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Partial hepatectomy and liver regeneration in pigs—The response to different resection sizes
JOURNAL
OF SURGICAL
45, 176-180 (1988)
RESEARCH
Partial Hepatectomy and Liver Regeneration in PigsThe Response to Different Resection Sizes’ D. KAHN, CH.M., FCS(SA), R. HICKMAN, M.D., CH.M., J. TERBLANCHE, CH.M., FCS(SA), FRCS, AND ST. VON SOMMOGGY, M.D. Department of Surgery and Medical Research Council Liver Research Group, University of Cape Town, Cape Town, South Africa
Submittedfor publication October24, 1986 Liver regeneration has been extensively studied in the rat and dog models but pigs have seldom been
used.They resembleman closely in their omnivorous diet and their gastroenterological and endocrinological responses.This paper describes techniques of 15, 50,65, and 70% partial hepatectomy in the pig. Thymidine kinase activity and mitotic index were used as indices of liver regeneration. The timing and events of the regenerative response in the pig compared favorably with other animal modelsand the maximum regenerative responseoccurred on the third postoperative day, irrespective of the size of the partial hepatectomy. The 15%partial hepatectomy, which shows a minimal responseto resection, provides a suitable “primed” model for the study of stimulatory substances. o 1988 Academic press, IIIC.
INTRODUCTION
The morphological changes associated with hepatic regeneration after partial hepatectomy have been well documented in the rat model [ 1, 21. Dogs have been used less extensively and the timing and events of the regenerative response have been characterized [3-51. Pigs have seldom been used in liver regeneration studies [6], although in their gastroenterological and endocrinological response in other studies they more closely resemble man. The present study represents the first in a large animal which simulates that in the rat [I] and studies the effects of different sizes of hepatectomy, viz., 15, 50, 65, and 70%. The regenerative response was measured using thymidine kinase activity and mitotic indices as described previously [6].
Materials and Methods Large White X Landrace pigs of either sex and weighing 17-24 kg were used in this study. All definitive operations were per’ Financial assistancewas received from the Medical ResearchCouncil of South Africa and the Staff Research Fund of the University of Cane Town. 0022-4804/88 $1.50 Copyright Q 1988 by Academic FTess,Inc. All rights of reproduction in any form reserved.
formed under general anesthesia, intravenous thiopentone sodium being used for induction and anesthesia being maintained with oxygen and nitrous oxide administered through an endotracheal tube. All surgical procedures were commenced between 08.00 and 09.00 AM. A catheter was inserted into the internal jugular vein for the administration of fluids. The abdomen was opened via a long midline incision and the falciform and left triangular ligaments were divided. Four kinds of hepatectomy were studied, viz., 15, 50, 65, and 70% partial hepatectomy. Postoperatively, the animals received intravenous glucose/electrolyte solutions for 24 hr. Thereafter animals were allowed free accessto food and water. Open wedge liver biopsies were taken on the second, third, fourth, and fifth postoperative days via a mini-laparotomy under light anesthesia. Each liver biopsy was divided into two, half being frozen immediately in liquid nitrogen for measurement of thymidine kinase activity, and half being placed in formaldehyde for histological assessment.The method for assaying thymidine kinase activity has been described previously [6].
176
KAHN ET AL.: LIVER REGENERATION
IN PIGS
FIG. 1. A diagram of the techniques of 15, 50, and 65% hepatic resection using vascular control with a ribbon tape, and of 70% resection by vessel ligation and finger-fracture.
Figure 1 illustrates the degree of resection in each of the four groups. (a) Partial hepatectomy-15% (4 animals). A l-cm ribbon was tied tightly around the base of the left lateral lobe, the lobe was excised, and the ribbon was tightened to control the arterial and venous bleeding. The cut surfacewas then oversewn using a continuous 2-O chromic catgut suture. The ribbon was removed and individual bleeding sites were controlled with interrupted sutures. (b) Partial hepatectomy-50% (11 animals). The technique of 50% partial hepatectomy in the pig has been described previously [I]. A ribbon was tied tightly around the base of the left lateral lobe and the lobe was excised as described above. Another ribbon was tied tightly around the base of the
middle lobe which was excised including the gallbladder. The ribbon was tightened to control the bleeding and the cut surface was oversewn using a continuous 2-O chromic catgut suture. The ribbon was removed and individual bleeding sites were controlled with interrupted sutures. (c) Partial hepatectomy--65% (8 animals). This procedure was identical to (a) except that a single ribbon was tied tightly around the basesof the left lateral and middle lobes of the liver. (d) Partial hepatectomy-70% (8 animals). The 70% resection was achieved using a finger-fracture technique. The initial steps in this operation consisted of dissection in the porta hepatis and ligation of the branches of the portal vein and hepatic artery to the
178
JOURNAL OF SURGICAL RESEARCH: VOL. 45, NO. 2, AUGUST 1988
left lateral and middle lobes of the liver. The two lobes were then almost totally removed using a finger-fracture technique. Statistical analyses were made using the Mann-Whitney test for unpaired data and P < 0.05 was accepted as significant.
