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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.
Control
Hormone 1
Hormone 2
Hormone 3
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
Pituitary
Gland
Thyroid
Gland
Adrenal
Gland
Thymus
Gland
Testes
Prostate
Sem.
Vesicles
Body
Weight
Organ
Size
Castrate
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.