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1 J. Physiol. (1977), 273, pp With 3 text-figurea Printed in Great Britain COMPENSATORY RENAL HYPERTROPHY IN HYPOPHYSECTOMIZED RATS BY S. E. DICKER*, A. L. GREENBAUM AND CHRISTINE A. MORRIS From the Departments of Chemistry and of Biochemistry, University Lollege London, 20, Gordon Street, London WC1H OAJ (Received 10 May 1977) SUMMARY 1. After hypophysectomy, both body and kidney weights fall, but at different rates. The rate at which the kidney decreases in weight is faster than that of the whole body. 2. Seven days after unilateral nephrectomy, the dry weight of the remaining kidney of hypophysectomized rats, with the exception of rats which had been hypophysectomized for 2 days only, was always heavier than the kidney of control hypophysectomized rats of similar body weight. 3. The difference between the dry weight of kidneys of unilaterally nephrectomized hypophysectomized and control hypophysectomized rats increased from 15 % in early hypophysectomized (9 days) to about 35 % in late hypophysectomized animals (23 days). 4. The implantation of renal cortical cells from 2 day hypophysectomized rats into unilaterally nephrectomized control litter-mates inhibited compensatory renal hypertrophy in the latter. When a similar operation was made using kidney cells from animals which had been hypophysectomized for 23 days, there was no significant inhibition of compensatory renal hypertrophy. 5. The renal contents of adenosine-3',5'-monophosphate (cyclic AMP) and of guanosine-3',5'-monophosphate (cyclic GMP) in rats hypophysectomized for 2 days were of the same order as those in normal rats, but were markedly lower in rats hypophysectomized for 23 days. 6. In contrast to what had been observed in normal rats, in hypophysectomized (2 or 23 days) rats, unilateral nephrectomy did not affect significantly the levels of cyclic nucleotides in the remaining kidney. 7. Cross-circulating anephric normal rats with 2 day hypophysectomized animals resulted in an increase of cyclic GMP content in their kidneys. * Emeritus Leverhulme Fellow.

2 242 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS The cross-circulation between anephric normal rats and 23 days hypophysectomized rats had no effect on the level of renal cyclic GMP of the latter. 8. When rats hypophysectomized for either 2 or 23 days and which had been nephrectomized were cross-circulated with normal rats, there were no changes in the content of cyclic GMP in the kidneys of the latter. INTRODUCTION First attempts to investigate the dependence of compensatory renal hypertrophy on the presence of the pituitary body appear to have been made towards 1930, and most earlier results seem to agree that the removal of the pituitary gland prevents the development of hypertrophy of the remaining kidney after unilateral nephrectomy (for a review of the subject until 1950, see Astarabadi & Essex, 1953). However, in 1953, Astarabadi & Essex reported that unilateral nephrectomy performed 3-4 weeks after hypophysectomy in rats resulted in a hypertrophy of 'a significant extent' of the remaining kidney. A few years later Astarabadi (1962) published results according to which if unilateral nephrectomy preceeded hypophysectomy by 2 weeks, the remaining kidney 'underwent considerable regression in size,' and concluded that the 'presence of a renotrophic principle in the hypophysis is required for compensatory renal hypertrophy'. The same author (Astarabadi, 1963a, b) confirmed this in a series of experiments in which unilateral nephrectomy was performed 4-6 days after hypophysectomy; there were no signs of compensatory renal hypertrophy. In 1966, Fogelman & Goldman observed that the removal of one kidney 24 hr after hypophysectomy led to a slight increase in weight of the remaining kidney, which lasted for 2 days only, and was not followed by further hypertrophy. Ross & Goldman (1970) used young growing male rats, which, even after hypophysectomy, continued to gain weight at a rate of at least 5 g per week. They removed one kidney 3-5 weeks after hypophysectomy and 6 days later observed the hypertrophy of the remaining kidney, together with an increase of renal protein content. The interpretation of their results is complicated by the fact that they used immature animals which continued to grow even in the absence of the pituitary body. Recently, Poffenbarger & Prince (1976) reported results of unilatera nephrectomy in rats 14 days after hypophysectomy and which were killed 2 weeks later. The presence or absence of renal hypertrophy was derived from a linear regression analysis of kidney weight to body weight established for control and hypophysectomized animals over a range of body weights from 150 to 400 g. They concluded that compensatory renal

