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Renal gluconeogenesis in pregnant and non-pregnant sheep
OKO-7
RENAL
GLUCONEOGENESIS NON-PREGNANT ANNE
[)epartment
Abstract-1. 2. Similar
of Physiology.
IN PREGNANT SHEEP
t I X.‘iiO;WOi
-0291
SO? tHtM
AND
FAULKNER
Hannah Research
Institute,
Ayr. KA6 5HL. Scotland
Glucose production was determined in ovine kidney tubules using a variety of precursors. rates of glucose production were observed with tubules isolated from kidneys of fed or
3-day starved sheep. 3. No significant differences in the rates of gluconeogenesis were observed in kidney tubules prepared from late-pregnant or non-pregnant animals. 4. In some instances the rates of gluconeogenesis observed excess of the sum of the rates observed when these precursors
INTRODL’CTION
Ruminants, unlike single-stomached animals, absorb little or no glucose from the gut (Katz & Bergman, 1969; Bergman er ul., 1970: Lindsay, 1970). Therefore they are almost entirely dependent on gluconeogenesis to fulfil their glucose requirements. An adult sheep of approximately 60 kg body weight can synthesisc glucose at the rate of about 5 g/hr (Bergman et al., 1970) some I@-lS’:i, of this being produced by the kidneys (Kaufman & Bergman, 1974). When glucose requirements increase as in pregnancy or lactation, the rate of glucose production increases by-more than two fold (Bergman, 1963; Bergman & Hogue, 1967). Increases in the rate of both hepatic (Bergman et ul.. 1970) and renal (Kaufman & Bergman, 1971; Kaufman & Bergman, 1974) gluconeogenesis are observed at this time i,z vioo. This report describes an investigation into the itl-airro rates of gluconeogenesis in kidney tubules prepared from pregnant and nonpregnant sheep and also from fed and three-day starved sheep in order to determine the mechanisms controlling gluconeogenesis in the kidney. .MATERlALS
AND
METHODS
.~uf~riul~ Chemicals. All enzymes and coenzymes were purchased from the Boehringer Corporation (London) Ltd. (Lewes, U.K.). All other chemicals were obtained from British Drug Houses Ltd. (Pool, Dorset). ,&~imals. The sheep were either Cheviots or FinnDorset crosses and weighed between 5C-80 kg. Animals were killed with a captive bolt humane killer. bled from the neck and the kidneys removed as soon as possible (3-5 min), after death. Pregnant animals were I-3 weeks pre-purtum.
Merids Ovine kidney tubules were prepared by the method previously described for the isolation of rat kidney tubules (Dawson. 1972). Approximately 5 g kidney cortex was used. Isolated tubules were incubated in Krebs Ringer bicarbonate medium, gassed with 95% O2 + 5% CO, (Krebs & Heseleit. 1932) at 37’C in a shaking water bath in the presence of various gluconeogenic precursors. After 1 hr the incubations were terminated by the addition of 50~1 HCIO, (12 M). and the precipitated protein removed by 291 N.(
I
3-4
G
in the presence
of two precursors
was in
were supplied individually.
