Pituitary News, Issue 2 - Autumn 1996.

When supplies of GH were limited GH replacement was restricted to the treatment of children. Recent advances in technology allowing GH to be made in large amounts has permitted GH to be replaced even after growth has ceased. This has lead to a reanalysis of the role of GH throughout life.

Professor Desmond G Johnston
Imperial College School of Medicine, London

Growth hormone (GH) is the pituitary hormone recognised as being essential for normal growth in childhood. Absence of GH in children limits growth while too much causes them to become abnormally tall. In adults, too much GH causes a condition called Acromegaly, but deficiency in adults had been considered previously to have no importance. In any case, GH replacement in adults was not possible, as supplies were limited and were restricted to treatment of children. The technology to make GH in large amounts by biosynthetic means has permitted GH to be replaced even after growth has ceased. This has led to a reanalysis of its role throughout life.

Adults who are likely to be GH-deficient include people with disorders of the Pituitary gland, who are often deficient in other pituitary hormones. Pituitary tumours are the commonest cause, but GH deficiency may also arise as a consequence of treatment of the Pituitary tumour by surgery or Radiotherapy. Other causes include certain kinds of brain tumour, severe head injury and certain inflammatory conditions. Many people who were GH-deficient in childhood continue to be GH-deficient when adult.

Deficiency of GH is diagnosed by blood tests. GH is secreted normally in short bursts over the 24 hours, with most being released overnight during sleep. Single measurements of GH are often very low during daylight hours, even in people with quite normal GH production. In order to demonstrate deficiency, therefore, a stimulation test is required. Several such tests exist, the most popular being the insulin stimulation test.

In those adults who have been demonstrated to be GH-deficient, we now know that GH treatment does have certain effects which may be beneficial. It has so-called anabolic effects, by which is meant action to build up certain tissues such as muscle. The ability to perform exercise also improves in many people. There is a tendency to lose body fat, particularly around the middle, but the total body weight is frequently unchanged. In addition, GH treatment has desirable actions on the levels of certain fats in the blood stream. All these changes would be beneficial to the circulation if maintained over many years. On the other hand, GH increases the tendency to develop diabetes in people who are prone to the condition. It does this through its action on the hormone insulin and, if this action were sustained for many years, it might have adverse effects not just for diabetes, but also for the circulation. Long-term GH therapy therefore has potential benefits, but there is also a reason for some caution and treatment needs to be monitored carefully.

GH treatment requires injection, usually once daily before retiring to bed. Between one third and two thirds of people who take GH in this way feel generally better, both physically and mentally. These people appreciate the improvement in their body composition, with more muscle and less fat, and the increased capacity for exercise. Symptoms of fatigue and depression occur more commonly in hypopituitary subjects than in the general population and these symptoms may improve with GH therapy. Side-effects of treatment may occur in the early stages. The most frequent of these are fluid retention and aches and pains in the joints. These are usually short-lived and often disappear with a reduction in dosage.

The decision on whether or not an adult with hypopituitarism should receive GH treatment is complex and should be discussed between patient and specialist. As with all treatments which are taken long-term, experience over twenty years or more will be necessary before all the benefits and disadvantages are clear. Some patients may find attractive the option of a trial for six months. At the end of that time, the benefits and problems can be discussed for that individual. Some people find the idea of daily injections intolerable and do not want such treamtent. In practice, however, the majority of those who take the injections find them much less of a problem that they anticipated. Of course, some people find even minor side-effects a nuisance, particularly if they felt well before starting. Some who feel no different on treatment do not wish to continue. On the other hand, those who feel physically and mentally better, and think they look better, on therapy opt to stay on treatment long-term. It is unfortunately not possible to predict in advance those who will benefit in terms of symptoms.

Treatment requires regular assessment of GH effects. This includes periodic clinical assessments, measuring body fat levels and checking blood sugar concentrations. Where symptoms improve, the clinical features are good and the blood tests are favourable, it seems wise to continue treatment. Improvement in body composition, or in the blood tests alone, may be a reason to continue treatment, even in the absence of any change in symptoms. This requires discussion with the specialist. Treatment is expensive, but if shown to be of benefit, the expense is justified.