The chemical structure of plateletactivating factor (PAF), released from sensitized basophils in the allergic reaction, has been determined as 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine.
Since then, various homologues and analogues of PAF have been synthesized, and many reports are available concerning the relation between the structure and the biological activity of this phospholipid. It is now clear that the fatty alkyl residue at sn-1, the acetyl residue at sn-2 and phosphocholine at sn-3 positions of glycerol are essential for the full activity of PAF.
However, there are few reports on the biological activities of its positional isomer,1-0acety1-2-0-hexadecyl-rac-glycero-3-phosphocholine (16: 0 2-alkyl PAF). I tested the platelet aggregating activity and vascular permeability of 16: 0 2-alkyl PAF, which was synthesized by Prof. T. Muramatsu.16: 0 2-alkyl PAF had shown a melting point of 200°C. A characteristic mass spectrum of 16: 0 2-alkyl PAF, which can be distinguished from 16: 0 PAF, was obtained on their diacetyl derivatives.
Platelet aggregating activity and vascular permeability of 16: 0 2-alkyl PAF were about one fiftieth and one tenth those of 16: 0 PAF, respectively. These biological activites were inhibited by CV-3988 and L-652,731, both PAF receptor antagonists.

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It has been reported that lysophosphatidylcholine (LPC) and sphingomyelin (SPH) from rat uterus inhibited the PAF-induced aggregation of washed rabbit platelets. However, rat platelets are not responsive to PAF.
In this paper, I studied the in hibitory effects of LPC and SPH on PAF-induced vascular permeability of the rat.
Intradermal in jection of PAF increased the infiltration of Brilliant blue 6B into the skin in a dose-dependent manner. The vascular permeability induced by 3Ong 18: 0 PAF was reduced significantly by 16: 0 LPC at concentrations of 5 and 10 ug. However, at concentrations greater than 50 ug/site, it enhanced the permeability, probably due to its cytolytic activity. Vascular permeability was also inhibited significantly by L-652,731 and CV-3988, which are PAF antagonists. On the other hand,18: 1 LPC and SPH had no effect at all concentrations tested.
16: 0 LPC did not inhibit the increse of vascular permeability induced by histamine (10 ug/site), bradykinin (4 ug/site) or serotonin (0.3 ug/site). The physiological significance of endogeneous LPC is discussed.

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Subrenal capule assay (SRCA) which was first developed by Bodgen et al. has been noted as an in vivo sensitivity test against antineoplastic agents in solid tumors. This method has enabled us to perform a sensitivity test with a small piece of sample and to evaluate the result within a short period. Excellent coincidence of the result of this test with clinical effects has been reported. However, reports of SRCA for brain tumors are rare. Since immunocompetent mice are used in this test, there is a possiblity that host reponse appears even within the limited period of 6 days. Though many investigators manifested their suspicion on the viability of tumors or evaluation of the antineoplastic effect of agents, only a few reports have concerned basic study of SRCA and have investigated the efficacy of this method.
The author experimented SRCA to evaluate the efficacy of this m ethod in immunocompetent ddY mice. A small piece of 19 rat glioma, an established brain tumor cell line, was transplanted into the subrenal space of mice and the survival of the tumor was observed daily. The volume of the tumor and the histological alterations were examined after the administration of antineoplastic agents into mice. Surgical specimens were then used to evaluate the usefulness of this method in clinical cases of brain tumors.
Experimental results showed an increase in the volume of the tumor and infiltration of inflammatory cells even in immunocompetent mice. In the mice receiving cyclophosphamide injection one day before the experiment, the tumor size tended to increase until 12th day and histological examination revealed infiltration of tumor cells into the renal substance and the development of new intratumoral vessels. In the comparison between the mice receiving antineoplastic agents and the mice receiving no antineoplastic agent, the mice with a previous injection of cyclophosphamide showed a distinct difference in the tumor size and were useful for evalution of the antineoplastic effect, compared with those without cyclophosphamide injection.
Clinical results showed that SRCA was easy in tumor such as metastatic br a in tumors for which en bloc resection was available but it was difficult in elastic tumors such as glioma for which only a piece-meal removal was available. Since permeability of antineoplastic agents is disturbed due to the presence of the blood-brain barrier in gliomas, an extended study is necessary before clinical application of SRCA for this kind of tumor.

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