centrifugation at 2500 x g for 5 min. The supernatant was neutralised with KOH (5 M) and precipitated KC104 removed by centrifugation. The supernatant was assayed for glucose (Slein, 1963) and ATP (Lamprecht & Trautschold, 1963). Aliquots of the tubule preparations were dried to constant weight and the results expressed as pmol/hr/g dry weight. One gram of fresh ovine kidney was equivalent to 0.23 g dry weight. Data are presented as means k standard errors of the mean .Results were compared using the Student’s r-test for unpaired observations. RESL! LTS
Tubules prepared from sheep kidneys were capable of synthesising glucose from a number of precursors (Table 1). Relatively high rates of gIuconeogenesis were obtained with propionate, lactate, glycerol. succitrate and glutamate as substrates, but lower rates were observed when other amino acids were supplied as the glucose precursor. No significant differences were seen in the rates of gluconeogenesis from any of these precursors in tubules prepared from fed nonpregnant, pregnant or starved animals. Incubation of the kidney tubules in the presence of 5 mM glucose demonstrated that no glucose utihsation was occurring during the incubation period which might have led to an underestimation of the gluconeogenic rates. Higher rates of gluconeogenesis were obtained when more than one precursor was supptied during the incubation (Table 2). Incubation of the kidney tubules with glycerol in combination with succinate or L-alanine produced rates of glucose synthesis significantly in excess of the sum of the rates obtained with each substrate individualiy (Table 3). In the rat liver and kidney it has been shown that glycerol metabolism is associated with a decreased cellular ATP content (Burch et ui., 1970). and an increased cytosolic NADH/NAD (Williamson ct ul., 1969). It would seem likely that this is also occurring in the ovine kidney tubules and that the addition of metabolites which reverse this trend stimuiates giuconeogenesis. The ATP content of the ovine kidney tubules was determined after incubation. In the presence of glycerol alone or in combination with lactate. a value of 3.9 + 0.7 (5) pmol/g dry wt. was obtained. This increased significantly (P < 0.05) to 6.15 f 0.75 (5) pmoI/g dry wt. when L-glutamate or succinate were included in the incubations.
292
AWNI Table
1. Renal gluconeogenesis
from individual
Glucose Non-pregnant Precursor
Fed
Propionate Lactate Glycerol Succinate t_-Alanine L-Glutamate L-Glutamine L-Aspartate Glycine
48.8 43.8 57.5 87.9 16.9 51.5 11.0 6.3 1.5
FAI
LKKI K
precursors
production
in pregnant
(pmol/hr/g
Starved
+_ 14.5(5) + 12.2 (5) f 12.4(5) f 21.4(5) +- 3.7 (5) It 15.8 (5) f 3.4(5) i_ 4.2 (5) + 1.0(5)
48.5 49.1 39.5 71.2 17 53.5 13.5
+ 13 (4) * 3.1 (4) k 8.5 (4) k II (4) f 1.5(4) * 20(4) f 5.5 (4) nd. nd.
50.8 43.7 66.3 56.4 16.7 50.1 14.2 9.5 1.9
and non-pregnant
dry wt.) Pregnant Fed + f + + + i i + f
15 (6) 7.6 (6) 13.1 (6) 13.9 (6) 1.3 (6) 4.6 (6) 5.2(6) 6.7 (6) 0.8 (6)
sheep
Starved 41.5 54.5 51.5 55.2 17.1 47.5 13.5
+ 11.2(4) + 17.2 (4) * 7.5 (4) + 27 (4) k 8.5 (4) f 95 (4) * 5 (4) n.d. n.d.
All precursors were supplied at a concentration of 5 ~mol/ml and incubations contained 335 mg dry wt. of tubules. Results are expressed as mean If- SE, with the number of animals given in parentheses. Values are corrected for glucose production in the absence of precursors. Endogenous glucose production was 12.2 i_ 5 htmol/hr/g dry wt n.d. not determined. DISCl:SSION
Total renal production high as 4 mmol,/hr/sheep
output. These values arc comparable to those reported for sheep kidney slices (Krebs & Yoshida, 1963). However. when more than one precursor was available. rates of glucose synthesis in the kidney tubules were comparable to the maximum rates observed in titv. Thus the capacity for maximum glucose synthesis was present in all four groups of animals. In the rat. dietary changes result in changes in the capacity of the kidney to produce glucose irt tdro. Starvation or a low carbohydrate diet resulted in a
case
of glucose in r?co can be as during pregnancy and lacta-
tion (Kaufman & Bergman. 197 1; Kaufman & Bergman. 1974). The rates of glucose synthesis observed in the kidney tubules in tlirro from individual precursors would be inadequate to account for these high rates of gluconeogenesis seen in riro (assuming a weight of 5Og for a sheep’s kidney). Lactate or glycerol would yield
only
1.3 mmol
glucose/hr
for the total
Table 2. Renal gluconeogenesis
Precursors Glycerol Glycerol Glycerol Glycerol Glycerol Glycerol
Succinate Lactate L-Glutamate L-Alanine L-Aspartate Propionate
227 Xl.5 127 96.2 89.3 143
f f + + + +
glu-
from two precursors
Fed + + + + + +
renal
in pregnant
Glucose production Non-pregnant Starved
39(5) 12.7(5) 18(5) 15.1 (5) 9.8 (5) 28.2 (5)
198 71 126 99
F 40 (4) i 13(4) + 18(4) + 20 (4) nd. n.d.
