ABSTRACT
Axolotls have been used in a series of experiments designed to test the growth-retarding properties of the parathyroid glands of mammals, prepared so as to include the anti-growth hormone. Such retardation of growth has been obtained, and is proportional to dosage. This extends the growth-retarding effect of this hormone to the Anamnia, and to forms which presumably have no parathyroid themselves.
A lightening of colour in normally dark pigmented individuals was noted after a considerable period (about eight weeks) of treatment.
INTRODUCTION
In view of the suitability of axolotls (Amblystoma mexicanum) for the demonstration of phenomena related to growth, and the ease with which such experiments can be controlled, it appeared to us to be useful to test upon these animals the growth retarding properties of extracts of parathyroid glands previously noted in other animals (Thompson, 1931 ; Robinson and Thompson, 1932).
METHODS
Twelve axolotls were used in the experiment, each animal being kept in a separate dish of clean water which was frequently changed. The animals were kept at room temperature, and were fed by hand, tri-weekly, with meat cut into small pieces.
Intra-abdominal injections were given three times a week, alternating with feeding days. In this way reflex vomiting of the food was eliminated.
During the first eleven weeks various solutions were used for injection purposes, including normal saline, Ringer’s solution, extract of meat prepared in the same way as the extract of parathyroid glands active in retarding growth, and extracts of parathyroid glands prepared in other ways (Eastland, Evers and Thompson, 1932); these parathyroid preparations have been shown to be inactive as regards their effect on growth. At the end of this period the experimental group of four animals received for the period of ten weeks injections of parathyroid extract which had been shown to be active in inducing retardation of growth in rats (Robinson and Thompson, 1932). Two of the four experimental animals received a dose of 1 c.c. three times a week, and the remaining two axolotls 0·5 c.c. three times a week. The eight control animals received injections of parathyroid gland extract rendered inactive by hydrogen peroxide. At the end of this period injections were stopped and then for a further six weeks the control animals received the active extract in similar doses, whilst the experimental animals were injected with inactive extracts of parathyroid glands. The animals were weighed weekly.
RESULTS
During the preliminary period, when various extracts and solutions were administered, no significant variation of growth-rate in the experimental animals from the controls was observed (Text-fig. 1). After, however, a week’s injection of active parathyroid extract, the weight of the animals given a larger dose became approximately stationary after an initial loss (Text-figs, 1, 2, 3 and 4).
Average weights are given for the experimental group (four animals) and the control group (eight animals) AB, CD = periods of injection of active parathyroid extract into experimental and control animals respectively. Inactive extracts were injected into the animals not receiving the active extract during these periods During the initial period ending at A the control animals received injections of saline or meat extracts, or were untreated, whilst the experimental animals received inactive extracts. From D to the end of the experiment all animals remained untreated.
Average weights are given for the experimental group (four animals) and the control group (eight animals) AB, CD = periods of injection of active parathyroid extract into experimental and control animals respectively. Inactive extracts were injected into the animals not receiving the active extract during these periods During the initial period ending at A the control animals received injections of saline or meat extracts, or were untreated, whilst the experimental animals received inactive extracts. From D to the end of the experiment all animals remained untreated.
Showing the effect of a 1 c c. dosage of active parathyroid extract on a single control and a single experimental animal Periods AB, CD correspond to those in Text-fig. 1.
The quantitative effect of different dosages of parathyroid extract on growth-rate. At the close of Period II (A−B, Text-figs. 1 and 2), the original controls were broken up into two lots of experimentáis, and the original two lots of experimentáis combined to form one group of controls. The growth-rates are given in grams per day per 100 gm. weight of animal.
The quantitative effect of different dosages of parathyroid extract on growth-rate. At the close of Period II (A−B, Text-figs. 1 and 2), the original controls were broken up into two lots of experimentáis, and the original two lots of experimentáis combined to form one group of controls. The growth-rates are given in grams per day per 100 gm. weight of animal.
The control group of animals continued to grow as before, so that instead of being lighter they became heavier than the experimental group. When the injections ceased the experimental animals began to grow again at the original rate, that is, parallel with the controls, or somewhat faster. The same effect was obtained in the control group as the experimental when injecting with active extract (Text-figs. 1, 4).
Average gams in individual weight per day of groups of axolotls treated with active and inactive extracts of parathyroid glands. Period II and Period III correspond respectively with periods AB, CD of fig. 1. The results given in fig. 1 are here presented in a different form.
This nicely demonstrates the quantitative action of the extract (Text-fig. 3).
No ill effects upon the axolotls were observed as the result of the injections, and the amount of food eaten by the two groups was equivalent. Toward the end of the ten weeks’ period of injections all the normal (pigmented) animals being given parathyroid extract were observed to be developing a lighter colour owing to constriction of the melanphores (Pl. 1). No pigmentary change was observed in the albinos. No other effects were observed. This did not occur with the controls when they were injected, presumably because the time was not sufficient. Indications of slight lightening were, however, noted in some places.
The retardation of growth obtained by the injection of the parathyroid extract was therefore quite definite, proportional to dosage and persistent as long as the injections were continued, thus corresponding to the effects already demonstrated in other animals.
One further point should be mentioned. It appears that in Amphibia, no parathyroids are developed until metamorphosis, when they form in relation with the degenerating gill-pouches (see Baldwin 1930 for another species of Amblystoma). The growth-retarding hormone of the parathyroid would thus appear to be equally effective in Vertebrates whether or no they themselves possess parathyroids.
ACKNOWLEDGEMENTS
We desire to express our appreciation of the assistance given by Dr M. H. B. Robinson and Mr D. A. Kempson.
