Virtual Rat Endocrine Activity
Based on USING “VIRTUAL RATS” FOR UNDERSTANDING ENDOCRINE PHYSIOLOGY by Sandhia Varyani, Eilynn Sipe, J. P. Layshock, & Stephen E. DiCarlo, Dept. of Physiology, Northeastern Ohio University College of Medicine.
The purpose of this exercise is for you to understand basic principles and important concepts regarding the endocrine system. In this exercise, you will observe the effects of unknown hormones on “virtual rats” and use your knowledge of the endocrine system in determining the hormone used. Control “virtual rats” are provided as normals to which all other values should be compared. Upon careful comparison of the hormone-treated “virtual rats” with the control “virtual rats”, you will be able to determine the unknown hormone. This activity is based on the negative feedback control pathways for testosterone, cortisol and thyroid hormones.
PROCEDURE:
In this exercise, you will determine the identity of an unknown hormone by observing the effect it has on the organs of the male rat. The data for this lab were compiled from seven pairs of male rats; one pair was the control group and the remaining six pairs were experimental groups. In each set, there was an “intact” rat and a “castrate rat.” Castration was removal of the testes to eliminate testosterone production. The two rats (normal and castrate) of each group were treated alike in all other ways (food, water, etc).
All rats, except for those in the control group were injected with a hormone (ACTH, cortisol, LH, TRH, testosterone or TSH) on a daily basis for two weeks, sacrificed humanely and autopsied. Organ weights were measured at autopsy. Using your predictions of hormone effects and the autopsy data, match the rat groups with the hormone they were injected with. The following figure represents the rat organs weighed.
The organs to the left appear on each rat. The pituitary is not drawn to scale; it is drawn larger than actual size. The seminal vesicles and prostate are targets of testosterone.
To help in determining the identity of the unknown hormones, look for changes between the control values and the values of the unknown hormone (both the intact and castrate animal). The changes between the control rats and the rats that were treated with the unknown hormone should be 20% if they are to be considered significantly different. If the change is less than 20%, it is attributed to experimental error or biological error. Experimental errors may include small errors in calibration procedures, measurements, or instrumentation. Any variability that occurs because of the differences between animals is considered biological error.
The command center for the endocrine system is the hypothalamus, a small portion of the brain. The hypothalamus acts as an endocrine organ that secrets oxytocin and antidiuretic hormone (ADH), also known as vasopressin. These hormones travel down the pituitary stalk to the posterior pituitary gland, where they are released into the bloodstream. In addition, the hypothalamus also regulates anterior pituitary gland function through the release of thyroid-releasing hormone (TRH), corticotropin-releasing hormon (CRH) and gonadotropin-releasing hormone (GnRH).
These releasing hormones travel through a specialized blood vessel system that connects the hypothalamus to the anterior pituitary gland. From here, they stimulate the synthesis and secretion of anterior pituitary hormones, which include thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), adrenocorticotropic hormone (ACTH) and prolactin. Each of these hormones is released into the bloodstream to affect specific target organs.
For example, the hypothalamus secretes TRH, which travels to the pituitary gland to release TSH; TSH travels to the thyroid gland (the target organ) and stimulates the release of thyroid hormone. It is important to note that the hypothalamus releasing hormones are required for the synthesis and release of the anterior pituitary hormones. Because the anterior pituitary gland secrets multiple hormones, it is frequently referred to as a ‘master gland.’
The pathways of three hormones are examined in this experiment: thyroid hormone, cortisol, and testosterone. The hormonal pathways are similar in all three cases. The hypothalamus secretes a releasing hormone to regulate each of the hormones secreted from the anterior pituitary. The hypothalamus acts as a command center. If the hypothalamus is not stimulated, the hypothalamic-releasing hormones will not stimulate the anterior pituitary to secrete its hormones.
Thyroid hormone: The hypothalamus releases TRH, which travels to the anterior pituitary via the bloodstream to stimulate the production of TSH. TSH travels to the thyroid to stimulate the production and release of thyroid hormone. Thyroid hormones influence the growth rate of body tissues and is needed for proper central nervous system development. It increases basal metabolic rate (BMR) and heat production. An excess of thyroid hormone can negatively feedback to inhibit release of more thyroid hormone, TSH and/or TRH.
Hyperthyroidism is the excessive production of thyroid hormone. The most common cause is Grave’s disease, which causes increased BMR, constant warmth, nervousness, and enlargement of the thyroid gland. Hypothyroidism, by contrast, causes low BMR, decreased appetite, and abnormal nervous system development.
Cortisol: ACTH is released from the anterior pituitary in response to CRH secreted from the hypothalamus. ACTH stimulates the adrenal glands to secrete cortisol, which promotes the breakdown of proteins and fats, and helps the body adapt to stress. Cortisol functions to provide fuel through catabolism of body materials. Under normal conditions, excess cortisol in the bloodstream will negatively feedback to inhibit CRH release, to inhibit ACTH release and/or to inhibit further cortisol release. Cortisol can also act as an immunosuppressive and anti-inflammatory. In large doses, it can cause shrinkage of the immune system glands. For this case study, they will be represented by the thymus, an organ of the immune system.
Cushing’s syndrome is the result of excess secretion of cortisol. Symptoms include personality changes, hypertensioin, osteoperosis, and weight loss. Protein degredation caused by cortisol can lead to wasting. Hyposecretion of cortisol causes defects in metabolism, confusion, and an inability to adapt to srress.
Testosterone: LH is released from the anterior pituitary in response to GnRH secreted from the hypothalamus. In males, LH travels to connective tissue in the testes, to cells called Leydig cells. The Leydig cells release testosterone, which is responsible for the male sex drive and secondary sex characteristics, such as increased body hair and a deeper voice. An excess of testosterone can cause an increase (anabolic) in muscle mass. Negative effects of testosterone are male pattern baldness and increased secretion of the sebaceous
glands, which can lead to acne. Figure 3 presents the relative anatomy of the male reproductive tract.
Decreased testosterone can cause abnormal male development and low sperm counts. Excess testosterone in developing males can cause premature sexual development.
You can use the table below to organize your predictions or to record results. Note that endocrine organs that are hypersecreting tend to hypertrophy (increase in size) and those that are hyposecreting tend to atrophy (decrease in size). Place a + to denote an increase in size, a - to denote a decrease in size in an organ and “ NC” if no change occurs.
Intact / Castrate / Intact / Castrate / Intact / Castrate / Intact / Castrate
Pituitary Gland
Thyroid Gland
Adrenal Gland
Thymus Gland
Testes
Prostate
Sem. Vesicles
Body Weight
Organ Size
Hormone 4 / Hormone 5 / Hormone 6
Intact / Castrate / Intact / Castrate / Intact / Castrate
Pituitary Gland
Thyroid Gland
Adrenal Gland
Thymus Gland
Testes
Prostate
Sem. Vesicles
Body Weight
Organ Size
This is your set of control rats; the data are the results of the autopsy.
Determine the identity of Hormone 1 using the data from the autopsy listed below.
Determine the identity of Hormone 2 using the data from the autopsy listed below.
Determine the identity of Hormone 3 using the data from the autopsy listed below.
Determine the identity of Hormone 4 using the data from the autopsy listed below.
Determine the identity of Hormone 5 using the data from the autopsy listed below.
Determine the identity of Hormone 6 using the data from the autopsy listed below.