Catecholamines – The Mechanism and Relations of Catecholamines

The mechanism of catecholamines and their relationship with thyroid hormones

Catecholamines are neurotransmitters when they are synthesized in the adrenal medulla and originate in the sympathetic nervous system and brain and circulating hormones. catecholamines include dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). And as a neurotransmitter, each catecholamine is released into the cavity between two neurons, or nerve cells, and then binds to the subsequent/next neuron through specific receptors.
Catecholamine also act as both hormone and neurotransmitter, catecholamine is important for the maintenance of homeostasis through the nervous system.

 

Mechanism of catecholamines –

To describe the mechanism of catecholamines we can take the example of one of the catecholamines such as epinephrine (adrenaline);- as we know the receptor is present on the outer surface of the plasma membrane, now we are assuming that the receptor of adrenaline present in the outer surface of the plasma membrane, the adrenaline hormone which is coming, binds with this receptor that’s present in the outer surface of the plasma membrane than in

 

Synthesis and Metabolism of Catecholamines (USMLE)

 

1ststep – the hormone release

 2nd steps – the hormone-receptor complex forms (this complex always formed on the surface of the plasma membrane because as we know the receptor present on the surface. That’s mean 1st receptor are

 3rd steps – hormone receptor

 

Now as soon as the hormone-receptor complex is formed, this protein undergoes some conformational changes and because of these conformational changes, and enzymes that are present in the inner side of the membrane get active, the name of enzymes is adenyl cyclase.

Now, this active enzyme is going to bring, about the reaction, this reaction is broken down of ATP into cyclic AMP and two inorganic phosphates,( from triphosphate into monophosphate and two phosphates are released ) this reaction takes places in the presence of magnesium(Mg ) ions.

Now, this cyclic AMP is going to act as a second messenger, now this cyclic AMP helps in the conversion of an enzyme which is known as protein kinase (inactive ) into protein kinase (active ).

Basically, the function of cyclic AMP is to convert inactive protein kinase into active protein kinase.

Now, this active protein kinase will help in the conversion of phosphorylase (inactive) into phosphorylase (active). Now, this Active form of phosphorylase helps in the conversion of glycogen phosphorylase (inactive) into glycogen phosphorylase (active). Also during this reaction an enzymes participate is known as now this active glycogen phosphorylase helps in this conversion of glycogen into glucose phosphate and this glucose phosphate gets converted into glucose .why this known as quick hormone/stress hormone  . the reason behind this single cyclicAMP can produce one-two million of molecules within one or two minutes, also this reaction can be amplified, if the number of cyclic amps will more then the produce more number of glucose inside the blood, and we can get more number of ATP. because as we know in stress in the situation body needs more energy, so through this mechanism body fulfills the need for energy. this reaction also knows as a cascade reaction, because every single step there are multiple molecules formed, and these molecules participate in the upcoming reaction.

 

Hypothalamic Pituitary Thyroid Axis

 

The physiological effects of thyroid hormones

The physiological effects of thyroid hormones are well known and Catecholamines in particular Epinephrine, but not all, of thyroid hormone actions. Hemodynamic effects of epinephrine intravenous infusion, such as Tachycardia in those with hyperthyroidism, increased systolic blood pressure with little change in diastolic pressure, increased cardiac output Low peripheral resistance. Norepinephrine produces infusions, Over-all vasoconstriction as systolic and diastolic pressures increase, Reflex bradycardia, slight changes in cardiac output, and increased peripheral Resistance. Epinephrine, like thyroid hormone, increases oxygen consumption and BMR, and accelerates lipolysis with up-regulation of plasma free fatty acids, but, unlike thyroid hormones, it does not affect serum cholesterol levels.
Catecholamines cause glycogenolysis, with norepinephrine being only a fraction of the activity of epinephrine, resulting in hyperglycemia, glycosuria, and increased levels of blood pyruvate and lactate. Although thyroid hormone does not have an independent effect. Thyroid hormone affects aspects of metabolism, such as growth and maturation, unaffected by catecholamine.

Epinephrine, like thyroid hormone

Epinephrine, like thyroid hormone, increases oxygen consumption and BMR, and accelerates lipolysis with up-regulation of plasma free fatty acids, but, unlike thyroid hormones, it does not affect serum cholesterol levels. Catecholamines cause glycogenolysis, with norepinephrine being only a fraction of the activity of epinephrine, resulting in hyperglycemia, glycosuria, and increased levels of blood pyruvate and lactate. Although thyroid hormone does not have an independent effect. Thyroid hormone affects aspects of metabolism, such as growth and maturation, unaffected by catecholamine.

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