Abstract
1. The general properties of spirally cut strips of rabbit aorta as pharma-cological test objects have been described. Such strips possess only a very small amount of spontaneous tone and never exhibit rhythmic contractions. When freshly mounted in muscle chambers they undergo a gradual elongation and gradual increase in sensitivity to stimulating drugs over a period of about two to three hours. If a fully sensitized strip is caused to contract maximally by temporary exposure to a high concentration of epinephrine, it reverts to a state of low sensitivity.
2. Drugs which were found to give only contraction of aortic strips fall in the following order as to potency: norepinephrine and epinephrine > histamine > acetyicholine.
3. Sodium nitrite causes complete relaxation of strips initially placed in a state of low to moderate tone by the previous addition of a stimulating drug. It also appears to be able to completely suppress spontaneous tone of aortic strips. However, in the face of maximal tone due to high concentrations of epinephrine, it causes only slight relaxation.
4. Isopropylarterenol causes relaxation at low concentrations. However, at high concentrations it causes contraction.
5. The time-characteristics of contraction on addition, and of relaxation after washout, of epinephrine and certain other drugs have been described.
6. Concentration-activity curves for epinephrine have been presented. The relation of the observed curves to theoretical curves predicted by Clark's equation has been discussed.
Footnotes
- Received December 29, 1952.