TITLE:
Obesity and leptin resistance: The role of growth hormone
AUTHORS:
Malgorzata Szczesna, Katarzyna Kirsz, Miroslaw Kucharski, Pawel Szymaszek, Dorota Anna Zieba
KEYWORDS:
GH; Leptin Resistance; Obesity; SOCS-3
JOURNAL NAME:
Health,
Vol.5 No.8C,
August
13,
2013
ABSTRACT: Decreased growth
hormone (GH) function in obese patients might contribute to associated
metabolic abnormalities. This study aimed to investigate the effect of
leptin, GH and periods of leptin sensitivity or/and insensitivity on the expression
of the SOCS-3 gene in the ovine pituitary and to examine the influence of
centrally administered leptin on GH release in sheep. Our first experiment investigated
the periods of leptin resistance and leptin sensitivity, which are known as the
long day (LD) and the short day (SD) periods, respectively, using ewes that
were surgically fitted with third ventricular cannulae. The ewes were assigned
randomly to one of three treatments and were centrally infused at 0, 1 and 2 h,
beginning at sunset. The treatments consisted of central infusions of either
Ringer-Locke buffer or leptin (0.5 or 1.0 μg/kg body weight (BW),
respectively). Our next experiment examined the pituitaries isolated from ewes
decapitated in either May or November. The explants were treated with
control or GH (100 or 300 ng/ml) or leptin
(50 or 100 ng/ml)—containing media and incubated for one of four different time
intervals. The in vivo experiments demonstrated variable effects of leptin on GH release depending on the period of
leptin sensitivity/ insensitivity. The in
vitro experiments demonstrated that leptin significantly influenced the
expression of the SOCS-3 gene during that SD compared to thatduring the LD. During
the SD, we observed that significantly low or high doses of GH affected the
expression of SOCS-3. These results indicated a strong correlation between
leptin or GH and SOCS-3, which might explain leptin resistance and the
associated perturbations in GH signaling.