3 RENAL HYPERTROPHY AFTER HYPOPHYSECTOMY 243 hypertrophy was of the same order of magnitude in hypophysectomized as in non-hypophysectomized animals. Looking at these results as a whole, it would appear that up to about a week after hypophysectomy there is little, or no, compensatory renal hypertrophy (Astarabadi, 1963a, b; Fogelman & Goldman, 1966) whereas when unilateral nephrectomy was performed 2-5 weeks after hypophysectomy, compensatory hypertrophy of the remaining kidney followed (Astarabadi & Essex, 1953; Poffenbarger & Prince, 1976). So far, nobody seems to have explained this anomaly, and it is still generally accepted that the presence of a renotrophic factor of hypophyseal origin is necessary for the development of compensatory renal hypertrophy. It was therefore thought of interest to reinvestigate the problem by recording the effects of unilateral nephrectomy in rats which had been hypophysectomized for 2, 9, 16, 23 and 30 days. Furthermore, since Dicker, Morris & Shipolini (1977) had partially purified a kidney growth inhibitor of renal origin and Dicker & Greenbaum (1977) had drawn attention to the possible role of cyclic nucleotides (adenosine-3',5'-monophosphate and guanosine-3',5'- monophosphate) on the development of compensatory renal hypertrophy, it was logical to see whether changes in the renal content of the inhibitor and/or cyclic nucleotides had any bearing on the occurrence or absence of compensatory renal hypertrophy in hypophysectomized rats. METHODS All animals were adult Wistar male rats, bought from Anglia Laboratory Animals where the operation for hypophysectomy had been performed. The operation was done through the floor of the skull in which a hole had been drilled with a dental burr. Animals were chosen for their initial similar body weight. They were despatched 24 hr after the operation together with non-operated control rats. No mortality was observed among the hypophysectomized rats, from the time they were received. Left unilateral nephrectomy was performed 2, 9, 16 and 23 days after hypophysectomy, and the animals were killed 7 days later. The removal of the left kidney was done through a lumbar incision, care being taken to leave the adrenal gland intact, in 8itu. The operation lasted 2 min on average. Animals were kept in individual cages for the whole period of observation and their weight recorded at regular intervals. They were all fed the same standard diet of pellets, supplemented by a 20% glucose solution as drinking water. Completeness of the hypophysectomy was checked by macroscopic inspection of the sella turcica when the animals were killed. The degree of compensatory renal hypertrophy was estimated by placing the removed kidneys in stoppered weighing bottles. They were weighed before being dried, and then put in an incubator at 104 0C, over phosphorus pentoxide, where they were kept for 48 or 72 hr, until constant weight was reached. Adenosine-3',5'-monophosphate (cyclic AMP) and guanosine-3',5'-monophosphate (cyclic GMP) were estimated as previously described (Dicker & Greenbaum, 1977). In cross-circulation experiments, the carotid artery of one rat was anastomosed

4 244 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS to the jugular vein of another and a jugular vein from the first rat was anastomosed to the carotid of the other, by use of fine polyethylene tubing. The technique was similar to that described by Van Vroonhoven, Soler-Montesinos & Malt (1972) and Dicker & Greenbaum (1977). Animals used for cross-circulation experiments were litter mates. They were anaesthetized by i.p. injections of Inactin (Na-ethylmethyl-propyl-malonyl thiourea (10 mg/100 g body wt.) (Internationale Apotheke, Pachter, Hamburg); they received also an intraperitoneal injection of heparin (250 u./100 g body wt.). Litter-mates were also used for implantation of renal cortical cells. Under sterile condition the cortex was dissected out from the removed kidney, chopped finely and passed through a syringe as described by Guder, Siess & Wieland (1969). The resulting brei, consisting essentially of isolated cells and broken tubules, was injected intradermally (Dicker et al. (1977)). Results are given as means and their standard errors. RESULTS The initial weights of the rats before hypophysectomy were similar. The mean body weight of a first group of thirty animals was g, that of another batch of thirty-eight rats was g. These values are not statistically different. Out of the first group of thirty animals six were killed before hypophysectomy and used as controls. The remainder were hypophysectomized and killed 2, 9, 16, 23 and 30 days later. From Table 1 it will be seen that two days after hypophysectomy the average loss of body weight was of the order of 15 %, but that of the kidneys (wet weight) averaged 5 % only. A week later (9th day after hypophysectomy), however, the weight losses of body and kidneys averaged 21 and 26 % respectively. From the 9th day onwards, the body weight remained fairly stable at about 75 % of the preoperative values, while kidney weights continued to decrease steadily until, by 30 days after hypophysectomy, they were some 45 % lighter than before hypophysectomy. With the exception of what happened 48 hr after hypophysectomy, from the 9th to the 30th day after the operation changes in water and dry solids contributed approximately equally to changes of total renal weights, when expressed as percentage of body weight. Expressing changes of kidney weights (wet or dry) in terms of unit (100 g) body weight led to a paradoxical increase of renal weight on the 2nd day after hypophysectomy which contrasted with a subsequent fall (Fig. 1). The second group of thirty-eight rats hypophysectomized had an initial body weight of g. Six were killed before hypophysectomy and were used as controls, the remainder was operated for unilateral nephrectomy on the 2nd, 9th, 16th and 23rd day after hypophysectomy and killed 7 days later, i.e. on the 9th, 16th, 23rd and 30th day. Changes in body weights were not significantly different from those of the previous

