of fibrinogen "2". During clotting the A subunits of fXIII are cleaved by thrombin to form fXIIIa (transglutaminase) and in the presence of calcium ions, activated A2* subunits dissociate from the B subunits. When purified plasma fXIII or recombinant cellular factor XIII (A2) was incubated with fibrinogen in the presence of calcium ions (> or =50 microM) a non-synerizing gel formed concomitant with formation of gamma dimers, followed by Agamma polymers, and eventually gamma trimers and gamma tetramers. As is the case of fXIIIa, the fXIII-mediated crosslinking rate was enhanced in the presence of thiols. After an initial lag period, fXIII catalyzed fibrinogen crosslinking at approximately 75% of the rate of fXIIIa under typical crosslinking conditions (100 Loewy u/ml, 5 mM CaCl2 & 500 microM DTT). Fibrin was crosslinked about 8 times more rapidly by fXIII than was fibrinogen, and after an initial lag period fXIII crosslinked fibrin at nearly the same rate as fXIIIa. Substituting plasma for purified fXIII as the source for fXIII resulted in robust fibrinogen crosslinking activity. In contrast to the high level of fXIII-mediated crosslinking activity observed with fibrinogen or fibrin as substrates, when transglutamination was measured using cadaverine incorporation into casein, fXIII was 30-fold less active than fXIIIa. Thus, factor XIII displays constitutive enzymatic activity with respect to fibrinogen and fibrin. The results further indicate that uncleaved fXIII in plasma provides a potent source of readily available crosslinking activity in clotting blood. Fibrinogen 2, whose gamma'chains bind fXIII B subunits, was crosslinked 3.5 times more slowly by fXIII than was fibrinogen 1 (lacking gamma' chains), suggesting that complex formation between fibrinogen 2 and plasma fXIII plays a significant role in down-regulating potential plasma fXIII-mediated crosslinking activity. Since fibrin is a considerably better substrate for fXIII than is fibrinogen, the rate at which crosslinking takes place in a fibrinogen-containing plasma environment is much lower than it would be if fibrin were present.

Position of gamma-chain carboxy-terminal regions in fibrinogen/fibrin cross-linking mixtures.

There are conflicting ideas regarding the location of the carboxyl-terminal regions of cross-linked gamma-chain dimers in double-stranded fibrin fibrils. Some investigators believe that the chains are always oriented longitudinally along each fibril strand and traverse the contacting ends of abutting fibrin D domains ("DD-long" cross-linking). Other investigations have indicated instead that the chains are situated transversely between adjacent D domains in opposing fibril strands (transverse cross-linking). To distinguish between these two possibilities, the gamma dimer composition of factor XIIIa-cross-linked fibrin/fibrinogen complexes that had been formed through noncovalent D/E interactions between fibrinogen D domains and fibrin E domains was examined. Two factor XIIIa-mediated cross-linking conditions were employed. In the first, fibrin/fibrinogen complexes were formed between (125)I-labeled fibrinogen 2 ("peak 2" fibrinogen), each heterodimeric molecule containing one gamma(A) and one larger gamma' chain, and nonlabeled fibrin 1 molecules ("peak 1" fibrin), each containing two gamma(A) chains. If DD-long cross-linking occurred, (125)I-labeled gamma(A)-gamma(A), gamma(A)-gamma', and gamma'-gamma'dimers in a 1:2:1 ratio would result. Transverse cross-linking would yield a 1:1 mixture of (125)I-labeled gamma(A)-gamma(A) and gamma(A)-gamma' dimers, without any gamma'-gamma' dimers. Autoradiographic analyses of reduced SDS-PAGE gels from protocol 1 revealed (125)I-labeled gamma(A)-gamma(A) and gamma(A)-gamma' dimers at a ratio of approximately 1:1. No labeled gamma'-gamma' dimers were detected. Protocol 2 used a converse mixture, (125)I-fibrin 2 and nonlabeled fibrinogen 1. DD-long cross-linking of this mixture would yield only nonradioactive gamma(A)-gamma(A) dimers, whereas transverse cross-linking would yield a 1:1 mixture of (125)I-labeled gamma(A)-gamma(A) and gamma(A)-gamma' dimers. Autoradiographic analyses of this mixture yielded (125)I-labeled gamma(A)-gamma(A) and gamma(A)-gamma' dimers in a 1:1 ratio. These findings provide no evidence that longitudinal (DD-long) gamma chain positioning occurs in cross-linked fibrin and indicate instead that most, if not all, gamma-chain positioning in an assembled fibrin polymer is transverse.

