Review Article
Year: 2017 | Month: May | Volume: 7 | Issue: 5 | Pages: 332-344
The Effect of Leptin on the Hypothalamic-Pituitary Gonadal Axis and Puberty
Zewdu Jima Takle1, Tesfaye Girma Legesse2
1Department of Physiology, 2Department of Nutrition,
Saint Paul’s Hospital Millennium Medical College, Addis Ababa, Ethiopia
Corresponding Author: Zewdu Jima Takle
ABSTRACT
Leptin is a hormone secreted by adipose tissue. Many researches done on leptin revealed that leptin plays a key role in regulation of energy, food intake and neuro-endocrine system. One of the neuro-endocrine axis that expresses the effect of leptin is the reproductive system i.e. hypothalamo-pitutary gonadal (HPG) axis. As several studies demonstrated, leptin affects HPG axis at different levels. Hypothalamus, a center for feeding and endocrine system, is the major target site for expression of the effect of leptin, as this area of the brain contains leptin receptors. So, these receptors for leptin may mediate endocrine functions and HPG axis is one of them. There are a number of studies done to come across the effect of leptin on HPG axis and all of them evidenced that leptin has direct and indirect effect on HPG axis and gonadotropin releasing hormone (GnRH) is one of the key sites. But there are arguable findings among these researches regarding mechanism of action for leptin. Even though many experiments demonstrated that leptin may directly affects GnRH through its receptor on GnRH, there are some that showed the effect of leptin on GnRH is indirect i.e. through GnRH synapsing neurons. The other target area for leptin is anterior pituitary. It is demonstrated that leptin receptors are also found in anterior pituitary and administration of leptin stimulated luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from anterior pitutary. In addition, leptin receptors are located in gonads, injection of leptin to different experimental animals showed reversal of sterility and inhibition of steroidogenesis. On the other hand, many researches done to reveal the correlation between leptin and puberty, the results are controversial. As many findings demonstrated, increase in leptin concentration just before the onset of puberty is seen in humans and rats. On the contrary, some researches evidenced that there is no any correlation between level of leptin and onset of puberty and also there are findings showed the effect of leptin is permissive rather than primary triggering factor for the onset of puberty.
Key words: Anterior pituitary; Follicle stimulating hormone (FSH); Gonadotropin releasing hormone (GnRH); Gonads; Hypothalamo-pitutary Gonadal (HPG) Axis; Hypothalamus; leptin receptors; Leptin; Leuthenazing hormone (LH); Steroidgenesis