Plasma free fatty acids and serum insulin in subjects feeding at 12-hour intervals; effects of methionyl growth hormone and of acipimox, an inhibitor of lipolysis

Nutrition and the circadian timing system

Life on earth has evolved under the daily rhythm of light and dark. Consequently, most creatures experience a daily rhythm in food availability. In this review, we first introduce the mammalian circadian timing system, consisting of a central clock in the suprachiasmatic nucleus (SCN) and peripheral clocks in various metabolic tissues including liver, pancreas, and intestine. We describe how peripheral clocks are synchronized by the SCN and metabolic signals. Second, we review the influence of the circadian timing system on food intake behavior, activity of the gastrointestinal system, and several aspects of glucose and lipid metabolism. Third, the circadian control of digestion and metabolism may have important implications for several aspects of food intake in humans. Therefore, we review the human literature on health aspects of meal timing, meal frequency, and breakfast consumption, and we describe the potential implications of the clock system for the timing of enteral tube feeding and parenteral nutrition. Finally, we explore the connection between type 2 diabetes and the circadian timing system. Although the past decade has provided exciting knowledge about the reciprocal relation between biological clocks and feeding/energy metabolism, future research is necessary to further elucidate this fascinating relationship in order to improve human health.

Acute pharmacologic blockade of lipolysis normalizes nocturnal growth hormone levels and pulsatility in obese subjects

Obesity is associated with blunted growth hormone (GH) levels and pulsatility and elevated plasma free fatty acids (FFA) levels. To evaluate whether the two phenomena are correlated, in the present study we investigated the effects of an acute pharmacologic blockade of lipolysis on nocturnal GH levels and pulsatility in 10 obese and 10 control subjects. At 9 PM on two different nights with a 1-night interval in between, all subjects received either a single oral tablet of placebo or acipimox slow release (ACX-SR, 500 mg) in randomized order. Blood samples were drawn from 10 PM to 6 AM for evaluation of FFA, glycerol, GH, immunoreactive insulin (IRI), glucose, and insulin-like growth factor-I (IGF-I) levels. After placebo, FFA and glycerol levels were higher (P < .02) and GH levels, areas, peak amplitude, and peak increment (assessed by the Cluster algorithm) were lower in obese than in control subjects (P < .01). After ACX-SR, FFA and glycerol levels were reduced in both groups (P < .02 v placebo), and in obese subjects they became similar to those observed in control subjects after placebo. ACX-SR had no effect on GH levels and pulsatility in control subjects. GH levels, areas, peak, amplitude, peak increment, and interpeak valley levels were all increased after ACX-SR in obese subjects (P < .05 or less v placebo) and became similar to those observed in normal subjects after placebo, but no correlation was found between the reduction in FFA levels and the increase in GH levels and pulsatility.(ABSTRACT TRUNCATED AT 250 WORDS)

Site of production of IGF1 in the normal and stimulated mouse thyroid

Insulin-like growth factor 1 (IGF1) has emerged as an essential factor in the follicular cell growth response in vitro to TSH, although its source within the thyroid in vivo is not clear. We have studied the localisation of IGF1 mRNA by in situ hybridization using digoxigenin labelled oligoprobes in tissue sections of mouse thyroid. Our results show that in the thyroid IGF1 mRNA is predominantly present in follicular cells and C cells rather than the stroma. Follicular cell levels are higher during postnatal thyroid growth and during the growth response to goitrogen administration, but decrease in the mature animal. This decrease in production is limited to the follicular cells, as IGF1 mRNA is still easily demonstrable in C cells and in the parathyroid. Immunocytochemistry for IGF1 peptide shows a weak and variable follicular cell content in both juvenile and mature mice, but a more uniform distribution during growth in response to a goitrogenic stimulus. These studies show that the follicular cells are the main source of IGF1 in the thyroid, and suggest that the role of IGF1 in follicular cell growth is as an autocrine factor.