Biomedical Engineering Reference
In-Depth Information
11
Therapeutic hormones
11.1 Introduction
Hormones are amongst the most important group of regulatory molecules produced by the body.
Originally, the term hormone was defi ned as a substance synthesized and released from a specifi c
gland in the body that, by interacting with a receptor present in/on a distant sensitive cell, brought
about a change in that target cell. Hormones travel to the target cell via the circulatory system.
This describes what is now termed a true endocrine hormone.
At its loosest defi nition, some now consider a hormone to be any regulatory substance that car-
ries a signal to generate some alteration at a cellular level. This embraces the concept of paracrine
regulators (i.e. produced in the immediate vicinity of their target cells) and autocrine regulators
(i.e. producer cell is also the target cell). Under such a broad defi nition, all cytokines, for example,
could be considered hormones. The delineation between a cytokine and a hormone is already quite
fuzzy using any defi nition.
True endocrine hormones, however, remain a fairly well defi ned group. Virtually all of the
hormones used therapeutically (discussed below) fi t into this grouping. Examples include insulin,
glucagon, GH and the gonadotrophins.
11.2 Insulin
Insulin is a polypeptide hormone produced by the beta cells of the pancreatic islets of Langer-
hans. It plays a central role in regulating blood glucose levels, generally keeping it within narrow
defi ned limits (3.5-8.0 mmol l 1 ), irrespective of the nutritional status of the animal. It also has a
profound effect on the metabolism of proteins and lipids and displays some mitogenic activity. The
latter is particularly evident in in vitro studies and at high insulin concentrations. Some of these
mitogenic effects are likely mediated via the IGF-1 receptor, and their physiological relevance is
questionable.
Although many cells in the body express the insulin receptor, its most important targets are
skeletal muscle fi bres, hepatocytes and adipocytes, where it often antagonizes the effects of
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