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Intestinal blood flow and drug absorption from the rat jejunum
Lüe Sciences Vol . ?, Part I, pp . 499-498, 1988. Printed in Great Britain.
Pergamon Press
INTESTINAL BLOOD FLO'.Y AND DRUG ABSORPTION FROM THE RA'P JEJUNUM H . Ochsenfahrt and D. Rinne Pharmakologisches Institut der Universität, 74 Tübingen, ~ilhelmstrasse 56, Germany (Received 4 December 198? ; in final form 19 February 1988) Phe ante :~ti~ial blood flow has recently been shown to influence the absorption of ?lucose (1, 2, 3), tritiated water (4), and water and solutes (5) . The relationship between intestinal blood flow and the absorption of drugs has hardly been studied up to now . Hence, the influence of blood flow changes on the intestinal absorption of antipyrine and salicylic acid was investigated in the rat . These both substances were taken as representatives of basic and acidic drugs . F~;ethods Eiale 'Mistar rats weishing 260 + 23
f
q were anaesthetized with
urethane and heparinized . A suitable jejunal loop was selected (distance from the flexure duodenojejunalie 25 .3 + 6.3 *cm, length of the loop 8 .1 + 1 .3 } em) and ligated at both ends . The loop was peri~uaed with isotonic buffered saline solution (pH 8 or pH 6) containing 0 .5 /uCi/ml of 14 C-labelled antipyrine (specific activity 2 .95 mCi;ml~:) or salicylic acid (specific activity 15 .5 mCi;m :~.:) . The perfusion rate was 0 .1 ml/min . The vein of the loop was cannulated with a small needle and the venous outflow continuo~igly collected and weighed . The drug concentration in w
st3ndar3 deviation 499
494
RAT J&TUNUM
Vol. 7, No. 9
the venous blood was determined by liquid scintillation counting . The absorption rate was calculated from blood concentration and venous outflow. The amount of lost blood was substituted by concomitant blood infusions into the right jugular vein, The blood for these infusions was drawn from other rata immediately before the experiment . For further details see (4, 5) . The experiments consisted of 3 periods of 15 minutee duration with 10 minutee intervals after the first and the second period . The first period began 10 minutee after`atarting the perfusion of the intestinal loop . At the beginning of the intestinal perfusion and during the intervals between the periods the blood flow was adjusted to the desired value by high, low or intermediate infusion rates . The periods were arranged according to the following schemes : Scheme I :1~1at period high blood flow, 2nd period intermediate blood flow, and 3rd period low blood flow ; scheme II : 1st period low, 2nd period intermediate, and 3rd period high blood flow . The results were evaluated by an analysis of variance . tiesulta With antipyrine . (Table 1) we obtained similar results for both schemes : Diminishing the intestinal blood flow by a factor of 9 reduced the absorption rate to about 30 per cent of the maximal value, while the blood concentration of the drug increased by a factor of 3 . Inversely, an increase of blood flow when starting at low values was followed by an increased absorption rate and a decreased blood concentration . The ratio of blood-to-gut concentration was between 0 .06 and 0 .18 . In a control group in which the blood flow was held constant for 1 hour
Vol. 7, No . 9
495
RAT JEJUNUM
TABLE 1 Influence of Intestinal Blood Flow on Blood Concentration and
Absorption Rate of t4 C-labelled Antipyrine (169 .5 nlt/ml) During Jejunal Perfusion with Isotonic Buffered Drug Solution (pH 8) . d r° n I
II
w b ° ~ .°
Blood flow
Drug concentration in venous blood nM/ml
Absorption rate nM/min "g 15 .4 + 0 .6
xN
â,
ml/min " ga
10
1 2 3
1 .46 + U .05b 0 .62 (0 .04) ° 0 .17
10 .7 + 0 .9 20 .7 (0 .8)
1
0 .19 + 0 .04
30 .6 + 0 .8 19 .4 (0 .8) 11 .7 P<0 .01
10
2 3
0 .56 (0 .04) 1 .10
27 .9
P<0 .01 d
12 .8 (0 .6) 5 .0
5 .9 + 0 .6 10 .7 (0 .8) 12 .9
P<0 .01
P<0 .01
