might compensate for the removal of the other by undergoing hypertrophy. that the thymus exercises an inhibitory influence on the growth of the

Transcription

1 THE THYMUS AND SEXUAL ORGANS. III. THEIR RELATIONSHIP TO THE GROWTH OF THE ANIMAL. BY D. NO1EL PATON. (From the Physiological Department, University of Glasgow.) I. MALE ANIMALS. IN 1904_051 I carried out some investigations on the functionis of the thymus in the guinea-pig, an animal from which the organ can be easily removed. I then came to the conclusions: 1st, that removal of the thymus has no influence on the rate of growth of the animal; 2nd, that it is accompanied by a more rapid development of the testes before sexual maturity is approached; and 3rd, that after this period, the growth of the testes is uninfluenced by the removal of the thymus. Hend erson2 had previously shown that in castrated cattle and guineapigs the thymus attains a greater size than in uncastrated animals. I suggested that there is a reciprocal action between these organs and that the thymus exercises an inhibitory influence on the growth of the testes. In discussing my previous results with Dr Cathcart he suggested that the more rapid development of the testes in young animals after removal of the thymus might indicate that the two organs had a similar stimulating influence upon the growth of the animal and that each might compensate for the removal of the other by undergoing hypertrophy. Such a view would also explain the large size of the thymus in castrated animals. To test this theory experiments have now been performed in which both thymus and testes have been removed from very young guinea-pigs and the rate of growth of these animals compared with that of normal animals. In order to check the results obtained, the effect of simple castration and of simple removal of the thynmus on the rate of growth has also been studied. These 1 This Journal, xxxi. p ib. xxxi. p (with A. Goodall) and xxxii. p PH. XLII. 18

2 268 D. N. PA TON. experiments have further afforded material for checking and extending the results of my previous observations. The experiments were carried out between September 1909 and October A. The influence of thymus extraction on the growth of the testes in sexually immature guinea-pigs. In my previous investigations I found that the average weight of the testes and epididymes (after removal of the vasa deferentia and the fat lobules attached to the testes) of six normal guinea-pigs between 125 and 200 grms. (of an average weight of 152 grms.) to be 0-18 grm., and that of thymusless animals to be 0'23 grm. From these results and from the further observatioii that the average weight of testes in 14 normal animals between 200 and 300 grms. was 0-60 grm. while in 16 thymusless animals of the same weight it was 0'88 grm., I drew the conclusion that in the immature animal the presence of the thymus inhibits the growth of the testicles. In the present series of experiments the testes were removed from 38 young guinea-pigs of between 70 and 200 grms. (see Appendix). And thus material is afforded for checking the accuracy of my previous average of the weight of testes in these young animals. The thymus was removed from 42 animals1. The results are shown in Table I. TABLE I. Weight of thymus in grms. Weight of testes in grms. No. of Actual ent, of No. of Actual ent. of Body weight in grins.2 animals (average) bcdy weight animals (average) body weight Between 60 & 80 (6) (2) & 100 (9) (6) * & 120 (13) (14) * & 140 (9) (6) * & 220 (5) (10) * Taking the 18 guinea-pigs between 120 and 200 grms., animals of a weight corresponding to that of the animals dealt with in my previous experiments, the results were: Ayerage body Average weight of weight m grmas testes in grms '177 as against 0-18 in my previous observations. 1 As the present investigation does not concern specially the size of the thymus, individual weighings are not given in the Appendix (p. 282). 2 Throughout the paper weights are given in grms. and fractions of grms.

