Hormonal messages

N9. Nunez, E. A., Free fatty acids as modulators of the steroid hormone message. Prostaglandins Leuk. Essent. Fatty Acids 48, 63-70 (1993). 

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... 

This response in the muscle to calcium, which increases during contraction, allows for individual, active muscles to increase glycogenolysis without necessitating the hormonal message, epinephrine, which would affect all muscles. 

Thus, there is an interaction between these two effectors. Both the hormonal message of glucagon plus the presence of alanine will be additive or synergistic in its effects on this enzyme. 

Hormones act through binding to specific cellular receptors. Second messengers are often used to transmit the hormonal message to the target metabolic pathway. cAMP is one such second messenger. Cyclic AMP -dependent signal transduction mechanisms involve three separate proteins (1) a hormone receptor, (2) adenylate cyclase, and (3) a G protein (see here). 

Second messenger, intracellular mediators of the externally received hormonal message, e.g., cAMP, cGMP, Ga +, inositol-l,4,5-triphosphate (IP3), diacyl-glycerol (DG). 

A number of factors are concerned with the stimulation of the glands to secrete gastric juice. Initially, in the cephahc phase, stimuli such as the sight and smell of food act via the vagus nerve. Then, in the gastric phase, secretion is maintained by chemical sensors and distension of the stomach. Finally, the presence of digesta in the duodenmn ehdts secretion by neural and hormonal messages. 

Haksar et al. (1973) treated rat adrenal cells with sialidase and observed a decrease in response to adrenocorticotropic hormone (ACTH) stimulation as measured by corticosterone production. No effect was observed on the cell s response to cyclic AMP or dibutyryl cyclic AMP, indicating that the observed effect of sialidase treatment must be due to impairment of some step prior to cyclic AMP formation. They proposed two possibilities (1) the sialic acid residues on the cell membrane provide affinity for the ACTH, thereby aiding in activation of the receptor, or (2) the sialic acid facilitates the transmission of the signal from the ACTH-receptor interaction to adenylcyclase. Similar studies with other hormones and isolated cell systems might indicate involvement of cell surface sialyl residues in transduction of other hormonal messages. Sialyltransferase and sialidase present in the cell membrane may serve to provide the environment and controls for transduction of the hormonal message. 

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