Expression of a leptin receptor in immortalized gonadotropin-releasing hormone-secreting neurons

Leptin is secreted by adipocytes and regulates food intake and energy balan ce through the activation of specific receptors (OB-R). Recent evidence sug gests that it is also involved in the control of reproductive processes, by possibly acting on central and peripheral targets. In particular, it has b een shown that leptin may indirectly stimulate GnRH release from hypothalam ic fragments by acting on interneurons impinging on GnRH-secreting neurons. The possibility that leptin might additionally modulate the activity of Gn RH-secreting neurons in a direct way has been addressed in the present stud y, by using the immortalized GnRH-secreting cell line GT1-7. The presence o f OB-R messenger RNA (mRNA) (long form) was detected by RT-PCR analysis of total RNA from GT1-7 cells. An OB-R protein is also expressed in these cell s, as shown by immunocytochemistry and by Western blot analysis. The latter has revealed the presence of a single immunoreactive OB-R with an approxim ate size of 130 kDa. To study the functionality of these receptors, the eff ect of leptin treatment on GnRH secretion and gene expression in GT1-7 cell s were evaluated. Under static conditions, GnRH release was stimulated by e xposure to low concentrations of leptin (10(-12) M after 30 min; 10 M after 60 min). The 10(-1)2 M dose was selected for studying the effect of leptin on GnRH secretion under dynamic conditions. To this purpose, GT1-7 cells w ere placed in a perifusion system; treatment with leptin (10-12 hi) for 60 min stimulated GnRH release with no changes of pulse frequency. On the cont rary, exposure to leptin (10(-12)-10(-10) M) for 1, 3, 6, and 24 h did not affect GnRH gene expression in GT1-7 cells. The present results indicate th at GT1-7 cells possess OB-Rs and that leptin may directly affect their func tion. Taken together with the available reports, these findings suggest tha t leptin might participate in the regulation of reproductive processes by a cting at multiple levels, both centrally and peripherally.