INT . J . RADIAT . BIOL .,
1977,
VOL .
31,
NO .
5, 459-465
Ribonucleic acid synthesis in regenerating liver of irradiated adrenalectomized rats
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MOSTAFA N . ABDEL-HALIMf Radiobiology Research Laboratory, University of Wisconsin Medical School' Departments of Radiology and Human Oncology, Madison, Wisconsin 53706 , U .S .A . (Received 7 December 1976 ; accepted 18 February 1977)
The effect of whole-body irradiation on RNA synthesis in regenerating and non-growing livers was studied in intact and adrenalectomized rats . The animals were divided into four sub-groups : (1) control ; (2) irradiation only ; (3) partially-hepatectomized ; and (4) irradiated partially-hepatectomized . Newly-synthesized RNA was determined by 30 or 40 min uptake of (6- 14 C) orotic acid . Both nuclear and polyribosomal RNA synthesis in regenerating livers of adrenalectomized rats were depressed below their control levels, regardless of whether irradiation was 2 hours before or 2 hours after partial hepatectomy . Specific radioactivity values of regenerating livers of adrenal intact and adrenalectomized rats were elevated above those of the nongrowing livers from irradiated and unirradiated rats .
1 . Introduction Previous studies have demonstrated that whole-body irradiation increased RNA synthesis and the proportion of heavy polyribosomes in rats with intact livers (Omata, Ichii and Yago 1968, Cammarano, Pons, Chinali and Gaetani 1969, Baeyens, Goutier and Vangheel 1970, Yatvin 1970, Popov, ValevaDimitrova and Hadjiolov 1971, Abdel-Halim and Yatvin 1976) . The increase in liver RNA synthesis of irradiated rats is believed by many to be mainly mediated by the adrenals (Omata et al. 1968, Baeyens et al . 1970, Yatvin 1970, Abdel-Halim and Yatvin 1976), but others have favoured a process that does not involve the adrenals (Cammarano et al. 1969, Popov et al . 1971) . In regenerating rat liver, on the contrary, irradiation reduces both RNA synthesis and the formation of heavy polyribosome aggregates, suggesting that irradiation inhibits the synthesis of new messenger RNA (Uchiyama, Fausto and Van Lancker 1965, Yatvin and Lathrop 1966, Berg and Goutier 1967, Fausto and Van Lancker 1969) . These studies were undertaken mainly on intact rats, but our study was designed to investigate the role of the adrenal glands on RNA synthesis in regenerating liver of adrenalectomized rats in an attempt to elucidate a hormonal mechanism(s) by which ionizing radiation induces its effect on RNA synthesis in regenerating liver . Cortisone acetate was administered to increase survival in partially-hepatectomized adrenalectomized rats . Interference of the exogenous cortisone in RNA synthesis was eliminated by : (1) injecting minimum doses ; (2) the administration schedule t Post-doctoral fellow, NIH Grant CA-05104 . Pharmacology .
Now with the Department of
460
M. N. Abdel-Halim
before killing, where neither plasma and adrenal corticosterone concentration (Eechaute, Demeester and Leusen 1962, Hameed and Haley 1964) nor RNA synthesis (Abdel-Halim and Yatvin 1976) was elevated in non-growing livers of irradiated adrenal intact rats at about 24 hours after irradiation ; and (3) administering it also to control rats .
2.
