Step 1: Understanding the Question:
We need to compare the potency of synthetic adrenaline with the naturally occurring hormone in the body.
Step 2: Key Concept:
Adrenaline has one chiral center, so it can exist as two mirror-image forms, R and S. Receptor binding is stereospecific, meaning one form fits the adrenergic receptor far better than the other.
Step 3: Detailed Explanation:
The adrenaline the adrenal medulla releases is almost purely the R-enantiomer, and this is the form responsible for essentially all the physiological action, from raising heart rate to dilating airways.
Synthetic adrenaline, made by non-selective chemical synthesis, is produced as a racemic mixture: half R and half S.
The S-enantiomer binds the receptor far more weakly, so it adds very little to the overall effect.
Averaging a fully potent R-half with a nearly inactive S-half brings the total potency of the mixture down to roughly half of what pure natural R-adrenaline achieves.
Step 4: Final Answer:
Synthetic adrenaline's biological activity works out to about 50% of natural R-adrenaline.