THE RATE O F UTERINE GROWTH RESULTING FROM CHRONIC DISTENTION SAMUEL R. M. REYNOLDS * AND SANFORD KAMINESTER Department of Physiology, L o n g Island College of Nedicine, Brooklyn THREE FIGURES Certain growth changes take place in the uterus of an untreated, ovariectomized rabbit when this organ is distended with a pellet of suitable size. It has been found (Reynolds and Kaminester, '36) that the pellet should be more than half yet less than twice the size of the uterus in order that appreciable growth takes place. The largest growth response is obtained when the pellet and uterus are of approximately equal sizes. These relationships were ascertained f o r a distention period of 2 weeks, commencing 1 week after ovariectomy. No evidence was obtained on the rate at which the growth responses in the uterus take place, nor was it ascertained that growth was complete at this time. The present experiments furnish this information. PROCEDURES The experiments were of two types. I n the first group, two or three paraffin pellets (m.p. 56") were inserted per vaginam into the uteri of mature rabbits in the manner described before (Reynolds and Kaminester, '36). At stated times after insertion of the pellets the distention sites were taken, fixed and studied, both for the histological features and the amount of Aided by a grant from the Committee for Problems in Research of Sex, National Research Council. * Fellow of the John Simon Guggenheim Memorial Foundation. Member of the Department of Obstetrics and Gynecology, Long Island College of Medicine. 281 282 S. R. M. REYNOLDS A N D S. KAMINESTER increase in gross size of the tissues. Comparison of these changes in the distention sites was made with segments of untouched, undistended parts of the corresponding uteri. The times a t which the tissues were taken after insertion of the pellets were a ) immediately after distention (acute distention); b ) 24 hours after distention; c ) 4 days and d ) some additional distention sites were taken on the fourteenth day i n order to confirm and extend the earlier series (Reynolds and Raminester, ’36). The method by which the growth resulting at the distention sites was estimated has been described before. Similarly, the method by which the degree of distention was ascertained has been reported ; briefly, it consists of determining the ratio of the cross sectional area of the undistended part of a uterus (including its lumen) to the crosssectional area of the distended pellet. Thus, a 1: 1 (1.0) distention ratio means that the uterus and pellet are of equal CI’OSS sectional areas ; a 2 : 1 (2.0) ratio means that the uterus is twice the size of the pellet and a 1: 2 (0.5) ratio, that the uterus is one-half the size of the pellet. The size in each case is determined by plaiiimeter measurements of camera lucida drawings of average cross sections. The second groixp of experiments differed from the first in the method of distention employed and were performed in order to obtain information regarding the capacity of the uterus of the untreated, ovariectomized rabbit to become adapted to progressively increasing distention, as the uterus must do in the more complex state of pregnancy. Instead of iising paraffin pellets of constant size as in the first group of experiments, fluid was allowed to accumulate in the lumen of the uterus between two ligatures placed about an inch apart. I n this way, the uterus was progressively distended, although the rate a t which fluid accumulated is not linown. After 4 days, the distended segment (along with an undistended portion of uterus for control purposes) was fixed with the fluid in situ. T t was possible to ascertain the end amount of distention in each instance, and of course the growth increments in the tissues were measurable a s before. UTERINE GROWTH A N D CHRONIC DISTENTION 283 RESULTS Acute diste9ztio.n. As noted already, the histological features associated with acute distention show that there is considerable loss of fluid and blood from the tissues about the pellet. With the larger degrees of distention, the endometrium is reduced t o a thin layer in which the epithelium rests upon the myometrium in some places. The myometrium is thin and avascular. Rarely, small hemorrhages may be seen, but otherwise there is little evidence of trauma. Measurements from six sites at which the distention ratio was 1.0 or less show that a reduction in size of the tissues of 18 to 357% takes place. The immediate effect of distention, therefore, is to force blood and tissue juices from the distention sites. T w e d y - f our hours after disteiztioqi. Figure 1 shows that by the twenty-fourth hour o r thereabout after insertion of the pellets, eleven out of fourteen distention sites regained or exceeded by a little their original size, as gauged by comparison with untouched, undistended parts of the same uteri. The impression that one obtains from studying these tissues under the microscope is that the changes which take place during the first 24 hours of distention consist of a restitution of the fluid matrix of the tissues ; ordinary histological methods fail to show any sign of cellular growth such as may be demonstrated on the fourth day and later, as described below. Distenti0.n for 4 days and longer. I n figure 2, the percentage increases in size of the various distention sites after 100 hours of distention are shown (triangles), along with the growth after 14 days of distention (dots). These points, through their manner of distribution, show that by the fourth day of distention, the size of the tissues about the pellets is as large as it will become, with this mode of distention. At least, no increase in size is found to take place between the fourth and the fourteenth days of distention. I n confirmation of the earlier data (Reynolds and Raminester, ' 3 6 ) ,the present results show that the pellets are effective stimuli for growth when they are more than half the size of the undistended uteri, and that maximal growth responses are obtained when the pellet and 284 S. R. M. GEYNOLDS AND S. KAMINESTER the uterus are of approximately equal sizes. With still larger degrees of distention, the pellets are less and less effective as growth-promoting stimuli. The reasons for this have been discussed elsewhere (Reynolds and Allen, '37). I n addition to the fact that the gross enlargement of the tissues is achieved by the fourth day after distention is the further fact that the histological changes resulting from iiisertion of the pellets are also completed by this time. The 1, 100. 