Materials and methods
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2 .1 . Animals All experiments were performed with rats of the Holtzman strain (Holtzman Co ., Madison, Wisconsin, U .S .A .) weighing 180-200 g. They were kept in a room lighted from 7 a .m . to 7 p .m . and fed standard laboratory chow . The rats were fasted for 20 hours but allowed to drink before being killed by decapitation . The livers were then removed quickly and homogenized, and both total and subcellular fractions (i .e . nuclear, polyribosomal and nonsedimentable) were obtained, as described previously (Abdel-Halim and Yatvin 1976) . 2.2 . Surgical procedures Adrenalectomy was performed, as reported earlier (Abdel-Halim and Yatvin 1976) . Partial hepatectomy was performed by the method of Higgins and Anderson (1931) . 2.3 . Schedule and groups of animals The effect of gamma-radiation administered 2 hours before or 2 hours after partial hepatectomy on RNA synthesis in regenerating liver was studied in intact and adrenalectomized (adx) rats. There were four sub-groups : (1) control, (2) irradiated only, (3) partially-hepatectomized, and (4) irradiated partiallyhepatectomized . Two injections (2 mg/rat) of cortisone acetate (Merck, Sharpe and Dohme, West Point, Pensylvannia, U .S .A .) were administered intrapertioneally (ip) to the adx only sub-groups : the first 12 hours before irradiation and the second 1 hour before partial hepatectomy. 2 .4 . Irradiation The rats were immobilized in a plastic cage and placed 95 cm from the source of a 9000 Ci Picker 60 Co teletherapy unit for a total dose of 1800 rad to the whole body at a dose-rate of 100 rad/min . 2 .5 . Radioactive labelling RNA labelling was achieved by ip injection of 8 µCi/rat (0 . 206 mg) of (6- 14 C) orotic acid (New England Nuclear) 30 or 40 min before they were killed . The pooled livers of three rats were used for each determination and all experiments were repeated at least three times . 2 .6 . Ribonucleic acid determination RNA was determined by the method of Fleck and Munro (1962) .
RNA synthesis in regenerating liver
461
2 .7 . Liquid scintillation counting The incorporation of (6- 14 C) orotic acid into RNA was determined by the liquid scintillation counter . All samples were counted under the same conditions, i .e . 0 . 5 ml of RNA extract in 10 ml of Scintisol counting medium . 2 .8 .
Specific radioactivity calculation The specific radioactivity (SRA) is defined as CPM/O . D . 260nm'
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3.
Results
3 .1 . RNA Synthesis 8 hours after partial hepatectomy Specific radioactivity values of total, nuclear, polyribosomal and nonsedimentable RNA from regenerating livers of irradiated and unirradiated intact and adx rats killed 8 hours after hepatectomy are shown in figure 1 . Irradiation delivered before or after partial hepatectomy resulted in a significant (P 5 0 . 025) decrease in polyribosomal RNA synthesis in regenerating livers of both adrenal intact and adx rats compared with their representative controls . I
STANDARD ERROR
PN
ADRENAL INTACT
PN
ADRENALECTOMIZED
© pH+IRR I ® pH+IRR IRR . PRE-SURGERY
IRR. POST-SURGERY TOTAL
600
400
200 E 3,000
r r 1mol 10 -1 11, .
NUCLEAR
POLYRIBOSOMAL
r
NON-SEDIMENTABLE
r Figure 1 . Mean specific radioactivity (measured as CPM/O .D .2BO nm) of liver RNA determined from adrenal intact and adx rats . Irradiation (1800 rad) was administered either 2 hours before or 2 hours after partial hepatectomy and the animals were killed 8 hours after partial hepatectomy . The radioactive precursor was injected intraperitoneally 30 min before killing .
462
M . N. Abdel-Halim
However, a 55 per cent (P=0 . 005) and 23 per cent (P=0 . 005) decrease in nuclear RNA SRA below the control level were only obtained in the irradiated adx rats before and after hepatectomy, respectively . The SRA of nonsedimentable RNA in regenerating livers of irradiated intact rats was depressed 13 per cent (P=0 . 05) below the control level when the rats were irradiated 2 hours before partial hepatectomy .
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3 .2 . RNA Synthesis 24 hours after partial hepatectomy The SRA's of total RNA in regenerating livers of both irradiated intact and adx rats 24 hours after hepatectomy were similar to their unirradiated partiallyhepatectomized controls (figure 2) . Polyribosomal and non-sedimentable RNA SRA values in regenerating livers from irradiated adx rats were depressed O CONTROL ® pH GM IRR
l STANDARD ERROR
® pH+IRR ADRENAL INTACT
ADRENALECTOMIZED TOTAL
MEN
\\
\~\
Figure 2 . Mean specific radioactivity (measured as CPM/0 .1)' M ur) of liver RNA determined from adrenal intact and adx rats . Irradiation (1800 rad) was administered 2 hours before partial hepatectomy and the rats were killed 24 hours after hepatectomy . The radioactive label was injected 40 min before killing .
