Circadian Rhythm of Serum Vaspin in Healthy Male Volunteers: Relation to Meals

Abstract

Visceral adipose tissue-derived serine protease inhibitor (vaspin) is a novel adipokine with insulin-sensitizing effects. However, the physiological role for vaspin in human metabolic regulation remains to be established. We studied the 24-h profiles of circulating vaspin concentrations in relation to meal ingestion in normal adults. Blood samples were drawn 39 times throughout a 24-h period from 10 healthy male subjects provided with meals on a fixed schedule. On a separate day, four subjects were fasted and then provided with an unexpected meal to clarify the effect of meal consumption on serum vaspin levels. Serum vaspin concentrations were determined by ELISA. Serum vaspin levels were highest in the early morning before breakfast and fell to trough levels within 2 h after breakfast. Serum vaspin levels also showed a preprandial rise and postprandial fall at lunch and dinner, although at lesser degrees than at breakfast. Intermeal vaspin concentrations reached a nadir in the mid-afternoon and showed a nocturnal rise, with peak nighttime vaspin levels being approximately 250% of nadir levels. Unscheduled food ingestion after a prolonged fast significantly reduced serum vaspin levels, suggesting that energy intake itself has a suppressive effect on serum vaspin levels. The diurnal pattern of serum vaspin concentrations was exactly reciprocal to that of insulin and of glucose. Serum vaspin levels have a meal-related diurnal variation, suggesting a role for vaspin in metabolic regulation. However, the reciprocal relationship between serum vaspin and insulin may negate the importance of vaspin as an physiological insulin sensitizer.