General Considerations of Hormones

I. OVERVIEW OF HORMONES, RECEPTORS, AND ENDOCRINOLOGY

A. Introduction

B. Classes of Hormone Molecules

C. Classification of Hormonal Communication Systems

D. General Concept of a Hormone Receptor

E. Hormones and Cascade Systems

II. BIOSYNTHESIS OF HORMONES

A. Introduction

B. Biosynthesis of Peptide and Protein Hormones

C. Regulation of Hormone Secretion

D. Oncogenes and Hormones

III. HORMONE RECEPTORS

A. Cellular Organization

B. Membrane Receptors

C. Intracellular Receptors

D. Measurement of Hormone-Receptor Interactions

E. Regulation of Hormone Receptors

IV. MECHANISM OF HORMONE ACTION

A. Hormone Entry into Target Cells

B. Receptor-Mediated Transmembrane Signaling

C. Steroid Hormone Regulation of Gene Transcription

V. SUMMARY References

I. OVERVIEW OF HORMONES, RECEPTORS, AND ENDOCRINOLOGY

A. Introduction

The domain of endocrinology represents a scientific description of how, in a higher organism, cell A communicates with cell B via the sending of chemical messen gers termed "hormones." A detailed understanding of a particular endocrine system likely will include an understanding of the following: (a) the anatomical description of cells A and B and their immediate environment (are they part of a gland?), as well as the distance of separation of A from B; (b) the chemical structure of the messenger, H (the hormone); (c) the details of the biosynthesis of the hormone by cell A; (d) the mode of transfer of H from cell A to cell B; (e) the detailed mechanism by which cell B uses receptors to detect the presence of H; (f) how cell B transduces the presence of H to initiate and sustain a biological response; and (g) how cell B communicates via a feedback loop with cell A to indicate the adequate presence of the hormone.

The study of endocrinology over the past century quite naturally has been dependent upon the scientific methodologies available to probe the various endocrine systems. Thus, in the interval 1900-1960, endocrinology was largely pursued at the physiological level. This resulted in the discovery of approximately 25 hormones; the detail of specification of the hormone structure was usually inversely proportional to the size of the hormone. Accordingly, the complete structure of thyroxin (molecular weight 770) was defined in 1926, while the sequence and structure of the small protein hormone insulin would not be obtained until 1953 (amino acid sequence) and 1969 (three-dimensional structure).

The biochemical era of endocrinology began in approximately 1955-1960 and extends to the present time. The availability of radioactive isotopes of carbon (I4C), hydrogen (3H), phosphorus (32P), etc., coupled with advances in chemical methodology (chromatography, mass spectrometry, nuclear magnetic resonance spectroscopy (NMR), and X-ray crystallography), has

HORMONES, SECOND EDITION

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