and non-pregnant (pmol/hr;g
dry wt.) Pregnant
Fed 209 90 136 121 86 109
+ + i + + +
sheep
Starved
41 (6) 16(6) 42(6) 31.8(6) 20(6) 42 (6)
183 72 102 111
+ 42 (4) + 12(4) f 15(4) * 13(4) nd. n.d.
All precursors were supplied at a concentration of 5 nmoljml and incubations contained 3-5 mg dry wt. of tubules. Results are expressed as mean f SF., with the number of animals given in parentheses. Values are corrected for glucose production in the absence of precursors. Endogenous glucose production was 12.2 i 5 nmol/hr/g dry wt. n.d. not determined.
Table
3. Comparison
of rates of renal gluconeogenesis incubated separately or together Glucose
production
Substrates incubated together Glycerol Glycerol Glycerol Glycerol Glycerol Glycerol
+ + + + + +
Succinate Lactate L-Glutamate L-Alanine L-Aspartate Propionate
205 80 124 108 87 125
+ + + I + +
18(19) 6.4 (19) 13(19) 10.5(19) 11 (11) 24(11)
from
two
precursors
(nmol/hr/g dry wt.) Sum of substrates incubated separately 123 102 106 72 70 98
+ 18(19)*** + 10(19)* f. 9 (19) + 10(19)** * 9(11) rf: 13(19)
Results from all four groups of animals in Tables I and 2 have been combined. Values are means & SE Values significantly different *P < 0.05. **P -c 0.02. ***P < 0.01.
Renal gluconeogcncsis
two-fold stimulation of gluconeogenesis in kidney slices (Krebs et LI/.. 1963). In the sheep no such changes were observed (Tables I & 2). There was no significant difference in gluconeogenic rates in tubules prepared from kidneys of starved or fed animals. Similar results have been obtained with sheep in ~ico when there was either a small decrease or no change in renal glucose output following a three-day fast (Kaufman & Bergman, 1974). Renal glucose output has been shown to increase by over two fold during pregnancy in the sheep in ho (K,lufman & Bergman. 1974). However. when rates of ghcose synthesis in kidney tubules isolated from latepregnant ewes were compared to those obtained from non-pregnant animals. no significant differences were obtained. Irrespective of the precursor supplied. the rates of gluconeogenesis were similar to the two groups of animals (Tables 1 & 2); the capacity of the cells for gluconeogenesis would appear to be unchanged during late pregnancy. These results suggest that there are no long-term changes within the kidney tubules which could be responsible for the increased rates of renal gluconeogenesis observed in uuo in ewes during late pregnancy. This increase might result from increased substrate availability, increased renal blood flow (Kaufman & Bergman, 19’4) or from transient changes in kidney metabolism possibly effected by hormone action. In the rat an increased requirement for glucose synthesis in r.im as in starvation or diabetes. results in an increased capacity for renal gluconeogenesis in vitro (KI-ebs (‘2trl.. 1963). This report provides evidence that thi\ is not true for the sheep kidney. The ruminant liver also appears to be able to increase its glucose output without major changes in enzyme activity. Baird & Heitzman (1970) found little change in the activities of the gluconeogenic enzymes as a result of lactation in the cow although hcpatic glucose output increases three fold during lactation. These authors (Baird & Heitzman. 1970) have suggested that. in the ruminant liver. key enzymes involved in gluconeogenesis may be less responsive to physiological changes than they are in the rat. In view of the data presented here. this suggestion is also applicable to the ruminant kidney. Thus there appear to be major differences in the mechanisms by which ruminants and nonruminants can regulate the rates of gluconeogenesis in response to changing physiological circumstances.
cortex
il~,k,io,\./c’d~~rl~~‘)lt~ Miss technical
assistance.