3 THYMUS AND SEXUAL ORGANS. Since the object of the present series of experiments was to study the influence of removal of the organs on the growth of the guineapigs, none of the thymusless animals were killed while still under 200 grms. They were all allowed to live till they reached 300 grms. the usual size at which sexual maturity is approached. But the close correspondence in the weight of testes of normal guinea-pigs in the present and in the former series of observations strengthens the probability that a satisfactory average result was obtained from the six thymusless animals previouisly examined, and that the conclusion that the weight of testes in these animals was about 27 per cent. more than that of normal animals was justified. Solil has challenaed the accuracy of my results. His criticism however is invalid since in his series of experiments only two of the pairs of guinea-pigs examined were killed before sexual maturity was reached. The others were killed when weighing between 480 and 680 grms. His further criticism that my results were vitiated by my experiments being done in summer, the season of sexual activity, is also beside the mark since my observations were made upon sexually immature animals. Soli bases his contention that removal of the thymus is followed not by increased but by decreased growth of the testes mainly on his experiments on fowls, in which the thymus is a permanent structure. At first sight his results seem fairly conclusive, but a closer analysis of his records shows that further experiments are required before the conclusion which he reached is justified. In his 16 experiments, in each of which the size of the testes in a thymusless bird is compared with that in a normal bird, we find (1) In three no marked change. (2) In two a greater weight of testes in the thymusless animal than in the normal (on an average 75 p.c. more). (3) In 11 a less weight of testes. (a) Of these 11, six showed a smaller gain in the weight of the animal without the thymus, i.e. the nutrition of the body was less perfect, and the smaller weight of testes may be thus explained. (b) Of these 11, four showed an equal or greater increase in the weight of the thymusless bird, and a less weight of testes (an average 70 p.c. less-excluding No. 5). (In No. 16 the rate of growth is'not recorded.) 1 Contributo alla Funzione del Timo, Modena (and Arch. Ital. de Biol. t. LII. p )

4 270 D. N. PA TON. Thus, five showed greater growth of testes in the thymusless animal or no marked difference between thymusless and normal animals. Six showed reduced rate of growth and decreased size of testes in thymusless animals. Since the state of nutrition might determine the size of the testes, these six experiments should be excluded. Four showed greater growth of body weight but smaller testes in the thymusless animals. Such results cannot be considered as conclusive. Hart and Nordmann' state that in dogs removal of the thymus caused delayed growth and prevented the onset of sexual maturity. The animals died within a year with dilatation of ventricles of the heart and atrophy of their walls. The marked disturbances caused by the removal of the intra-thoracic thymus in the dog must be taken into account in considering these results. B. Removal of the thymus has no effect upon the size of the testes in guinea-pigs above 300 grms. The present series of observations gives further corroboration to the conclusion, entirely ignored by Sol i, that "Above 300 grms. the growth of the testes must be independent of the thymus," and that "the difference between the weight of the organs in thymusless and normal animals is no longer manifest" (loc. cit. p. 30). In the present series of observations 21 normal guinea-pigs and 7 from which the thymus had been removed at an early age were killed at from 295 to 310 grms. The average weight of the testes was Normal grms. less grm. Soli's guinea-pigs (13 pairs) were killed at from 480 to 680 grms., at a period when the thymus was atrophic, and no conclusions as to its influence upon the testes can be drawn from them (loc. cit. p. 113). His results merely confirm my conclusions. C. The eftect of simultaneous removal of thymus and testes upon the rate of growth of the guinea-pig. In investigating the influence of various factors upon the rate of growth of guinea-pigs, the difficulty arises that the rate varies very 1 Berl. klin. Wodachs. 1910, p. 815.

5 THYMUS AND SEXUAL ORGANS. greatly in different individuals even of the same stock and kept under similar conditions'. To eliminate this disturbing factor, in each experiment a considerable number of animals were dealt with to give a fair average, and the animals used for operation and as checks were selected from the same batch when received in the laboratory and were kept throughout under precisely the same conditions, each lot being kept in a separate large space in which the animals had plenty of room. All were fed upon bran, oats and turnips. The small number of deaths shows that the conditions under which the animals lived were satisfactory. The effect of removal of thymus and testes was studied in 36 animals, 16 of which had the organs removed, while 20 were kept as checks. Lot I. Jan In three months (90 days). Two operated animals grew from 135 to 260 grms. 125 grms. gain= 920/o Three check,,,, 126 to 303,, 177,,, 140/ Checks TABLE II. Lees thymus & testes Initial W. End W. Initial W. End W Average Lot II. May In two months (60 days). Two operated animals grew from 177 to 272 grms. Five check,,,, 189 to 348,, 95 grms. gain = 530/0 159,,,, =830/0 Checks "- A -' Initial W. End W Average TABLE III. Less thymus & testes Initial W. _ -i End W. _/ See Minot, This Journal, xii. p

