Regulation of Peptide Hormone Receptors in the Pituitary-Gonadal Axis: Receptors to Gonadotropins and Gonadotropin Releasing Hormone

Abstract

Most peptide hormones exert their effects on target cells via interaction with specific receptors located on the cell membrane (for review see Amsterdam et al., 1981a). This interaction often results in changes in the concentration of the cellular receptors for the homologous hormone. Plasma membrane receptors for hormones and neurotransmitters are usually decreased or “down regulated” by exposure to their respective ligands (Prives et al., 1979; Amsterdam et al., 1979a,b,c, 1980a, 1981a). However, at least three hormones: prolactin (Posner et al., 1975), angiotensin II, (Hauzer et al., 1978), and gonadotropin releasing hormone (GnRH) (Frazer et al., 1981, Amsterdam et al., 1981a), have been found to increase cellular receptors; however, even these ligands can cause receptor loss under appropriate experimental conditions. In gonadal cells, receptor sites to luteinizing hormone (LH)/human chorionic gonadotropin (hCG) were shown to be decreased by exogenous gonadotropins both in vivo and in vitro (Amsterdam et al., 1979c, 1980a, 1981a; Amsterdam and Lindner,1983). However, the nature of the ligand (hCG and LH purified from different species) will affect the rate of internalization of the receptor bound hormone (Mock and Niswender, 1983). Interestingly, we also found recently that changes in the amount of sugar on the glycoprotein hormone can affect the rate of internalization (Amsterdam et al., 1983; Zor et al., 1984b). In addition, elevation in the number of LH receptors can be observed under specific experimental conditions prior to their disappearance (Huhtaniemi et al., 1981; Amsterdam et al., 1981a). Recently, receptors to follicular stimulating hormone (FSH) were also shown to be “up-regulated” either by the native or the deglycosylated hormone (Knecht et al., 1983; Zor et al., 1984b).