SNS receptors

Question 1

Alpha 1 receptors

Answer 1

Drugs: adrenaline, metaraminol, noradrenaline

Effect: systemic vasoconstrictor

Tissue: vascular smooth muscle and myocardial tissue

How they act: Gq protein-coupled – activating phospholipase enzymes

Question 2

Alpha 2 receptors

Answer 2

Drug: clonidine

Effect: Reduce sympathetic tone

Tissue: Vascular smooth muscle

How they act: Gi protein-coupled – inhibits adenylyl cyclase

Question 3

Beta 1 receptor

Answer 3

Drugs: Dobutamine, isoprenaline, noradrenaline

Effect: Positive chronotrope and inotrope

Tissue: Kidneys, heart

How they act: Gs protein-coupled - activates cAMP and protein kinase pathway

Question 4

Beta 2 receptor

Answer 4

Drugs: Isoprenaline and salbutamol

Effect: vasodilation and bronchial dilation

Tissue: vascular and bronchial smooth muscle

How they work: Gs protein-coupled - activates cAMP and protein kinase pathway

Question 5

Dopaminergic 1 receptor

Answer 5

Drugs: Fenoldopam, dopexamine, dopaminergic

Effect: vasodilation in kidneys and splanchnic circulation

Tissue: renal and mesenteric vessels

How they act: Gs protein-coupled - activates cAMP and protein kinase pathway

Question 6

Vasopressin 1

Answer 6

Drug: vasopressin

Effect: vasoconstriction

Tissue: vascular smooth muscle, liver, platelets

How they act: Gq protein-coupled - activating phospholipase enzymes

Question 7

Vasopressin 2 receptor

Answer 7

Drug: vasopressin

Effect: Synthetic ADH – mediates water reabsorption in collecting ducts in response to osmoreceptors

Tissue: renal collecting ducts

How they act: Gs protein-coupled - activates cAMP and protein kinase pathway

Question 8

Non-adrenoceptor mediated vasodilation or nitric oxide donors.

Answer 8

cGMP is activated when NO binds to guanylyl cyclase (GC) enzyme. GC concerts CTP into cGMP.
This activated protein kinase G which causes calcium levels to decrease = smooth muscle relaxation.

cGMP decreased both preload and afterload by causing vasodilation of veins and arteries. cGMP-mediated smooth muscle dilators reduce myocardial work and O2 consumption while also increasing oxygenation by vasodilation of the coronary arteries.

e.g. nitrates cause vasodilation and reduce preload. Reduce diastolic wall stress to improve sub endocardial blood flow. This improves the oxygen supply and demand ratio which reduces anginal pain