Light/Dark Cycle-dependent Metabolic Changes in Adipose Tissue of Pinealectomized Rats

Abstract

We investigated the effects of pinealectomy on adipose tissue metabolism at different times of day. Adult male Wistar rats were divided into two groups: pinealectomized and control (sham-operated). Eight weeks after surgery, the animals were killed at three different times (at 8.00 a.m., at 4.00 p.m. and 11.00 p.m.). We collected blood samples for glucose, insulin, corticosterone, and leptin determinations, and periepididymal adipocytes for in vitro insulin-stimulated glucose uptake, oxidation, and incorporation into lipids. Pinealectomy caused insulin resistance as measured by 2-deoxyglucose uptake (a fall of approximately 40 % in the maximally insulin-stimulated rates) accompanied by hypercorticosteronemia at the three time points investigated without changes in plasma insulin an or leptin levels. Furthermore, pinealectomy increased the insulin-induced glucose incorporation into lipids (77 %) at 4.00 p.m. and insulin-induced glucose oxidation in the morning and in the afternoon, while higher rates were observed in the evening and in the morning in control rats. In conclusion, cell responsiveness to insulin was differentially affected by pineal ablation and time of day, and persistent insulin resistance was obtained in pinealectomized rats. We hypothesize that pinealectomy exposes the animal to an inadequate match between energy requirements and fuel mobilization.

Circulating melatonin and the risk of breast and endometrial cancer in women

“…In humans, an association between night shift work and the metabolic syndrome is thought to exist 35. At least in one study, exogenous melatonin reduced weight gain, particularly among obese women,36 and melatonin may influence appetite 37…”

Molecular clocks, type 2 diabetes and cardiovascular disease

“…[72][73][74][75] It is clear that melatonin is vital to this process, mediating the seasonal photoperiodic information through the clock system. [76][77][78][79][80][81][82][83][84] Disrupting the melatonin signal or increasing the duration of light leads to changes in metabolism and adiposity consistent with the summer/autumn phenotype, with fat storage and insulin resistance. 79,80,85 Persistent phase shifting of the light/dark cycle in other animals disrupts sleep/wake cycles and eating patterns, mimicking shift work.…”

“…[76][77][78][79][80][81][82][83][84] Disrupting the melatonin signal or increasing the duration of light leads to changes in metabolism and adiposity consistent with the summer/autumn phenotype, with fat storage and insulin resistance. 79,80,85 Persistent phase shifting of the light/dark cycle in other animals disrupts sleep/wake cycles and eating patterns, mimicking shift work. 86,87 Not only has this been shown to disrupt peripheral clock gene expression 86 but it is associated with weight gain 87 and premature death.…”

Night Shift Work and the Risk of Endometrial Cancer

“…In addition to its potential antiestrogenic activities (7), melatonin seems to modulate aromatase activity in mammary tumors (8). Melatonin further seems to play an important role in fat metabolism, and increased adiposity is associated with an increased risk of endometrial cancer (9)(10)(11)(12).…”