Bernhard Kleine

Hormones from Mevalonate: Juvenile Hormone and Steroid Hormones

With mevalonic acid as the common origin in vertebrates and invertebrates, a variety of hormones is synthesized from isoprenyl oligomers, squalene and cholesterol. Most relevant for vertebrates are steroid hormones based on the polycyclic sterane frame. In arthropods, however, noncyclic juvenile hormones are derived from farnesoate or farnesoic acid methyl esters and ecdysteroids are based on cholesterol.

Invertebrate Protein and Peptide Hormones

When analyzing invertebrates in the 1930s and 1940s, Berta and Hans Schaller developed the idea of neurosecretion using the large oceanic snail A. californica (Califonia sea hare) with its few and relatively large neurons. Neuropeptides have been found in all metazoans. Where whole genome sequences are available such as in bees A. mellifera) sequence motifs (signal peptides, cleaving sites of prohormone convertase, terminal glycine) could be investigated. In bees, 200 different potential neuropeptides were identified and the majority of those could be confirmed by chemical analysis (Hummon et al. 2006). In further insects, that is, D. melanogaster or C. elegans, the two model organisms of developmental biology, the potential inventory of neuropeptides is identified.

Hormones Derived by Amino Acid Conversion

The hormones derived from amino acids include catecholamines, serotonin, melatonin, and the thyroid hormones thyroxine and triiodothyronine.

Hormones and the Endocrine System

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Diseases of the Endocrine System

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Boosting Performance: Legally or Not

The endocrine system is so intimately tied to elementary body functions that malfunctions within the endocrine system are pathogenic and potentially life threatening. To understand human endocrinology, the elucidation of defects is even more required because from the defects the healthy, normal situation might be inferred. If, for example, an enzyme defect inhibits steroid hormone biosynthesis and results in major, fatal imbalances of water homeostasis, we recognize the central role of steroidogenic enzymes for the control of renal functions. Since aromatase mutations not only cause sex reversal, but also lead to growth failures, we perceive the action of estrogen for chondrocyte maturation (see Sect. 11.6.3). Experiments in humans, for example, to knock out target genes by molecular biological means which in mice have given stunning and astonishing results are generally forbidden; therefore, endocrinologists depend on the analysis of genetic variations, even though this may be very difficult in certain situations. Information on genes defects in endocrine diseases will complete the discussion of the endocrine system and its elements, especially with respect to an extended description of genes and their products.

Hormones: Some Definitions

The (ab)use of analeptics in daily life, above all as performance-enhancing drugs in endurance sports, has been made possible by new insights into endocrine regulation of basic metabolic circuits. National and international antidoping rules and regulations list the following compound classes as forbidden: analeptics, anesthetics, anabolics, diuretics, peptide hormones, beta blockers, and substances masking forbidden compounds.

History of Hormones and Endocrinology

Protozoans sense signals from the environment on their cell surface and adapt to these messages. They do not require the kinds of messages which help cells in multicellular organisms to communicate information to one another about their conditions, their requirements, and how they can serve other cells. Once multicellular organisms with different organs and their different functions had developed from protozoans, it became necessary to develop message transport within the organism. Two systems evolved: the nervous system and the endocrine system. There is a third system, the immune system, which also processes information.

Endocrine Active Organs

Medical history is built on traditions from the Middle East (Egyptian, Jewish, Arabian), the Far East (mostly Chinese), and Europe, with Greek, Roman, medieval, and modern elements. Because of geographical distances, language or religious communication barriers, or rejection of older traditions, the European medical community had to rediscover facts which were known in ancient Egypt, China, or Arabia a long time ago. Whether an endocrinological profession was known in ancient times may be doubted.

Evolution of the Endocrine System

In this chapter, by presenting the anatomy of endocrine organs, we wish to demonstrate the differences between endocrine glands such as the adrenal glands and the thyroid gland and endocrine tissues of the gastrointestinal tract and neurosecretion in the brain.