TABLE 2 Influence of Intestinal Blood flow on ülood Concentration and Absorption Rate of t4 C-labelled Salicylic Acid (32 .3 nM/ml) During Jejunal Perfusion with Isotonic Buffered Drug Solution (pH 6) . m
ô
w o
°n
I
II
(a) (è) (c) (d)
v
~ .°
~° â â, ml/min " g
Orug concentration in venous blood nA1/ml
Absorption rate nN!/min " g
10
2 .08 + 0 .23
2 .95 + 0 .12 2 .47 (0 .13) 1 .79 P
9 .72 + U .33 3 .46 (0 .28) 1 .52 P
1 .99 + 0 .12 2 .19 (0 .16)
10
1
Blood flow
2 3
1 .43 + 0 .04 0 .65 (0 .03) 0 .21
1
0 .21 + 0 .04
2 3
O .e3 (0 .03) 1 .25
3 .81 (0 .19) 8 .79 P<0 .01
1 .87
P>0 .05
wet tissue standard error based on error variance ataad3rd error based on variance between rata sir;r.ii~ic~tnce level i~or comparison of periods by analysis of v~~riance
RAT JB~TUNUM
d98
Vol. 7, No . 9
no aignifioant change of blood concentration and absorption rate was observed . The absorption of salicylic acid was also influenced by the blood flow although there was a clear difference : A decrease of the blood flow diminished the absorption rate and increased the blood concentration in a manner similar to the experiments with antipyrine, but an increase of the blood flow (scheme II) did not significantly influence the absorption rate . The ratio of the blood-to-gut concentration varied between 0 .05 and 0 .30 . In a control group with constant blood flow a decline of both blood concentration and absorption rate with time could be seen . Discussion The data presented above emphasize the influence of the blood
r
flow on the intestinal absorption, though the correlation seems not to be simple . The theoretical aspects have been discussed elsewhere (6) . Aa expected, the absorption of antipyrine is oloaely related to the blood flow . But for salicylic acid, a significant difference between scheme I and scheme II was found in that a decline of the absorption capacity with time was observed . Similar results were found by studying the absorption of water and solutes from hypo- and isotonic solutions (5) . Acoording to the hypothesis of Brodie (7), 3chanker (8), and Hogben (9) organic substances are mainly absorbed in the undiseociated form . The fact that fairly strong acids such as salicylic acid are absorbed to a considerable extent from the intestine should be due to a virtual pH at the site of absorption which is slightly acidic (pH 5 .3 - 6 .1) and largely independent of the pH of the solution within the intestinal lumen (9) . How-
Vol. 7 No . 9
RAT JEJUNUM
49T
ever, Nogami et al . found a relatively rapid penetration also for the dissociated form of salicylic acid (10) and amidopyrine (11) in an in vitro preparation of the intestine . The delayed absorption of salicylic acid when rising the blood Mow may now be explained by several mechanisms : 1 . Salicylic acid (pKa = 3 .0) is at least in part absorbed in the dissociated form through water-filled pores according to Nogami et al ., and its absorption rate is therefore more or less dependent on water absorption . 2 . A change in blood flow pattern with a decrease of mucosal blood flow (12, 13) in the 3rd period (scheme II) may influence the absorption of salicylic acid indirectly via water ab :~orption or 9irectl,y by diminishing the transport rate . 3 . The ability of t~ :e luninAl cell boundary to maintain a local or virtual pH is reduced as a consequence of inaulficient blood supply
(14) in the first period . A charms of the virtual
pH would not necessarily influence the absorption of the undissociated lipophilic antipyrine because of its very low pKa (= 1 .4) . Summary The correlation between intestinal blood flow and the absorption of antipyrine and salicylic acid way investigated in vivo in the rat jejunum . The absorption rate of the undisaociated lipophilic atitinyrine was closely relKted to the blood flow, while that of the ionised salicylic acid failed to increase when the intestinal blood flow was raised from low to high values . It may be assunPd that this is due to a lack of water absorption or to a charms of the 'virtual' pH at the -~ucosal surface .
