We all knew what hormones were back in the day. They were chemicals released by an endocrine gland into the blood where they went everywhere and affected distant organs. The classic example were the sex hormones (estrogen, progesterone, testosterone) eleased by the gonads affecting the reproductive organs, and not least the brain.
Things have changed mightily, and just about every tissue in the body does this now. There are at least 20 adipokines released by fat — examples are adiponectin, adipsin, and of course leptin. Muscle may be also getting into the act with irisin (although that is controversial). Other muscle produced hormones (myokines) include atrial natriuretic peptide released by the heart and skeletal muscle releases at least 8 more.
There is even more stuff released into local tissue fluids which don’t get into the blood so they aren’t hormones. You can regard all neurotransmission this way. Paracrines are compounds which act only on cells close to them (because they don’t get into the blood). Examples include the huge class of prostaglandins and polypeptide growth factors such as the 22 member fibroblast growth factor family.
What to make of [ Cell vol. 166 pp. 424 – 435 ’16 ] which describes PM20D1 (Peptidase M20 Domain containing 1) which is secreted by fat cells. It’s an enzyme which builds compounds from substances already in the blood. The chemistry is simplicity itself — it takes a long chain fatty acid and an amino acid and forms the fatty acid amide — or an N-acyl amino acid.
What does the product do? It causes uncoupling of oxidative phosphorylation by mitochondria, so it just produces heat (something useful to an animal in the cold). Administration of N-acyl amino acids to mice increases energy expenditure and improves glucose metabolism. It’s possible that they could be used therapeutically.
Another example of how little we knew about what is going on inside us.
Chemiotics II 