What is the Origin of Physiological Permissiveness?

This concept is a classic principle of hormonal regulation, distinguishing itself from synergistic (additive effects) and antagonistic (opposing effects) interactions between hormones. It is rooted in the molecular mechanisms of cellular sensitivity and receptor biology. The discovery of this interaction helped explain complex clinical presentations where multiple hormone systems appear dysfunctional.

What is the Mechanism of Physiological Permissiveness?

The primary mechanism involves the permissive hormone increasing the target cell's responsiveness to the second hormone, often by up-regulating the number of receptors available for the second hormone to bind. For example, thyroid hormone is known to increase the density of beta-adrenergic receptors on target cells, thereby greatly amplifying the effect of catecholamines like epinephrine on heart rate and metabolic rate.

Physiological Permissiveness ∞ Area

Physiological Permissiveness

Meaning

Physiological permissiveness is a fundamental biochemical phenomenon in endocrinology where the presence of one hormone, the permissive hormone, is absolutely required for a second hormone to exert its full, expected biological effect on a target cell or tissue. The permissive hormone may have little to no effect on its own but is an essential precondition for the second hormone’s maximal efficacy. This interaction is critical for the integrated function of the endocrine system.