H. T.
Kennedy
gave
expert
793
in sheep REFERENCES
BAIHI) G. D. 6i Hi ITZMAN R. J. (1970) Gluconeogcnesis in the cow. The effects of a glucocorticoid on hepatic mtermediary metabolism. Biocl~c~n. J. 116. X65-X74. BI.HGMAN. E. N. (1963) Quantitative aspects ol” glucose metabolism in pregnant and non-pregnant sheep. Am. J. Ph+n/. 204. 147~ 152. BIRGMAN, E. N. & Hoc;~. 1). E. (1967) Glucose turnover and oxidation rates m lactating sheep. .Am. J Phv.sio/. 213. 137X 13X4. BI RGMA~ E. N.. KATZ M. L. & KAI EMAN C. F. (1970) Quantitative aspects of hepatic and portal glucose metabolism and turnover in sheep. A~u. J. Ph~~srol. 219. 7x5 793. BI,K(.H H. B.. LOWKY 0. H., MIINHAKI)T L.. MAX P. & CH\~.LK. (1970) Effect of fructose. dlhydroxyacetone. glycerol and glucose on metabolites and related compounds in liver and kidney. J. hiol. Clam. 245. 2092m2102. D~wsoh A. G. (1972) Preparation and some properties of a suspension of fragmental tubules from rat ktdney. Bio&VU. J. 130. 525 532. KATZ M. L. & BIKC;MA\ E. N. (1969) Hcpatic and portal metabolism of glucose. free fatty acids and ketone bodies in the sheep. A,n. J. Physiol. 216. 953 960. KAL’FMAN C. F. & BIKGMAN E. N. (1971) Renal glucose. free fatty acid. and ketone body metabolism in the unanaesthetized sheep. Am. J. Physiol. 221, 967-972. KAI!~MAN C. F. & BI KGMAi%E. N. (1974) Renal ketone body metabolism and gluconeogenesis in normal and hypoglycemic sheep. Am. J. Phtwol. 226. X27-X32. KKI HSH. A. & H~xsr LI 1~ K. (1932) I!rea formatlon in the animal body. Z. Phytiol. C‘hm. 210. 33 -66. KIWIIIS H. A. 6i YOSHILM T. (1963) Renal gluconeogsnesis. 2. The gluconeogenlc capacity of the kidney cortex of various species. H/o~/uv?I. J. 89, 39X 400. KKI HS H. A.. BI Nhl TT D. A. H.. Ill ‘iAS()lII T P.. c;ASC’OYUl T. & YOSHIUA T. (1963) Renal gluconeogcncsls. The effect of diet on the gluconeogemc capacity of ratkidney-cortex slices. Biochem. J. 86, 22 27. LAMPRECHT W. & TRAUTSCHOLD I. (1963) ‘Determination of ATP with hexokinase and glucose 6-phosphate dehydrogenase’ in Methods of Enzymatic Analysis (Edited by Bergmeyer). p. 543. Academic Press. New York. LINDSAY D. B. (1970) ‘Carbohydrate metabolism in ruminants’ in Physiology of Diyestion and Mefuhol~sm in the Ruminant (edited by Phillipson), pp. 438-451. Oriel Press Ltd, Newcastle upon Tyne. SLElN M. W. (1965) ‘D-Glucose determination with hexokinase and glucose 6-phosphate dehydrogenase’ In .Merhods of EnzymaticAnalysis (Edited by Bergmeyer). p. 117. Academic Press, New York. WILLIAMSON D. H.. Vt~oso D.. ELLINGTOU E. V. & KREBS H. A. 11969) Changes in the concentration of hepatic mctabolites on administration of dihydroxyacctone or glycerol to starved rats and their relationship to the control of ketogenesis. Biochc~~. J. 114. S75 584.
RENAL
GLUCONEOGENESIS NON-PREGNANT ANNE
[)epartment
Abstract-1. 2. Similar
of Physiology.