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6 246 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS series of control hypophysectomized rats. Similarly, the weights of the kidneys removed at the time of nephrectomy agreed very closely with those observed in the control series (Table 1). Accordingly, detailed data are not presented. In view of this similarity, it became obvious that calculations based on changes in body weight could be dispensed with, thus allowing a straight comparison between weights (wet or dry) of kidneys before and 7 days after unilateral nephrectomy. This showed that, with the exception of rats operated for unilateral nephrectomy 2 days after 120 _ -8 K.W. (d.w.)/l 00 g B.W 100 s 80 B.W K.W. (d.w.) L I I I Number of days after hypophysectomy Fig. 1. Average percentage changes of body and kidney weights after hypophysectomy. B.W.: body weights; K.W. (d.w.): kidney dry weights. Note: by expressing changes of kidney weights in terms of 100 g body weight, there is a paradoxical increase in kidney weight, 2 days after hypophysectomy. The percentage changes were calculated from the numerical data of Table 1. Since they are a graphical representation of the data of Table 1, the number of estimations are the same as those of Table 1; they were omitted for purpose of clarity. hypophysectomy and killed on the 9th day, at any time after hypophysectomy 7 days after unilateral nephrectomy the weight of the remaining kidney was heavier than that of corresponding kidneys of non-nephrectomized hypophysectomized rats. It also showed that although the time allowed for observation of development of compensatory renal hypertrophy was the same throughout (i.e. 7 days), the difference between the dry weights of kidneys removed and the remaining kidneys in unilaterally nephrectomized animals increased from 15 on the 16th day to 35 % on the 30th day after hypophysectomy. The dry weight of the hypertrophied kidneys was, however, always well below that of the control nonhypophysectomized animals (Fig. 2).

7 RENAL HYPERTROPHY AFTER HYPOPHYSECTOMY 247 Implantation. of renal cortex from hypophysectomized into unilaterally nephrectomized litter-mates Dicker et al. (1977) have shown that the implantation of renal cortical cells from a normal rat into a unilaterally nephrectomized animal decreased the rate of compensatory renal hypertrophy. It was therefore of interest to see whether the implantation of renal cortical cells from an hypophysectomized rat into a control unilaterally nephrectomized normal rat would similarly affect the development of compensatory renal hypertrophy. Four litters of rats were reared from birth until they were adult. H (6) 200 (8) E a)~~~~~~~~~~~~~~~~~~~6 100) _ Number of days after hypophysectomy Fig. 2. Changes in kidney dry weight (mg) in hypophysectomized and hypophysectomized unilaterally nephrectomized rats. Hypophysectomy was performed on day 0. Unilateral nephrectomy was then performed on days 2, 9, 16 and 23; 0-a, dry weights of kidneys removed at operation. The dry weights of the remaining kidneys were estimated 7 days later (--., on the days 9, 16, 23 and 30). In brackets, number of estimations. Note that while the difference between unilaterally nephrectomized and non nephrectomized hypophysectomized rats was 15 % on day 16, it steadily increased with time and was 35 % on day 30. H: hypophysectomy. Values are means + s.e. of mean. For reasons beyond our control their initial body weights were heavier than those of the previous series with weights ranging from 250 to 300 g. Each litter was divided into two groups. One group was hypophysectomized, the other not. The hypophysectomized rats were operated for

