Abstract
We have described before that different forms of physical exercise induce bidirectional
changes of insulin binding of monocytes (Michel G., Vocke T., Fiehn W., Weicker H.,
Schwarz W., Bieger W.P.: Am J Physiol 246: E 156-E 159, 1984). In vitro experiments suggested these changes to be due to
dialyzable serum components. In this study, we investigated several hormones and metabolites
as to their capacity to alter insulin binding in vitro. Somatostatin (100pg/ml) and
prostaglandin B1 (10nmol/l) were the only hormonal agents producing a small and reversible (somatostatin)
increase in monocyte insulin binding. Ketones were only effective at concentrations
unphysiologically high. Acidosis diminished insulin binding to monocytes to about
35% of that found at pH 7.6. Lactate (10mmol/l) induced a 28% drop in cellular insulin
binding at low pH. The effect persisted after removal of the agent and may hence account
for some of the decrease in cellular insulin binding observed after exhaustive exercise.
Although the effect of acidosis was reversible in vitro, it may add considerably to
the effect of lactate under in vivo conditions. The dialyzable serum factors responsible
for the enhancement of binding affinity after long-term moderate exertion remain unknown.
Free fatty acids proved effective in increasing monocyte insulin binding (14% with
1 mmol/l oleic acid) in vitro.
Key words
physical exertion - monocytes - insulin binding - acidosis - lactate - free fatty
acids