Coexisting dysfibrinogenemia (gammaR275C) and factor V Leiden deficiency associated with thromboembolic disease (fibrinogen Cedar Rapids).

Fibrinogen Cedar Rapids is a heterozygous dysfibrinogenemia (gammaR275C) that was associated with thromboembolism during and following pregnancy in three second-generation family members who also were heterozygotic for factor V Leiden (V R506Q). Like other dysfibrinogenemias with substitutions at position 275 of the gamma-chain, fibrinogen Cedar Rapids is characterized by defective end-to-end intermolecular fibrinogen and fibrin 'D : D' associations, a fibrin network structure that is composed of thicker and more highly branched fibers, normal fibrin 'D: E' associations, and normal factor XIII-mediated crosslinking of fibrinogen and fibrin. In addition, Cedar Rapids fibrinogen and fibrin displayed delayed plasmin lysis rates. Compared with normal fibrinogen, platelet aggregation or platelet fibrinogen receptor clustering was defective in the presence of fibrinogen Cedar Rapids. Most subjects with gammaR275 mutations do not experience clinical thrombotic disorders, suggesting that the combination of a factor V Leiden defect and a gammaR275C dysfibrinogenemia predisposes to thromboembolic disease.

Correlation between temperature and vibration thresholds and somatosensory evoked potentials.

The psychophysically assessed thermal specific, thermal pain and vibration sensitivities were correlated to somatosensory evoked potentials in eighteen patients with definite multiple sclerosis. In the psychophysical tests, modality specific stimuli were used. Somatosensory potentials were electrically evoked. The abnormalities of both the temperature and the vibration sensitivity were to same extent related to the somatosensory evoked potentials. Dorsal columns-medial lemnisc and anterolateral-spinothalamic demyelinating lesions were presumed. The psychophysical tests supplement the clinical, laboratory, neuroradiologic and electrophysiological tests. These should be included in the battery of diagnostic tests in multiple sclerosis.

Fibrinogen Niigata with impaired fibrin assembly: an inherited dysfibrinogen with a Bbeta Asn-160 to Ser substitution associated with extra glycosylation at Bbeta Asn-158.

A novel BbetaAsn-160 (TAA) to Ser (TGA) substitution has been identified in fibrinogen Niigata derived from a 64-year-old asymptomatic woman, who is heterozygotic for this abnormality. The mutation creates an Asn-X-Ser-type glycosylation sequence, and a partially sialylated biantennary oligosaccharide was linked to the BbetaAsn-158 residue. The functional abnormality was attributed to delayed lateral association of normally formed double-stranded protofibrils based on normal cross-linking of fibrin gamma-chains and tissue-type plasminogen activator-catalyzed plasmin generation by polymerizing fibrin monomers. Enzymatic removal of all the N-linked oligosaccharides from fibrinogen Niigata accelerated fibrin monomer polymerization that reached the level of untreated normal fibrin monomers, but the thrombin time was prolonged from 18.2 seconds to 113 seconds (normal: 11.2 seconds to 8.9 seconds). By scanning electron micrographic analysis, Niigata fibrin fibers were found to be more curvilinear than normal fibrin fibers. After deglycosylation, Niigata fibers became straight being similar to untreated normal fibrin fibers, whereas normal deglycosylated fibrin appeared to be less-branched than untreated normal or deglycosylated Niigata fibrin. Although normal and Niigata fibrins were similar to each other in permeation and compaction studies, deglycosylated normal and Niigata fibrins had much higher permeability and compaction values, indicating that deglycosylation had brought about the formation of more porous networks. The enzymatic deglycosylation necessitates an Asn to Asp change at position Bbeta-158 that is responsible for reducing the fiber thickness because of either local repulsive forces or steric hindrance in the coiled-coil region.

Subclinical neuropathy in type I diabetic children.

