Hormone synthesis secretion

Endocrine Events Susceptible to Manipulation. There are a series of events which are common to the production and action of any hormone. These events include hormone synthesis, secretion and transport hormone-target cell receptor interaction target cell response and hormone degradation. Several of these events are susceptible to manipulation by external influences that might be devised into control strategies. 

For delayed effects of iodide, it is difficult to separate the direct effects on the thyroid and the secondary action on thyroid hormone synthesis, secretion and serum levels, unless the experiments are performed in hypophysect-omized animals or subjects, or as responses to administered TSH. An effect of iodide on a hypophysectomized animal has been shown for (1) the inhibition of TSH-induced thyroid hormone synthesis (Katakai and Yamada, 1966) (2) the trapping of iodide (Taurog et ai, 1958) (3) the inhibition of TSH-induced thyroid hormone secretion Yamada and Lewis, 1968) or spontaneous secretion in autonomous adenomas (Green and Ingbar, 1962) and (4) the inhibition of TSH-induced thyroid growth (Bray, 1968). Of course, direct effects in vitro are also independent of the T4—TSH loop, but their in vivo relevance should be proved these effects are examined in Chapter Mechanism(s) of Action of Iodide, third part. 

Lithium is associated with hypothyroidism in up to 34% of patients, and hypothyroidism may occur after years of therapy. Lithium appears to inhibit thyroid hormone synthesis and secretion. Patients with underlying autoimmune thyroiditis are more likely to develop lithium-induced hypothyroidism. Patients may require LT4 replacement even if lithium is discontinued. 

Thionamide drugs interfere with peroxidase-catalyzed reactions. In the thyroid gland, they inhibit the activity of the enzyme TPO, which is required for the intrathyroidal oxidation of I , the incorporation of I into Tg, and the coupling of iodotyrosyl residues to form thyroid hormones. Thus, these drugs inhibit thyroid hormone synthesis and with time, also secretion. Propylthiouracil, but not methimazole, also inhibits Dl, which deiodinates T4 to Tj. Because of this additional action, propylthiouracil is often used to provide a rapid alleviation of severe thyrotoxicosis. 

A. The clinical effects are not apparent until the preexisting intrathyroidal stores of thyroid hormone are depleted. This may take several weeks. This class of drugs do inhibit the action of the enzyme TPO and thus inhibit thyroid hormone synthesis. They do not inhibit secretion of preexisting stored thyroid hormone. 

Mecfianism of Action Afat-soluble vitamin that is essential for absorption, utilization of calcium phosphafe, and normal calcification of bone. Therapeutic Effect Stimulates calcium and phosphate absorption from small inf esf ine, promof es secretion of calcium from bone fo blood, promofes renal tubule phosphate resorption, acts on bone cells to stimulate skeletal growth and on parathyroid gland to suppress hormone synthesis and secretion. 

TEicosanoids are paracrine hormones, substances that act only on cells near the point of hormone synthesis instead of being transported in the blood to act on cells in other tissues or organs. These fatty acid derivatives have a variety of dramatic effects on vertebrate tissues. They are known to be involved in reproductive function in the inflammation, fever, and pain associated with injury or disease in the formation of blood clots and the regulation of blood pressure in gastric acid secretion and in a variety of other processes important in human health or disease. 

Pituitary hormone stimulation of steroid hormone synthesis and secretion. 

The occupancy of hormone receptors can fluctuate greatly and is ultimately determined by the concentration of free hormone in the blood. The major determinants of hormone concentrations are (1) the rate of hormone secretion from endocrine cells and (2) the rate of hormone removal by clearance or metabolic inactivation. As we have seen, most hormones (with the exception of steroids) are stored in secretory granules. When the hormone is needed, the granule membranes fuse with the plasma membrane to liberate their contents into the bloodstream. This event is triggered by signals from other hormones or by neural signals. Stimulation of hormonal secretion is usually coupled with an increase of hormone synthesis, so that hormonal stores are replenished. 

Control of hormone synthesis and secretion in the anterior pituitary. Neurosecretory neurons in the hypothalamus liberate polypeptides that either stimulate or inhibit hormone synthesis by specialized pituitary cells containing the appropriate receptors. For example, GnRH stimulates gonadotroph cells in the pituitary to synthesize and secrete LH and FSH. These pituitary hormones then impinge on target cells, typically stimulating them to make other low-molecular-weight hormones. The end products of these cascades feedback-inhibit hormone production at either or both hypothalamic and pituitary levels. 

Mitochondria play a central role in a variety of biological processes, including ATP synthesis, steroid hormone synthesis, the urea cycle, lipid and amino acid metabolism, and cellular Ca2+ homeostasis. Ca2+ is an essential regulator of vital processes, such as secretion, motility, metabolic control, synaptic plasticity, proliferation, gene expression and apoptosis. Therefore, the location, amplitude,... 

Stimulating Hormone (TSH) secretion without induction of hypothyroidism Inhibition of thyroid hormone synthesis or release with the induction of hypothyroidism (or occasionally hyperthyroidism)... 

The thyroid gland is made up of multiple follicles that consist of a single layer of epithelial cells surrounding a lumen filled with colloid (thyroglobulin), the storage form of thyroid hormone. A diagram of the steps in thyroid hormone synthesis and secretion is shown in Figure 25.6. 

Figure 33-2. Hypothalamic-pituitary-adrenal axis. Corticotropin-releasing hormone (CRH) acts to increase pituitary ACTH secretion, which enhances steroid hormone synthesis by the adrenal, including production of cortisol (hydrocortisone), which controls CRH/ACTH secretion via negative feedback.

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