Glucagon hormone precursor

Hormones can modify the concentration of precursors, particularly the lipolytic hormones (growth hormone, glucagon, adrenaline) and cortisol. The lipolytic hormones stimulate lipolysis in adipose tissue so that they increase glycerol release and the glycerol is then available for gluconeogenesis. Cortisol increases protein degradation in muscle, which increases the release of amino acids (especially glutamine and alanine) from muscle (Chapter 18). 

Peptide Hormones Peptide hormones may have from 3 to 200 or more amino acid residues. They include the pancreatic hormones insulin, glucagon, and somatostatin, the parathyroid hormone, calcitonin, and all the hormones of the hypothalamus and pituitary (described below). These hormones are synthesized on ribosomes in the form of longer precursor proteins (prohormones),... 

However, it is now known to exist in various nerve tracts and neuroendocrine tissues and it has general inhibitor actions. It can also inhibit release of other pituitary hormones (including thyroid-stimulating hormone (TSH) and prolactin). other endocrine hormones including pancreatic hormones (insulin and glucagon), peptide hormones from a variety of neuroendocrine tumours (e.g. VIPomas and glucagonomas) and also the release of most intestinal hormones. It is produced in the gut, the pancreas and in some peripheral nerves (see hypothalamic hormones PITUITARY hormones). Somatostatin is a cyclic peptide of 14 residues (SRIF-14) but is formed from a precursor of 28 residues (SRIF-28). 

Box 25-1 lists the clinical conditions in which hormones that regulate glucose, namely insulin, proinsulin, C-peptide, and glucagon, have been measured. Although there is interest in the possible clinical value of measurement of the concentrations of insulin and its precursors, the assays are useful primarily for research purposes. There is no role for routine testing for insulin, proinsulin, or C-peptide in patients with diabetes mellitus. It must be emphasized that the diagnostic criteria for diabetes mellitus do not include measurements of hormones, which remain predominantly research tools. 

The increase in cAMP is a hormonal message which has an effect in two major target organs, liver and muscle, but different hormones affect increased cAMP in each. In the liver, the hormone is glucagon, whereas in the muscle, the hormone is epinephrine. In the liver, glycogen breakdown (i.e., glycogenolysis) can serve as a source of hexose phosphate, a precursor of blood glucose in the... 

The pancreas contains endocrine cells, which secrete hormones directly into the bloodstream, and exocrine cells, which secrete zymogen precursors of digestive enzymes into the upper small intestine. The endocrine tissue contains cell clusters known as islets of Langerhans, which contain at least four different cell types (A, D, P, and B), each specialized for synthesis of one hormone. The A cells produce glucagon the D cells, somatostatin and the P cells, a recently discovered pancreatic hormone. Insulin is synthesized in the B cells, which sense glucose levels and secrete insulin in response to increased levels of blood glucose. 

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