6 272 D. N. PA TON. Lot III. Oct In 54 days, when the first reached 300 grms.- Seven operated animals grew from 125 to 216 grms. 91 grms. gain= 72 0/0 to check,,,, 122 t6 264,, 142,,,, =117 /o Checks Initial W. End W Average 122 TABLE IV. Castrated Initial W. End W The result may be tested in another way. Of the 14 animals under observation starting between and 160 grms. the weight of 300 grms. was reached in eight weeks or less by Normal of the 7 Operated of the 7 Lot IV. Sep In ten guinea-pigs five of which had thymus and testes removed in September 1909 the following results were obtained. In 30 days- Five operated animals grew from 134 to 199 grms. Gain 65 grms. or 48 0/0,, check,,,,,, 162 to 282,,,, 120,,,, /0 TABLE V. Checks Less testes-thymus Initial W. End W. Innitial W. End W Average In six weeks there reached 300 grms.- Aninmals less thymus and testes... 1 of 5. Checks of 5. These results indicate that simultaneous removal of thymus and testes in very young guinea-pigs checks the growth of the animals.

7 THYMUS AND SEXUAL ORGANS. 273 That this is not due to the shock of the operation is shown by a study of the curve of growth. Chart I shows this in Lot IV, the checks being indicated by the broken line. The initial rate of growth is much the same in checks and in animals operated upon and the difference is most marked when the animals have reached a weight of over 200 grms. An attempt has beenl made to study the question of whether there is any relationship between the rate of growth and the size of the testes and thymus. The guinea pigs used as checks or with thymus removed were divided into three groups. A. Those which attained 300 grms. in less than 14 month (4 animals). B.,,, between 14 and 2i months (6 animals). C.,,,,,, 24 and 34 months (11 animals). The average weights of testes and thymus in grms. were: A. B. C. No. of animals Testes 1'27 1P No. of animals In Group C the weight of one thymus is omitted as it was quite abnormally large-weighing 0 54 grm.

8 274 D. N. PA TON. There thus seems to be some indication of a direct relationship between the rate of growth and the size of the testes and thymus. But what the nature of this relationship is cannot be definitely determined. It may be that in the better nourished and more rapidly growing animals the testes and thymus share in the rapid growth. It is suggested by the results of removal of these organs that their greater development may react upon the growth of the animal. To ascertain how far simple removal of the testes on the one hand and of the thymus on the other modifies the rate of growth the following experiments were performed. D. The effect of removal of the testes alone on the rate of growth. This was studied in four guinea pigs along with four checks. The influence of castration in increasing the weight of adult animals is of course well known. The present investigation is concerned with its effect on the rate of growth of sexually immature animals. Taking the date at which the first animal reached 300 grms., 68 days, the growth of these eight animals was as below Checks TABLE VI. Testes removed Initial W. End W. Initial W. End W Average Increase or, after 54 days as in the case of the third series of removals of testes and thymus Checks gained grms. Castrated animals gained grms. The weight of 300 grms. was reached in 72 days or less by: Checks of 4. Castrated of 4. Removal of the testes, the thymnus being intact, seems to have no effect upon the rate of growth of young guinea-pigs.

9 THYMUS AND SEXUAL ORGANS. 275 E. The influence of removal of the thymus on growth. Dr Goodall and I (loc. cit. p. 54) came to the conclusion from two experiments that removal of the thymus has no influence on the growth of the animal. Lucien and Parisot (C. R. Soc. biol. t , p. 264) found that in young rabbits (sex unstated) removal of the thymus delays growth for some time. The following observations have now been made on the rate of growth of six thymusless and three check guinea-pigs during 54 days (Table VII A) and after 77 days (Table VII B). Average Gain Checks TABLE VII A. less Initial W. After 54 days Initial W. After 54 days grms. or 61 0/0 60 grims. or 500/0 Average Gain Checks TABLE VII B. less Initial W. After 77 days Initial W. After 77 days grms. or 108 0/0 125 grims. or 104 /0 The weight of 300 grnis. was reached in 107 days by: Checks of 3. less of 6. Removal of the thymus, the testes being intact, seems generally to have little or no influetice oti the rate of growth of guinea-pigs.

