But these beliefs about peptide hormones were questioned as laboratory after laboratory found that antiserums to peptide hormones, when injected into the brain, bind in places other than the hypothalamus, indicating that either the hormones or substances that cross-react with the antiserums are present. The immunological method of detecting peptide hormones by means of antiserums, however, is imprecise. Cross-reactions are possible and this method cannot determine whether the substances detected by the antiserums really are the hormones, or merely close relatives. Furthermore, this method cannot be used to determine the location in the body where the detected substances are actually produced.
New techniques of molecular biology, however, provide a way to answer these questions. It is possible to make specific complementary DNAs that can serve as molecular probes to seek out the messenger RNAs of the peptide hormones. If brain cells are making the hormones, the cells will contain these mRNAs. If the products the brain cells make resemble the hormones but are not identical to them, then the cDNAs should still bind to these mRNAs, but should not bind as tightly as they would to mRNAs for the true hormones. The cells containing these mRNAs can then be isolated and their mRNAs decoded to determine just what their protein products are and how closely the products resemble the true peptide hormones.
The molecular approach to detecting peptide hormones using cDNA probes should also be much faster than the immunological method because it can take years of tedious purifications to isolate peptide hormones and then develop antiserums to them. Roberts, expressing the sentiment of many researchers, states: I was trained as an endocrinologist. But it became clear to me that the field of endocrinology needed molecular biology input. The process of grinding out protein purifications is just too slow.
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