8 248 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS unilateral nephrectomy 2 or 23 days after the removal of the pituitary gland and the renal cortical cells of the removed kidney were implanted into a unilateral nephrectomized control litter mate, while the cortical A B TAiBLE 2. Effect of implantation of renal cortical cells from hypophysectomized rats into unilaterally nephrectomized control litter-mates Treatment I Unilateral nephrectomy in normal rats (control). No implantation (12) II Implantation of renal cortical cells from normal rats into unilaterally ± (6) nephrectomized normal litter-mates I Implantation of renal cortical cells from 2 days hypophysectomized (6) rats into unilaterally nephretomized normal litter-mates IV Implantation of renal cortical cells from 23 days hypophysectomized (6) rats into unilaterally nephrectomized normal litter-mates I Unilateral nephrectomy in 23 days hypophysectomized rats. No implantation II Implantation of renal cortical cells from normal rats into 23 days hypophysectomized and unilaterally nephrectomized litter-mates Dry weight of kidneys (g/100 g B.W.) Day 0 Day (12) ± (6) (6) (6) (8) ± (8) (6) III Implantation of renal cortical cells from 2 days hypophysectomized ± (4) rats into 23 days hypophysectomized and unilaterally nephrectomized litter-mates (6) (4) Average increase Day 0: kidney weight (dry) of the removed kidney, and Day 7: kidney weight (dry) of the remaining kidney, 7 days after unilateral nephrectomy, both expressed as g/100 g body weight. In brackets, number of estimations. Data are means + s.e. cells of the normal rats were implanted into the unilaterally nephrectomized (2 or 23 days) hypophysectomized litter-mates. All animals were killed 7 days after the exclusion of one kidney. From Table 2, it will be seen that the implantation of renal cortical cells from a rat hypophysectomized for 2 days into a control unilaterally

9 RENAL HYPERTROPHY AFTER HYPOPHYSECTOMY 249 nephrectomized animal inhibited compensatory hypertrophy in the latter (A, III). When the same operation was done with rats which had been hypophysectomized for 23 days, no significant inhibition of renal hypertrophy was observed (A, IV). Table 2 also shows that the implantation of renal cortical cells from either control (B, II) or 2 day (B, III) hypophysectomized litter-mates into 23 days hypophysectomized unilaterally nephrectomized animal decreased the expected enlargement of the remaining kidney of the latter from 35 % (see Fig. 2) to 12 and 13 % respectively. Cyclic AMP and cyclic GMP content in kidneys of hypophysectomized rats, before and after unilateral nephrectomy Fourteen rats hypophysectomized for 2 days and twelve rats hypophysectomized for 23 days were unilaterally nephrectomized. Cyclic nucleotides were estimated in the removed kidneys for control values, and in the remaining kidneys 5, 10 and 20 min after the exclusion of the other kidney. The levels of cyclic AMP and cyclic GMP in the control kidneys of rats hypophysectomized for 2 days were (14) and (14) x mole/g wet tissue. These values are of the same order as those reported by Dicker & Greenbaum (1977) in normal rats. In the control kidneys of 23 days hypophysectomized rats, however, the renal contents of cyclic AMP and cyclic GMP had decreased to (12) and *43 (12) x 1012 mole/g wet tissue, respectively. In contrast with what had been observed in normal rats, where the exclusion of one kidney was followed 10 min later by a threefold increase of cyclic GMP content, accompanied by a moderate fall of cyclic AMP in the remaining kidney (Dicker & Greenbaum, 1977), in hypophysectomized animals no significant changes in the level of either cyclic nucleotide were observed in the remaining kidney 5, 10 or 20 min after unilateral nephrectomy (Fig. 3). Effects of cross-circulation between hypophysectomized and normal rats Litter-mates were used. In the first series of experiments rats which had been hypophysectomized for either 2 or 23 days were cross-circulated with normal anephric litter-mates of similar weight (Table 3, BI and BII). In the second series of experiments, normal rats were cross-circulated with litter-mates which had been hypophysectomized for either 2 or 23 days and had both kidneys removed (Table 3, AI and A II). In all cases, the double nephrectomy preceded the start of the cross-circulation by about 30 min, and the cross-circulation was maintained for 10 min. Cyclic GMP was estimated in all kidneys.