72 per cent (P=0 . 005) and 79 per cent (P=0 . 005), respectively, below the unirradiated partially-hepatectomized levels, whereas it remained unchanged in the irradiated adrenal intact rats . The SRA of the RNAs studied in the intact livers of both irradiated adrenal intact and adx rats were below control values .
RNA synthesis in regenerating liver
463
Specific radioactivity values of RNAs in regenerating livers of unirradiated rats were highly increased (PO-005) above those of the intact livers in both irradiated and unirradiated adrenal intact and adx rats (figure 2) .
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4.
Discussion This study revealed that ionizing radiation reduced RNA SRA in the regenerating livers of adx rats irradiated 2 hours before partial hepatectomy, which suggests that ionizing radiation may influence RNA synthesis via the adrenal glands . This conclusion is supported by the fact that normal RNA synthesis in the regenerating livers of irradiated intact rats was unchanged, whereas a significant decrease in RNA SRA was obtained in regenerating livers of irradiated adx rats compared with their unirradiated partially-hepatectomized controls (figures 1 and 2) . Berg and Goutier (1967) reported that both nuclear and cytoplasmic RNA synthesis (25 min pulse-labelling) were reduced in regenerating livers when adrenal rats were irradiated 1 hour before partial hepatectomy and killed 12 hours after hepatectomy, whereas normal nuclear RNA synthesis was resumed 15 hours after partial hepatectomy, but there was still a reduction in cytoplasmic RNA SRA . In our study irradiation resulted in a reduction in the SRA of the polyribosomal RNA . This may result from the sensitivity or the breakdown of the polyribosomes (messenger RNA, ribosome subunits or both) in the cytoplasm . The unchanged nuclear RNA SRA indicates that the nuclear RNA machinery was not injured by gamma-rays . Those factors which interrupted polyribosomal RNA synthesis earlier (8 hours) had apparently disappeared from the cytoplasm in regenerating livers isolated from irradiated rats killed 24 hours after partial hepatectomy where normal RNA synthesis was maintained (figure 2) . This is in contrast to the study of Fausto and Van Lancker (1969) in which they obtained reduction in SRAs of both nuclear and cytoplasmic RNA 24 hours after partial hepatectomy and X-irradiated 6 hours before being killed . The differences in response may be explained by the variation in the experimental conditions . Unlike those of irradiated intact rats, the reduction in polyribosomal SRA in the regenerating livers of the irradiated adx rats was probably a reflection of decreased RNA synthesis in the nucleus . Moreover, RNA SRA was maintained below the control level up to 24 hours after partial hepatectomy . The decrease in RNA synthesis in regenerating livers of irradiated adx rats may be related in part to the absence of the endogenous glucocorticoid induced by ionizing radiation . Interestingly, RNA synthesis was increased in unirradiated partiallyhepatectomized rats with or without the adrenal glands (figure 2) . Chandler and Neuhaus (1968) and Liu and Neuhaus (1968) found that 2 hours after laparotomy and manual manipulation of the liver, RNA synthesis was inhibited by 50 per cent . By 8 hours, it had reached its maximum synthetic level, and they invoked the hypothesis of Drews and Brawerman (1967) of glucocorticoid enhancement of RNA synthesis to explain their results . In the current study, the increase in RNA synthesis in regenerating livers of unirradiated adx rats above the control level suggests a non-glucocorticoid response . This may also suggest that different mechanism(s) on RNA synthesis induces by stress (i .e . laparotomy or partial hepatectomy) on growing and non-growing livers .
