An important area of medical research is pharmacology where scientists study exactly how drugs and natural body substanccs exert their effects on the tissues. An understanding of the chemical processes involved can be valuable in providing a more rational basis for the design of new treatments. Unfortunately, many pharmacologists rely on animals despite numerous contradictory results. As a result of experiments with dogs, acetylcholine, a chemical produced by nerve endings, was widely believed to dilate the coronary arteries. But in human coronary tissue it causes a narrowing of the vessels which is thought to lead to heart spasm in a living person.(1) Another body chemical, bradykinin, relaxes blood vessels in human brain tissue but contracts them in dogs.(2)
Further species differences have been found with the leukotrienes (LT), natural substances involved in inflammation. Leukotrienes known as LTC4 and LTD4 constrict blood vessels in the guinea pig's skin but dilate corresponding tissues from people and pigs.(3) Yet another case is the prostaglandins (PG), a family of substances discovered over 50 years ago in human seminal fluid: in heart tissue from cats and rabbits, PGE1 has no effect on contractile force or heart rate but increases them in rats, guinea pigs and chickens.(4)
Some pharmacologists have recognised that “direct extrapolation from animals to humans is frequently invalid,” so that “recently much interest has focussed on use of human autopsy or biopsy tissue as a means of overcoming these limitations.”(5)
1) S.Kalsner, Journal of Physiology, 1985, vol.358, 509-526.
2) K.Schror & R.Verheggen, Trends in Pharmacological Sciences, 1988, vol 9, 71-74.
3) P.J.Piper et al, Annals of the New York Academy of Sciences, 1988, vol.524, 133-141.
4) S.Bergstrom et al, Pharmacological Reviews, 1968, vol.20, 1 -48.
5) Trends in Pharmacological Sciences, 1987, vol.8, 289-290.
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