498
RAT JEJUNUM
Vol. 7, No. 9
References 1 . V . VARRO, L . CSERNAY, G . BLAHO, and F . SZARVAS, Am . J . dig . Dis . 4,
138 (1964) .
2 . R . A . NELSON and R. J . BEARGIE, Am . J . Phyaiol . ~, 375 (1965) . 3 . J . H . WILLIAMS, Jr ., ~I . MAGER, and E . D . JACOBSON, J . Lab . clin . Med . §~, 853 (1964) . 4 . D . WINKE, Naunyn-Schmiedeberge Arch . Pharmak . exp . Path . ?~, 199 (1966) " 5 . D . WINKE,
(to be published) .
6 . D . WINKE and H . OCHSENFAHRT, J . theoret . Biol . ~, 293 (1967). 7 . H . B . BRODIE and C . A . b1 . HOGBEN, J . Pharm . Pharmac . ~, 345 (1957) . 8 . L . S . SCHANKER, D . J . TOCCO, B . B . BRODIE, and C . A . .N, . HOGHEN, J . Pharmac . exp . Ther . 1~, 81
(1958) .
9 " C . A . 5" . HOGBEN, D . J . TOCCU, B . B . BRODIE, and L . S . SCHANKER, J . Pharmac, exp . Ther . 1~, 275 (1959) " 10 . H . NOGA1~!I and T . KATSIiZAAA, Chem, pharm . Bull ., Tokyo 9, 532 (1961) . 11 . H . NOG6kiI and T . b1ATSU7.A'rYA, Chem . pharm . Bull . , Tokyo 1055 (1962) . 12 . V . VARRO, Internist 7,
250 (1966) .
13 . B . FOLKOW, D . H . LEiNIS, 0 . LUPiDGR~:N, S . fELLA2iDER, and I . ~VALLENTIN, Acta phyeiol . acand . _ , 458 (1964) . 14 . J . W. L . ROBIPISON, J .-C1 . J?:QUIER, J .-P . FI~:L$ER, and V . MIRKOVITCH, J . Burg . ses . ~, 150 (1965) "
Pergamon Press
INTESTINAL BLOOD FLO'.Y AND DRUG ABSORPTION FROM THE RA'P JEJUNUM H . Ochsenfahrt and D. Rinne Pharmakologisches Institut der Universität, 74 Tübingen, ~ilhelmstrasse 56, Germany (Received 4 December 198? ; in final form 19 February 1988) Phe ante :~ti~ial blood flow has recently been shown to influence the absorption of ?lucose (1, 2, 3), tritiated water (4), and water and solutes (5) . The relationship between intestinal blood flow and the absorption of drugs has hardly been studied up to now . Hence, the influence of blood flow changes on the intestinal absorption of antipyrine and salicylic acid was investigated in the rat . These both substances were taken as representatives of basic and acidic drugs . F~;ethods Eiale 'Mistar rats weishing 260 + 23
f
q were anaesthetized with
urethane and heparinized . A suitable jejunal loop was selected (distance from the flexure duodenojejunalie 25 .3 + 6.3 *cm, length of the loop 8 .1 + 1 .3 } em) and ligated at both ends . The loop was peri~uaed with isotonic buffered saline solution (pH 8 or pH 6) containing 0 .5 /uCi/ml of 14 C-labelled antipyrine (specific activity 2 .95 mCi;ml~:) or salicylic acid (specific activity 15 .5 mCi;m :~.:) . The perfusion rate was 0 .1 ml/min . The vein of the loop was cannulated with a small needle and the venous outflow continuo~igly collected and weighed . The drug concentration in w
st3ndar3 deviation 499
494
RAT J&TUNUM
Vol. 7, No. 9
the venous blood was determined by liquid scintillation counting . The absorption rate was calculated from blood concentration and venous outflow. The amount of lost blood was substituted by concomitant blood infusions into the right jugular vein, The blood for these infusions was drawn from other rata immediately before the experiment . For further details see (4, 5) . The experiments consisted of 3 periods of 15 minutee duration with 10 minutee intervals after the first and the second period . The first period began 10 minutee after`atarting the perfusion of the intestinal loop . At the beginning of the intestinal perfusion and during the intervals between the periods the blood flow