The Anterior Pituitary: Growth Hormone and Prolactin
The pituitary is the 'master gland', and its front lobe releases the hormones that command the others. Two of its own hormones have their own drugs and their own diseases — growth hormone and prolactin — and one of them hides a delightful surprise: the drug that treats too much prolactin comes straight from the Parkinson's chapter.
The pituitary gland, hanging just beneath the brain, is often called the master gland because its hormones control the thyroid, the adrenals, the gonads and more — the axes from the foundations chapter. But two of the anterior pituitary's hormones act more directly on the body and have their own pharmacology: growth hormone, which drives growth and metabolism, and prolactin, which drives milk production. Each can be produced in too little or too much, and the disorders — and their treatments — are surprisingly memorable, especially because one of them reaches back to a hormone system you've already met in the brain.
Growth hormone: too little, too much
Deficiency stunts growth; excess causes gigantism or acromegaly. Growth hormone does what its name says in children — it drives the growth of bones and tissues. Too little of it in childhood causes short stature, treated by giving synthetic growth hormone (a manufactured protein, injected) to restore normal growth. Too much growth hormone, usually from a pituitary tumour, causes overgrowth: in children, before the growth plates fuse, this produces gigantism (excessive height); in adults, whose long bones can no longer lengthen, it instead thickens the bones and soft tissues, producing acromegaly — enlarged hands, feet, jaw and facial features, along with metabolic problems. Treatment of the excess aims to shrink or remove the tumour (surgery), or to suppress growth hormone with drugs — most notably somatostatin analogues like octreotide, which mimic the body's own natural 'stop' signal for growth hormone. So the growth-hormone story is symmetrical: give it when there's too little, block it (or remove the source) when there's too much.
Prolactin — and a surprise from the brain
Prolactin's job is to stimulate breast milk production. The interesting condition is too much of it (hyperprolactinaemia), often caused by a small pituitary tumour (a prolactinoma). High prolactin causes inappropriate milk production, absent periods and infertility in women, and low libido and infertility in men. Now for the elegant part, which links straight back to the brain chapters: prolactin is unusual in that it is normally kept suppressed by dopamine — dopamine is the brake on prolactin release. So the logical treatment for too much prolactin is to press that brake harder, using dopamine agonists (cabergoline, bromocriptine) — the very same class of drugs used in Parkinson's disease. These drugs shrink prolactinomas and normalise prolactin remarkably well. This also explains a common side effect in reverse: antipsychotic drugs, which BLOCK dopamine (from the CNS chapter), release the brake and often raise prolactin, sometimes causing milk production or menstrual changes. Dopamine controls prolactin — remember that, and both the treatment and a whole class of side effects fall into place.
- Growth hormone deficiency (children) → short stature; treat with synthetic growth hormone.
- Growth hormone excess → gigantism (children) or acromegaly (adults); treat with surgery/octreotide.
- Prolactin stimulates milk; excess (prolactinoma) → milk production, absent periods, infertility.
- Dopamine SUPPRESSES prolactin → treat high prolactin with dopamine agonists (cabergoline, bromocriptine).
- Antipsychotics (dopamine blockers) can RAISE prolactin — a predictable side effect.
Prolactin is the one hormone that is controlled mainly by INHIBITION, and that single fact ties three chapters together with a bow. Dopamine constantly suppresses prolactin, so: to treat too much prolactin, you boost dopamine with an agonist — the same cabergoline/bromocriptine you met in Parkinson's. And to explain why antipsychotics cause milk production and period changes, you remember they block dopamine — releasing the brake and letting prolactin rise. One relationship, 'dopamine holds prolactin down', simultaneously gives you the treatment for a pituitary tumour and a side effect of psychiatric drugs. Endocrinology rewards you for spotting these cross-links; they turn separate facts into a connected web.
- Forgetting that too much growth hormone in adults causes acromegaly, not extra height.
- Treating high prolactin with a dopamine blocker — you need a dopamine AGONIST.
- Overlooking antipsychotics as a cause of raised prolactin (milk production, missed periods).
- Not investigating a pituitary tumour behind persistent hormone excess.
How do you treat high prolactin from a prolactinoma?
- Growth hormone: deficiency → short stature (give GH); excess → gigantism/acromegaly (surgery/octreotide).
- Prolactin excess (prolactinoma) → milk, absent periods, infertility.
- Dopamine suppresses prolactin → treat with dopamine agonists (cabergoline/bromocriptine).
- Antipsychotics (dopamine blockers) can raise prolactin — a predictable side effect.
- Katzung BG. Basic & Clinical Pharmacology — Hypothalamic & Pituitary Hormones.
- Brunton LL, et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics — Pituitary hormones & their hypothalamic releasing factors.
- Endocrine Society — Guidelines: acromegaly & hyperprolactinaemia.
- Whalen K. Lippincott Illustrated Reviews: Pharmacology — Pituitary hormones.
