The Effect of Gonadectomy on the Weight of the Kidney, Thymus, and Spleen of Mice

The effects of gonadectomy on the size of the body and of the various organs, especially of the endocrine glands, have been studied by several investigators who, however, record very different results. According to Hatai (1915), the result of castration in the rat is considerably to increase the weight of the suprarenal, hypophysis, and thymus. On the other hand Moore (1922) found that in the castrated guinea-pig the suprarenal and hypophysis are considerably lighter than in the normal males.

In a previous study (1924) we demonstrated that in the mouse there exists a distinct sexual difference in respect of the size of the suprarenal, this gland being considerably larger in the female than in the male. This size difference is due to differences in the degree of development of the zona reticularis, which is well developed in the female, whereas in the mature male it has almost entirely disappeared. In castrated males, when compared with the normal, the suprarenals show an enlargement which, likewise, is for the most part due to an increase in the size of the zona reticularis. On the other hand, ovariotomy in the female is not followed by any increase in the size of the zona reticularis, and consequently the size of the gland as a whole remains unchanged.

The present paper deals with similar sexual differences in the weight of the kidney, thymus, and spleen of the mouse and with the effect of gonadectomy.

We wish to express our thanks to Prof. C. Ishikawa, Prof. R. Goldschmidt, and Dr F. A. E. Crew for their help during the course of this study. The expenses of the investigation were defrayed by a grant from “Keimeikwai “(an association the object of which is to give pecuniary assistance to scientific investigations), to which we also wish to extend our cordial thanks.

The animals used in the present study were reared in the Anatomical Laboratory for Veterinary Science, University of Tokyo. In the majority of cases they were operated on at the age of twenty days, though in certain cases the operation was delayed until thirty to forty days, in order that the effect of age on the results of gonadectomy could be examined. Individuals belonging to the same litter were divided into two lots, viz. operation and control ; but in order to avoid variation in external conditions, operated mice were kept in the same cages as the controls, but any litter of more than six individuals was divided into two cages. When ninety days old all mice were weighed and killed with chloroform, the organs being removed and weighed immediately.

In his investigation Hatai divided a litter into two lots, one for operation the other for control ; and comparison was made between the two lots. He used this method because he believed that variability of body weight in a litter is only about one half that in the total population. Moore, however, holds a different opinion as regards the guinea-pig ; he says : “Comparison of animals of the same litter does not afford more convincing argument in favour of weight comparison.” It must, however, be noted that in his experiments on gonadectomy Moore used only 46 animals.

In analysing our data it was found that even in the same litter there is considerable variation as regards body weight. It is reasonable to postulate that size in animals is the expression of the interaction of a number of factors (three or more). If so many factors are concerned in the production of one character, it may be assumed that only in extremely rare cases can a homozygous race be obtained. It is therefore probable that the animals used in the present experiment differed considerably with regard to their genetic constitution, and consequently it becomes difficult to obtain reliable results especially if only a limited number of animals is concerned. Comparison of animals of the same litter does not afford any more reliable results, because, as stated above, each animal may belong to a different genotype. In view of these facts, and in order to determine exactly the existing sexual differences with regard to certain characters and also the results of gonadectomy in the two sexes, it was found necessary to use a large number of animals and to make a statistical analysis of the data collected.

Male mice are on the average about 7.5 per cent, heavier than female. When the mean value of the body weight of the males is compared with that of the females, the difference is found to be approximately 7.6 times its probable error : M (♂) = 22.70 ± 0.085 ; ± M (♀) =21.11 ±0.19 (Table I.).

When the average body weight of normal and castrated males is compared, it is found that the difference is but slight, the castrated being only 1.3 per cent, heavier. The difference of mean values of body weights between normal and castrated males (M (♂) = 22.99 ± 0.126), as seen in Table I., is smaller than twice its probable error and may be regarded as insignificant. It can thus be concluded that castration in the male has no effect upon body weight.

When the average body weight of normal females is compared with that of ovariotomised animals, it is seen that the latter are about 7.34 per cent, heavier than the former. The difference of the mean values for the body weights of normal and spayed females is approximately five times its probable error. This is significant, indicating that spaying has a definite effect upon body weight (Table I.).

In the rat Hatai found that the body length is absolutely less in castrated than in the normal animals, and concluded that castration embarrasses growth of body length. Moore obtained similar results in the guinea-pigs. In the case of the mouse, however, it was found that castrated males are considerably longer than the normal.