464
M. N. Abdel-Halim
The most significant feature of our study was the suggestion that in regenerating liver, ionizing radiation may influence RNA synthesis in part via the adrenal glands, although other factors may control the major bulk of that synthesis . The mechanism(s) by which irradiation acts on RNA synthesis in regenerating livers may differ from that present in non-growing livers . ACKNOWLEDGMENTS
Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
This work was supported in part by Grant CA-08318 from NIH . acknowledge the interest and advice of Drs . R . Durand and M . Yatvin .
I
L'effet de l'irradiation integrale sur la synthese RNA dans les foies regenerateurs et non-regenerateurs a ete etudie dans des rats surrenaux et non-surrenaux . On a divise ces animaux en quatre subdivisions (1) le groupe de controle, (2) ceux qui etaient irradies seulement, (3) ceux qui n'etaient que partiellement hepatises, (4) ceux qui etaient irradies et partiellement hepatises . Le RNA nouvellement synthesise a ete determine par une prise de 1'acide orotique (6- 14C) pendant une trentaine ou une quarantaine de minutes . Les resultats des etudes actuelles indiquent que : (1) les syntheses RNA nucleaires et polyriboniques dans les foies regenerateurs des rats non-surrenaux etaient poussees au-dessous de leurs niveaux etablis, sans se soucier du temps de I'hepatisation, qu'elle soit deux heures avant ou deux heures apres ; (2) des radioactivites specifiques des foies regenerateurs des rats surrenaux et non-surrenaux ont ete elevees au-dessus de celles des foies non-regenerateurs des rats irradies et nonirradies .
Es wurden die Folgen einer Ganzkorperbestrahlung auf die Synthese von Ribonukleinsaure in regenierenden and nicht wachsenden Lebern sowohl bei Ratten mit unversehrten Nebennieren als such bei solchen mit operativ entfernten Nebenieren untersucht . Die Tiere wurden in 4 Untergruppen eingeteilt : (1) Kontrollgruppe, (2) Tiere, die nur bestrahlt wurden, (3) Tiere, denen die Leber teilweise entfernt worden war, and (4) die mit teilweise entfernter Leber bestrahlt wurden . Das Ausmaf3 der RNS-Synthese wurde durch den Einbau von 6-14C- Orotsaure uber 30-40 Min verfolgt . Die Ergebnisse der Untersuchungen zeigen (1) sowohl die nukleare als auch die polyribosomale RNS-Synthese war in regenerierenden Lebern von Ratten mit operativ entfernten Nebennieren niedriger als in der Kontrollgruppe, ohne Unterschied, ob die Bestrahlung 2 Stunden vor oder 2 Stunden nach der partiellen Hepatektomie stattgefunden hatte . (2) die spezifische Aktiviti t von sich neu bildenden Lebern war sowohl bei Ratten mit unversehrten Nebennieren als auch bei solchen mit operativ entfernten Nebenieren uber jene von nicht wachsenden Lebern bei bestrahlten and bei nicht bestrahlten Ratten erhoht .
REFERENCES ABDEL-HALIM, M . N ., and YATVIN, M . B ., 1976, Radiat . Res ., 65, 327 . BAEYENS, W ., GOUTIER, R., and VANGHEEL, V ., 1970, Strahlentherapie, 140, 204 . BERG, T . L ., and GOUTIER, R ., 1967, Archs int . Physiol. Biochim ., 75, 49 . CAMMARANO, P ., PONS, S ., CHINALI, G ., and GAETANI, S ., 1969, Radiat . Res ., 39, 289 . CHANDLER, A . M ., and NEUHAUS, O . W ., 1968, Biochim . biophys . Acta, 166, 186 . DREws, J ., and BRAWERMAN, G ., 1967, Y . biol . Chem ., 242, 801 . EECHAUTE, W ., DEMEESTER, G ., and LEUSEN, 1 ., 1962, Archs int . Pharmacodyn . Ther ., 135,235 .
