Considerable species differences also exist in the action of naturally occurring body chemicals on blood vessels in the brain:(20) noradrenaline contracts human cerebral vessels but has no such effect on similar vessels from cows while human cerebral basilar arteries are relaxed by bradykinin whereas dog basilar arteries are contracted. Further species variations have been reported with natural substances called leukotrienes(LT). LTC4 and LTD4 constrict guinea pig skin blood vessels but dilate human and pig skin blood vessels.(21) And the prostaglandins (PG), a family of substances discovered over 50 years ago in human seminal fluid, show considerable differences in cardiovascular responses between the species: in heart tissue from cats and rabbits, PGE1 has no effect on contractile force or in heart rate but increases them in rats, guinea pigs and chickens.(22)
These examples highlight the dangers of animal-based research but as Else Muller-Schweinitzer of the pharmaceutical company Sandoz has explained,(23)
"Despite the limited relevance for human pharmacology of most of the animal tissues, the use of human material in pharmacological studies is still the exception rather than the rule."
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