Summary and Discussion
Paper of HAMMERSEN: During the discussion of his presentation, Professor HAMMERSEN emphasized that the distribution of nerves varies considerably in different species and in different blood vessels, and hence, observations on one species cannot be generalized, without experimental studies, to another species. In general, he found that the electron microscopic results are in good agreement with fluorescense microscopic studies of innervation in blood vessels. Regarding the question of myoneural synapses, he emphasized that, contrary to the notoriously great neuromuscular distances in many other blood vessels, synaptic clefts of only 200 Å can be found in guina pig portal vein: These seem to be the shortest neuromuscular distances reported to date. In general, he found that the neuromuscular distance, in a given species, is shorter in the portal vein than in the other blood vessels examined by him. Although he found that portal veins are generally well innervated, it appeared that not every smooth muscle cell in the media receives its own innervation, but only a certain fraction of the fibers. The structures through which cell to cell propagation occurs in portal veins are presumably the nexuses and/or gap junctions. The observations of both Professor HAMMERSEN’ s and Professor SOMLYO’s laboratories concurred that the number of mitochondria is often considerably greater in guinea pig than in rabbit portal vein smooth muscle.