10 276 D. N. PA TON. The history of one animal from which the thymus was removed is of interest. The removal was done on Oct. 12th when the animal weighed 95 grms. Although active and apparently healthy, by Jan. 23rd (after about 3j months-103 days) it weighed only 160 grms., and had thus gained only 65 grms. After this its weight fell and on Feb. 8th (nearly four months after the operation) it weighed 125 grms. and -was obviously ill. It was then killed by chloroform and the testes found to weigh only 012 grm.-the average weight of the testes of a guinea-pig of about a fortnight or three weeks of age. The question here arises, was the small size of the testes the result of malnutrition or was the checked growth the result of the want of compensatory hypertrophy of the testes after removal of the thymus? The perfect health in which the animal appeared to be till Jan. 23rd seems to negative the former conclusion. Microscopic examination of the testes showed them to be as undeveloped as that of an animal of about a fortnight old. The possibility of a retardation in the rate of growth of thymusless animals suggested by this last experiment may be co-related with the results of Hart and Nordman and of Lucien and Parisot, as well as of those of Basch and of Soli, showing decrease in the development of the bones. It is quite possible that in some species the action of the thymus on growth may preponderate over the influence of the testes so that when it is removed the testes may fail to exercise a compensating action. The reciprocal action thus demonstrated between the thymus and the testes suggests the existence of similar connections between other organs. Thus, the well-known effect of the thyroid upon growth and the more problematic relationship of the pituitary to skeletal development tend to connect them with the thymus and testes. Soli (toc. cit.) states that in castrated animals he finds a hypertrophy of the pituitary and, in the absence of this, of the thyroid. Material has been collected for the histological investigation of the various organs after removal of the testes or ovaries and of the thymus alone or with one or other of these organs. It might be anticipated that, if this reciprocal action between thymus and testes exists, the one organ would tend to be large when the other is small. But this is not found to be the case and in different individuals of the same size where one organ is well developed the other is generally proportionately developed. But in some cases wide discrepancies are to be found between the relative weights of these organs.

11 THYMUS AND SEXUAL ORGANS. Thus, taking from Table VIII five guinea-pigs of grms., the following weights of testes and thymus were noted: Testes Testes * ' P or of three of 13.5 grins.: Testes Testes ' or taking five seen: guinea-pigs of 300 grms. the following differences are Testes Testes (70 1P P But if the animals be arranged according to weight, with the weights of testes and thymus appended, and if averages for different periods of growth be taken, it is seen that there is a definite relationship between the weights of these organs which may be expressed as the quotient of ThymUs Testes and which varies throughout the growth of the animals. The following table gives such a series of figures. In it the animals under 300 grms. are arranged according to body weight, those with a weight of approximately 300 grms. according to the weight of testes. This table shows that in the growth of the guinea-pig from 70 to 220 grms. the testes grow proportionately to the growth of the animal, but that, before 300 grms. is reached, their growth has become accelerated and is out of proportion to the growth of the body. The growth of the thymus is proportionately somewhat more rapid than the growth of the body in animals from 70 to about 135 grms. After this, till 300 grins. is reached, it appears to be fairly proportionate to the growth of the body. 1 This thymus was of exceptional size. 277

12 Body weight TABLE VIII. A. Animals below 300 grmns. Testes Average weight Actual weight ' ' Per cent. of Per cent. of Testes Actual body weight Actual body weight Testes 1094 * '140 '120 '080 *111 *103 *105 *112 '120 '060 '108 *13 *106 '13 0'98 '103 '202 '120 '080 '149 '189 '112 '185 '135 '215 '106 *144 '134 '240 '140 '170 '155 '152 '128 '12 '175 ' '135 '283 '146 '210 '210 '210 '160 '290 '175 '290 '140 '317 '140 '120 '210 '230 '164 '13 '244 '192 1'50 '140 '250 '160 '240 '150 '220 '150 '096 '24 *15 1'60 '260 '160 '400 '320 '330 '14 '24 ' B. Aninals between Actual weight Body weight Testes 295 '67 ' '69 ' '79 ' '82 ' '85 ' '85 ' '90 ' '90 ' '92 ' '94 ' '94 ' '96 ' '06 ' '15 ' '22 ' '23 ' '26 ' '26 ' '41 ' ' '59 '50 Average 303 1'04 '38 Per cent. of body wt. 0'34 0' and 320 grnas. Average weight Testes Testes '77 '40 '52 '92 '41 '44 1X *33 '28 '36 '24 '34

