Summary. Observations have been made on the effects of nen'e sHimilatiiMi ami ilniys on an isoliitctl porfusetl segiuent of the central artery of the rahliit ear.Stiiiuiliilinn ;ii)i)Ii('(I tniiisiiiiirally, i3i?ri-arterially or to tlic ventral aiiriciilur nerve caused vascoioiistriclion.The vascoconstrictor respmise to peri-arterial stiniulution wa.s due to excitation of ner\e fibres arising from the .superior cerxical sangUon. The response was enhanced after eocaine, and alxjlishet! or grealiy reduced after guanethidjne, proeaine and dihenyline.Noradrenaline priKliiccd va.sccK-onslrietor responses wliicli wcre enhanced after naiinlionectomy and after cocaine, and aholislicd ljy dilirnyline.Acetyl choline caused dilatation, but only when the tone of the artery was ruised by sympatlietie stimulation. Tlie effect of act-tyl choline was greatly rcducet) after atropine.

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Summary. .\ sensitive automated assay was developed for llie determination nf histamine.The endogenous histamine eontent {)f inlaet rabbit thoraeic aorta, and of its separated atKentitial and medial layers was determined. The hi.stainine content of the intatt aorta was fouTid to lie only partiallv sensiti\e lo eompuuiid 4H/S0, The isolated aurta aeenmulated labelled hi.staniine against a concentration gradient. Tht-uptake was abolished by cooling to 1°, but was unalfeeted by oxyjien lack.The uptake process was sensitive to a \'ariety of agents including extraneuronal catecholamine uptake inhibitors (deoxycorticosterone acetate, normetanephrine) as well as inhibitors ()f eateeholaniine and histannne metabolism (tranykj-promiiie. Ii\ (Irallazine).The npl;ike uas not afietti'd by amodiaquiii, a bistaniine N-methyl-transferase inhibitor, by the metal)olites 1.4-niethyIhislainiiie or imidazole acetic acid, by compomid 48/80 or by Ihu basic amino atid arginine.INTRODUCTION.

SUMMARY Infusion of reserpine into the brachial artery produces a very marked and prolonged vasodilatation which is confined to the skin of the limb. During the dilatation there is no detectable increase in sensitivity to noradrenaline nor any reduction in the response of the vessels to ephedrine or to reflex sympathetic activity. While some degree of noradrenaline depletion of the tissues cannot be excluded, the findings suggest that if such depletion occurs, it must in some way release vascular tone without causing other manifestations of depletion.