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Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
FAUSTO, N ., and VAN LANCKER, J . L., 1969, Archs Biochem . Biophys ., 135, 231 . FLECK, A., and MUNRO, H ., 1962, Biochim . biophys . Acta, 55, 571 . HAMEED, J . M . A ., and HALEY, T . J ., 1964, Radiat . Res ., 23, 620 . HIGGINS, G. M ., and ANDERSON, R . M ., 1931, Archs Path ., 12,186 . Liu, A . L ., and NEUHAUS, O . W., 1968, Biochim . biophys. Acta, 166, 195 . OMATA, S ., ICHII, S ., and YAGO, M ., 1968, .7. Biochem., Tokyo, 63, 695 . Popov, P . G ., VALEVA-DIMITROVA, L . I ., and HADJIOLOV, A . A ., 1971, Z . Naturf. B, 26, 1282 . UCHIYAMA, T., FAUSTO, M ., and VAN LANCKER, J . L ., 1965, Archs Biochem . Biophys ., 110, 191 . YATVIN, M . B ., and LATHROP, T . P., 1966, Biochem. biophys . Res . Commun ., 25, 535 . YATVIN, M . B ., 1970, Experientia, 26, 253 .
1977,
VOL .
31,
NO .
5, 459-465
Ribonucleic acid synthesis in regenerating liver of irradiated adrenalectomized rats
Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
MOSTAFA N . ABDEL-HALIMf Radiobiology Research Laboratory, University of Wisconsin Medical School' Departments of Radiology and Human Oncology, Madison, Wisconsin 53706 , U .S .A . (Received 7 December 1976 ; accepted 18 February 1977)
The effect of whole-body irradiation on RNA synthesis in regenerating and non-growing livers was studied in intact and adrenalectomized rats . The animals were divided into four sub-groups : (1) control ; (2) irradiation only ; (3) partially-hepatectomized ; and (4) irradiated partially-hepatectomized . Newly-synthesized RNA was determined by 30 or 40 min uptake of (6- 14 C) orotic acid . Both nuclear and polyribosomal RNA synthesis in regenerating livers of adrenalectomized rats were depressed below their control levels, regardless of whether irradiation was 2 hours before or 2 hours after partial hepatectomy . Specific radioactivity values of regenerating livers of adrenal intact and adrenalectomized rats were elevated above those of the nongrowing livers from irradiated and unirradiated rats .
1 . Introduction Previous studies have demonstrated that whole-body irradiation increased RNA synthesis and the proportion of heavy polyribosomes in rats with intact livers (Omata, Ichii and Yago 1968, Cammarano, Pons, Chinali and Gaetani 1969, Baeyens, Goutier and Vangheel 1970, Yatvin 1970, Popov, ValevaDimitrova and Hadjiolov 1971, Abdel-Halim and Yatvin 1976) . The increase in liver RNA synthesis of irradiated rats is believed by many to be mainly mediated by the adrenals (Omata et al. 1968, Baeyens et al . 1970, Yatvin 1970, Abdel-Halim and Yatvin 1976), but others have favoured a process that does not involve the adrenals (Cammarano et al. 1969, Popov et al . 1971) . In regenerating rat liver, on the contrary, irradiation reduces both RNA synthesis and the formation of heavy polyribosome aggregates, suggesting that irradiation inhibits the synthesis of new messenger RNA (Uchiyama, Fausto and Van Lancker 1965, Yatvin and Lathrop 1966, Berg and Goutier 1967, Fausto and Van Lancker 1969) . These studies were undertaken mainly on intact rats, but our study was designed to investigate the role of the adrenal glands on RNA synthesis in regenerating liver of adrenalectomized rats in an attempt to elucidate a hormonal mechanism(s) by which ionizing radiation induces its effect on RNA synthesis in regenerating liver . Cortisone acetate was administered to increase survival in partially-hepatectomized adrenalectomized rats . Interference of the exogenous cortisone in RNA synthesis was eliminated by : (1) injecting minimum doses ; (2) the administration schedule t Post-doctoral fellow, NIH Grant CA-05104 . Pharmacology .