50
1
RESULTS
General OperativeDetail The described technique proved to be simple and reproducible. The hepatectomies alone were accomplished within 5- 10 min dand the oversewing was done within a further 15-20 min. With consistently tight ligation of the ribbons at the baseof the liver, the blood loss was minimal and if major bleeding occurred, this could be rapidly controlled by tightening of the ribbons. In less than 5% of animals in (c), death occurred rapidly overnight which was attributed to removal of an excessiveamount of liver.
Extent of the Resection To determine the extent of the resections, separate groups of animals were subjected to the various partial hepatectomies as described above. Immediately afterward, the animals were sacrificed and the remnant liver was removed. The resected and remnant lobes were weighed and the size of the hepatectomy was determined. Resection of the left lateral lobe resulted in a 15.51 +- 0.83% (SEM) partial hepatectomy. Removal of the left lateral and middle lobes separately constituted a 50.53 k 1.22% resection. The left lateral and the middle lobes, removed using a single ribbon, constituted 64.68 + 1.19% (SEM). Resection of the left lateral and middle lobes of the liver using a finger-fracture technique resulted in a 70.14 * 1.65% (SEM) partial hepatectomy. Comparison of the 15 or 50% resections with either the 65 or 70% resections showed significant differences (P < 0.00 1). There was not, however, any significant difference between the 65 and 70% resections.
I
0
1
2
3
4
5
DAYS
FIG. 2. Thymidine kinase activity (dpm per mg protein) in the liver after 15, 50, 65, and 70% partial hepatectomy. Results are expressed as means f SEM, and * indicates a significant difference (P < 0.05) from 0 values.
Changesin Thyrnidine Kinase Activity (Fig. 2) Thymidine kinase activity increased slightly after 15% partial hepatectomy but the changes were not significant. Following 50,65, and 70% partial hepatectomy, thymidine kinase activity increased significantly and reached a peak on the third postoperative day. (P < 0.05 compared with preoperative values). Thereafter, the levels of activity decreasedbut were still significantly elevated on the fifth postoperative day (P < 0.05). Thymidine kinase activities on the third day after 50, 65, and 70% partial hepatectomy were 18,342, 32,486, and 41,586 dpm/mg protein, respectively. The differences between the thymidine kinase activity after 50% partial hepatectomy and 65 and 70% partial hepatectomy were significant (P < 0.05) but there was no difference between 65 and 70% partial hepatectomy.