24hour.s E A-distention by f/ud uccumuldian B- distention by pe//ets Fig. I 50. fi9.3 f 0 t O'-. 3 0 2.0 . 15- - I to Increusiny dstentim Uterus :Pe//ef Rut/o I Uterus :Pellet Dafm ' 55 1, $ a 201 Uterus. Pellet Ratio Fig. 1 Chart showing the size of distention sites relative to non-distended sites of rabbit uteri, expressed as percentage of the latter. Correlated with the amount of distention in each case. 9 distention ratio of 2.0 means that the uterus was twice the size of the pellet; of 1.0, the uterus and pellet were of equal size; of 0.5, the uterus was half the size of the pellet. Similarly for other figures. Time of distention, 24 hours. Fig.2 Chart showing growth of chronically distended uteri after 4 days (triangles) and 14 days (dots). Paraffin pellets were used, 4 inch in length and of known, uniform diameters. No increase in size of uteri between the fourth and fourteenth days. See text for description of histological features. Fig. 3 Chart showing the effect of progressive, increasing distention (curve A ) by accumulation of fluid in the lumen of uteri; distention period, 4 days. Curve B, redrawn from figure 2. UTERINE GROWTH AND CHRONIC DISTENTION 285 cells of all parts of the tissues about the pellets undergo marked hypertrophy, as shown by an increase in ratio of cytoplasmic t o nuclear material; the nuclei become vesicular ; the vascular bed is somewhat increased; the tissues are edematous, especially in the deeper portions of the endometrium, and hyperplasia, even of the smooth muscle (Allen, et al., '37), takes place. These results show, therefore, that the initial response of the uterus to distention is to replace the tissue fluids lost as a result of insertion of the pellets. Then, according to the effectiveness of the degree of distention, growth changes are evident in all the tissues. These structural changes are largely complete in less than 4 days, so far as may be judged by these experiments. Evidence has been presented elsewhere which shows that the essential nature of the distention stimulus is the creation of an appropriate increase in tension upon the tissues (loc. cit.), but if the tension becomes too great, the nutrition of the tissues may be impaired through impoverishment of the blood supply. Progressive distention by accumulation with fluid. I n this group of experiments the least amount of distention obtained exceeded a uterus : pellet ratio of 1:1.59 (distention ratio of 0.63) or, as shown in figure 3, a point far down on the right of curve B, redrawn from figure 2. I n contrast t o curve B, curve A of figure 3 shows that the growth responses increase in amount as the distention increases, as far as the data go. The greatest growth response was one of 255% increase, or a three and a half-fold increase, at a distention ratio of 1:12.5 (i.e., the pellet was 12.5 X the size of the undistended uterus). This is the largest amount of stretching obtained thus far in untreated, ovariectomized rabbits, and was possible only because the uterus grew as it became increasingly distended. Clearly, therefore, when the uterus is progressively distended it is capable of both rapid and extensive adaptive alterations in structure pari passu with the increasing distention. Mention may be made in passing of the extent of uterine growth which takes place in the rabbit during pregnancy. 286 S . R. M. REYNOLDS AND S. KAMINESTER Hammond’s data ( ’ 3 5 ) on this subject show7 that a five- to eightfold increase takes place. This figure compares favorably with that stated by Stieve (’32). I t is striking, therefore, that the three and a half-fold increase that was observed in the instance cited above took place in 4 days, and in the absence of ovarian or other hormones associated with gestation. The role of distention during gestation has been discussed in two other places (Reynold’s, ’37 a, b). SUMMARY The rate of the changes in uterine structure and size resulting from chronic uterine distention is described. It i s found that the growth changes, including both hypertrophy and hyperplasia, even of smooth muscle, are completed in less than 4 days after insertion of paraffin pellets of uniform and known sizes. It is further observed that when distention is achieved by progressive accumulation of fluid within the uterus the growth response is proportional to the degree of distention, a s f a r a s the data go. It is further found that the percentage increase in size of the uterus of the untreated, ovariectomized rabbit under the latter conditions approaches in some instances that which takes place during normal pregnancy in the rabbit. L I T E R A T U R E CITED ALLEN,EDGAR, G. W. SMITH A N D 6. R. M. REYNOLDS 1937 Hyperplasia of smooth muscle. Proc. Sac. Exp. Biol. and Med. ( I n press.) HAMMOND, J. 1935 The rliaiiges in the reproductive organs of the rabbit during pregnancy. Trans. Dynamics of Development, vol. 10, pp. 93-115. REYNOLDS,S. R. M. 1937 a Chronic uterine distention and its relation t o the end of gestation. Am. J. Obst. Gynec., vol. 33, pp. 968-978. 1937 b Harmonic and physical factors i n uterine growth. Symposia on Quantitative Biology, vol. 5 (in press). Published by the Biological Laborator), Cold Spring Harbor, L. I. REYNOLDS, S. R. &I., A N D W. AT. ALLEN 1037 The effect of progestin on t h r growth response of the uterus t o chronic distention. Anat. Rec., vol. 68, pp. 481-488. REYNOLDS,8. R. II., AND 8. K.4hlINESTER 1936 Distention, a stimulus for uterine growth in untreated, ovariectomized rabbit. Am. J. Physiol., VOI. 116, pp. 510-515. STIEVE,H. 1932 Uber die Neubildungen von Muskelzellen in der Wand der schwangeren menschlichen Geblrmutter. Central. f. Gydkol., Bd. 56, S.1442-1447.