Comparing the average body length of females with that of the normal males, it is found that it is about 1.2 per cent, greater in the former ; thus the difference is very slight. Statistical analysis shows that the difference of the mean values for body length between the males and females (M (♂) = 6.085 ± 0.0072 ; M (♀) = 6.156 ± 0.018) is approximately 3.7 times as large as its probable error, i.e. not so significant as to warrant grouping into different classes.

Comparing the average body length of normal males with that of the castrated, it is found that the body length of the latter is about 1.9 per cent, greater than that of the former. The difference of mean values for body length in the two classes is approximately eleven times as large as its probable error ⁠, and is therefore significant (Table II.). It is reasonable to attribute this increase in body length to the effects of castration.

When the average body length of spayed females is compared with that of the normal, it is evident that the difference is very slight, the latter being only 0.36 per cent, greater than the former. The difference of mean values for body length in the two classes (Table II.) is approximately equal to its probable error i.e. it is not significant.

In the guinea-pig Moore found that the average body length of the normal female is slightly greater than that of the spayed. In the rat different results were obtained by Hatai, who concluded that the absolute body length is slightly greater in spayed females. It is, however, unjustifiable to attribute such slight variation to the effects of gonadectomy.

As far as we know no one has previously described the effects of gonadectomy on the weight of the kidney. It will be shown that the weight of the kidney in the mouse differs according to the sex of the individual, it being considerably heavier in males than in the females. Since the kidney is a most important excretory organ, it is very probable that it has some important relation to the metabolism of the body. Moreover, it is reasonable to assume that the weight of an organ is correlated with its functional activity, i.e. the functional activity may increase in proportion to the weight of the organ. Since the male kidney is heavier than the female, it can be argued that the metabolic activity of the male is higher than that of the female.

On comparing the average weight of the kidney of the male with that of the female, it is found that the former is considerably heavier. The difference (about 45 per cent.), is so great that the statistical method of comparison is not necessary in this case (M (♂) = 0.418 ± 0.00303 ; M (♀) = 0.289 ± 0.0024. It is, of course, true, that with the increase of the body weight the weights of the various organs likewise increase. But since the average body weight of the normal males is only 7.5 per cent, greater than that of the females, it is evident that the difference in the weight of the kidney in the two sexes is significant (Table IV.).

When the average weight of the kidneys of castrated males is compared with that of normal ones, it is found that the latter is about 53 per cent, heavier. As this difference is even greater than that existing between the weights of kidneys of normal males and females, it is clear, even without a statistical analysis, that it cannot be due simply to variation ⁠. As stated above, castrated males are slightly heavier than normals, and thus the difference of the relative weights of the kidneys is greater than that of the actual weights (Table IV.). Hence it may be concluded that castration inhibits the growth of the kidney to a remarkable extent.

Comparing the average weight of the kidneys of spayed females and that of the normal, it is seen that the latter is about 8.6 per cent, greater ⁠. As stated above, spayed females are considerably heavier than normal, and accordingly the difference of relative weights between them is greater than that of actual weights (Table IV.).

It is seen that the difference in weight of the kidneys of the two sexes disappears after gonadectomy, when the weight in either sex approaches that of the female. Tables I. and II. demonstrate the differences of the actual and relative weights of the kidneys in normal and operated individuals. It is of importance to note that as the result of gonadectomy in the male the kidney becomes greatly decreased in weight, while in the spayed female it undergoes but a slight diminution in weight (figs. 3 and 4). On the basis of what has been said above in respect of the metabolic activity of the two sexes, we may infer that castrated males approach the female type of metabolism, while in spayed females only a slight change occurs. The metabolic changes of the castrate are caused by the absence of the internal secretion of the testis. The very considerable reduction of the weight of the kidney after castration may be one of the most important signs of the depression of the metabolic activity.

Sexual differences. — It has been stated that gonadectomy is followed by a considerable increase in the size of the thymus in both sexes, but no previous investigator has recorded the fact that there exists a sexual dimorphism as regards the weight of the thymus. In the mouse the thymus is considerably heavier in the female than in the male (fig. 5), the difference being on the average 81 per cent. (M (♂) = 0.021 ± 0.00035 ; M (♀) = 0.038 ± 0.00073). Since the body weight of the male is about 7.5 per cent, greater than that of the normal female, it is evident that the difference of percentage weights of the thymus between the two sexes is greater than that of absolute weights (Tables VI, VII, VIII.).