Now with the Department of
460
M. N. Abdel-Halim
before killing, where neither plasma and adrenal corticosterone concentration (Eechaute, Demeester and Leusen 1962, Hameed and Haley 1964) nor RNA synthesis (Abdel-Halim and Yatvin 1976) was elevated in non-growing livers of irradiated adrenal intact rats at about 24 hours after irradiation ; and (3) administering it also to control rats .
2.
Materials and methods
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2 .1 . Animals All experiments were performed with rats of the Holtzman strain (Holtzman Co ., Madison, Wisconsin, U .S .A .) weighing 180-200 g. They were kept in a room lighted from 7 a .m . to 7 p .m . and fed standard laboratory chow . The rats were fasted for 20 hours but allowed to drink before being killed by decapitation . The livers were then removed quickly and homogenized, and both total and subcellular fractions (i .e . nuclear, polyribosomal and nonsedimentable) were obtained, as described previously (Abdel-Halim and Yatvin 1976) . 2.2 . Surgical procedures Adrenalectomy was performed, as reported earlier (Abdel-Halim and Yatvin 1976) . Partial hepatectomy was performed by the method of Higgins and Anderson (1931) . 2.3 . Schedule and groups of animals The effect of gamma-radiation administered 2 hours before or 2 hours after partial hepatectomy on RNA synthesis in regenerating liver was studied in intact and adrenalectomized (adx) rats. There were four sub-groups : (1) control, (2) irradiated only, (3) partially-hepatectomized, and (4) irradiated partiallyhepatectomized . Two injections (2 mg/rat) of cortisone acetate (Merck, Sharpe and Dohme, West Point, Pensylvannia, U .S .A .) were administered intrapertioneally (ip) to the adx only sub-groups : the first 12 hours before irradiation and the second 1 hour before partial hepatectomy. 2 .4 . Irradiation The rats were immobilized in a plastic cage and placed 95 cm from the source of a 9000 Ci Picker 60 Co teletherapy unit for a total dose of 1800 rad to the whole body at a dose-rate of 100 rad/min . 2 .5 . Radioactive labelling RNA labelling was achieved by ip injection of 8 µCi/rat (0 . 206 mg) of (6- 14 C) orotic acid (New England Nuclear) 30 or 40 min before they were killed . The pooled livers of three rats were used for each determination and all experiments were repeated at least three times . 2 .6 . Ribonucleic acid determination RNA was determined by the method of Fleck and Munro (1962) .
RNA synthesis in regenerating liver
461
2 .7 . Liquid scintillation counting The incorporation of (6- 14 C) orotic acid into RNA was determined by the liquid scintillation counter . All samples were counted under the same conditions, i .e . 0 . 5 ml of RNA extract in 10 ml of Scintisol counting medium . 2 .8 .
Specific radioactivity calculation The specific radioactivity (SRA) is defined as CPM/O . D . 260nm'
Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
3.
Results
3 .1 . RNA Synthesis 8 hours after partial hepatectomy Specific radioactivity values of total, nuclear, polyribosomal and nonsedimentable RNA from regenerating livers of irradiated and unirradiated intact and adx rats killed 8 hours after hepatectomy are shown in figure 1 . Irradiation delivered before or after partial hepatectomy resulted in a significant (P 5 0 . 025) decrease in polyribosomal RNA synthesis in regenerating livers of both adrenal intact and adx rats compared with their representative controls . I
STANDARD ERROR
PN
ADRENAL INTACT
PN
ADRENALECTOMIZED
© pH+IRR I ® pH+IRR IRR . PRE-SURGERY
IRR. POST-SURGERY TOTAL
600
400
200 E 3,000
r r 1mol 10 -1 11, .
NUCLEAR
POLYRIBOSOMAL
r
NON-SEDIMENTABLE
r Figure 1 . Mean specific radioactivity (measured as CPM/O .D .2BO nm) of liver RNA determined from adrenal intact and adx rats . Irradiation (1800 rad) was administered either 2 hours before or 2 hours after partial hepatectomy and the animals were killed 8 hours after partial hepatectomy . The radioactive precursor was injected intraperitoneally 30 min before killing .