Changesin Mitotic Index (Fig. 3) Mitotic figures were not evident in the liver biopsies taken preoperatively. Similarly,
KAHN ET AL.: LIVER REGENERATION
IN PIGS
179
response was accurately documented using thymidine kinase activity and mitotic activ15. 70%** ity as indices of liver regeneration. In the 3 . present study, the techniques of 15, 50, 65, mo and 70% partial hepatectomy in the pig were described and again the regenerative response was accurately measured using our previous indices of liver regeneration. In this study the regenerative response was influenced by the amount of liver removed at * operation, with the maximum response occurring after 70% partial hepatectomy. Similar results were obtained following 10,30,40, and 68% resection in rats [I] and following i 4 i 5 iJ i 44 and 72% resection in dogs [3]. DAYS Regeneration of the pig liver has been FIG. 3. Mitotic index (mitoses per 1000 cells) in the shown to be as fully predictable as hepatic liver after 15, 50, 65, and 70% partial hepatectomy. Re- regeneration in other animal models. The sults are expressedas means f SEM, * indicates a signifitiming of the response compares favorably cant difference (P < 0.05) from 0 values, and ** indicates with other large animal models. The maxiP < 0.01. mum response in the pig, as in the dog, occurs at 3 days and contrasts with the 24-hr peak in the rat. mitotic figures were not seen in the liver The anatomy of the blood supply and biliary biopsies taken on the second, third, and drainage of the porcine liver [8] is such that the fourth days after 15% partial hepatectomy. right lateral lobe has to be excluded from any The mitotic indices increased significantly form of resection. The infrahepatic inferior after 50, 65, and 70% partial hepatectomy vena cava enters the right lateral lobe and and levels on the third postoperative day would have to be divided if the lobe were rewere 6.5 t 1.5, 10.9 f 1.35, and 13.8 + 3.2 moved. Also the portal vein and bile duct are mitoses per 1000 cells, respectively. At Day intimately related to the right lateral lobe and 3, the significance of all rises was P < 0.01 give off branches to this lobe before supplying and at Days 2, 4, and 5, the significance of or draining the other lobes. Thus if the right the rise as compared with preoperative lateral lobe were resected the portal blood supvalues was P < 0.05. ply and biliary drainage of the remaining lobes would be jeopardized. Partial hepatectomy in DISCUSSION the pig therefore involves resection of the left Liver regeneration has been extensively lateral and middle lobes of the liver. studied in the rat [ 1,2]. Dogs have been used The techniques of 65 and 15%partial hepto a limited extent [ 3-51 and the morphologi- atectomy in the pig proved to be simple and cal changes after partial hepatectomy have reproducible. The animals tolerated the probeen described [ 31.The pig on the other hand cedures well and blood loss was minimal. Arhas seldom been used; a technique of partial terial and venous bleeding was easily conhepatectomy has been described previously trolled with the tape around the base of the but the technique was complicated and lobes, allowing adequate time to oversew the the regenerative response was not docu- cut surface. The porcine liver contains a large mented [7]. amount of fibrous tissue and therefore holds In a previous study from this laboratory, a the sutures well. technique of 50% partial hepatectomy in the The technique of 70% partial hepatectomy pig was described [6] and the regenerative using a finger-fracture method was more dif-
180
JOURNAL OF SURGICAL RESEARCH: VOL. 45, NO. 2, AUGUST 1988
ficult, took longer, and resulted in a greater amount of blood loss. Sixty-five percent partial hepatectomy is the model of choice for most studies of liver regeneration in the pig. There is a significant increase in thymidine kinase activity with the maximum increase occurring on the third postoperative day. There was no significant changes in thymidine kinase activity after 15% partial hepatectomy. This confirms the finding in rats that there is a critical amount of liver which has to be resected before a regenerative responseis initiated [ 11.It is, however, a particularly useful in vivo model for assaying various factors which are thought to stimulate liver regeneration [9]. Unfortunately, because of the small regenerative response after 15% partial hepatectomy, this model cannot be used to assessvarious substances which may inhibit liver regeneration. The use of a large animal model in the study of liver regeneration has certain advantages.Samplesof blood and tissue can be harvested from multiple sites [lo] and the volumes of tissue and blood removed are less limited. More importantly, each animal can be sampled or studied serially [6, 10, II] and thus sequential changes in the regenerative response [6], hormones [lo], blood flow [ 111, etc., in each animal can be assessed.The pig has a further advantage in that it resembles man more closely in its gastrointestinal and endocrine functions and thus results obtained would have added clinical significance. One of the factors limiting the use of large animals has been the previously prohibitive cost of measuring the regenerative response after partial hepatectomy. Thymidine kinase activity has been shown to be an inexpensive index of liver regeneration especially suitable for use in a large animal model and for studying the regenerative response serially [6]. Thus, in summary, the techniques of 15, 50, 65, and 70% partial hepatectomy in the pig are described, and the regenerative response is accurately documented using thymidine kinase activity and mitotic index as indices of liver regeneration.