OBJECTIVES: Small and large, somatic and autonomic nerve fibre functions were neurophysiologically evaluated in 33 asymptomatic neurologically free type I diabetic children and 69 age-matched healthy controls. METHODS: The evaluation of large and small somatic nerve fibre function was performed by conventional nerve conduction studies, thermal specific and thermal pain sensitivity tests, as well as autonomic nerve fibre functions by sympathetic skin response and R-R interval variation assessment. RESULTS: A significant difference was established between the healthy and the diabetic group. Neurophysiologically determined subclinical neuropathy was found in 87% of type I diabetic children. The majority of abnormal recordings were found on the lower limbs. The dysfunction of the somatic motor large nerve fibre type in the lower limbs was altered in 57% of patients, somatic sensory large in 39%, somatic sensory small in 45%, and sympathetic in 45%. The leading abnormal measure was a delayed sympathetic skin response on the foot (42% of diabetic children) followed by a reduced amplitude of sural nerve action potential (36%). The whole spectrum of recordings showed scattered involvement of nerve functions. There was no selective susceptibility of nerve fibre types exposed to a noxious factor. CONCLUSION: A complex neurophysiological assessment, including standard nerve conduction studies as well as psychophysical examination and autonomic nerve function tests, evaluating the function of small and large nerve fibres, is recommended for evaluating the subclinical neuropathy in asymptomatic type I diabetic children.

The location of the carboxy-terminal region of gamma chains in fibrinogen and fibrin D domains.

Elongated fibrinogen molecules are comprised of two outer "D" domains, each connected through a "coiled-coil" region to the central "E" domain. Fibrin forms following thrombin cleavage in the E domain and then undergoes intermolecular end-to-middle D:E domain associations that result in double-stranded fibrils. Factor XIIIa mediates crosslinking of the C-terminal regions of gamma chains in each D domain (the gammaXL site) by incorporating intermolecular epsilon-(gamma-glutamyl)lysine bonds between amine donor gamma406 lysine of one gamma chain and a glutamine acceptor at gamma398 or gamma399 of another. Several lines of evidence show that crosslinked gamma chains extend "transversely" between the strands of each fibril, but other data suggest instead that crosslinked gamma chains can only traverse end-to-end-aligned D domains within each strand. To examine this issue and determine the location of the gammaXL site in fibrinogen and assembled fibrin fibrils, we incorporated an amine donor, thioacetyl cadaverine, into glutamine acceptor sites in fibrinogen in the presence of XIIIa, and then labeled the thiol with a relatively small (0.8 nm diameter) electron dense gold cluster compound, undecagold monoaminopropyl maleimide (Au11). Fibrinogen was examined by scanning transmission electron microscopy to locate Au11-cadaverine-labeled gamma398/399 D domain sites. Seventy-nine percent of D domain Au11 clusters were situated in middle to proximal positions relative to the end of the molecule, with the remaining Au11 clusters in a distal position. In fibrin fibrils, D domain Au11 clusters were located in middle to proximal positions. These findings show that most C-terminal gamma chains in fibrinogen or fibrin are oriented toward the central domain and indicate that gammaXL sites in fibrils are situated predominantly between strands, suitably aligned for transverse crosslinking.

Early asymmetric neuropathy in primary Sjögren's syndrome.

We report three female patients, 43, 47, and 50 years old, with a rare asymmetric form of clinically pure sensory neuropathy associated with primary Sjögren's syndrome. In all three patients glandular involvement was accompanied by peripheral nerve disease. Sensory conduction studies showed completely normal results in two of three patients. Yet assessment of thermal-specific thresholds and thermal pain thresholds, combined with autonomic function tests (sympathetic skin response and R-R interval variation) supported the clinical suspicion of peripheral nerve disorder. Sjögren's syndrome must be considered in asymmetric sensory neuropathies of unknown cause.

[Quantitative determination of the function of thin nerve fibers]. / Die quantitative Bestimmung der Funktion der dünnen Nervenfasern.

Quantitative assessment of thermal and pain sensitivity (Marstock method on a SOMEDIC Thermotest, Somedic AB Stockholm, Schweden) was made and the function of autonomic nervous system (sympathetic skin response and R-R interval variation) indicating the function of small nerve fibres (A-delta and C) was determined in 44 patients with symptoms of the presumed sensory neuropathy. The function of the large nerve fibres was evaluated by the classic nerve conduction study. The methods of small nerve fibres evaluation exhibited greater sensitivity as the classic nerve conduction study. The dysfunction of small nerve fibre function was morphologically proved by sural nerve biopsy.

