Final answer:
Isoprenaline (also known as Isoproterenol) is the agent that displays a pure beta agonist effect in the circulation, selectively targeting beta-adrenergic receptors and thus can increase heart rate and blood pressure. Hence, option (1) is correct.
Step-by-step explanation:
The agent that has a pure beta agonist effect in the circulation is Isoprenaline. Beta agonists bind to beta-adrenergic receptors, which are G-protein coupled receptors that, once activated, increase intracellular cyclic AMP (cAMP) activity. This mechanism can lead to heart muscle contraction, smooth muscle relaxation, and glycogenolysis.
Adrenaline (epinephrine) and Noradrenaline (norepinephrine) have beta agonistic effects but also alpha agonistic effects, which means they don't have a pure beta effect. Dopamine has beta agonistic properties as well, but at lower doses, it primarily affects dopaminergic receptors and at higher doses it affects both beta and alpha receptors.
In comparison, Isoprenaline (Isoproterenol) is a synthetic catecholamine with selective agonism on beta-adrenergic receptors, making it a pure beta agonist that can increase heart rate and blood pressure.