SUMMARY
The techniques of 15, 50, 65, and 70% partial hepatectomy in the pig have been described and the regenerative response has been characterized using thymidine kinase activity and mitotic index as indices of regeneration. Regeneration of the pig liver has been shown to be as fully predictable as hepatic regeneration in other animal models. The peak regenerative response occurred on the third postoperative day. REFERENCES 1. Bucher, N. L. R. Regeneration of the mammalian liver. Znt. Rev. Cytol. 15: 245, 1963. 2. Bucher, N. L. R., and Malt, R. A. Morphological and biological aspects.In N. L. R. Bucher and R. A. Malt (Eds.), Regeneration ofLiver and Kidney. Boston: Little, Brown, 1971. P. 23. 3. Francavilla, A., Porter, K. A., Benichou, J., Jones, A. F., and Starzl, T. E. Liver regeneration in dogsMorphologic and chemical changes. J. Surg. Res. 25: 409, 1978. 4. Price, J. B., Takeshige, K., Max, M. H., and Voorhees, A. B. Glucagon as the portal factor modifying hepatic regeneration. Surgery 12: 74, 1972. 5. Starzl, T. E., Francavilla, A., Porter, K. A., Benithou, J., and Jones A. F. The effects of splanchnic viscera removal upon canine liver regeneration. Surg. Gynecol. Obstet. 147: 1983, 1978. 6. Kahn, D., Stadler, J., Terblanche, J., and van Hoom-Hickman, R. Thymidine kinase: An inexpensive index of liver regeneration in a large animal model. Gastroenterology 79: 907, 1980. 7. Gallot, D., Gouet, O., Bidallier, M., Coloigner, M., Opolon, P., and Huguet, C. A simplified bloodless procedure for extensive hepatectomy. Experimental study in the pig. Eur. Surg. Rex 8: 236, 1976. 8. Comprodon, R., Solsona, J., Guerrero, J. A., Mendoza, C. G., Segura, J., and Fabregat, J. M. Intrahepatic vascular division in the pig. Basis for partial hepatectomies. Arch. Surg. 112: 38, 1977. 9. Kahn, D., Hickman, R., Terblanche, J., and Kirsch, R. Hepatic stimulator substance in extracts from regenerating porcine liver-Basic physiological properties. Submitted for publication. 10. Kahn, D., van Hoom-Hickman, R., Child, P., and Terblanche, J. Transhepatic changes in insulin and glucagon following partial hepatectomy in the pig: The effect of hypoglycemia. Surg. Gynecol. Obstet. 158: 475, 1984. 1I. Kahn, D., van Hoorn-Hickman, R., and Terblanche, J. Liver blood flow after partial hepatectomy in the pig. J. Surg. Res. 37: 280, 1984.
OF SURGICAL
45, 176-180 (1988)
RESEARCH
Partial Hepatectomy and Liver Regeneration in PigsThe Response to Different Resection Sizes’ D. KAHN, CH.M., FCS(SA), R. HICKMAN, M.D., CH.M., J. TERBLANCHE, CH.M., FCS(SA), FRCS, AND ST. VON SOMMOGGY, M.D. Department of Surgery and Medical Research Council Liver Research Group, University of Cape Town, Cape Town, South Africa
Submittedfor publication October24, 1986 Liver regeneration has been extensively studied in the rat and dog models but pigs have seldom been
used.They resembleman closely in their omnivorous diet and their gastroenterological and endocrinological responses.This paper describes techniques of 15, 50,65, and 70% partial hepatectomy in the pig. Thymidine kinase activity and mitotic index were used as indices of liver regeneration. The timing and events of the regenerative response in the pig compared favorably with other animal modelsand the maximum regenerative responseoccurred on the third postoperative day, irrespective of the size of the partial hepatectomy. The 15%partial hepatectomy, which shows a minimal responseto resection, provides a suitable “primed” model for the study of stimulatory substances. o 1988 Academic press, IIIC.
INTRODUCTION
The morphological changes associated with hepatic regeneration after partial hepatectomy have been well documented in the rat model [ 1, 21. Dogs have been used less extensively and the timing and events of the regenerative response have been characterized [3-51. Pigs have seldom been used in liver regeneration studies [6], although in their gastroenterological and endocrinological response in other studies they more closely resemble man. The present study represents the first in a large animal which simulates that in the rat [I] and studies the effects of different sizes of hepatectomy, viz., 15, 50, 65, and 70%. The regenerative response was measured using thymidine kinase activity and mitotic indices as described previously [6].