When the average weight of the thymus of castrated males is compared with that of the normal, it is found that there is a marked difference, namely an excess of about 146 per cent, in favour of the castrates ⁠. The difference is manifestly greater than that existing between the weight of the thymus of normal males and females ; thus it follows that as the result of castration the thymus becomes greatly enlarged (Tables VI, VII.). This conclusion is in agreement with that of other investigators who used different material.

The average weight of the thymus of spayed females is about 3.7 per cent, greater than that of the normal ⁠. It will be remembered that the body weight of the spayed female is considerably greater than that of the normal ; the difference of the relative weights, as shown in Table VII, is also found to be considerably greater. It has, however, to be noted that the difference of mean values of the weights of the thymus in the normal and the spayed females is but 3.5 times its probable error (cf. Table VIII.) ; it cannot therefore be stated definitely whether this is a case of an enlargement of the thymus as a result of gonadectomy, or merely a case of fluctuating variation.

As seen in fig. 5, the frequency distribution of the thymus weight of the castrated males and spayed females is very similar to that of the normal females. This is even better shown by a statistical calculation (Table VI.). The same relation is seen on comparing the relative weight of this organ. It can thus be concluded that as the result of castration the weight of the thymus becomes greatly increased, approaching almost that of the female, while in the spayed female the increase in weight of the thymus is not so striking.

Thus, as in the case of the kidney, the castrated males, the normal and the spayed females display a great similarity in respect of the weight of the thymus. This fact leads us to the conclusion that there is an intimate functional relation, either direct or indirect, between the testis and the thymus ; while no close association can be seen between the thymus and the ovary.

As far as could be ascertained, Moore is the only investigator who has observed the functional relation existing between the spleen and the sex glands. He recorded (1922) that in the guinea-pig there is a slight sexual dimorphism as regards the weight of the spleen which is greater in the female ; and that in the castrated male there occurs a slight increase, in the spayed female, a slight decrease in weight.

In the mouse there exists a sexual dimorphism with regard to the weight of the spleen, that of the female being on an average 6.5 per cent, heavier than that of the male (M (♂) = 0.081 ±0.0023 ; M (♀)= 0.134±0.0058). As the body weight of the male is about 7.5 per cent, greater than that of the female, it will become obvious that the difference of the relative weights of the spleen (in relation to body weight) is greater than that of the absolute weights. Hence it is evident that there is a distinct sexual difference in the weight of the spleen.

The weight of the spleen of the castrated males is on an average much greater than that of the normal, there being an increase of 54 per cent. Since the body weight of the castrated male is about 7.5 per cent, greater that than of the normal, the relative weight of the spleen of the castrated individual is also considerably greater than that of the normal. Statistical calculation shows that the difference of mean values of the castrated and the normal males is approximately eleven times its probable error (fig. 8). It is thus seen that the spleen of the castrated male is strikingly heavier than that of the normal, and is in this respect similar to the spleen of the normal female. This relationship is clearly illustrated in fig. 8.

On comparing the average weight of the spleen of the spayed and the normal female, it is found that the former is somewhat lighter than the latter. However, the difference is only about 3.9 per cent. ⁠, and since the difference in body weight between the normal and the spayed female is also very slight, there is no marked difference between the actual and the relative weight of the spleen (Table XI.).

Thus, as in the cases of the thymus and the kidney, castration results in an enormous increase in the weight of the spleen, which approaches that of the female ; while spaying produces no change in the weight of the organ. Also, the normal and the spayed females and the castrated males show great similarity as regards the weight of the spleen, a result which is in strict conformation with that obtaining in the cases of the kidney and the thymus.

According to Lipschütz (1924) “by castration the sexually differentiated type, i.e. the male or female, loses more or less its sexual character and shows a tendency to become a sexually indifferent form common to both sexes.” Further, he says : “There can be no doubt that in the mammal there is no development of characters characteristic of the other sex after castration.” The results of the present study do not conform with Lipschütz’s hypothesis of the “asexual type”: as the result of gonadectomy in the male the weight of the kidney, thymus, and spleen approaches that of the female, i.e. a character develops which is typical of the opposite sex. This observation is completely in accord with the results of our previous study on the suprarenals of the mouse.