Summary: Regional blood-brain glucose transfer was studied in pentobarbitone-anaesthetized rats using a pro grammed intravenous infusion technique that maintained steady levels of unlabeled (up to 55 mM) and tracer n-glucose in the circulating plasma. Regional cerebral blood flow, glucose phosphorylation rate, and tissue glu cose content were also measured under comparable con ditions. Data were analysed in terms of irreversible Mi chaelis -Menten kinetics assuming independent influx and efflux (Type I) and reversible Michaelis-Menten ki netics (Type II) across both the luminal and the abluminal membranes of the endothelial cell. The latter analysis corresponds to simple stereospecific membrane pores. The mathematical model allowed for changes in tissue glucose content and back-diffusion of tracer during the Glucose is transported across the blood-brain barrier principally by a process of facilitated diffu sion (Crone, 1965;Lund-Andersen, 1979).

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and in the hand (Silvertsson, 1970, Acta Physiologica Scandinavica, Suppl. 343) is increased in hypertension. Secondly, the vasodilatation produced by exercise results in approximately the same change in resistance in hypertensives as in normals but as resistance falls, the difference between the normal and the hypertensives is unchanged. Finally, the peripheral resistance in dogs varies inversely with the cardiac output from one day to the next. The production of hypertension does not alter this relationship but shifts the resistance curve to a higher level. Again resistance varies spontaneously but the difference from the normal is fixed.The findings, taken together, indicate that in hypertension the process leading to an increased resistance does not interact with the vascular smooth muscle activity but remains relatively fixed despite wide fluctuations in vascular tone. D.The control mechanisms of the circulation have been studied systematically using engineering principles of control system analysis. Mechanisms that have received special attention are the following:(1) Renal ischaemia gives (a) increased secretion of r a i n and formation of angiotensin; (b) peripheral vasoconstriction; (c) elevated arterial pressure; (d) elimination of the renal ischaemia.(2) Increased arterial pressure gives (a) baroreceptor excitation; (b) sympathetic inhibition; (c) reduced arterial pressure back toward normal.(3) Decreased arterial pressure gives (a) increased aldosterone secretion; (b) salt and water retention; (c) enhanced blood volume; (d) elevation of arterial pressure back toward normal.(4) Increased arterial pressure gives (a) increased loss of water and salt through the kidneys; (b) decreased body fluid volume; (c) decrease of arterial pressure back toward normal.The gains of the first three of these mechanisms varied from 1.6 to 8, all relatively low values. However, the gain of the fourth mechanism, the kidney mechanism for pressure and fluid volume regulation, approached infinity over a period of several days. Therefore, this last control system completely overshadowed all the others for long-term control of arterial pressure. A major conclusion of this study is that the functional relationship between arterial pressure and output of salt and water by the kidneys must be changed from normal if chronic hypertension is to be sustained, regardless of the initiating cause of the hypertension.

1.The intestinal absorption of carnosine, glycylglycine, glycyl-D-phenylalanine, glycyl-L-phenylalanine, glycyl-L-proline and L-prolylglycine were investigated after intraluminal injection of dipeptide into anaesthetized rats.2. With all six dipeptides, the intact substance was detected by ion-exchange chromatography in blood samples taken from the superior mesenteric vein.3. The rate of hydrolysis of the dipeptides in tissue homogenates was measured in vitro.4. The relative rates of hydrolysis varied by a factor of 300; there was an apparent inverse relationship between rate of hydrolysis and detection of intact peptide. 5. Peptide absorption was accompanied by increases in venous concentrations of the component amino acids, which appeared in proportions appropriate to the view that peptide absorption preceded hydrolysis.6. It is suggested that slowly hydrolysed dipeptides may pass intact through the intestine wall under physiological conditions.