. med. J3., 1968, 4, 430-431 : ummary: The effects of dextran 70 (Mw 70,000; Macrodex), heparin, dipyridamole (Persantin), and prostaglandin E1 on the behaviour of platelets were investigated at sites of endothelial trauma induced with a ruby biolaser in arterioles in the rabbit ear chamber. This technique has several advantages over previous methods of studying platelet activity.Dextran 70 (2 g./kg. body weight) caused a profound reduction in platelet activity four to six hours after its administration. Heparin (12 mg./kg. body weight) had no effect. The effect of dipyridamole (2.5 mg./kg. body weight) was profound immediately after its administration, but was transient. In preliminary experiments single intravenous injections of prostaglandin E1 (25 and 125 lmg./kg. body weight) had no detectable effect.
SummaryIn a model using an isolated rabbit mesenteric preparation microvessels were transected and the time until haemostatic plugs formed was registered. Perfusion of platelet rich plasma gave no haemostasis whereas whole blood did. Addition of chlorpromazine or adenosine to the whole blood significantly prolonged the time for haemostasis, and addition of ADP to the platelet rich plasma significantly shortened it. It is concluded that red cells are necessary for a normal haemostasis in this model, probably by a combination of a haemodynamic and ADP releasing effect.The fundamental role of platelets in haemostatic plug formation is unquestionable but there are still problems concerning the stimulus for this process to start. Three platelet aggregating substances have been discussed – thrombin, adenosine diphosphate (ADP) and collagen. Evidence speaking in favour of thrombin is, however, very minimal, and the discussion has to be focused on collagen and ADP. In an in vitro system using polyethylene tubings we have shown that "haemostasis" can be obtained without the presence of collagen but against these results can be argued that it is only another in vitro test for platelet aggregation (1).To be able to induce haemostasis in this model, however, the presence of red blood cells is necessary. To further study this problem we have developed a model where haemostatic plug formation can be studied in the isolated rabbit mesentery and we have briefly reported on this (2).Thus, it is possible to perfuse the vessels with whole blood as well as with platelet rich plasma (PRP) and different pharmacological agents of importance.
SummaryAn experimental model combining controlled stasis and endothelial destruction by sodium morrhuate has been used to investigate the effect of dextran on venous thrombus formation in rabbits. Dextran 70 (1 g/kg body weight in a 10% solution), given 3 hours before thrombosis induction, significantly reduced the incidence of venous thrombosis when compared to a saline control. Dextran 40 (1 g/kg body weight in a 10% solution) and dextran 70 (0.6 g/kg body weight in a 6% solution) had no significant effect under these conditions. When given 10 or 120 minutes before initiation of thrombosis none of the dosages of dextran had any preventive effect. The results indicate that the haemodynamic effects of dextran were not involved in its preventive effect in this study. The effect of dextran was probably due to a combination of an effect on platelet reactivity and a change of the structure of fibrin formed during growth of the thrombi.
The effect of reversible cerebral ischaemia on brain oedema development was studied with a gravimetric method. Cerebral blood flow changes after ischaemia were correlated with alterations in brain specific gravity. Forebrain ischaemia (15 min) was induced in rats by reversible bilateral ligation of both carotid arteries plus induction of controlled hypotension to 50 mm Hg. The specific gravity of different brain structures was determined in a Percoll column up to 24 h after ischaemia. In addition, regional cerebral blood flow was measured by 14C-iodoantipyrine autoradiography. Cerebral ischaemia resulted in reduction of cerebral blood flow to less than 1% of normal in cortical structures and the caudatoputamen. One hour after the end of ischaemia blood flows were still reduced to 30-50% of the control level indicative of delayed postischaemic hypoperfusion. Specific gravity in cortex and hypothalamus reached a maximal decrease 10 min after the end of the ischaemia, and was still significantly reduced at 1 h, while it was normal again 6 hrs later. Regression analysis between regional cerebral blood flows and the corresponding specific gravities were made at various time points, but no significant correlations could be established. Other mechanisms, like vasoconstriction, rheologic or metabolic factors may be causative for the delayed postischaemic hypoperfusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.