1. The effect of moderate endurance exercise on blood glucose concentration and on glucoregulatory hormones was studied in nine thyrotoxic and five myxoedematous humans before and 3 months after anti-thyroid and substitution therapy, respectively. 2. At rest, the fasting concentrations of insulin and pro-insulin correlated positively with the prevailing total tri-iodothyronine concentration, whereas the concentrations of noradrenaline and cortisol correlated inversely with the tri-iodothyronine concentration. 3. During exercise the plasma insulin, pro-insulin and C-peptide concentrations decreased. The plasma glucagon concentration increased slightly in thyrotoxic patients before and after treatment and was largely unchanged in myxoedematous patients in either state. 4. The plasma noradrenaline concentration increased before and after treatment in both groups, with concentrations two times higher in the myxoedematous than in the thyrotoxic patients. Treatment for 3 months did not change this pattern. The plasma adrenaline concentration increased in both groups, but in the untreated thyrotoxic patients the increase was two to three times greater than that after treatment or that in the myxoedematous group. 5. The blood glucose concentration decreased in eight of nine untreated thyrotoxic patients, but was largely unchanged after treatment or in the myxoedematous patients. A strong negative correlation was found between the decline in blood glucose concentration and the increase in plasma adrenaline concentration in the thyrotoxic group. 6. Thus, during exercise untreated thyrotoxic patients are prone to hypoglycaemia, show an inadequate glucagon response, and exhibit a large counter-regulatory increase in plasma adrenaline concentration.

1. The effects of medium glucose concentration (0–20 mmol/l) and flow (100–33% of normal) on lactate uptake at low lactate concentration were studied in perfused livers from 48-h-starved rats with perfusate pH values of 7.4 and 6.8. 2. Lactate uptake was independent of glucose concentration in the range 5–10 mmol/l, but was slightly inhibited with time at 20 mmol/l glucose. This pattern was independent of perfusate pH. 3. At both pH values lactate uptake decreased proportionally with flow, and at low flow lactate was produced by the livers. The effect of flow was greatest at pH 7.4 where a net lactate production was found at 48% of normal flow, whereas at pH 6.8 lactate production was not seen until the flow was reduced to 33% of normal. 4. When glucose was omitted from the perfusate lactate production ceased at both pH values. 5. The effect of low pH on lactate uptake and production in liver probably reflects inhibition of glycolysis by low pH.

1. The effect of pH on lactate uptake was studied in perfused liver of rats starved for 48 h. 2. At both low pH (6.8) and normal pH (7.4) lactate uptake was a linear function of lactate concentration in input medium in the range 0.4–1.5 mmol/l. 2. In the lower concentration range (0.4–0.8 mmol/l) the rate of lactate uptake was 30% higher at pH 6.8 than at pH 7.4. 4. At pH 6.8 lactate uptake was independent of whether P co 2 was 2.7 or 5.3 kPa. 5. We suggest the increased rate of lactate uptake at low pH and concentrations lower than 0.8 mmol/l was due to the stimulatory effect of H + on the lactate carrier.