13 THYMUS AND SEXUAL ORGANS. 279 II. FEMALE ANIMALS. Henderson in his paper (loc. cit.) states that the thymus of heifers per unit of weight is intermediate between that of bulls and oxen, and adds that " in heifers which had been pregnant for several months the thymus exhibited a much more marked atrophy than is the case with those which had not exercised the reproductive function." Goodall' 'finds that the thymus in guinea-pigs from which the ovaries have been removed persists just as it persists in the male. In my experiments (loc. cit. p. 31) I found that guinea-pigs deprived of the thymus at an early age became pregnant at about the same time as nornral animals. The average weight of eight thymusless when they took the male was 374 grms. and that of six normal animals 388 grins. The results of ovariotomy and of ovariotomy with removal of the thymus on the rate of growth were studied in the present series of experiments with the following results: In 53 days, when the weight of 300 grms. was reached by the first of the batch. Nine Checks Initial W. End W se 118 Incres Or eliminating from 119 Increase TABLE IX. Ovariotomy and Removal Initial W. End W the checks all above Ovariotomy Initial W. End W Taking only the six checks below 160, in these 53 days the following numbers reached 300 grms.:- Checks. Ovaries and thymus removed. Ovaries removed. 1 of 6. 1 of 7. 1 of 4. Ovariotomy and ovariotomy with thymus extraction appear to exercise no effect on the rate of growth of immature female guinea-pigs. 1 This Journal, xxxii. p

14 280 D. N. PA TON. III. INFLUENCE OF CASTRATION UPON THE THYMUS. In our previous observations on the growth of the thymus the influence of sex was not considered. The present experiments afforded some further evidence of the influence of castration on the size of the thymus in guinea-pigs of about 300 grms. A. Males. In 14 normal animals at abouit 300 grms. the averag,e weight of the thymus was *362 grm., and in six castrated animals 499 grm. In the former the smallest was *27 and the largest '54, in the latter the smallest was '338 and the largest '69. B. Females. In the female guinea-pigs of about 300 grms. seven normal animals had a thymus of the average weight of '540 grm. (smallest '33, largest '688), while four animals with ovaries removed had an average weight of '544 (smallest '465, largest '616). Ovariotomy thus seems to have little influence on the growth of the thymus before the age of sexual maturity. Its influence rather appears to be to retard the subsequent involution. In the earlier stages of growth the thymus of the female approximates in weight to that of the male of the same size. Average of nine females of average weight of 116 grms. 0'175 grm. Average of nine males of average weight of grms. 0'175 grm. When 300 grms. is reached a marked difference is found in the thymus in the two series. Males average of 21 of average weight of 303 grms. 0X36 grm. Females average of five of average weight of 315 grms. 0'540 grm.

15 THYMUS AND SEXUAL ORGANS. 281 CONCLUSIONS. These observations tend to show that in the guinea-pig the thymus and testes both exercise an influence on the growth of the sexually immature animal and that, after the removal of one of these organs, the other can compensate for its loss and in doing so may undergo a more rapid growth, or, in the case of the thymus, may persist for a longer period. In the female the same evidence of the influence of the thymus and ovaries upon growth has not been observed, but further experiments are required. (The expenses of this investigation were defrayed from a grant received from the Carnegie Trust.)

16 282 D. Ny. PA TON. Body weight Actual Average APPENDIX. Testes weight Actual Average ' *096 *10 '12 *10 '12 '19 11 *123 *13 '15 *14 *12 *11 '13 *15 '14 *11 '14 *15 '21 '14 *14 '143 '16 '17 '14 '21 '16 '14 '163 '14 '17 '18 '18 '15 '16 '20 '34 '19 '26 '197 Per cent. of Body weight '137 '130 '126 '124 '118