Materials and Methods Large White X Landrace pigs of either sex and weighing 17-24 kg were used in this study. All definitive operations were per’ Financial assistancewas received from the Medical ResearchCouncil of South Africa and the Staff Research Fund of the University of Cane Town. 0022-4804/88 $1.50 Copyright Q 1988 by Academic FTess,Inc. All rights of reproduction in any form reserved.
formed under general anesthesia, intravenous thiopentone sodium being used for induction and anesthesia being maintained with oxygen and nitrous oxide administered through an endotracheal tube. All surgical procedures were commenced between 08.00 and 09.00 AM. A catheter was inserted into the internal jugular vein for the administration of fluids. The abdomen was opened via a long midline incision and the falciform and left triangular ligaments were divided. Four kinds of hepatectomy were studied, viz., 15, 50, 65, and 70% partial hepatectomy. Postoperatively, the animals received intravenous glucose/electrolyte solutions for 24 hr. Thereafter animals were allowed free accessto food and water. Open wedge liver biopsies were taken on the second, third, fourth, and fifth postoperative days via a mini-laparotomy under light anesthesia. Each liver biopsy was divided into two, half being frozen immediately in liquid nitrogen for measurement of thymidine kinase activity, and half being placed in formaldehyde for histological assessment.The method for assaying thymidine kinase activity has been described previously [6].
176
KAHN ET AL.: LIVER REGENERATION
IN PIGS
FIG. 1. A diagram of the techniques of 15, 50, and 65% hepatic resection using vascular control with a ribbon tape, and of 70% resection by vessel ligation and finger-fracture.
Figure 1 illustrates the degree of resection in each of the four groups. (a) Partial hepatectomy-15% (4 animals). A l-cm ribbon was tied tightly around the base of the left lateral lobe, the lobe was excised, and the ribbon was tightened to control the arterial and venous bleeding. The cut surfacewas then oversewn using a continuous 2-O chromic catgut suture. The ribbon was removed and individual bleeding sites were controlled with interrupted sutures. (b) Partial hepatectomy-50% (11 animals). The technique of 50% partial hepatectomy in the pig has been described previously [I]. A ribbon was tied tightly around the base of the left lateral lobe and the lobe was excised as described above. Another ribbon was tied tightly around the base of the
middle lobe which was excised including the gallbladder. The ribbon was tightened to control the bleeding and the cut surface was oversewn using a continuous 2-O chromic catgut suture. The ribbon was removed and individual bleeding sites were controlled with interrupted sutures. (c) Partial hepatectomy--65% (8 animals). This procedure was identical to (a) except that a single ribbon was tied tightly around the basesof the left lateral and middle lobes of the liver. (d) Partial hepatectomy-70% (8 animals). The 70% resection was achieved using a finger-fracture technique. The initial steps in this operation consisted of dissection in the porta hepatis and ligation of the branches of the portal vein and hepatic artery to the
178
JOURNAL OF SURGICAL RESEARCH: VOL. 45, NO. 2, AUGUST 1988
left lateral and middle lobes of the liver. The two lobes were then almost totally removed using a finger-fracture technique. Statistical analyses were made using the Mann-Whitney test for unpaired data and P < 0.05 was accepted as significant.
50
1
RESULTS
General OperativeDetail The described technique proved to be simple and reproducible. The hepatectomies alone were accomplished within 5- 10 min dand the oversewing was done within a further 15-20 min. With consistently tight ligation of the ribbons at the baseof the liver, the blood loss was minimal and if major bleeding occurred, this could be rapidly controlled by tightening of the ribbons. In less than 5% of animals in (c), death occurred rapidly overnight which was attributed to removal of an excessiveamount of liver.
Extent of the Resection To determine the extent of the resections, separate groups of animals were subjected to the various partial hepatectomies as described above. Immediately afterward, the animals were sacrificed and the remnant liver was removed. The resected and remnant lobes were weighed and the size of the hepatectomy was determined. Resection of the left lateral lobe resulted in a 15.51 +- 0.83% (SEM) partial hepatectomy. Removal of the left lateral and middle lobes separately constituted a 50.53 k 1.22% resection. The left lateral and the middle lobes, removed using a single ribbon, constituted 64.68 + 1.19% (SEM). Resection of the left lateral and middle lobes of the liver using a finger-fracture technique resulted in a 70.14 * 1.65% (SEM) partial hepatectomy. Comparison of the 15 or 50% resections with either the 65 or 70% resections showed significant differences (P < 0.00 1). There was not, however, any significant difference between the 65 and 70% resections.
