AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 458-R464, Copyright © 1982 by American Physiological Society
Glucose and lactate kinetics and interrelations in an antarctic bird (emperor penguin)
R. Groscolas and A. Rodriguez
The isotope single-injection method was used to investigate the glucose and
lactate kinetics and the interrelationships between the glucose and lactate
pools in fasting emperor penguins. In these remarkably fast-resistant
birds, mean lactate concentration, replacement rate, pool, space, and
transit time were 1.5 mmol.1-1,53 mumol.min-1.kg-1, 900 mumol.kg-1, 60% of
body mass, and 17 min, respectively. Mean glucose concentration,
replacement rate, pool, space, and transit time were 20 mmol.1-1, 23
mumol.min-1.kg-1, 4,300 mumol.kg-1, 24% of body mass, and 196 min,
respectively. Maximum conversions of lactate into glucose and of glucose
into lactate were 29 +/- 2.9% and 75.5 +/- 4.2%, respectively, which
indicates that lactate is an effective gluconeogenic precursor and a major
fate of glucose metabolism in fasting penguins. The lactate replacement
rate and incorporation into glucose were related to the plasma lactate
concentration, which suggests that the rate of formation of glucose from
lactate is dependent on the availability of lactate. The glucose
replacement rate and reduction into lactate were related with the plasma
glucose concentration, suggesting that the rate of lactate formation from
glucose is dependent on the plasma glucose concentration. These data
suggest that in the fasting emperor penguin glucose and lactate
availability is capable of regulating the rate at which these substrates
are utilized and interconverted. To our knowledge, this is the first
evidence for such regulatory capacities in birds.
