Regulation of leptin synthesis and secretion before …
And new evidence suggests that insulin-mediated signaling components may play a key part in regulating that addiction. Injection of insulin into the brains of rodents, for example, increases the amount and activity of dopamine transporters in the substantia nigra, a midbrain structure involved in reward, addiction, and movement. Furthermore, obese and diabetic leptin-deficient mice have low levels of tyrosine hydroxylase, an enzyme involved in dopamine synthesis, in their midbrain dopamine neurons.
regulates leptin synthesis and secretion in ..
Obesity is associated with high plasma levels of leptin, and leptin participates at the hypothalamic and pituitary levels in the regulation of GH secretion.
Previous studies have indicated that adipose tissueis not only an energy-storing organ, but also secretes variouscytokines. Leptin is an adipocytokine that is predominantlyproduced in white adipose tissue. Circulating leptin levels areproportional to the quantity of body fat (). The adipokine leptin has emerged asa significant factor involved in bone metabolism. Leptin acts onthe peripheral and central nervous systems in order to regulatebone metabolism (). To date,experimental animal studies investigating the impact of leptin onthe skeleton have produced conflicting results. Turner () investigated the effects ofleptin deficiency on bone metabolism. The results demonstrated thatin comparison with wild-type (WT) mice, leptin-deficient (ob/ob)mice and leptin receptor-deficient (db/db) mice had a lower rate ofbone formation and a reduced osteoblast-lined perimeter. However,subcutaneous replacement of leptin in ob/ob mice resulted in anincrease in bone formation, along with an increasedosteoblast-lined perimeter ().In addition, the authors utilized gene therapy in order toselectively increase leptin levels in the hypothalami of ob/obmice. This resulted in normalization of the mouse bone mass, inaccordance with the results obtained using subcutaneousadministration of the hormone (). The leptin replacement studydemonstrated no difference between the indirect central and directperipheral actions of leptin on bone metabolism, as peripherallyadministered leptin is able to cross the blood-brain barrier. Theperipheral and central pathways involving leptin exert a positiveeffect on bone metabolism ().
Peptide Hormones - The Medical Biochemistry Page
AB - The collective evidence from studies in rodents and humans indicate that leptin is a regulated hormone, whose actions straddle several behavioral, physiological, cellular, and molecular processes across diverse organ systems. This chapter discusses the physiological, hormonal, and metabolic factors involved in the synthesis and secretion of leptin and the regulation of circulating leptin levels in humans. Although leptin secretion was rarely measured directly in the existing reports, increases and decreases in circulating leptin levels are assumed to reflect similar changes in adipose tissue leptin production. The latter assumption is untenable in renal failure, where decreased leptin clearance becomes a factor in leptin abundance. The physiological factors that influence leptin secretion include gender, age, adiposity, physical exercise, feeding, and caloric restriction. Several hormones, including insulin, glucocorticoids, growth hormone, estradiol, testosterone, insulin-like growth factor-I, and somatostatin also modulate leptin secretion. In addition to alteration of circulating leptin levels, evidence of an effect on leptin synthesis (as indicated by adipose tissue leptin mRNA abundance) has been demonstrated for the effects of obesity and some of the hormones, such as insulin and glucocorticoids. Although mRNA abundance generally reflects synthesis, effects on mRNA stability have not been routinely investigated; thus, it is assumed that an increase in mRNA signifies increased synthesis. Where tissue evidence is lacking, it is assumed that the direction of alteration in circulating leptin levels reflects leptin production at the adipocyte level.
Leptin Part Deux: Liver - Living an Optimized Life
Leptin is 16 kDa, 146 amino acid residue peptide hormone that is thought to play a central role in the regulatory role of adipose tissue on energy metabolism. Leptin is synthesised by adipocytes and released to the circulation, where it acts as an afferent signal to the central nervous system, relaying information about the degree of adiposity to the hypothalamus. Hyperthalomic leptin resistance is associated with obesity and an increased risk of type 2 diabetes and hyperinsulinemia. However, the direct effects of hyperinsulinaemia on leptin secretion by adipocytes remain unclear. The aim of this study was to examine leptin secretion in vitro by adipocytes from type 2 diabetic and normal donors under normoinsulinaemic and hyperinsulinaemic conditions. The results of this study showed that for normal adipocytes, exposure to 10 and 100 ng/ml insulin for 72 hours caused an increased leptin secretion of 5.68 ± 0.82 pg/ml/104 cells (P4 cells (P4 cells (P4 cells (P4 cells (P