Hypopituitarism

Hypopituitarism is a condition when there is a deficiency of a pituitary hormone or hormones. Pituitary hormones are hormones produced by the pituitary gland such as the growth hormone, prolactin, luteinizing hormone, etc. If there are no pituitary hormones, then we talk about panhypopituitarism (pan = all) - the deficiency of all pituitary hormones.

Hypopituitarism can have several causes. There can be a tumour which damages the pituitary, for example, a pituitary adenoma, a common benign tumour in the anterior pituitary typically found in adults. Another possible causes can be brain injury, surgical excision of a tumour in the pituitary (which would damage the pituitary) or radiation of the pituitary. Hypopituitarism can also be a result of pituitary apoplexy, a stroke with sudden bleeding into the pituitary gland, which is often quite severe.

Let’s now take a look at the individual hormones and see what happens if they stop working.

Growth Hormone Deficiency

Somatotropin (growth hormone) has three major effects, it promotes growth, it helps to utilize fat as a source of energy, and it also has a diabetogenic effect. Why is it called diabetogenic? Growth hormone decreases absorption of glucose in skeletal muscle and adipose tissue and it also increases glucose production in the liver. As you can imagine, if the organism does not absorb that much glucose and it actually produces even more, there is a higher glucose concentration in blood. And for that reason, more insulin needs to be secreted. Now, if someone has an actual diabetes, they are, in a way, in a similar situation: they have a high concentration of glucose, which requires more insulin, which they don’t have, or the tissue is resistant to it. Growth hormone creates something similar: the high glucose concentration and the need for more insulin. That's why its effect is called diabetogenic.

So, what happens if there is not enough growth hormone? The patient is not going to be able to grow, there is going to be decreased lean body mass as a result of the organism not being able to utilize fat as a source of energy, and there can a fasting hypoglycemia – low blood glucose levels between meals as the diabetogenic effect is also not going to work.

Luteinizing and Follicle-Stimulating Hormone Deficiency

First, let's review the hormones' effect. The luteinizing hormone stimulates ovulation and testosterone synthesis. The follicle-stimulating hormone is responsible for stimulating sperm maturation, follicular development and estrogen synthesis.

If the hormones are deficient, new oocytes and follicles cannot develop and female patients are going to suffer from amenorrhea, the absence of menstruation, and infertility. Men are going to suffer from the loss of pubic hair, decreased libido and even impotence.

Prolactin Deficiency

Prolactin which stimulates milk production and also milk secretion during breastfeeding. If there is no prolactin, there will therefore be no lactation.

Adrenocorticotropic Hormone Deficiency

The adrenocorticotropic hormone is responsible for stimulating the synthesis and secretion of adrenal cortical hormones, most importantly cortisol. Cortisol is a glucocorticoid, which means that it stimulates gluconeogenesis, the synthesis of glucose.

If there is a deficiency of the adrenocorticotrop hormone, the patient is going to suffer from hypoglycemia – low blood glucose - and they may lose some weight. Normally, some glucose is converted into fat, but as there is not any cortisol, and the patient suffers from hypoglycemia, there is no glucose to be coverted.

Thyroid-Stimulating Hormone Deficiency

Finally, the thyroid-stimulating hormone stimulates the synthesis and secretion of thyroid hormones. One of the many important effects of thyroid hormones is that they increase heart rate and heart contractility and they also increase the utilization of fat.

With no thyroid-stimulating hormone, there can be no more fat utilization and the patient is going to gain weight. They can also suffer from low blood pressure as the heart rate and contractility cannot be increased.

References:
Costanzo, L. S. (2018). Physiology. Elsevier.
Hammer, G. D., & McPhee, S. J. (2014). Pathophysiology of Disease: An Introduction to Clinical Medicine. McGraw-Hill Education.
Kumar, V., Abbas, A. K., & Aster, J. C. (Eds.). (2015). Robbins and Cotran pathologic basis of disease. Elsevier Saunders.
McCance, K. L., & Huether, S. E. (2019). Pathophysiology: The Biological Basis for Disease in Adults and Children. Elsevier.