Hormones

Anthony W. Norman, Gerald Litwack

• Editore: Academic Press
• Anno: 2014
• ISBN:
  9781483258102
• Argomento: Biological Sciences
• Categoria: Biophysics

Hormones provides a comprehensive treatment of human hormones viewed in the light of modern theories of hormone action and in the context of current understanding of subcellular and cellular architecture and classical organ physiology. The book begins with discussions of the first principles of hormone action and the seven classes of steroid hormones and their chemistry, biosynthesis, and metabolism. These are followed by separate chapters that address either a classical endocrine system, e.g., hypothalamic hormones, posterior pituitary hormones, anterior pituitary hormones, thyroid hormones, pancreatic hormones, gastrointestinal hormones, calcium regulating hormones, adrenal corticoids, hormones of the adrenal medulla, androgens, estrogens and progestins, and pregnancy and lactation hormones; or newer domains of hormone action which are essential to a comprehensive understanding of hormone action, including prostaglandins, thymus hormones, and pineal hormones. The book concludes with a presentation of hormones of the future, i.e., cell growth factors. This book is intended for use by first-year medical students, graduate students, and advanced undergraduates in the biological sciences. It is also hoped that this book will fill the void that exists for resource materials for teaching cellular and molecular endocrinology and that it will be employed as an equal partner with most standard biochemistry textbooks to provide a comprehensive and balanced coverage of this realm of biology.

Chapter 1

General Considerations of Hormones

Publisher Summary

The classic categories of hormones based upon their chemical structures are steroids, polypeptides, and amino acid and fatty acid-derived compounds. Each of these classes except the last has been considered for many years to be the exclusive products of endocrine glands. These substances are synthesized and stored in endocrine gland cells awaiting the appropriate signal for their release, usually by a process of exocytosis into the bloodstream. When the hormones are polypeptides, creating a problem of permeability from the extracellular space to the interior of small blood vessels, the local capillaries are usually fenestrated (that is, thinning or opening of the walls to allow permeation of polypeptides) to accommodate this need.

I Classification of Hormones

A Introduction

B The Hormones

II Receptors for Hormones

III Mechanisms of Hormone Action

A Cell Membrane Constituents

B Polypeptide Hormones

C Mechanism of Internalization of Polypeptide Hormone–Receptor Complexes

D Mechanism of Certain “Immediate” Effects of Polypeptide Hormones at the Cell Membrane; Stimulation of Adenylate Cyclase

E Role of Phospholipid Metabolism at the Cell Membrane

F Mechanisms of Action of Steroid and Thyroid Hormones

G Impact of Molecular Biology on Understanding Hormone Action

H Cellular Location of Steroid Hormone Action

I Receptor Polymorphism

J Second Messengers

K Cascade Mechanisms

IV Evolution of Hormones

V Physical Parameters of Hormone–Receptor Interactions

VI Newer Developments Impacting on the Understanding of Hormone Action

VII Summary

References

I CLASSIFICATION OF HORMONES

A Introduction

The classic categories of hormones, based upon their chemical structures, are steroids, polypeptides, and amino acid and fatty acid-derived compounds. Each of these classes excepting the last has been considered for many years to be the exclusive products of endocrine glands. These substances are synthesized and stored in endocrine gland cells awaiting the appropriate signal for their release, usually by a process of exocytosis into the bloodstream. When the hormones are polypeptides, creating a problem of permeability from the extracellular space to the interior of small blood vessels, the local capillaries are usually fenestrated (i.e., thinning or opening of the walls to allow permeation of polypeptides) to accommodate this need. Once in the bloodstream, the endocrine hormone can travel to a distant cellular target which it recognizes through high-affinity receptors located on the surface of its cellular membrane (polypeptide and certain amino acid-derived hormones; see Fig. 1-1) or within its cytoplasm or cellular nucleus (steroid hormones). The receptor for the amino acid-derived hormone, thyroxine or triiodothyronine, is located within the nuclear genome of the target cell. Increasing evidence suggests that steroid hormone receptors (especially for estrogens and vitamin D₃) reside within the nucleus and do not have cytoplasmic locations except by artifact after the cell is broken. The situation for the glucocorticoid receptor is less clear.

Figure 1-1 Overview of traditional endocrine hormone glandular cell; release and action.

As time progresses, our understanding of what a hormone is must be redefined. A growing realization is that classical endocrine hormones and neurotransmitters may be more similar than different. Thus, we treat epinephrine as a hormone of the adrenal medulla and norepinephrine as a major neurotransmitter, but their structures (Fig. 1-2) are obviously similar and their activities, for example, on vascular cells, may clearly overlap. The hormones with nervous activity which operate across synapses may be defined as paracrine hormones, those substances which are secreted like traditional endocrine hormones, but which operate over a shorter, defined distance, as shown in Fig. 1-3. The opioid peptides, like β-endorphin and the enkephalins, may be a recent example of paracrines, in some cases, and of endocrines as well, in other cases. Finally, we must recognize a newer class of hormones which can be gathered under the heading of autocrine hormones. These are hormones that are synthesized and released by the same cell upon which the hormones act. They may also act on neighboring cells. Examples of autocrine hormones would be the prostaglandins and some of their relatives, such as thromboxanes, leukotrienes, and prostacyclin, the last of which also may have somewhat traditional endocrine hormone-like activity (Fig. 1-4). Consequently, we conceive of three major groups of hormones based not on their structures or on the nature of their receptors as much as on the extent of their radius of action: endocrine, paracrine, and autocrine in the order of decreasing effective distances (see Table 1-1).

Table 1-1

Classes of Hormones Based on Distance of Action^a

Class	Endocrine	Paracrine	Autocrine
Polypeptide	+ + + +	(+)
Steroid	+ + + +
Amino acid-derived	+ + + +	+ + + +
Fatty acid-derived	+		+ + + +

^a+ signs indicate the extent of secretory type. “Endocrine” means that the class of hormones is secreted, usually by exocytosis, and travels through the bloodstream to distant target cells; “paracrine” indicates that the cell secretes this class of hormones and they travel only a short distance to neighboring cellular targets; “autocrine” means that a class of hormones is secreted by a cell which may act on that cell’s own receptors.

Figure 1-2 Structures of the hormone, epinephrine, and the neurotransmitter, norepinephrine.

Figure 1-3 Example of a neurohormone operating in a synapse. In the case of some amine hormones or neurotransmitters, their synthesis may be confined to the nerve ending, whereas other substances are synthesized in the cell body and transported to the nerve ending as shown here.

Figure 1-4 Example of an autocrine hormone operating on the same cell which released it. The active hormone may reach its receptor from the cell interior without having been secreted first, as shown in this example.

We also need to recognize that nature occasionally constructs a mechanism, in addition to the use of receptors, as a means to ensure that hormones, oft...