was adjusted to the desired value by high, low or intermediate infusion rates . The periods were arranged according to the following schemes : Scheme I :1~1at period high blood flow, 2nd period intermediate blood flow, and 3rd period low blood flow ; scheme II : 1st period low, 2nd period intermediate, and 3rd period high blood flow . The results were evaluated by an analysis of variance . tiesulta With antipyrine . (Table 1) we obtained similar results for both schemes : Diminishing the intestinal blood flow by a factor of 9 reduced the absorption rate to about 30 per cent of the maximal value, while the blood concentration of the drug increased by a factor of 3 . Inversely, an increase of blood flow when starting at low values was followed by an increased absorption rate and a decreased blood concentration . The ratio of blood-to-gut concentration was between 0 .06 and 0 .18 . In a control group in which the blood flow was held constant for 1 hour
Vol. 7, No . 9
495
RAT JEJUNUM
TABLE 1 Influence of Intestinal Blood Flow on Blood Concentration and
Absorption Rate of t4 C-labelled Antipyrine (169 .5 nlt/ml) During Jejunal Perfusion with Isotonic Buffered Drug Solution (pH 8) . d r° n I
II
w b ° ~ .°
Blood flow
Drug concentration in venous blood nM/ml
Absorption rate nM/min "g 15 .4 + 0 .6
xN
â,
ml/min " ga
10
1 2 3
1 .46 + U .05b 0 .62 (0 .04) ° 0 .17
10 .7 + 0 .9 20 .7 (0 .8)
1
0 .19 + 0 .04
30 .6 + 0 .8 19 .4 (0 .8) 11 .7 P<0 .01
10
2 3
0 .56 (0 .04) 1 .10
27 .9
P<0 .01 d
12 .8 (0 .6) 5 .0
5 .9 + 0 .6 10 .7 (0 .8) 12 .9
P<0 .01
P<0 .01
TABLE 2 Influence of Intestinal Blood flow on ülood Concentration and Absorption Rate of t4 C-labelled Salicylic Acid (32 .3 nM/ml) During Jejunal Perfusion with Isotonic Buffered Drug Solution (pH 6) . m
ô
w o
°n
I
II
(a) (è) (c) (d)
v
~ .°
~° â â, ml/min " g
Orug concentration in venous blood nA1/ml
Absorption rate nN!/min " g
10
2 .08 + 0 .23
2 .95 + 0 .12 2 .47 (0 .13) 1 .79 P
9 .72 + U .33 3 .46 (0 .28) 1 .52 P
1 .99 + 0 .12 2 .19 (0 .16)
10
1
Blood flow
2 3
1 .43 + 0 .04 0 .65 (0 .03) 0 .21
1
0 .21 + 0 .04
2 3
O .e3 (0 .03) 1 .25
3 .81 (0 .19) 8 .79 P<0 .01
1 .87
P>0 .05
wet tissue standard error based on error variance ataad3rd error based on variance between rata sir;r.ii~ic~tnce level i~or comparison of periods by analysis of v~~riance
RAT JB~TUNUM
d98
Vol. 7, No . 9
no aignifioant change of blood concentration and absorption rate was observed . The absorption of salicylic acid was also influenced by the blood flow although there was a clear difference : A decrease of the blood flow diminished the absorption rate and increased the blood concentration in a manner similar to the experiments with antipyrine, but an increase of the blood flow (scheme II) did not significantly influence the absorption rate . The ratio of the blood-to-gut concentration varied between 0 .05 and 0 .30 . In a control group with constant blood flow a decline of both blood concentration and absorption rate with time could be seen . Discussion The data presented above emphasize the influence of the blood
r