Identification and characterization of the thrombin binding sites on fibrin.

Thrombin binds to fibrin at two classes of non-substrate sites, one of high affinity and the other of low affinity. We investigated the location of these thrombin binding sites by assessing the binding of thrombin to fibrin lacking or containing gamma' chains, which are fibrinogen gamma chain variants that contain a highly anionic carboxyl-terminal sequence. We found the high affinity thrombin binding site to be located exclusively in D domains on gamma' chains (Ka, 4.9 x 10(6) M-1; n, 1.05 per gamma' chain), whereas the low affinity thrombin binding site was in the fibrin E domain (Ka, 0.29 x 10(6) M-1; n, 1.69 per molecule). The amino-terminal beta15-42 fibrin sequence is an important constituent of low affinity binding, since thrombin binding at this site is greatly diminished in fibrin molecules lacking this sequence. The tyrosine-sulfated, thrombin exosite-binding hirudin peptide, S-Hir53-64 (hirugen), inhibited both low and high affinity thrombin binding to fibrin (IC50 1.4 and 3.0 microM respectively). The presence of the high affinity gamma' chain site on fibrinogen molecules did not inhibit fibrinogen conversion to fibrin as assessed by thrombin time measurements, and thrombin exosite binding to fibrin at either site did not inhibit its catalytic activity toward a small thrombin substrate, S-2238. We infer from these findings that there are two low affinity non-substrate thrombin binding sites, one in each half of the dimeric fibrin E domain, and that they may represent a residual aspect of thrombin binding and cleavage of its substrate fibrinogen. The high affinity thrombin binding site on gamma' chains is a constitutive feature of fibrin as well as fibrinogen.

Plasma factor XIII binds specifically to fibrinogen molecules containing gamma chains.

The difference between peak 1 and peak 2 fibrinogen lies in their gamma chains. Peak 1 molecules contain 2 gamma A chains; peak 2 molecules contain 1 gamma A and 1 gamma chain, the latter of which contains a 20 amino acid extension (gamma 408-427) replacing the carboxyl-terminal 4 amino acids of the gamma A chain (gamma A 408-411). While the existence of gamma chains in plasma fibrinogen molecules has been known for many years, their function remains unknown. When fibrinogen is purified from plasma, the factor XIII zymogen (A2B2) copurifies with it and is found only in the peak 2 fibrinogen when this fraction is separated from peak 1 fibrinogen by ion-exchange chromatography on DEAE-cellulose. Factor XIII alone applied to the same DEAE column elutes at a position between peak 1 and peak 2. When mixtures of peak 1 fibrinogen plus factor XIII or peak 2 fibrinogen plus factor XIII are applied to DEAE columns, the peak 1/factor XIII mixture elutes in two peaks, whereas the peak 2/factor XIII mixture elutes in the peak 2 fibrinogen position. Gel sieving on Superose 6 of peak 1/factor XIII mixtures results in two protein peaks, the first of which contains the fibrinogen. Most factor XIII activity elutes in the second peak with a small amount of activity emerging with the trailing end of the fibrinogen peak. Gel sieving of mixtures of peak 2 and factor XIII results in a single protein peak with all factor XIII activity emerging with the leading edge of the fibrinogen peak. The interaction between peak 2 fibrinogen and plasma factor XIII appears to be through binding to the B subunit of factor XIII since placental or platelet factor XIII (A2), which does not contain B subunits, elutes independently from peak 2 fibrinogen on DEAE-cellulose chromatography. The results indicate that peak 2 fibrinogen gamma chains have a physiologically significant affinity for the B subunits of plasma factor XIII and that through this interaction fibrinogen serves as a carrier for the plasma zymogen in circulating blood.

Sympathetic skin response in parkinsonian patients.

Sympathetic skin response (SSR) was recorded in 23 patients with idiopathic Parkinson's disease (IPD) using mechanical as well as electrical stimuli. Significant delay of SSR latencies and decrease in amplitude of SSR compared to healthy volunteers were found (p < 0.05). Furthermore the clinical parameters of the autonomic impairment correlated well with the Webster score. Central mechanisms might be responsible for these findings and the role of central sympathetic pathway damage in parkinsonian patients is discussed.