IN PREGNANT SHEEP
t I X.‘iiO;WOi
-0291
SO? tHtM
AND
FAULKNER
Hannah Research
Institute,
Ayr. KA6 5HL. Scotland
Glucose production was determined in ovine kidney tubules using a variety of precursors. rates of glucose production were observed with tubules isolated from kidneys of fed or
3-day starved sheep. 3. No significant differences in the rates of gluconeogenesis were observed in kidney tubules prepared from late-pregnant or non-pregnant animals. 4. In some instances the rates of gluconeogenesis observed excess of the sum of the rates observed when these precursors
INTRODL’CTION
Ruminants, unlike single-stomached animals, absorb little or no glucose from the gut (Katz & Bergman, 1969; Bergman er ul., 1970: Lindsay, 1970). Therefore they are almost entirely dependent on gluconeogenesis to fulfil their glucose requirements. An adult sheep of approximately 60 kg body weight can synthesisc glucose at the rate of about 5 g/hr (Bergman et al., 1970) some I@-lS’:i, of this being produced by the kidneys (Kaufman & Bergman, 1974). When glucose requirements increase as in pregnancy or lactation, the rate of glucose production increases by-more than two fold (Bergman, 1963; Bergman & Hogue, 1967). Increases in the rate of both hepatic (Bergman et ul.. 1970) and renal (Kaufman & Bergman, 1971; Kaufman & Bergman, 1974) gluconeogenesis are observed at this time i,z vioo. This report describes an investigation into the itl-airro rates of gluconeogenesis in kidney tubules prepared from pregnant and nonpregnant sheep and also from fed and three-day starved sheep in order to determine the mechanisms controlling gluconeogenesis in the kidney. .MATERlALS
AND
METHODS
.~uf~riul~ Chemicals. All enzymes and coenzymes were purchased from the Boehringer Corporation (London) Ltd. (Lewes, U.K.). All other chemicals were obtained from British Drug Houses Ltd. (Pool, Dorset). ,&~imals. The sheep were either Cheviots or FinnDorset crosses and weighed between 5C-80 kg. Animals were killed with a captive bolt humane killer. bled from the neck and the kidneys removed as soon as possible (3-5 min), after death. Pregnant animals were I-3 weeks pre-purtum.
Merids Ovine kidney tubules were prepared by the method previously described for the isolation of rat kidney tubules (Dawson. 1972). Approximately 5 g kidney cortex was used. Isolated tubules were incubated in Krebs Ringer bicarbonate medium, gassed with 95% O2 + 5% CO, (Krebs & Heseleit. 1932) at 37’C in a shaking water bath in the presence of various gluconeogenic precursors. After 1 hr the incubations were terminated by the addition of 50~1 HCIO, (12 M). and the precipitated protein removed by 291 N.(
I
3-4
G
in the presence
of two precursors
was in
were supplied individually.
centrifugation at 2500 x g for 5 min. The supernatant was neutralised with KOH (5 M) and precipitated KC104 removed by centrifugation. The supernatant was assayed for glucose (Slein, 1963) and ATP (Lamprecht & Trautschold, 1963). Aliquots of the tubule preparations were dried to constant weight and the results expressed as pmol/hr/g dry weight. One gram of fresh ovine kidney was equivalent to 0.23 g dry weight. Data are presented as means k standard errors of the mean .Results were compared using the Student’s r-test for unpaired observations. RESL! LTS
Tubules prepared from sheep kidneys were capable of synthesising glucose from a number of precursors (Table 1). Relatively high rates of gIuconeogenesis were obtained with propionate, lactate, glycerol. succitrate and glutamate as substrates, but lower rates were observed when other amino acids were supplied as the glucose precursor. No significant differences were seen in the rates of gluconeogenesis from any of these precursors in tubules prepared from fed nonpregnant, pregnant or starved animals. Incubation of the kidney tubules in the presence of 5 mM glucose demonstrated that no glucose utihsation was occurring during the incubation period which might have led to an underestimation of the gluconeogenic rates. Higher rates of gluconeogenesis were obtained when more than one precursor was supptied during the incubation (Table 2). Incubation of the kidney tubules with glycerol in combination with succinate or L-alanine produced rates of glucose synthesis significantly in excess of the sum of the rates obtained with each substrate individualiy (Table 3). In the rat liver and kidney it has been shown that glycerol metabolism is associated with a decreased cellular ATP content (Burch et ui., 1970). and an increased cytosolic NADH/NAD (Williamson ct ul., 1969). It would seem likely that this is also occurring in the ovine kidney tubules and that the addition of metabolites which reverse this trend stimuiates giuconeogenesis. The ATP content of the ovine kidney tubules was determined after incubation. In the presence of glycerol alone or in combination with lactate. a value of 3.9 + 0.7 (5) pmol/g dry wt. was obtained. This increased significantly (P < 0.05) to 6.15 f 0.75 (5) pmoI/g dry wt. when L-glutamate or succinate were included in the incubations.
