The Method of Testing the Blood for Adrenin
It was desirable to use as a test tissues to which the blood was naturally related. As will be recalled, adrenin affects viscera even after they have been removed from the body, just as if they were receiving impulses via sympathetic fibres, and further, that sympathetic fibres normally deliver impulses which cause contraction of the internal genitals and relaxation of the stomach and intestines. The uterus has long been employed as a test for adrenin, the presence of which it indicates by increased contraction. That isolated strips of the longitudinal muscle of the intestine, which are contracting rhythmically, are characteristically inhibited by adrenin in dilutions of 1 part in 20 millions, had been shown by Magnus in 1905. Although, previous to our investigation in 1910, this extremely delicate reaction had not been used as a biological signal for adrenin, it possesses noteworthy advantages over other methods. The intestine is found in all animals and not in only half of them, as is the uterus; it is ready for the test within a few minutes, instead of the several hours said to be required for the best use of the uterus preparation;[11] and it responds by relaxing. This last characteristic is especially important, for in defibrinated blood there are, besides adrenin, other substances capable of causing contraction of smooth muscle,[12] and liable therefore to lead to erroneous conclusions when a structure which responds by contracting, such as uterus or artery, is used to prove whether adrenin is present. On the other hand, substances producing relaxation of smooth muscle are few, and are unusual in blood.[13]
We used, therefore, the strip of intestinal muscle as an indicator. Later Hoskins[14] modified our procedure by taking, instead of the strip, a short segment of the rabbit intestine. The segment is not subjected to danger of injury during its preparation, and when fresh it is almost incredibly sensitive. It may be noticeably inhibited by adrenin, 1 part in 200 millions!
The strip, or the intestinal segment, was suspended between minute wire pincers (serres fines) in a cylindrical chamber 8 millimeters in diameter and 5 centimeters deep. By a thread attached to the lower serre fine the preparation was drawn into the chamber, and was held firmly; by the upper one it was attached to the short end of a writing lever (see [Fig. 2]). When not exposed to blood, the strip was immersed in a normal solution of the blood salts (Ringer’s). The blood or the salt solution could be quickly withdrawn from or introduced into the chamber, without disturbing the muscle, by means of a fine pipette passed down along the inner surface. The chamber and its contents, the stock of Ringer’s solution, and the samples of “quiet” and “excited” blood were all surrounded by a large volume of water kept approximately at body temperature (37° C.). Through the blood or the salt solution in the chamber oxygen was passed in a slow but steady stream of bubbles. Under these circumstances the strip will live for hours, and will contract and relax in a beautifully regular rhythm, which may be recorded graphically by the writing lever.
Figure 2.—Diagram of the arrangements for recording contractions of the intestinal muscle.
The first effect of surrounding the muscle with blood, whether “quiet” or “excited,” was to send it into a strong contraction which might persist, sometimes with slight oscillations, for a minute or two (see [Figs. 4] and [5]). After the initial shortening, the strip, if in quiet blood soon began to contract and relax rhythmically and with each relaxation to lengthen more, until a fairly even base line appeared in the written record. At this stage the addition of fresh “quiet” blood usually had no effect, even though the strip were washed once with Ringer’s solution before the second portion of the blood was added. For comparison of the effects of “quiet” and “excited” blood on the contracting strip, the two samples were each added to the muscle immediately after the Ringer’s solution had been removed, or they were applied to the muscle alternately and the differences in effect then noted. The results obtained by these methods are next to be presented.
REFERENCES
[1] Jacobi: Archiv für experimentelle Pathologie und Pharmakologie, 1891, xxix, p. 185.
[2] Biedl: Archiv für die gesammte Physiologie, 1897, lxvii, pp. 456, 481.