I
0
1
2
3
4
5
DAYS
FIG. 2. Thymidine kinase activity (dpm per mg protein) in the liver after 15, 50, 65, and 70% partial hepatectomy. Results are expressed as means f SEM, and * indicates a significant difference (P < 0.05) from 0 values.
Changesin Thyrnidine Kinase Activity (Fig. 2) Thymidine kinase activity increased slightly after 15% partial hepatectomy but the changes were not significant. Following 50,65, and 70% partial hepatectomy, thymidine kinase activity increased significantly and reached a peak on the third postoperative day. (P < 0.05 compared with preoperative values). Thereafter, the levels of activity decreasedbut were still significantly elevated on the fifth postoperative day (P < 0.05). Thymidine kinase activities on the third day after 50, 65, and 70% partial hepatectomy were 18,342, 32,486, and 41,586 dpm/mg protein, respectively. The differences between the thymidine kinase activity after 50% partial hepatectomy and 65 and 70% partial hepatectomy were significant (P < 0.05) but there was no difference between 65 and 70% partial hepatectomy.
Changesin Mitotic Index (Fig. 3) Mitotic figures were not evident in the liver biopsies taken preoperatively. Similarly,
KAHN ET AL.: LIVER REGENERATION
IN PIGS
179
response was accurately documented using thymidine kinase activity and mitotic activ15. 70%** ity as indices of liver regeneration. In the 3 . present study, the techniques of 15, 50, 65, mo and 70% partial hepatectomy in the pig were described and again the regenerative response was accurately measured using our previous indices of liver regeneration. In this study the regenerative response was influenced by the amount of liver removed at * operation, with the maximum response occurring after 70% partial hepatectomy. Similar results were obtained following 10,30,40, and 68% resection in rats [I] and following i 4 i 5 iJ i 44 and 72% resection in dogs [3]. DAYS Regeneration of the pig liver has been FIG. 3. Mitotic index (mitoses per 1000 cells) in the shown to be as fully predictable as hepatic liver after 15, 50, 65, and 70% partial hepatectomy. Re- regeneration in other animal models. The sults are expressedas means f SEM, * indicates a signifitiming of the response compares favorably cant difference (P < 0.05) from 0 values, and ** indicates with other large animal models. The maxiP < 0.01. mum response in the pig, as in the dog, occurs at 3 days and contrasts with the 24-hr peak in the rat. mitotic figures were not seen in the liver The anatomy of the blood supply and biliary biopsies taken on the second, third, and drainage of the porcine liver [8] is such that the fourth days after 15% partial hepatectomy. right lateral lobe has to be excluded from any The mitotic indices increased significantly form of resection. The infrahepatic inferior after 50, 65, and 70% partial hepatectomy vena cava enters the right lateral lobe and and levels on the third postoperative day would have to be divided if the lobe were rewere 6.5 t 1.5, 10.9 f 1.35, and 13.8 + 3.2 moved. Also the portal vein and bile duct are mitoses per 1000 cells, respectively. At Day intimately related to the right lateral lobe and 3, the significance of all rises was P < 0.01 give off branches to this lobe before supplying and at Days 2, 4, and 5, the significance of or draining the other lobes. Thus if the right the rise as compared with preoperative lateral lobe were resected the portal blood supvalues was P < 0.05. ply and biliary drainage of the remaining lobes would be jeopardized. Partial hepatectomy in DISCUSSION the pig therefore involves resection of the left Liver regeneration has been extensively lateral and middle lobes of the liver. studied in the rat [ 1,2]. Dogs have been used The techniques of 65 and 15%partial hepto a limited extent [ 3-51 and the morphologi- atectomy in the pig proved to be simple and cal changes after partial hepatectomy have reproducible. The animals tolerated the probeen described [ 31.The pig on the other hand cedures well and blood loss was minimal. Arhas seldom been used; a technique of partial terial and venous bleeding was easily conhepatectomy has been described previously trolled with the tape around the base of the but the technique was complicated and lobes, allowing adequate time to oversew the the regenerative response was not docu- cut surface. The porcine liver contains a large mented [7]. amount of fibrous tissue and therefore holds In a previous study from this laboratory, a the sutures well. technique of 50% partial hepatectomy in the The technique of 70% partial hepatectomy pig was described [6] and the regenerative using a finger-fracture method was more dif-