462
M . N. Abdel-Halim
However, a 55 per cent (P=0 . 005) and 23 per cent (P=0 . 005) decrease in nuclear RNA SRA below the control level were only obtained in the irradiated adx rats before and after hepatectomy, respectively . The SRA of nonsedimentable RNA in regenerating livers of irradiated intact rats was depressed 13 per cent (P=0 . 05) below the control level when the rats were irradiated 2 hours before partial hepatectomy .
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3 .2 . RNA Synthesis 24 hours after partial hepatectomy The SRA's of total RNA in regenerating livers of both irradiated intact and adx rats 24 hours after hepatectomy were similar to their unirradiated partiallyhepatectomized controls (figure 2) . Polyribosomal and non-sedimentable RNA SRA values in regenerating livers from irradiated adx rats were depressed O CONTROL ® pH GM IRR
l STANDARD ERROR
® pH+IRR ADRENAL INTACT
ADRENALECTOMIZED TOTAL
MEN
\\
\~\
Figure 2 . Mean specific radioactivity (measured as CPM/0 .1)' M ur) of liver RNA determined from adrenal intact and adx rats . Irradiation (1800 rad) was administered 2 hours before partial hepatectomy and the rats were killed 24 hours after hepatectomy . The radioactive label was injected 40 min before killing .
72 per cent (P=0 . 005) and 79 per cent (P=0 . 005), respectively, below the unirradiated partially-hepatectomized levels, whereas it remained unchanged in the irradiated adrenal intact rats . The SRA of the RNAs studied in the intact livers of both irradiated adrenal intact and adx rats were below control values .
RNA synthesis in regenerating liver
463
Specific radioactivity values of RNAs in regenerating livers of unirradiated rats were highly increased (PO-005) above those of the intact livers in both irradiated and unirradiated adrenal intact and adx rats (figure 2) .
Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
4.
Discussion This study revealed that ionizing radiation reduced RNA SRA in the regenerating livers of adx rats irradiated 2 hours before partial hepatectomy, which suggests that ionizing radiation may influence RNA synthesis via the adrenal glands . This conclusion is supported by the fact that normal RNA synthesis in the regenerating livers of irradiated intact rats was unchanged, whereas a significant decrease in RNA SRA was obtained in regenerating livers of irradiated adx rats compared with their unirradiated partially-hepatectomized controls (figures 1 and 2) . Berg and Goutier (1967) reported that both nuclear and cytoplasmic RNA synthesis (25 min pulse-labelling) were reduced in regenerating livers when adrenal rats were irradiated 1 hour before partial hepatectomy and killed 12 hours after hepatectomy, whereas normal nuclear RNA synthesis was resumed 15 hours after partial hepatectomy, but there was still a reduction in cytoplasmic RNA SRA . In our study irradiation resulted in a reduction in the SRA of the polyribosomal RNA . This may result from the sensitivity or the breakdown of the polyribosomes (messenger RNA, ribosome subunits or both) in the cytoplasm . The unchanged nuclear RNA SRA indicates that the nuclear RNA machinery was not injured by gamma-rays . Those factors which interrupted polyribosomal RNA synthesis earlier (8 hours) had apparently disappeared from the cytoplasm in regenerating livers isolated from irradiated rats killed 24 hours after partial hepatectomy where normal RNA synthesis was maintained (figure 2) . This is in contrast to the study of Fausto and Van Lancker (1969) in which they obtained reduction in SRAs of both nuclear and cytoplasmic RNA 24 hours after partial hepatectomy and X-irradiated 6 hours before being killed . The differences in response may be explained by the variation in the experimental conditions . Unlike those of irradiated intact rats, the reduction in polyribosomal SRA in the regenerating livers of the irradiated adx rats was probably a reflection of decreased RNA synthesis in the nucleus . Moreover, RNA SRA was maintained below the control level up to 24 hours after partial hepatectomy . The decrease in RNA synthesis in regenerating livers of irradiated adx rats may be related in part to the absence of the endogenous glucocorticoid induced by ionizing radiation . Interestingly, RNA synthesis was increased in unirradiated partiallyhepatectomized rats with or without the adrenal glands (figure 2) . Chandler and Neuhaus (1968) and Liu and Neuhaus (1968) found that 2 hours after laparotomy and manual manipulation of the liver, RNA synthesis was inhibited by 50 per cent . By 8 hours, it had reached its maximum synthetic level, and they invoked the hypothesis of Drews and Brawerman (1967) of glucocorticoid enhancement of RNA synthesis to explain their results . In the current study, the increase in RNA synthesis in regenerating livers of unirradiated adx rats above the control level suggests a non-glucocorticoid response . This may also suggest that different mechanism(s) on RNA synthesis induces by stress (i .e . laparotomy or partial hepatectomy) on growing and non-growing livers .
