Thyrotrophin-releasing hormone in clinical practice.

Thyrotrophin-releasing hormone (TRH), a tripeptide with the formula pyroglutamyl histidylprolinamide, was first isolated by Schally and his coworkers in 1969 and now has an established role in clinical endocrine practice. When given to animals in pharmacological doses it has a variety of neurotropic actions. These include arousal; increased respiration, muscle tone, and body temperature; and emotional behaviour. It also increases the LD5o of barbiturates. Side effects in man are minor and transient with the 200-,ug intravenous dose used in the standard TRH test. They include nausea, a desire to micturate, flushing, dizziness, an unusual taste, and an increase in the pulse rate. No adverse effects on the liver, kidney, or bone marrow have been reported. The widespread distribution of TRH in the cerebral cortex, hypothalamus, and spinal cord have led to the suggestion that it may act as a neurotransmitter, but in man there is no good evidence to support this view. It has no effect on the contingent negative variation, a sensitive indicator of the brain activity which results from other agents such as diazepam and nicotine (Ashton et al., 1976).