Abstract
Recent evidence that the non-GH dependent IGF-BP is not only a carrier protein but also has an active role in the growth process is enhanced by observations of a marked circadian rhythm. We have measured RIA levels of this IGF-BP over 12 or 24 hours in 11 poorly controlled diabetic adolescents & 7 normals (4 adolescents & 3 adults). In 5 diabetics, overnight profiles were also obtained with euglycaemia maintained by an insulin clamp. In normal adults IGF-BP was undetectable except for a nocturnal peak of 30-40ng/mL. In 2 diabetics receiving long-acting insulin in the evening, levels of 10-20ng/mL in the day and 100-120ng/mL at night were found. In 3 diabetics receiving long-acting insulin in the morning levels reached 410-460ng/mL at night concomitant with elevated plasma glucose, with which a close correlation was found. Maintenance of euglycaemia overnight failed to suppress the IGF-BP peak although this occurred earlier than on the unclamped night. However in one subject who became hypoglycaemic the nocturnal peak was considerably blunted. These findings show for the first time that in young diabetics whilst markedly elevated non-GH dependent IGF-BP levels are found the nyctohemeral rhythm is maintained irrespective of metabolic control. Levels are consistent with insulin being a major regulator of this IGF-BP in the circulation.
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