Mapping of distinct von Willebrand factor domains interacting with platelet GPIb and GPIIb/IIIa and with collagen using monoclonal antibodies

We have used monoclonal antibodies (M Abs) and proteolytic fragmentation to localize structurally the functional sites of human von Willebrand factor (vWF) responsible for interaction with membrane glycoproteins GPIb, GPIIb/IIIa, and with collagen. SpII (215 kd) and SpIII (320 kd), the S aureus V-8 protease homodimeric fragments representing the carboxy-terminal and amino-terminal segments of the vWF subunit, competitively inhibited the binding of multimeric vWF to thrombin-stimulated or ristocetin-stimulated platelets, respectively. Specific saturable binding of each fragment was observed to stimulate platelets appropriately and was inhibited only by selected M Abs that both bound to the specific fragment and inhibited the corresponding function. M Ab 9, which blocks thrombin-induced binding of vWF to platelets, inhibited binding of SpII to platelets and bound to SpII as well as to a dimeric, 86-kd thermolysin fragment composed of 42-kd and 23-kd subunits, each possessing the epitope. Binding of SpII was also inhibited by a M Ab to GPIIb/IIIa. Thus, it appears that a portion of the carboxy-terminal end of vWF contains the ligand site for the GPIIb/IIIa receptor. In contrast, M Ab H9, which blocks ristocetin- induced binding of vWF to platelets, inhibited binding of SpIII to platelets and bound to SpIII as well as to monomeric 33-kd and 28-kd subtilisin fragments. Binding of SpIII to platelets was also inhibited by a M Ab to GPIb. Thus, it appears that a small segment of the amino- terminal part of vWF contains the ligand for the platelet GPIb receptor. The collagen binding site of vWF was localized with M Ab B203, which inhibits vWF interaction with collagen. This M Ab also bound to SpIII as well as to monomeric 26-kd and 23-kd subtilisin fragments. Thus, the third functional site responsible for collagen binding appears to be localized on the amino-terminal portion of vWF, in a linear sequence different from those responsible for interaction with either of the platelet receptors. These assignments of functional sites should facilitate the localization of structural defects of vWF in the various forms of vWD and support the role of vWF as an adhesive protein with multiple interactive sites.     

Alcohol and GABA: ethanol intake modifies hippocampal nipecotic acid binding in ethanol-preferring and non-preferring rats

3H-nipecotic acid (3H-NIP) binding to GABA uptake recognition sites was studied in the hippocampus of 3 groups of male, Long Evans rats: Group 1: ethanol-naive rats (ENR); Group II: ethanol-preferring rats (DR) and non-preferring rats (NDR), which had consumed about 5 g.kg-1.d-1 and 1 g-1.d-1 of alcohol respectively in the form of a 12% ethanol solution prior to 3H-NIP binding analysis; Group III: DR and NDR who had had no access to ethanol for 21 d after the initial exposure of ethanol solution (28 d). Binding studies showed that ethanol drunk by both DR and NDR in Group II decreased 3H-NIP binding (Bmax decreased) with an enhancement of affinity (KD decreased). In rats subjected to withdrawal of ethanol (Group III), affinity of 3H-NIP for GABA uptake sites was higher than in controls (Group I), but lower than in Group II, Bmax in this group being higher than in the 2 other groups. In Group III, KD was higher in DR than in NDR. These results showed that ethanol intake, in a free-choice paradigm, altered 3H-NIP binding, and that differences in ethanol intake between DR and NDR were associated with differences in sensitivity of hippocampal GABA uptake sites. These differences in 3H-NIP binding could either precede ethanol intake, or be a direct result from it. The results, together with data from other laboratories suggest that: 1), 3H-NIP binding sites are involved in the regulation of ethanol intake; 2), 1 factor responsible for individual differences in ethanol response is reflected by the GABA uptake system.     

Pharmacokinetics and pharmacodynamics of zolpidem following repeated doses in hemodialyzed uraemic patients

Summary— Zolpidem, an imidazopyridine derivative, is a chemically novel, non-benzodiazepine hypnotic agent. Many uraemic patients complain of sleep disorders and ask for hypnotic medication which is well tolerated both clinically and biologically in such patients. We studied the pharmacokinetics and pharmacodynamics of zolpidem in 12 end-stage renal patients regularly treated by hemodialysis three times a week. Zolpidem (10 mg) was given orally for 14 or 21 days. Pharmacokinetic and pharmacodynamic evaluations were repeated at the end of the study on day 14 or day 21. C_max, T_max, t1/2 and the area under the curve were not modified in hemodialyzed patients. After daytime dosing, zolpidem induced the same level of sleepiness after the first and last dose and was well tolerated as a hypnotic agent after the night-time dosing. From these results, it can be said that zolpidem may be administered safely to patients with severe renal impairment without any modification of the dosage regimen.     

Lung scar cancer—a reappraisal

A retrospective clinicopathological study of 100 necropsy cases of lung carcinoma revealed three scar cancers. The scarring in a further 11 probably occurred secondary to the tumour. The premise that lung scars initiate malignancy is questioned.