292
AWNI Table
1. Renal gluconeogenesis
from individual
Glucose Non-pregnant Precursor
Fed
Propionate Lactate Glycerol Succinate t_-Alanine L-Glutamate L-Glutamine L-Aspartate Glycine
48.8 43.8 57.5 87.9 16.9 51.5 11.0 6.3 1.5
FAI
LKKI K
precursors
production
in pregnant
(pmol/hr/g
Starved
+_ 14.5(5) + 12.2 (5) f 12.4(5) f 21.4(5) +- 3.7 (5) It 15.8 (5) f 3.4(5) i_ 4.2 (5) + 1.0(5)
48.5 49.1 39.5 71.2 17 53.5 13.5
+ 13 (4) * 3.1 (4) k 8.5 (4) k II (4) f 1.5(4) * 20(4) f 5.5 (4) nd. nd.
50.8 43.7 66.3 56.4 16.7 50.1 14.2 9.5 1.9
and non-pregnant
dry wt.) Pregnant Fed + f + + + i i + f
15 (6) 7.6 (6) 13.1 (6) 13.9 (6) 1.3 (6) 4.6 (6) 5.2(6) 6.7 (6) 0.8 (6)
sheep
Starved 41.5 54.5 51.5 55.2 17.1 47.5 13.5
+ 11.2(4) + 17.2 (4) * 7.5 (4) + 27 (4) k 8.5 (4) f 95 (4) * 5 (4) n.d. n.d.
All precursors were supplied at a concentration of 5 ~mol/ml and incubations contained 335 mg dry wt. of tubules. Results are expressed as mean If- SE, with the number of animals given in parentheses. Values are corrected for glucose production in the absence of precursors. Endogenous glucose production was 12.2 i_ 5 htmol/hr/g dry wt n.d. not determined. DISCl:SSION
Total renal production high as 4 mmol,/hr/sheep
output. These values arc comparable to those reported for sheep kidney slices (Krebs & Yoshida, 1963). However. when more than one precursor was available. rates of glucose synthesis in the kidney tubules were comparable to the maximum rates observed in titv. Thus the capacity for maximum glucose synthesis was present in all four groups of animals. In the rat. dietary changes result in changes in the capacity of the kidney to produce glucose irt tdro. Starvation or a low carbohydrate diet resulted in a
case
of glucose in r?co can be as during pregnancy and lacta-
tion (Kaufman & Bergman. 197 1; Kaufman & Bergman. 1974). The rates of glucose synthesis observed in the kidney tubules in tlirro from individual precursors would be inadequate to account for these high rates of gluconeogenesis seen in riro (assuming a weight of 5Og for a sheep’s kidney). Lactate or glycerol would yield
only
1.3 mmol
glucose/hr
for the total
Table 2. Renal gluconeogenesis
Precursors Glycerol Glycerol Glycerol Glycerol Glycerol Glycerol
Succinate Lactate L-Glutamate L-Alanine L-Aspartate Propionate
227 Xl.5 127 96.2 89.3 143
f f + + + +
glu-
from two precursors
Fed + + + + + +
renal
in pregnant
Glucose production Non-pregnant Starved
39(5) 12.7(5) 18(5) 15.1 (5) 9.8 (5) 28.2 (5)
198 71 126 99
F 40 (4) i 13(4) + 18(4) + 20 (4) nd. n.d.
and non-pregnant (pmol/hr;g
dry wt.) Pregnant
Fed 209 90 136 121 86 109
+ + i + + +
sheep
Starved
41 (6) 16(6) 42(6) 31.8(6) 20(6) 42 (6)
183 72 102 111
+ 42 (4) + 12(4) f 15(4) * 13(4) nd. n.d.
