Hormones fast-acting

The concentration of insulin present in soluble insulin preparations (i.e. fast-acting insulins), is much higher (approximately 1 x KT2 3 mol I ). At this concentration, the soluble insulin exists as a mixture of monomer, dimer, tetramer and zinc-insulin hexamer. These insulin complexes have to dissociate in order to be absorbed from the injection site into the blood, which slows down the onset of hormone action. 

TAG mobihzation by hpolysis as a strictly regulated process has been known since the early 1960s, when it was estabhshed that fast-acting hormones such as ACTH and epinephrine increased hpolysis [219, 220], and that insuhn counteracted this activation [221-223]. It was soon recognized that cAMP was involved in the regulation of the catecholamine-sensitive lipolytic activity in adipose tissue... 

In addition to its structural role, phosphatidylinositol has a specialized function in membranes, acting as the source of inositol trisphosphate and diacylglycerol, which are produced as intracellular second messengers in response to fast-acting hormones and neurotransmitters (section 10.3.3). 

Responses to fast-acting hormones by covalent modification of enzyme proteins... 

A cell will respond to a fast-acting hormone only if it has cell-surface receptors that bind the hormone. The receptors are transmembrane proteins at the outer face of the membrane they have a site which binds the hormone, in the same way as an enzyme binds its substrate, by non-covalent equilibrium binding. 

Figure 10.7 The response to fast-acting (surface acting hormones — the role of G-proteins.

Only the first type of neurotransmitter release mediates the fast point-to-point synaptic transmission process at classical synapses (sometimes referred to as wiring transmission). All of the other types of neurotransmitter release effect one or another form of volume transmission whereby the neurotransmitter signal acts diffusely over more prolonged time periods (Agnati et al., 1995). Of these volume transmitter pathways, the time constants and volumes involved differ considerably. For example, diffusible neurotransmitters such as nitric oxide act relatively briefly in a localized manner, whereas at least some neuropeptides act on the whole brain, and can additionally act outside of it (i.e., function as hormones). There is an overlap between wiring and volume neurotransmission in that all classical neurotransmitters act as wiring transmitters via ionotropic receptors, and also act as volume transmitters via G-protein-coupled receptors. Moreover, neuromodulators in turn feed back onto classical synaptic transmission. 

They present the double advantage to be lipophihc (rapid onset) and to give place to fast biodegradation (short duration of action). However, they often conserve the intrinsic hepatotoxicity of the allyl group. Allobarbital is a sedative-hypnotic that is no longer used allylestrenol acts as a pure progestative hormone and alprenolol is a (3-blocker (Figure 20.19). 

Thus, in addition to hormonal effects (see here), the liver senses the fed state and acts to store fuel derived from glucose. The liver also senses the fasted state and increases the synthesis and export of glucose when blood glucose levels are low. (Other organs also sense the fed state, notably the pancreas, which adjusts its glucagon and insulin outputs accordingly.)... 

Phosphoenolpyruvate carboxykinase is induced. Oxaloacetate produces PEP in a reaction catalyzed by PEPCK. Cytosolic PEPCK is an inducible enzyme, which means that the quantity of the enzyme in the cell increases because of increased transcription of its gene and increased translation of its mRNA. The major inducer is cyclic adenosine monophosphate (cAMP), which is increased by hormones that activate adenylate cyclase. Adenylate cyclase produces cAMP from ATP. Glucagon is the hormone that causes cAMP to rise during fasting, whereas epinephrine acts during exercise or stress. cAMP activates protein kinase A, which phosphorylates a set of specific transcription factors (CREB) that stimulate transcription of the PEPCK gene (see Chapter 16 and Pig. 16.18). Increased synthesis of mRNA for PEPCK results in increased synthesis of the enzyme. Cortisol, the major human glucocorticoid, also induces PEPCK. 

Fig. 36.10. Regulation of hormone-sensitive hpase (HSL) in adipose tissue. During fasting, the glucagon/insuhn ratio rises, causing cAMP levels to be elevated. Protein kinase A is activated and phosphorylates HSL, activating this enzyme. HSL-P initiates the mobilization of adipose triacylglycerol by removing a fatly acid (FA). Other lipases then act, producing fatty acids and glycerol. Insulin stimulates the phosphatase that inactivates HSL in the fed state.

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