Question

question 67
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thyroid hormones increase the number of epinephrine receptors in a target cell for epinephrine, thereby increasing the effect of epinephrine in that cell. without the thyroid hormones, epinephrine would have only a weak effect.
this is an example of which of the following?
synergistic effect
antagonistic effect
downregulation
permissive effect

Explanation:

• Synergistic effect: Occurs when two hormones work together to produce a greater effect than the sum of their individual effects. But here, thyroid hormone enables epinephrine to have a stronger effect rather than both acting simultaneously in a simple additive - like synergy.
• Antagonistic effect: Happens when one hormone opposes the action of another. This is not the case as thyroid hormone is enhancing, not opposing, epinephrine's action.
• Downregulation: Refers to a decrease in the number of receptors. But the problem states an increase in receptors (due to thyroid hormones).
• Permissive effect: When one hormone makes the target cell more responsive to another hormone. Thyroid hormones increase the number of epinephrine receptors, making the cell more responsive to epinephrine (which has a weak effect without thyroid hormones). This fits the definition of a permissive effect.

Answer:

Permissive effect