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We reviewed the effects of glycaemic index (GI) of carbohydrates, consumed before exercise, on metabolism and performance. A carbohydrate with a high GI results in rapid absorption of glucose and a large and fast rise in blood insulin. A carbohydrate with a low GI results in a slower and smaller rise in blood glucose and insulin levels. Increased insulin levels inhibit fat oxidation and promote carbohydrate oxidation, which may result in faster glycogen depletion when high-GI carbohydrates are consumed before exercise. High-GI carbohydrates may also result in rebound hypoglycaemia, which would leave one with lower than normal blood glucose levels and hinder exercise performance. Most studies of low-versus high-GI carbohydrates consumed before exercise indicate that low-GI carbohydrates confer a better metabolic response (i.e. lower insulin release, increased fat oxidation and decreased glucose oxidation compared with high-GI carbohydrates). Despite this improved metabolic response, intake of low- and high-GI carbohydrates result in similar improvements in exercise performance. In the 20 studies we reviewed, low-GI carbohydrates were more beneficial for improvement in performance in seven studies, high-GI carbohydrates were more beneficial in one study, and there was no difference in performance improvement between carbohydrates of differing GI in 12 studies. We conclude that low-GI carbohydrates result in a more favourable metabolic response compared with high-GI carbohydrates when consumed before exercise, but this does not always result in a greater improvement in exercise performance.

Previous work that apparently showed a functional relationship between GFR and maximum bicarbonate reabsorption was done at a time when the effects on the latter of several factors (PCO2, plasma potassium concentration, and extracellular fluid volume expansion) were not recognized. The present study re-examines this relationship, while controlling these factors. In 14 hydropenic dogs, bicarbonate reabsorption per unt GFR increased linearly with increases in plasma bicarbonate concentration. At any level of plasma bicarbonate concentration,the absolute rate of bicarbonate reabsorption was functionally related to the GFR. In six volume-expanded dogs, bicarbonate reabsorption remained stable at 20-22 mmol/liter GFR as plasma bicarbonate was raised to greater than 40mM. The absolute rate of bicarbonate reabsorption increased with large increases in GFR induced by methylprednisolone and high-protein diet. In a third group of dogs, bicarbonate reabsorption varied directly with increases in GFR, while plasma bicarbonate concentration was held relatively constant above the threshold. We conclude there is a close functional relationship between the absolute rate of bicarbonate reabsorption and GFR in individual dogs.

We have used a myasthenic serum that in adult rat muscle is specific for acetylcholine receptors (AChRs) in the extra-junctional membrane to characterize the AChRs at developing endplates. Immunocytochemical experiments show that AChRs at endplates in the rat diaphragm bind the myasthenic antibodies during the first week after birth but lose their reactivity during the second and third postnatal weeks. AChRs at endplates in adult rat diaphragm do not bind the antibodies even after denervation; in contrast, AChRs at endplates in an adult chicken muscle (anterior latissimus dorsi) are recognized by the antibodies. The loss of immunological reactivity thus may be correlated with a change in the channel properties of the AChR and with the appearance of synaptic folds, two postnatal developmental changes that occur at the endplates of rats, but not of chickens.