Negative-feedback action

Whereas it is conceivable that a CRH/vasopressin hyperdrive contributes to behavioral, emotional, and hormonal symptoms of mood disorders, the question remains which mechanisms mediate this hyperactivity of CRH and vasopressin-secreting neurons. The gene expression of both neuropeptides is suppressed by ligand-activated glucocorticoid receptors. The efficiency of this negative feedback action of circulating corticosteroids depends on the number of corticosteroid receptors, their affinity, and the degree of interaction with other factors (e.g., heat shock protein) involved in the transcription machinery. 

Inhibition of the renin-angiotensin system with ACE inhibitors or ARBs may be incomplete because the drugs disrupt the negative feedback action of Ang II on renin secretion and thereby increase plasma renin activity. Other antihypertensive drugs, notably hydrochlorothiazide and other diuretics, also increase plasma renin activity. Aliskiren not only decreases baseline plasma renin activity in hypertensive subjects but also eliminates the rise produced by ACE inhibitors, ARBs, and diuretics and thereby results in a greater antihypertensive effect (Figure... 

Figure 2 Schematic model of the intracellular signaling mechanisms including phosphatidylinositol-specific phospholipase C (PI-PLC) isoforms, inositol-1,4,5-triphosphate (IP3) receptor, and protein kinase C (PKC) in the expression of delta opioid receptor agonist-induced spinal antinociception. In addition, PKC is considered to play a substantial role in an intracellular negative feedback action on the spinal delta opioid receptor-mediated antinociceptive pathway.

Legan SJ, Karsch FJ, Foster DL (1977) The endocrine control of seasonal reproductive function in the ewe a marked change in response to the negative feedback action of estradiol on luteinizing hormone secretion. Endocrinology 707 818-824. 

When the placenta separates, concentrations of fetal sex steroids drop abruptly. Serum estradiol in neonates decreases to basal concentrations withm 5 to 7days after birth and persists at this concentration until puberty. The negative feedback action of steroids is now removed, and gonadotropins are released. Postnatal peaks of LH and FSH are measurable for a few months after birth, peaking at 2 to 5 months and then dropping to basal concentrations. 

Thyroid hormones enter the extrathyroidal tissues by the action of specific transporters the organic anion transport protein (OATP) and the monocarboxylic transporter (MCT8) (Ekins et al. 1994 Friesema et al. 1999, 2005). Within some cells, deiodinating enzymes can remove an iodine atom from the T4 or T3 molecules and thereby modify the sensitivity of a cell to the actions of the thyroid hormones. The cellular actions of the thyroid hormones are mediated by nuclear receptor proteins, which bind to DNA and regulate transcription with at least two types of genes that encode these receptors (Barettino, Ruiz, and Stunnenberg 1994) these also provide a negative feedback action on the hypothalamic-pituitary axis. T4 is sometimes... 

If not the enzyme, one of its products might exert the regulatory function on DNA replication. The only deoxyribonucleotide without negative feedback action on ribonucleotide reductase, dCTP, has been advanced by Reichard to be involved. Addition of thymidine to hamster cells lowers the dCTP pool and concomitantly inhibits DNA synthesis even when dCTP has not become limiting as substrate . Under these conditions no more initiation of replication takes place and a specific correlation of the two results has been claimed. Conversely, direct inhibition of DNA synthesis by aphidico-... 

For the components shown in Figure 3.15, assume the action shown in Figure 3.16, and also assume an air to open actuator (I/I) for the valve. Note that the valve, process, and sensor/transmitter are all direct acting. Therefore, in order to get the desired negative feedback action (I/D overall loop action) the controller must be set to reverse action. 

Feedback Control In a feedback control loop, the controlled variable is compared to the set point R, with the difference, deviation, or error e acted upon by the controller to move m in such a way as to minimize the error. This ac tion is specifically negative feedback, in that an increase in deviation moves m so as to decrease the deviation. (Positive feedback would cause the deviation to expand rather than diminish and therefore does not regulate.) The action of the controller is selectable to allow use on process gains of both signs. 

All of these actions are directed at increasing serum calcium levels and decreasing serum phosphorus levels, although the activity of calcitriol also increases phosphorus absorption in the GI tract and mobilization from the bone, which can worsen hyperphosphatemia. Calcitriol also decreases PTH levels through a negative feedback loop. These measures are sufficient to correct serum calcium levels in the earlier stages of CKD. 

When the concentration of the free form of a hormone decreases, then more of this hormone will be released from the binding proteins. The free hormone is the biologically active form. It binds to the target tissue to cause its actions and is involved with the negative feedback control of its secretion. The binding of hormones to plasma proteins has several beneficial effects, including ... 

The final mechanism of action of PTH involves the activation of vitamin D3 through the stimulation of la-hydroxylase in the kidney. In the gastrointestinal tract, vitamin D3 is essential for the absorption of calcium. Enhanced absorption of calcium from dietary sources serves to further increase the concentration of calcium in the blood. Many foods, in particular, dairy products, which are rich in calcium, are fortified with vitamin D. The release of PTH from the parathyroid glands is regulated by plasma calcium levels through negative feedback. A decrease in the level of calcium in the blood stimulates the secretion of PTH and an increase in the calcium level in the blood inhibits it. 

Odorant recognition initiates a second-messenger cascade leading to the depolarization of the neuron and the generation of action potentials 821 Negative-feedback processes mediate adaptation of the olfactory transduction apparatus to prolonged or repetitive stimulation 823 Alternative second-messenger pathways maybe at work in olfactory transduction 823... 

Docke F, Rohde W, Sturzebecher B, Ledwon P, Dorner G (1990) Evidence that desensitization of the negative feedback of oestrogen and priming for the positive feedback of oestrogen depend upon a common mechanism of oestrogen action in rats. J Endocrinol 126 395-402... 

---