Hormone amine

Describe biochemical and functional distinctions among steroid hormones, protein/peptide hormones, and amine hormones... 

Table 10.1 Distinguishing Features of Steroid, Protein/Peptide, and Amine Hormones... 

Feature Steroid hormones Protein/peptide hormones Amine hormones Thyroid hormones Catecholamines ... 

Amine hormones include the thyroid hormones and the catecholamines. The thyroid hormones tend to be biologically similar to the steroid hormones. They are mainly insoluble in the blood and are transported predominantly (>99%) bound to proteins. As such, these hormones have longer half-lives (triiodothyronine, t3, = 24 h thyroxine, T4, = 7 days). Furthermore, thyroid hormones cross cell membranes to bind with intracellular receptors and may be administered orally (e.g., synthryoid). In contrast to steroid hormones, however, thyroid hormones have the unique property of being stored extra-cellularly in the thyroid gland as part of the thyroglobulin molecule. 

Water-soluble peptide and amine hormones (insulin and epinephrine, for example) act extracellularly by binding to cell surface receptors that span the plasma membrane (Fig. 23-4). When the hormone binds to its extracellular domain, the receptor undergoes a conformational change analogous to that produced in an allosteric enzyme by binding of an effector molecule. The conformational change triggers the downstream effects of the hormone. 

Peptide or amine hormone binds to receptor on the outside of the cell acts through receptor without entering the cell. 

FIGURE 23-4 Two general mechanisms of hormone action. The peptide and amine hormones are faster acting than steroid and thyroid hormones. 

Amine hormones and some agents of the second type have counterparts in the nervous system that function as neurotransmitters. 

Carcinoids, atypical carcinoids, small cell carcinomas, and large cell NE carcinomas have been reported as primary cervical tumors.All small cell cervical carcinomas studied to date have been cytokeratin-positive, and more than 90% have been positive for EMA. Reactivity for CEA with polyclonal antisera occurs in 77%. Small cell cervical carcinomas are positive for CK20 or TTF-1 in 14.3% and 20% of cases, respectivelyWith respect to NE markers, NSE is present in 95%, synaptophysin in 46%, chromogranin A in 43%, and CD57 in 37%. Similar frequencies of positivity for NE markers have been reported in more recent studies.These tumors may also contain peptide and amine hormones including serotonin (31%), ACTH (23%), and somatostatin (8%). 

D. Rudman The adipokinetic action of polypeptide and amine hormones upon the adipose tissue of various animal species.- J. Lipid Research 4, 119, 1963. 

With very few exceptions, the biological activities of synthetic steroids tend to parallel those of the naturally occurring hormones on which they are patterned. Compounds with distant pharmacological activity are, as a rule, quite rare. It is thus intriguing that inclusion of a tertiary amine at the 11 position of a pregnane leads to a compound with activity far removed from its close analogues. The agent in question, minaxalone (47), exhibits anesthetic activity. 

Such difficulties prompted research workers to look for some other index of NT function in humans. These range from studies on platelets, such as abnormalities in their amine uptake and MAO activity in depressed patients, to changes in the secretion of a hormone known to be controlled by a particular NT. Thus if NA controls growth hormone release, and the secretion of the hormone is changed in depressed patients, does that confirm a role for NA in the mediation of depression ... 

In cells that synthesize epinephrine, the final step in the pathway is catalyzed by the enzyme phenylethanolamine /V-methyltransferase. This enzyme is found in a small group of neurons in the brainstem that use epinephrine as their neurotransmitter and in the adrenal medullary cells, for which epinephrine is the primary hormone secreted. Phenylethanolamine N-methyltransferase (PNMT) transfers a methyl group from S-adenosylmethionine to the nitrogen of norepinephrine, forming a secondary amine [5]. The coding sequence of bovine PNMT is contained in a... 

Numerous reports of altered neurotransmitter and hormone functions which have been associated with the affective disorders are reviewed by Levell [142]. It was originally proposed that one or more of the neurotransmitter amines in the brain (norepinephrine, dopamine, serotonin) may be functionally elevated in manic patients and reduced in depressed patients [143]. For instance, an increase in the production of dopamine, observed in a number of case reports, is thought to be the cause of the switch into the manic phase in bipolar patients. For example, Bunney et al. reported an increase in the level of homovanillic acid (HVA), a... 

Urea ((NH2)2CO), a small and highly water soluble molecule, is an end product of amine and ammonia nitrogen metabolism and as such represents an example of biodetoxification (Section 6.4). The process is discussed in this section because it illustrates a genuine de novo biosynthetic pathway rather than detoxification involving chemical modification, via phase I and phase II reactions, of a pre-existing molecule as is the case for haem or steroid hormones. 

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