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1. The effect of metabolic acidosis of 4–6 h duration on cardiac output, blood pressure, heart rate, and hepatic and renal blood flow has been studied in the rat. 2. In anaesthetized rats, blood pressure and heart rate fell linearly with blood pH in both sham-operated and nephrectomized rats. There was no significant difference between the two groups in the effect of acidosis on either variable. 3. Cardiac output showed a significant fall with increasing acidosis in the conscious rat. 4. Estimated hepatic blood flow in conscious rats showed a significant positive correlation with blood pH in both sham-operated and nephrectomized animals. There was no significant difference in estimated hepatic blood flow between the two groups of animals at any blood pH. 5. In conscious rats, increasing acidosis caused a progressive decrease in estimated renal blood flow. 6. It is concluded that the increase in the previously described apparent renal contribution to lactate removal in the acidotic rat cannot be explained by any circulatory effect mediated by the kidney. The possible relevance of the findings to lactate homeostasis is discussed.

1. The isolated perfused kidneys of fed rats in normal acid-base status showed a constant rate of lactate removal from the perfusate between 5 and 90 min of perfusion at a perfusate pH of 7·4–7·5. 2. Lactate removal by kidneys of rats in normal acid-base status was stimulated within 30 min by a reduction in perfusate pH to 7·1–7·2, but depressed when perfusate pH was reduced further. 3. Kidneys taken from rats previously made acidotic and perfused with media of various pH values showed a progressive fall in the rate of lactate removal during the perfusion. 4. Glucose output by the kidneys of rats in normal acid—base status perfused with lactate as substrate was not affected by an alteration in perfusate pH. The kidneys of acidotic rats generally showed an increased rate of glucose output compared with those of control rats.

1. The rate of removal from the circulation of an intravenous lactic acid load has been studied in conscious rats, previously subjected either to bilateral nephrectomy or to a sham operation. 2. In rats with normal blood pH, the apparent contribution of the kidneys to removal of the lactic acid load is 30%; less than 12% of the renal contribution is attributable to urinary excretion. 3. In bilaterally nephrectomized rats made acidotic by administration of ammonium chloride, the rate of removal of a half-neutralized lactic acid load is progressively decreased with increasing severity of acidosis. No such effect is seen in sham-operated animals. 4. An increase in the ability of the kidney to remove lactate during acidosis compensates for approximately half of the simultaneous fall in the capacity of the remainder of the body for lactate assimilation. 5. Basal blood lactate concentrations fall in the presence of metabolic acidosis.

1. Concentrations of high-density-lipoprotein cholesterol and of glycosylated haemoglobins [HbA1(a+b+c)] were measured in non-fasting blood samples taken from 171 diabetic patients. 2. Mean concentrations of high-density-lipoprotein cholesterol were lower in men, and in patients not requiring insulin. 3. There was no correlation between concentrations of high-density-lipoprotein cholesterol and of HbA1(a+b+c) in the patients as a whole, but a significant positive correlation was found between these values in male diabetics not requiring insulin. 4. Changes in the concentrations of HbA1(a+b+c) were not correlated with changes in concentrations of high-density-lipoprotein cholesterol.

1. The segmented thermal clearance probe is a noninvasive instrument which measures heat thermal clearance, a variable directly proportional to superficial blood flow, with a depth sensitivity theoretically proportional to the sensor diameter. We compared an 18 mm sensor and a recently developed 57 mm sensor with the reference technique of xenon washout. 2. The theoretical depth sensitivity of the sensors was assessed using Perspex spacers. Ninety-five per cent of sensitivity had been lost at the respective depths of 3.5 mm and 7.1 mm for the 18 mm and 57 mm sensors. 3. A comparison was made between heat thermal clearance reading and 133Xe decay curves using the two probes for 15 min after injection of 133Xe at 2 mm and 6 mm depths in the anterior thigh in 41 subjects. The 57 mm sensor showed similar correlation with xenon washout at 2 mm injection depth (r = 0.89) and 6 mm injection depth (r = 0.86), whereas the 18 mm sensor showed greater correlation at 2 mm (r = 0.92) than at 6 mm (r = 0.62). 4. The 57 mm sensor was compared with xenon washout at 6 mm in eight insulin-treated diabetic subjects. The relationship was similar to that in non-diabetic subjects (r = 0.79), with no significant difference in slope or intercept. 5. It is concluded that the 57 mm thermal clearance probe may be used to study blood flow at the depth of insulin injection (6 mm) in diabetic and non-diabetic subjects.

1. We have employed a thermal clearance probe to study fingertip blood flow, which comprises predominantly arteriovenous anastomotic flow. 2. In non-diabetic subjects there was a marked variability in resting fingertip blood flow which was of similar magnitude to that in diabetic subjects without autonomic neuropathy. 3. In 20 diabetic subjects with increasing severity of autonomic neuropathy there was a reduction of spontaneous variability in flow (r= 0.59, P < 0.001), which was not related to differences in basal flow, in skin thickness or in age. 4. There was no relationship between maximal flow and severity of autonomic neuropathy (r= 0.08), although basal flow was decreased in subjects with moderate, but not those with severe, autonomic neuropathy (P < 0.01 and P > 0.4 compared with controls). 5. Our failure to find an increase in basal fingertip flow in autonomic neuropathy could imply that spontaneous variability of anastomic flow is lost before increased arteriovenous shunting becomes apparent, but it could result from the indirect heating employed in the study causing vasodilatation in subjects without neuropathy.

1. A thermal clearance probe was used to measure fingertip blood flow. When flow was occluded the baseline value was reproducible (coefficient of variation 2% between subjects), whereas basal and maximum flow were poorly reproducible even within subjects. 2. Synchronous changes in thermal clearance were seen when two probes were used on fingers and toes of different limbs (r = 0.77–0.97), in keeping with a central control mechanism. 3. Fingertip blood flow, as measured by thermal clearance, correlated with Po2 of venous blood draining from the dorsum of the hand (r = 0.72–0.92). 4. Contralateral hand cooling caused a sharp reduction of fingertip thermal clearance by 44.2 ± 3.7%. 5. Thermal clearance traces were damped in fingers with heavy keratinization, and improved when keratin was removed. 6. Comparisons with venous occlusion plethysmography (VOP) and photoelectric plethysmography (PPG) showed that thermal clearance correlates with both methods (r = 0.60–0.92 for VOP and 0.64–0.93 for PPG) but with much integration of the signal and a 10 s lag. 7. It is concluded that the probes used measure predominantly anastomotic flow and not nutrient skin blood flow alone.