180
JOURNAL OF SURGICAL RESEARCH: VOL. 45, NO. 2, AUGUST 1988
ficult, took longer, and resulted in a greater amount of blood loss. Sixty-five percent partial hepatectomy is the model of choice for most studies of liver regeneration in the pig. There is a significant increase in thymidine kinase activity with the maximum increase occurring on the third postoperative day. There was no significant changes in thymidine kinase activity after 15% partial hepatectomy. This confirms the finding in rats that there is a critical amount of liver which has to be resected before a regenerative responseis initiated [ 11.It is, however, a particularly useful in vivo model for assaying various factors which are thought to stimulate liver regeneration [9]. Unfortunately, because of the small regenerative response after 15% partial hepatectomy, this model cannot be used to assessvarious substances which may inhibit liver regeneration. The use of a large animal model in the study of liver regeneration has certain advantages.Samplesof blood and tissue can be harvested from multiple sites [lo] and the volumes of tissue and blood removed are less limited. More importantly, each animal can be sampled or studied serially [6, 10, II] and thus sequential changes in the regenerative response [6], hormones [lo], blood flow [ 111, etc., in each animal can be assessed.The pig has a further advantage in that it resembles man more closely in its gastrointestinal and endocrine functions and thus results obtained would have added clinical significance. One of the factors limiting the use of large animals has been the previously prohibitive cost of measuring the regenerative response after partial hepatectomy. Thymidine kinase activity has been shown to be an inexpensive index of liver regeneration especially suitable for use in a large animal model and for studying the regenerative response serially [6]. Thus, in summary, the techniques of 15, 50, 65, and 70% partial hepatectomy in the pig are described, and the regenerative response is accurately documented using thymidine kinase activity and mitotic index as indices of liver regeneration.
SUMMARY
The techniques of 15, 50, 65, and 70% partial hepatectomy in the pig have been described and the regenerative response has been characterized using thymidine kinase activity and mitotic index as indices of regeneration. Regeneration of the pig liver has been shown to be as fully predictable as hepatic regeneration in other animal models. The peak regenerative response occurred on the third postoperative day. REFERENCES 1. Bucher, N. L. R. Regeneration of the mammalian liver. Znt. Rev. Cytol. 15: 245, 1963. 2. Bucher, N. L. R., and Malt, R. A. Morphological and biological aspects.In N. L. R. Bucher and R. A. Malt (Eds.), Regeneration ofLiver and Kidney. Boston: Little, Brown, 1971. P. 23. 3. Francavilla, A., Porter, K. A., Benichou, J., Jones, A. F., and Starzl, T. E. Liver regeneration in dogsMorphologic and chemical changes. J. Surg. Res. 25: 409, 1978. 4. Price, J. B., Takeshige, K., Max, M. H., and Voorhees, A. B. Glucagon as the portal factor modifying hepatic regeneration. Surgery 12: 74, 1972. 5. Starzl, T. E., Francavilla, A., Porter, K. A., Benithou, J., and Jones A. F. The effects of splanchnic viscera removal upon canine liver regeneration. Surg. Gynecol. Obstet. 147: 1983, 1978. 6. Kahn, D., Stadler, J., Terblanche, J., and van Hoom-Hickman, R. Thymidine kinase: An inexpensive index of liver regeneration in a large animal model. Gastroenterology 79: 907, 1980. 7. Gallot, D., Gouet, O., Bidallier, M., Coloigner, M., Opolon, P., and Huguet, C. A simplified bloodless procedure for extensive hepatectomy. Experimental study in the pig. Eur. Surg. Rex 8: 236, 1976. 8. Comprodon, R., Solsona, J., Guerrero, J. A., Mendoza, C. G., Segura, J., and Fabregat, J. M. Intrahepatic vascular division in the pig. Basis for partial hepatectomies. Arch. Surg. 112: 38, 1977. 9. Kahn, D., Hickman, R., Terblanche, J., and Kirsch, R. Hepatic stimulator substance in extracts from regenerating porcine liver-Basic physiological properties. Submitted for publication. 10. Kahn, D., van Hoom-Hickman, R., Child, P., and Terblanche, J. Transhepatic changes in insulin and glucagon following partial hepatectomy in the pig: The effect of hypoglycemia. Surg. Gynecol. Obstet. 158: 475, 1984. 1I. Kahn, D., van Hoorn-Hickman, R., and Terblanche, J. Liver blood flow after partial hepatectomy in the pig. J. Surg. Res. 37: 280, 1984.