All precursors were supplied at a concentration of 5 nmoljml and incubations contained 3-5 mg dry wt. of tubules. Results are expressed as mean f SF., with the number of animals given in parentheses. Values are corrected for glucose production in the absence of precursors. Endogenous glucose production was 12.2 i 5 nmol/hr/g dry wt. n.d. not determined.
Table
3. Comparison
of rates of renal gluconeogenesis incubated separately or together Glucose
production
Substrates incubated together Glycerol Glycerol Glycerol Glycerol Glycerol Glycerol
+ + + + + +
Succinate Lactate L-Glutamate L-Alanine L-Aspartate Propionate
205 80 124 108 87 125
+ + + I + +
18(19) 6.4 (19) 13(19) 10.5(19) 11 (11) 24(11)
from
two
precursors
(nmol/hr/g dry wt.) Sum of substrates incubated separately 123 102 106 72 70 98
+ 18(19)*** + 10(19)* f. 9 (19) + 10(19)** * 9(11) rf: 13(19)
Results from all four groups of animals in Tables I and 2 have been combined. Values are means & SE Values significantly different *P < 0.05. **P -c 0.02. ***P < 0.01.
Renal gluconeogcncsis
two-fold stimulation of gluconeogenesis in kidney slices (Krebs et LI/.. 1963). In the sheep no such changes were observed (Tables I & 2). There was no significant difference in gluconeogenic rates in tubules prepared from kidneys of starved or fed animals. Similar results have been obtained with sheep in ~ico when there was either a small decrease or no change in renal glucose output following a three-day fast (Kaufman & Bergman, 1974). Renal glucose output has been shown to increase by over two fold during pregnancy in the sheep in ho (K,lufman & Bergman. 1974). However. when rates of ghcose synthesis in kidney tubules isolated from latepregnant ewes were compared to those obtained from non-pregnant animals. no significant differences were obtained. Irrespective of the precursor supplied. the rates of gluconeogenesis were similar to the two groups of animals (Tables 1 & 2); the capacity of the cells for gluconeogenesis would appear to be unchanged during late pregnancy. These results suggest that there are no long-term changes within the kidney tubules which could be responsible for the increased rates of renal gluconeogenesis observed in uuo in ewes during late pregnancy. This increase might result from increased substrate availability, increased renal blood flow (Kaufman & Bergman, 19’4) or from transient changes in kidney metabolism possibly effected by hormone action. In the rat an increased requirement for glucose synthesis in r.im as in starvation or diabetes. results in an increased capacity for renal gluconeogenesis in vitro (KI-ebs (‘2trl.. 1963). This report provides evidence that thi\ is not true for the sheep kidney. The ruminant liver also appears to be able to increase its glucose output without major changes in enzyme activity. Baird & Heitzman (1970) found little change in the activities of the gluconeogenic enzymes as a result of lactation in the cow although hcpatic glucose output increases three fold during lactation. These authors (Baird & Heitzman. 1970) have suggested that. in the ruminant liver. key enzymes involved in gluconeogenesis may be less responsive to physiological changes than they are in the rat. In view of the data presented here. this suggestion is also applicable to the ruminant kidney. Thus there appear to be major differences in the mechanisms by which ruminants and nonruminants can regulate the rates of gluconeogenesis in response to changing physiological circumstances.
cortex
il~,k,io,\./c’d~~rl~~‘)lt~ Miss technical
assistance.
H. T.
Kennedy
gave
expert
793
in sheep REFERENCES
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