HPLC in Endocrinology

The human endocrine system is a complex messenger network involving the source of hormone (endocrine gland; e.g., the pituitary), the bloodstream, which carries the hormone to its site of action (target tissue; e.g., adrenal gland), sites of in activation and excretion, and finally feedback mechanisms linking the response to the hormone with the endocrine gland ( Fig. 1 ). Hormones can be classified on the basis of their relative importance into three general groups: protein and peptide hormones, steroid hormones, and a miscellaneous group of hormones including catecholamines and prostaglandins. Protein and peptide hormones have very widely diversified actions; for example, protein hormones tend to be released mainly at the anterior pituitary, while many of the hypothalamic releasing hormones are peptides such as corticotropin-releasing factor (CRF). The latter stimulates the release of adrenocorticotropin (ACTH), another peptide, from the anterior pituitary, which promotes steroid synthesis in the cells of the adrenal cortex, resulting in increased release of the steroid hormones including Cortisol (113,17a,21-trihydroxy-4-pregnene-3,20-dione). Steroid hormones are derived from cholesterol and may conveniently be considered in three groups: mineralocordicoids, glucocorticoids (collectively called corticosteroids), and the sex hormones. The mineralocorticoids (e.g., aldosterone, llß,21-dihydroxy-18-al-4-pregnene-3,20-dione) are principally involved in salt and water metabolism. Cortisol is an example of a glucocorticoid which exerts powerful effects on a wide variety of metabolic events including protein and carbohydrate metabolism. The sex hormones are involved in the development and maintenance of the reproductive tract (e.g., estrogens in females, androgens in males) and in the control of estrus, menstrual cycles, and maintenance of pregnancy (estrogens and progesterone). Catecholamines, for example, adrenaline or noradrenaline, are neurotransmitters and are also derived from amino acids. Their many actions include increasing heart rate and blood pressure, bronchodilation, and relaxing smooth muscle in the gastrointestinal tract. Prostaglandins consist of long-chain fatty acids and appear to be synthesized by most cells of the body. They too have diverse actions including regulation of renal blood flow, inhibition of gastric acid secretion, and stimulating uterine contractility at parturition.