10 250 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS 900 r Cyclic AMP a) 0) 0 E 800 F 700 F Cyclic AMP F 500 L 80 r 2 days K 23 days 0) E ()(4) Cyclic GMP Cyclic GMP +(12) ( 36)(3 20 I Il Time (min) Time (min) Fig. 3. Changes of cyclic AMP and cyclic GMP content of the remaining kidney after unilateral nephretomy in rats hypophysectomized for either 2 or 23 days. Amounts of cyclic nucleotides in mole.g-1 wet tissue. Time in minutes. Unilateral nephretomy at. 0: cyclic AMP. x : cyclic GMP. Data are means + s.e. of mean. In brackets, number of estimations. TABLE 3. Effect of cross-circulation between hypophysectomized and normal rats on renal cyclic GMP content Treatment Cross-circulation between: A I Normal rats and 2 days anephric hypophysectomized litter-mates II Normal rats and 23 days anephric hypophysectomized litter-mates B I 2 days hypophysectomized rats and normal anephric litter-mates II 23 days hypophysectomized rats and normal anephric litter-mates s 20 Cyclic GMP content of kidneys (10-12 mole. g-' wet tissue) Hypophysectomized rats 60*3 ± 2-12 (6) 31-7 ± 5-64 (8) ± 1*25 (8) 44-8 ± 6.28 (6) Normal rats (6) (8) 69-8 ± 4-54 (8) 64O0 ± 6-89 (6) The mean cyclic GMP renal contents of 2 days and 23 days control hypophysectomized rats were 58-5 ± 3-48 (14) and 36-4 ± 5-43 (12) x mole. gel wet tissue, respectively (see text).

11 RENAL HYPERTROPHY AFTER HYPOPHYSECTOMY 251 The results show that when anephric rats hypophysectomized for either 2 or 23 days (Table 3, AI, AII) were cross-circulated with normal littermates, there were no significant changes in the cyclic GMP renal content of the latter. When, however, anephric normal rats were cross-circulated with animals hypophysectomized for 2 days (Table 3, BI) there was a moderate increase (of about 40 %) of cyclic GMP level in the kidneys of the latter. No significant changes in the renal content of cyclic GMP of 23 days (Table 3, BII) hypophysectomized animals were observed when cross-circulated with anephric normal litter-mates (Table 3, BI). DISCUSSION It would appear from the present investigation that, with the exception of rats hypophysectomized for 2 days only, at any other time after hypophysectomy, 7 days after unilateral nephrectomy the dry weight of the remaining kidney was always heavier than that of corresponding kidneys of control hypophysectomized rats (Fig. 2). When unilateral nephrectomy was performed 9 days after hypophysectomy and the animal killed 7 days later (i.e. on the 16th day), the remaining kidney was 15 % heavier than that of control hypophysectomized animals. This is of the same order of magnitude as that observed in normal unilaterally nephrectomized rats and agrees with Poffenbarger & Prince's (1976) observation. When unilateral nephrectomy was performed 23 days after hypophysectomy and the animals were killed 7 days later (i.e. on the 30th day) the difference between the dry weight of the remaining kidney and that of control hypophysectomized animals, killed on the 30th day, had increased to 35 %, which is about twice that found after 7 days in normal unilaterally nephrectomized rats. Dicker & Greenbaum (1977) have shown that the exclusion of one kidney in a normal rat produces an almost immediate marked, but short lived, increase of the cyclic GMP content of the remaining kidney. An increase of the level of cellular cyclic GMP is often interpreted as being a signal that leads to cell growth (Posternak, 1974). In animals which had been hypophysectomized for either 2 or 23 days the removal of one kidney did not produce any changes in the content of either cyclic GMP or cyclic AMP in the remaining kidney, over the period studied (Fig. 3). It may be argued, therefore, that the factor responsible for changes in cyclic nucleotides in the remaining kidney of normal animals is either of hypophyseal origin, or is related to the presence of the pituitary gland. Furthermore, the loss of the pituitary gland appears to be associated with a progressive inability of the renal cells to respond to the stimulus which, in normal rats, produces an increased level of

