Hormones primary action

The answer is c. (Katzung, pp 651-652.) Propylthiouracil is a thioamide that interferes with the production of thyroid hormone. Its primary action is prevention of thyroid hormone synthesis by blocking thyroid peroxidase catalysis leading to interference with iodine organification. 

Natriuretic Peptide Diuretics. Atrial natriuretic peptide (ANP). an endogenous diuretic, natriuretic, and vasodilator, is a peptide hormone primarily synthesized and stored hy atrial cardiocytes. and secreted hy the atria in response to mechanical stretch of the atria. ANP is also known as anarilide. CiijHnsNjoO.ijS-i atrial natriuretic factor (ANF) auricuiin cardionairin and alriopeptide. Its primary action Is in the kidney and the vascular system. 

Calcitonin Calcitonin is secreted hy the C cells ofthe thyroid gland in response to hypercalcemia. Its primary action is to oppose the actions of parathyroid hormone hy suppressing osteoclast actions. It also stimulates... 

Thyroid compounds are necessary for metabolism, growth, and development. T4 s primary action is related to calorigenesis and protein synthesis. Thyroid hormones potentiate the effects of catecholamines. About half of T4 is converted to T3. T3 is three to five times more potent than T4. 

Thymosins. Thymosins are hormone-like polypeptides produced by thymus epithelial cells. They regulate the maturation of T-cells moreover, they modulate interferon production and stimulate the expression of interleukin-2 and its receptor. A trial of thymosin fraction-5 in four homosexual patients with chronic hepatitis B demonstrated no effect after six months of treatment (202), while treatment of WHV-infected woodchucks with thymosin alpha-1 resulted in clearance of circulating WHV-DNA and a 50-300-fold decline in the levels of replicative intermediates in liver tissue (203). Subsequently, thymosin alpha-1 and thymosin fraction-5 were used to treat chronic hepatitis B in a human pilot study (204). Results were encouraging, and this was followed by several randomized, controlled multicenter trials of thymosin alpha-1 in the U.S. The primary action of thymosin is unknown, but it is probably related to its immune-enhancing effects. 

Hormone Primary Cell/ Tissue of Origin Actions Secretory Stimuli (and Inhibitors)... 

Glucocorticoid hormones regulate syntheses of specific mRNA species [14,15]. Interaction of the steroid-receptor complex with highly localized regions of chromatin is essential for this induction, but little of the molecular basis for this activation mechanism is understood. The primary action of glucocortiocoids is very rapid thus, any alterations in chromatin which are essential for this activation would be observed within a few minutes after steroid addition. Also, it is possible that proteins known to be associated with transcriptionally active genes, such as the HMG 14 and 17 [8, 9], are important. 

A significant contribution to the understanding of hormone action has been recently made by the discovery of the second messenger, adenosine-3, 5 -cyclic phosphate (cAMP) [28,29]. Many hormones, particularly the peptide ones, appear to act primarily at the cell surface where they interact with their specific receptor molecules. Such an interaction of hormone with receptor stimulates the membrane-associated enzyme, adenyl cyclase, which in turn catalyzes the production of intracellular cAMP from ATP [30,31]. Thus, this second messenger, the intracellular cAMP, becomes the mediator of hormone action, and itself regulates gene expression by as-yet-unknown mechanisms. The primary actions of many hormones are thus known, and what remains to be discovered are the actions of cAMP. 

First criterion if the primary action of the hormone takes place in the nucleus of the epidermis cells, ecdysone should be evidenced in these nuclei Injected H-labelled ecdysone is rapidly concentrated in the epidermis of the larvae, mainly in the nuclei. These results are consistent with the hypothesis, but they do not prove it, as the main localization of a hormone in a cell is not necessarily the site of action of the hormone. 

Very formidable technical obstacles face attempts to identify the primary actions of hormones in both plant and animal cells. These are in part due to the limited resolving power of existing biochemical techniques but also due to the special problems associated with obtaining satisfactory experimental systems. Diffusion patterns establishing complex concentration gradients of hormones are probably built up in developing plant tissues— these may be destroyed... 

ACE inhibitors do not completely block aldosterone synthesis. Since this steroid hormone is a potent inducer of fibrosis in the heart, specific antagonists, such as spironolactone and eplerenone, have recently been very successfully used in clinical trials in addition to ACE inhibitors to treat congestive heart failure [5]. Formerly, these drugs have only been applied as potassium-saving diuretics in oedematous diseases, hypertension, and hypokalemia as well as in primary hyperaldosteronism. Possible side effects of aldosterone antagonists include hyperkalemia and, in case of spironolactone, which is less specific for the mineralocorticoid receptor than eplerenone, also antiandrogenic and progestational actions. 

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