0728 - Pharmacological Determinants of PVR - RM

Question 1

Understand the role of ɑ- and beta adreno-receptors.

Answer 1

Adrenergic receptors serve to ‘activate’ the SY response across the body. Alpha adrenergic receptors are commonly found in the vasculature and serve to constrict it. They have high affinity for A/NA, but low affinity for isoproterenol.
Beta receptors are found in the heart (B1 - drive heart) and pulmonary systems (B2 - bronchodilation). They both have high affinity for isoproterenol, lower affinity for adrenaline, and lower still for NA.

Question 2

What is the effect of the beta 1 receptor?

Answer 2

Found in heart - drives pacemakers, conduction velocity, and contractility.

Question 3

What is the effect of the beta 2 receptor?

Answer 3

Found in arterioles - coronary, skeletal muscle, pulmonary and abdomen - serves to dilate (though effect ‘drowned out’ by alphas in abdomen), as well as dilating systemic veins.

Question 4

What is the effect of the alpha receptors?

Answer 4

Found in all arterioles and systemic veins, as well as salivary glands and abdomen - serves to constrict.

Question 5

What are the effects of isoproterenol (isoprenaline), adrenaline and noradrenaline on the Cardiovascular system (alpha, B1/2 receptors)?

Answer 5

Alpha - Equally responsive to A/NA, but not to isoproterenol - could give isoproterenol without activating them.
Beta 1 - Most responsive to isoproterenol, then almost equally to A/NA.
Beta 2 - Most responsive to isoproterenol, then A, then NA

Question 6

How do beta blockers lower BP?

Answer 6

The effect is indirect - lower CO (contractility and HR), as well as renin secretion (thus lower angiotensin), reduce effects of SY activation. So both the CO and the TPR side, but not directly.

Question 7

Why can vasodilation may result in decreased perfusion (haemodynamic steal)?

Answer 7

Vasodilation reduces resistance in the vascular wall. However, in pathological tissues, an atherosclerotic plaque will not vasodilate, keeping its resistance relatively stable. As the unoccluded arteries have less resistance, they will get considerably increased flow, with flow over the plaque possibly being reduced in absolute terms.