Other hormones and growth factors
As you have concluded by now, a host of hormones and growth factors are involved in physiological processes. In this chapter we have chosen to focus on some of the major endocrine organs and selected growth factors.
Indeed, entire courses of study are devoted to endocrinology or even narrow families of related messengers. As we discuss specific systems we will briefly describe the properties and actions of some of other hormones and growth factors. Some example include: (1) leptin, a hormone produced by adipose tissue that affects appetite; (2) erythropoietin, a kidney derived hormone that responds to a reduction in blood oxygen and stimulates synthesis of red blood cells; and (3) atrial naturetic peptide, a hormone from the heart that impacts blood pressure by affecting sodium resorption. Table 12.11 gives a listing of some of these other hormones and growth factors and some relevant physiological features.Some of the growth factors that have particular significance in animal research are briefly discussed in
| Table 12.11. Selected growth factors. | ||
| Growth Factor | Abbreviation | Properties |
| Epidermal growth factor | EGF | Proliferation Ofepithelium derived from epidermis, mammary development, cancer, and development. At least 10 family members (EGF, TGFα, Iteregulins) bind to type I receptor kinases (ErbB-1,2) |
| Transforming growth factor | TGF-β | Family of at least five proteins, that is, TGF-β1,2,3, and so on, involved in modification of the extracellular matrix (ECM) to influence tissue development; secreted bound to glycoproteins that are cleaved for activation |
| Fibroblast growth factor | FGF | Related family of 20 peptides, strong affinity for heparin-like glycosaminoglycans of the ECM. Many members are likely stromal tissue-derived mitogens. |
| Leptin | Produced primarily in adipocytes, involved in control of feed intake as well as other developmental processes | |
| Transforming growth factor | TGF | Member of superfamily of proteins that typically inhibit epithelial cell growth, important expression of ECM proteins, and glandular morphogenesis |
| Atrial natriuretic factor | ANP | Produced by heart atrium, secreted in response to stretch along with a related factor brain natriuretic factor (BNP); responses include vasodilation, inhibition of aldosterone secretion, and diuresis to normalize blood pressure |
the following sections. To serve as examples we have focused on several that are known to be important in mammary development or function. This is because lactation and mammary development are important in all mammals and are especially relevant with respect to the dairy industry. Second, some of the factors we have selected for discussion have been in the news in recent years because of relationships with cancer generally and with breast cancer specifically. This does not mean that these agents do not have more general roles in most animals; rather, our focus on the mammary gland gives us a common theme for this discussion and makes for relevant examples to illustrate some of the biological properties of these agents.
Last, it is difficult to overstate the significance of technical advancements in cell and molecular biology that have allowed a major expansion in our understanding of structural relationships between various messengers. Based on detailed structural analysis at the DNA, RNA, and protein levels, messengers not previously identified as being related have come to be grouped into families of molecules. In some cases, messengers are grouped based on structure of the protein, but other ligands are grouped based on similarity of the receptors to which they bind. For researchers this is a time of astonishingly rapid advancements and accumulation of enormously detailed information. Unfortunately, for students and others it can also be confusing as more details emerge to allow reclassification or new understanding. Again, our goal in this section is not to provide a comprehensive review of the myriad of growth factors but to illustrate the properties of some of these agents that are relevant in animal agriculture or are a part of recent medical news.