inhibiting hormone

An inhibiting hormone is the hypothalamus's brake pedal: a signal that tells the pituitary to slow or stop releasing a particular hormone. Where releasing hormones say go, inhibiting hormones say stop, and the balance between the two sets the actual output. Some pituitary hormones are governed mainly by the brake rather than the accelerator.

The two best-known examples are somatostatin, which inhibits growth hormone (and also TSH) release, and dopamine, which the hypothalamus delivers to inhibit prolactin secretion. Prolactin is unusual because its default is to be held down: it is under tonic inhibition by dopamine, so anything that cuts off the dopamine signal lets prolactin rise.

This braking logic has direct clinical consequences. Cutting the pituitary stalk or blocking dopamine with certain drugs releases prolactin from inhibition and raises its level, whereas dopamine-acting drugs are used to treat prolactin-secreting tumors. Somatostatin analogs, in turn, are mainstay treatments for growth hormone excess in acromegaly.