Adrenergic System and Drugs(catecholamines)

• Understanding Nervous system-

                                 CNS-Central Nervous System.Consist of Brain and Spinal cord

                                 PNS-Peripheral Nervous System.Consist of ganglia and nerves.Connect CNS to other 

                                           parts of body.It consist of two systems-

                                           Somatic nervous system & Autonomic nervous system

                                           Somatic nervous system is related to voluntary muscles like that of limbs 

                                           Autonomic nervous system is related to involuntary muscle and it further divided 

                                           into two systems as sympathetic and para sympathetic systems. 

                                 Sympathetic system-Its a thoracicolumbar system.It consist of spinal nerves only.This

                                           system uses nor adrenaline and acetylcholine as neurotransmitter.Acetylcholine is 

                                           released by the presynaptic neuron.Noradrenaline is relaesed by the post 

                                           synaptic neurone.

                                 Parasympathetic system-Its a cranisacral system.It consist of spinal and cranial nerves

                                    III,VII,IX & X.This system utilizes acetylcholine as a nurotransmitter.

• Adrenaline has got two receptors for conducting its action-Alpha receptors and Beta receptors.Alpha receptors are further of two types-Alpha 1 & Alpha 2.Beta receptors are of three types-Beta 1,Beta 2 & Beta 3.Each receptor is present on a specific site,for eg: Beta 1 is present heart;Beta 2 is present on bronchi,blood vessels,uterus; alpha 1 is present on blood vessels.
• At large doses of adrenaline alpha response predominates.
• Adrenaline cause increase in heart rate,force of contraction and conduction velocity.This response is due to beta 1 receptor action.
• Adrenaline can cause both vasoconstriction and vasodilatation.Adrenaline causes vasoconstriction in cutaneous,mucous membrane and renal beds.Its due to alpha 1 receptors.Vasodilatation occurs in skeletal and coronaries vessels.Its due to beta 2 receptors.
• When adrenaline is given slowly S.C. than it causes increase in systolic blood pressure(due to increase in cardiac output) but decrease in diastolic blood pressure(due to decrease in peripheral vascular resistance).Mean B.P. generally rises.
• When adrenaline is given rapidly through I.V. than adrenaline concentration increases rapidly in blood and as such alpha receptors become more active towards adrenaline.This leads to increase in both the systolic and diastolic blood pressure( due to increase in cardiac output as well as vasoconstriction even in skeletal muscles).But this increase is just for a short period of time.As the concentration of adrenaline decreases Diastolic Blood pressure drops again.
• Adrenaline causes broncho dilatation.This action is due to beta 2 receptor.
• Adrenaline increases blood flow to skeletal muscles and coronaries arteries.
• Adrenaline should not be given in cases of hyperthyroidism,Angina & hypertension.
• Should be cautiously used in pregnant ladies.
• Dose:0.2-0.5 mg S.C/I.M