Lecture question #1:

To develop bioassay for TSH.  I divided this into 5 steps, and gave you 2 points for each part listed below, for a possible total of 10 points.  Compare your answer with what is written below, and try to understand why you lost points.  This will give you some insight into how your quizzes and exams will be graded.

1. You need to determine some biological response that is caused by TSH.  You learned last year that TSH stimulates the thyroid gland to grow, and it stimulates it to secrete TH, so you could have selected either of these as the response that you would measure.  Some of you suggested the response you'd measure would be an increase in body temperature, or increased metabolic rate.  Although an increase in TSH would be expected to lead to an increase in these variables, these responses are several steps away from TSH, and so less reliable an indicator of TSH levels.  For example, if you inject TSH into an animal and get no change in body temperature, you wouldn't know whether this is because the TSH level was too low, or if the TSH was high, and TH secretion was high, but the target tissue response to TH was defective.

2. Get a system where you can measure the amount of TH secretion or the amount of thyroid growth in response to TSH that you'll administer.  Two possibilities suggest themselves, and most of you chose the first, which is more similar to the rooster comb example, although the second has actually been used as a bioassay:

Use animals (rats or mice) from which you've removed the pituitary glands.  This step is necessary, because you want to make sure that the thyroid is responding to the TSH that you inject, not to the animal's own TSH from its pituitary gland.

Alternatively, you could use an organ culture, where you remove thyroid glands from rats and grow them in dishes.  You can then administer TSH to the medium in which they grow, and measure the thyroid growth, or the release of TH into the medium. 

Many of you lost points for missing the pituitary-removal step.  Others wanted to use people who were hyperthyroid and hypothyroid as individuals who are exposed to high and low TSH, and measure their TH to determine the dose-response relationship.  But you should remember that hyperthyroid can occur either because there is high TSH, or because the of a thyroid problem that results in high TH secretion even without TSH stimulation, so this idea wouldn't work.  Others lost points for saying that you'd remove the pituitary from a bunch of people to create the dose-response curve, which is a definite no-no. 

3. Inject a different dose of TSH into each pituitary-less animal, and measure the biological response (eg, thyroid size after a certain period of time, or the amount of TH secreted in the blood) and plot these results to create a dose-response curve.  Many of you got this step, but stopped here.  The purpose of the bioassay is to allow you to assay (measure) something, so you should have continued to explain the next steps.

4. To determine the amount of hormone in a sample, you would inject that sample (of blood or urine, for example) into an animal as described above, that is, without a pituitary gland.  You would measure the biological response (TH secretion or T growth)

5. Find the value for the biological response on the d-r curve, and see what dose of hormone would correspond to that response.  This will tell you the amount of hormone in the unknown sample.