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Web Topic 5.2: Mechanism of Action of GnRH and Other Protein/Peptide Hormones

[Referenced on textbook p. 126]

Because GnRH and other protein and peptide hormones cannot pass through plasma membranes, receptors for these hormones have to be on the plasma membranes of the GnRH-sensitive cells, rather than in their cytoplasm or nuclei, as in the case of steroid receptors (see Web Topic 5.1). When contacted by GnRH, these receptors activate a second messenger system—that is, a cascade of internal chemical signals that culminate in the secretion of FSH or LH into the bloodstream (see Figure 1). These effects can occur without direct involvement of the cell’s genes, but there are also effects that depend on gene expression. These mechanisms of action are typical for protein, peptide, and other non-fat-soluble hormones (see Web Activity 5.5).

Figure 1  Mode of action of protein and peptide hormones such as GnRH.