464
M. N. Abdel-Halim
The most significant feature of our study was the suggestion that in regenerating liver, ionizing radiation may influence RNA synthesis in part via the adrenal glands, although other factors may control the major bulk of that synthesis . The mechanism(s) by which irradiation acts on RNA synthesis in regenerating livers may differ from that present in non-growing livers . ACKNOWLEDGMENTS
Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 01/20/15 For personal use only.
This work was supported in part by Grant CA-08318 from NIH . acknowledge the interest and advice of Drs . R . Durand and M . Yatvin .
I
L'effet de l'irradiation integrale sur la synthese RNA dans les foies regenerateurs et non-regenerateurs a ete etudie dans des rats surrenaux et non-surrenaux . On a divise ces animaux en quatre subdivisions (1) le groupe de controle, (2) ceux qui etaient irradies seulement, (3) ceux qui n'etaient que partiellement hepatises, (4) ceux qui etaient irradies et partiellement hepatises . Le RNA nouvellement synthesise a ete determine par une prise de 1'acide orotique (6- 14C) pendant une trentaine ou une quarantaine de minutes . Les resultats des etudes actuelles indiquent que : (1) les syntheses RNA nucleaires et polyriboniques dans les foies regenerateurs des rats non-surrenaux etaient poussees au-dessous de leurs niveaux etablis, sans se soucier du temps de I'hepatisation, qu'elle soit deux heures avant ou deux heures apres ; (2) des radioactivites specifiques des foies regenerateurs des rats surrenaux et non-surrenaux ont ete elevees au-dessus de celles des foies non-regenerateurs des rats irradies et nonirradies .
Es wurden die Folgen einer Ganzkorperbestrahlung auf die Synthese von Ribonukleinsaure in regenierenden and nicht wachsenden Lebern sowohl bei Ratten mit unversehrten Nebennieren als such bei solchen mit operativ entfernten Nebenieren untersucht . Die Tiere wurden in 4 Untergruppen eingeteilt : (1) Kontrollgruppe, (2) Tiere, die nur bestrahlt wurden, (3) Tiere, denen die Leber teilweise entfernt worden war, and (4) die mit teilweise entfernter Leber bestrahlt wurden . Das Ausmaf3 der RNS-Synthese wurde durch den Einbau von 6-14C- Orotsaure uber 30-40 Min verfolgt . Die Ergebnisse der Untersuchungen zeigen (1) sowohl die nukleare als auch die polyribosomale RNS-Synthese war in regenerierenden Lebern von Ratten mit operativ entfernten Nebennieren niedriger als in der Kontrollgruppe, ohne Unterschied, ob die Bestrahlung 2 Stunden vor oder 2 Stunden nach der partiellen Hepatektomie stattgefunden hatte . (2) die spezifische Aktiviti t von sich neu bildenden Lebern war sowohl bei Ratten mit unversehrten Nebennieren als auch bei solchen mit operativ entfernten Nebenieren uber jene von nicht wachsenden Lebern bei bestrahlten and bei nicht bestrahlten Ratten erhoht .
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