59 research outputs found
Interactions of leptin and thyrotropin 24-hour secretory profiles in short normal children
Thyroid hormones and leptin have effects on similar aspects of body
homeostasis, such as energy expenditure, thermogenesis, and metabolic
efficiency. Thus, the cross-talk between the thyrostat and the lipostat
might play a crucial role in the maintenance of body homeostasis. To
investigate the relationship between the hypothalamic-pituitary-thyroid
(HPT) axis and leptin under physiological conditions, we evaluated the
pulsatility and circadian rhythmicity and time-cross-correlated the 24-h
secretory patterns of leptin and TSH in 12 short normal prepubertal
children (6 girls and 6 boys). In both male and female subjects, leptin
was secreted in a pulsatile and circadian fashion, with a nocturnal
leptin surge that was more pronounced in males than in females. Mean
24-h leptin levels and total area under the curve were significantly
higher in girls than in boys. This was mainly due to the nighttime mean
leptin levels and total area under the curve, which were higher than
those in boys. The cross-correlated 24-h leptin and TSH levels revealed
significant positive and negative correlations. The positive one, of
leptin over TSH, suggests a positive feedback regulation by leptin on
the HPT axis, which might play an important role in triggering the
neuroendocrine response to starvation, including decreased thyroid
hormone levels. The negative correlation, of TSH over leptin, could
explain the compensatory changes in adipocyte metabolism, and indirectly
in circulating leptin levels, in response to alterations in thyroid
status. In conclusion, we suggest that under baseline physiological
conditions, the HPT axis has a prevailing inhibitory effect on leptin
secretion, whereas leptin has a prevailing positive effect on the HPT
axis. The sexual dimorphism in leptin levels does not seem to influence
in a major way the interactions between the HPT axis and leptin
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