SHARON SHACHAM, DAGAN HARRIS, HERZEL BEN-SHLOMO, INBAR COHEN, FIORENZA PRZEDECKI, HADAS LEWY, ISRAEL E. ASHKENAZI, RONY SEGER ,ZVI NAOR

Department of Biochemistry, George S. Wise Faculty of Life Sciences, and Department of Human Genetics and Molecular Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, 69978 Israel; and  Department of Biological Regulation, The Weizmann Institute of Science, Rehovot, 76100 Israel

Gonadotropin releasing hormone (GnRH), the first key hormone of reproduction, is synthesized and secreted from the hypothalamus in a pulsatile manner and stimulates pituitary gonadotrophs (5- 10% of the pituitary cells) to synthesize and release gonadotropin luteinizing hormone (LH) and follicle stimulating hormone (FSH). Gonadotrophs consist of 60% multihormonal cells (LH÷FSH) and 18% LH- and 22% FSH-containing cells. LH and FSH, members of the glycoprotein hormone family, stimulate spermatogenesis, folliculogenesis, and ovulation. Although GnRH plays a pivotal role in gonadotropin synthesis and release, other factors such as gonadal steroids and gonadal peptides exert positive and negative feedback mechanisms, which affect GnRH actions. GnRH actions include activation of phosphoinositide turnover as well as phospholipase D and A2, mobilization and influx of Ca 2+, activation of protein kinase 63 Copyright © 2001 by Academic Press. All rights of reproduction in any form reserved. 0083-6729/01 $35.00 64 SHARON SHACHAM ETAL. C (PKC) and mitogen-activated protein kinase (MAPK). A complex crosstalk between the above messenger molecules mediates the diverse actions of GnRH. Understanding the signaling mechanisms involved in GnRH actions is the basis for our understanding of basic reproductive functions in general and gonadotropin synthesis and release in particular. © 2ooi Academic Press.