Question

What might happen to blood pressure if epinephrine is administered alone. Draw a typical control diagram, identify and state the purpose of each reflex component, and indicate whether positive or negative feedback is responsible for restoring blood pressure. How does that control system differ with the addition of atropine?

Answer 1

Ans :  

Effect of epinephrine on BP :  

Epinephrine (adrenaline) is an endogenous catecholamine with potent α- and β-adrenergic stimulating properties. The α-adrenergic action increases systemic and pulmonary vascular resistance, increasing both systolic and diastolic blood pressure. The rise in diastolic blood pressure directly increases coronary perfusion pressure, thereby increasing coronary blood flow and increasing the likelihood of return of spontaneous circulation.  The β-adrenergic effect increases myocardial contractility and heart rate and relaxes smooth muscle in the skeletal muscle vascular bed and bronchi. Epinephrine also increases the vigor and intensity of ventricular fibrillation, increasing the likelihood of successful defibrillation.

Feedback loops -

Positive Feedback Loop

Under stress conditions, higher level of epinephrine, released at increased rate from the adrenal medulla, are present in the synaptic cleft between noradrenergic varicosities and effector cells, whence epinephrine is taken up by the amine “pumps” into the varicosities and to its storage vesicles. Epinephrine can be released together with norepinephrine and activate the presynaptic β₂-adrenoceptors, thus increasing further transmitter release.

Negative Feedback Loops

Epinephrine, originally released from the adrenal medulla and taken up into the sympathetic neuron, is released, together with norepinephrine, from the varicosity. While epinephrine triggers an autofacilitatory feedback loop, acting on presynaptic β₂-adrenergic receptors, norepinephrine, together with epinephrine, leads to an auto-inhibition of its release from sympathetic nerves mediated by presynaptic α₂-adrenoceptors

Adding atropine -

Atropine Sulfate Injection and Adrenalin (epinephrine) can both increase heart rate but are used for different conditions.

Atropine sulfate is an antimuscarinic agent used to treat bradycardia (low heart rate), reduce salivation and bronchial secretions before surgery, as an antidote for overdose of cholinergic drugs or mushroom poisoning.

Adrenalin is a chemical that narrows blood vessels and opens airways in the lungs. These effects can reverse severe low blood pressure, wheezing, severe skin itching, hives, and other symptoms of an allergic reaction. An injection of adrenalin is used to treat severe allergic reactions (anaphylaxis) to insect stings or bites, foods, drugs, and other allergens.