The surge of knowledge about the autonomic regulation of the human
cardiovascular system which commenced in the 1940s was a consequence
of many events. These included the information gained from animal
studies of the various reflexogenic zones which modulate the circulation,
the demonstration of the feasibility of cardiac catheterization in man; the
urgent need in the Second World War for information on the effects of
gravitational forces on the human cardiovascular system which were
encountered in military aircraft; the development of instrumentation and
techniques applicable to human studies; and the growing number of
clinician-scientists able to divise and conduct appropriate studies and of
informed volunteers willing to act as subjects for the experiments. To these
should be added the demonstration in 1948, in the splenic nerves of the
ox, that norepinephrine was the sympathetic neurotransmitter (von Euler
1948) and in the same year the development of the concept of two types
of adrenoceptors, alpha and beta (Ahlquist 1948).