12 252 S. E. DICKER, A. L. GREENBAUM AND C. A. MORRIS cyclic GMP in the renal cells. This view is consistent with the observation that in cross-circulation experiments between normal anephric rats and early hypophysectomized (2 days) litter-mates, there was some increase of the renal level of cyclic GMP in the kidneys of the latter, whereas in similar experiments performed with 23 days hypophysectomized rats, no increase of renal cyclic GMP level was observed (Table 3). This raises the question of whether an increase of cyclic GMP in the remaining kidney, as observed in normal animals (Schlondorff & Weber, 1976; Dicker & Greenbaum, 1977), is necessary for the development of compensatory renal hypertrophy. The observations (a) that in rats which have been hypophysectomized for at least 9 days, unilateral nephrectomy results in compensatory hypertrophy of the remaining kidney, and (b) that the magnitude of the hypertrophy response is directly correlated with the length of time elaspsed between hypophysectomy and unilateral nephrectomy, both suggest that compensatory renal hypertrophy develops independently of an immediate rise in the level of cyclic GMP in the renal cells. Furthermore, they indicate that if, as it is assumed, compensatory renal hypertrophy is controlled by a humoral factor (Van Vroonhoven et al. 1972), the latter acts independently of whether the pituitary gland is present or not. There are two points which need elucidation. First, why is there no appreciable compensatory renal hypertrophy in early (2 days) hypophysectomized animals? A possible, albeit not experimentally tested, explanation is that the stress of the operation is of such intensity, that what has been called the 'adaptation syndrome', normally controlled by the adrenal glands, is slow to develop. Secondly, why is compensatory renal hypertrophy greater in 23 days than in 9 days hypophysectomized rats? A possible explanation is that whereas in normal animals there is a kidney growth inhibitor of renal origin (Dicker et al. 1977) which may play a role in controlling compensatory renal hypertrophy, in hypophysectomized animals there is a progressive loss of activity of the renal growth inhibitor (Table 2). This then might account for a decreased control of the humoral factor, and hence a greater compensatory renal hypertrophy. In summary, it would appear from the results of the present experiments that (a) changes in cyclic nucleotide levels of the remaining kidney after unilateral nephrectomy are, directly or indirectly, under the control of the pituitary gland, (b) compensatory renal hypertrophy can occur in the absence of a short-term rise in the level of cyclic GMP in the renal cells, and (c) development of compensatory renal hypertrophy is not directly controlled by the hypophyseal gland.

13 RENAL HYPERTROPHY AFTER HYPOPHYSECTOMY 253 A grant from the Medical Research Council to S. E. D. is gratefully acknowledged. We would like to thank Dr B. Banks for allowing us to operate in her laboratory, in the Department of Physiology. S. E. D. would also like to thank Professor M. McGlashan for his kind hospitality and Professor C. Vernon for his interest in the work. REFERENCES ASTARABADI, T. (1962). The regression in size of the hypertrophic remaining kidney after hypophysectomy in rats. Q. Jl exp. Physiol. 47, ASTARABADI, T. (1963 a). The effect of hypophysectomy, adrenalectomy and ACTH administration on compensatory renal hypertrophy in rats. Q. Ji exp. Physiol. 48, ASTARABDI, T. (1963b). The effect of growth and lactogenic hormones on renal compensatory hypertrophy in hypophysectomised rats. Q. Ji exp. Phy8iol. 48, ASTARABADI, T. M. & EssEx, H. E. (1953) Effect of hypophysectomy on compensatory renal hypertrophy after unilateral nephrectomy. Am. J. Phyaiol. 173, DICKER, S. E. & GREENBAUM, A. L. (1977). Changes in renal cyclic nucleotide content as a possible trigger to the initiation of compensatory renal hypertrophy. J. Physiol. 271, DICKER, S. E., MORRIS, CHRISTINE, A. & SHIPOLINI, R. A. (1977). Regulation of compensatory kidney hypertrophy by its own products. J. Physiol. 269, FOGELMAN, A. & GOLDMAN, R. (1966). Effects of hypophysectomy and growth hormone on renal compensatory hypertrophy in rats. Proc. Soc. exp. Biot. Med. 122, GUDER, W., SIESS, E. & WIELAND, 0. (1969). Studies on glucose synthesis in rat kidney cell suspensions. FEBS Lett. 3, POFFENBARGER, P. L. & PRINCE, M. J. (1976). The role of serum nonsuppressible insulin-like activity (NSILA) in compensatory renal growth. Growth 40, POSTERNAK, T. (1974). Cyclic AMP and cyclic GMP. A. Rev. Pharmac. 14, Ross, J. & GOLDMAN, J. K. (1970). Compensatory renal hypertrophy in hypophysectomised rats. Endocrinology 87, SCHLONDORFF, D. & WEBER, H. (1976). Cyclic nucleotide metabolism in compensatory renal hypertrophy and neonatal kidney growth. Proc. natn. Acad. Sci. U.S.A. 73, VAN VROONHOVEN, T. J., SOLER-MONTESINOS, L. & MALT, R. A. (1972). Humoral regulation of renal mass. Surgery 72,