The histochemical localization of acetylcholinesterase (AChE)-containing nerves has been determined in the parametrial arterial supplies of dog, cat, rat, rabbit, sheep, pig and cow.
The main uterine arteries of dog and pig contained a plexus of nerves which stained for AChE and which were closely applied to the surface of the media. This plexus was absent from the secondary arterial branches. In contrast, the equivalent arteries of rat, cat, rabbit, sheep and cow were devoid of an AChE-positive nerve plexus.
In the light of other evidence, it is suggested that the uterine hyperaemia of pregnancy in dog and pig may be partly due to the action of cholinergic vasodilator nerves. Such a mechanism is unlikely to be involved in the other species examined.