P. Franchimont

Vasopressin and Oxytocin

The chapter discusses the methods that are suited to the assay of oxytocin and the two vasopressins. For a quantitative determination of the neurohypophyseal hormones, bioassay is the method of choice. Some of the bioassays are characterized by a very high precision, others by a higher sensitivity and specificity. The activity of neurohypophyseal hormones is expressed in international units when the Third International Standard for oxytocic, vasopressor, and antidiuretic substances is used. Although work on the radioimmunoassays of vasopressin and oxytocin is still in its infancy, it is already possible to use these methods to determine the post-hypophyseal hormones in plasma and other biological fluids. The radioimmunoassays presently available are not necessarily the most sensitive techniques and are sometimes even less sensitive than the bioassays. However, it is very likely that the improvement of these techniques will in the near future put more specific and sensitive assays at the disposal of biologist and clinician alike.

CHAPTER 4 – Adrenocorticotropin (ACTH)

Publisher Summary This chapter discusses the properties of adrenocorticopin (ACTH). Among the biological properties of ACTH, two in particular have been exploited in developing a bioassay for this hormone—depletion of adrenal ascorbic acid and secretion of corticosteroids by the adrenals. The animal is hypophysectomized either surgically or pharmacologically by the means of various agents: morphine, chlorpromazine, phenobarbital, and sodium pentobarbital. All these agents possess only a partial blocking power. The depletion of ascorbic acid is not a sufficiently sensitive method for a bioassay of ACTH in plasma. In addition, the optimal conditions for this test are difficult to satisfy. The extraction of ACTH by oxycellulose requires such great amounts of blood that the application of the method becomes impractical.

CHAPTER 2 – Immunological Methods

Publisher Summary This chapter discusses the immunological methods. The introduction of immunological techniques into the field of endocrinology constituted a considerable advance. With these techniques, it became possible to assay in vivo a series of protein hormones that are intimately involved in regulating the bodys metabolic processes. The injection of a protein hormone obtained from one species of animal readily induces the formation of antibody in an animal of another species, provided the hormone has a molecular weight of more than 10,000. The chemical structure of these hormones presents a species-specificity that is very helpful in the production of antibodies; the precise degree of species-specificity varies with the hormone considered. The chapter also discusses the techniques for visualizing the immunochemical reaction. These techniques may be perturbed by nonspecific factors, in which case they may be responsible for a lack of specificity. Adsorption of the hormone to wood charcoal was proposed for insulin and later for other hormones by Herbert.

CHAPTER 1 – Biological Methods

Publisher Summary This chapter discusses the biological methods for evaluating the protein and polypeptide hormone content of biological fluids. A feature common to all biological tests is that they attempt to reproduce one or more of the characteristic physiological or biochemical actions of the hormone while determining the quantitative relationship between the observed effect and the amount of the substance present in the assay sample. Biological assays require the use of pure strains of animals raised in standardized conditions. It is also necessary to ensure that the animals receive an unvarying diet and that they display no seasonal variations in reactivity. Even under these conditions, laboratories may obtain divergent results because of the differences in the strains of animals used. The ideal solution is to employ internationally established standards such as those supplied by the NIH in the United States and by the NMRC in Mill-Hill, England. Similar standards are in the process of being prepared in France.

CHAPTER 13 – Parathormone

Publisher Summary This chapter discusses a variety of diverse methods that have been developed for the bioassay of parathormone, also known as parathyroid hormone, in various fluids. In recent years, two bioassays have been used on a regular basis in many laboratories. The original method was subjected to the critical studies that were based on the determination of serum calcium in the intact dog 18 hours after subcutaneous injection of the assay preparation. The second method is based on the measurement of serum calcium levels in young rats 6 hours after parathyroidectomy and subcutaneous injection of the assay extract. The bioassay methods, apparently even the most satisfactory ones, are still subject to various forms of interference and are, thus, of limited utility. The methods are only useful if the results obtained are interpreted very critically and if interlaboratory controls are in effect. Another method has recently been recommended. This consists of assaying urinary phosphorus after intravenous injection of the test preparation.

CHAPTER 7 – Prolactin

Publisher Summary The chapter focuses on the properties of prolactin. Prolactin is a distinct hypophyseal hormone in sheep, goats, and cattle, and its chemical structure in these species has been studied extensively. There is still some question concerning the individuality of prolactin in man. Some workers conjecture that there may be a partial or total identity between human somatotropin and prolactin. This hypothesis is based on the finding that purified STH preparations contain a prolactin-like factor as shown by their ability to stimulate the pigeon crop gland and their mammotropic, lactogenic, and luteotropic properties in mammals. The administration of prolactin in the pigeon stimulates the crop glands by causing rapid proliferation and increased secretion of the epithelial cells. Of all the hypophyseal hormones, prolactin is certainly the least well known. Its chemical structure and biological action in man remain to be defined, and the available assays are mediocre and clearly inadequate for physiological and clinical application.