flow on the intestinal absorption, though the correlation seems not to be simple . The theoretical aspects have been discussed elsewhere (6) . Aa expected, the absorption of antipyrine is oloaely related to the blood flow . But for salicylic acid, a significant difference between scheme I and scheme II was found in that a decline of the absorption capacity with time was observed . Similar results were found by studying the absorption of water and solutes from hypo- and isotonic solutions (5) . Acoording to the hypothesis of Brodie (7), 3chanker (8), and Hogben (9) organic substances are mainly absorbed in the undiseociated form . The fact that fairly strong acids such as salicylic acid are absorbed to a considerable extent from the intestine should be due to a virtual pH at the site of absorption which is slightly acidic (pH 5 .3 - 6 .1) and largely independent of the pH of the solution within the intestinal lumen (9) . How-
Vol. 7 No . 9
RAT JEJUNUM
49T
ever, Nogami et al . found a relatively rapid penetration also for the dissociated form of salicylic acid (10) and amidopyrine (11) in an in vitro preparation of the intestine . The delayed absorption of salicylic acid when rising the blood Mow may now be explained by several mechanisms : 1 . Salicylic acid (pKa = 3 .0) is at least in part absorbed in the dissociated form through water-filled pores according to Nogami et al ., and its absorption rate is therefore more or less dependent on water absorption . 2 . A change in blood flow pattern with a decrease of mucosal blood flow (12, 13) in the 3rd period (scheme II) may influence the absorption of salicylic acid indirectly via water ab :~orption or 9irectl,y by diminishing the transport rate . 3 . The ability of t~ :e luninAl cell boundary to maintain a local or virtual pH is reduced as a consequence of inaulficient blood supply
(14) in the first period . A charms of the virtual
pH would not necessarily influence the absorption of the undissociated lipophilic antipyrine because of its very low pKa (= 1 .4) . Summary The correlation between intestinal blood flow and the absorption of antipyrine and salicylic acid way investigated in vivo in the rat jejunum . The absorption rate of the undisaociated lipophilic atitinyrine was closely relKted to the blood flow, while that of the ionised salicylic acid failed to increase when the intestinal blood flow was raised from low to high values . It may be assunPd that this is due to a lack of water absorption or to a charms of the 'virtual' pH at the -~ucosal surface .
498
RAT JEJUNUM
Vol. 7, No. 9
References 1 . V . VARRO, L . CSERNAY, G . BLAHO, and F . SZARVAS, Am . J . dig . Dis . 4,
138 (1964) .
2 . R . A . NELSON and R. J . BEARGIE, Am . J . Phyaiol . ~, 375 (1965) . 3 . J . H . WILLIAMS, Jr ., ~I . MAGER, and E . D . JACOBSON, J . Lab . clin . Med . §~, 853 (1964) . 4 . D . WINKE, Naunyn-Schmiedeberge Arch . Pharmak . exp . Path . ?~, 199 (1966) " 5 . D . WINKE,
(to be published) .
6 . D . WINKE and H . OCHSENFAHRT, J . theoret . Biol . ~, 293 (1967). 7 . H . B . BRODIE and C . A . b1 . HOGBEN, J . Pharm . Pharmac . ~, 345 (1957) . 8 . L . S . SCHANKER, D . J . TOCCO, B . B . BRODIE, and C . A . .N, . HOGHEN, J . Pharmac . exp . Ther . 1~, 81
(1958) .
9 " C . A . 5" . HOGBEN, D . J . TOCCU, B . B . BRODIE, and L . S . SCHANKER, J . Pharmac, exp . Ther . 1~, 275 (1959) " 10 . H . NOGA1~!I and T . KATSIiZAAA, Chem, pharm . Bull ., Tokyo 9, 532 (1961) . 11 . H . NOG6kiI and T . b1ATSU7.A'rYA, Chem . pharm . Bull . , Tokyo 1055 (1962) . 12 . V . VARRO, Internist 7,
250 (1966) .
13 . B . FOLKOW, D . H . LEiNIS, 0 . LUPiDGR~:N, S . fELLA2iDER, and I . ~VALLENTIN, Acta phyeiol . acand . _ , 458 (1964) . 14 . J . W. L . ROBIPISON, J .-C1 . J?:QUIER, J .-P . FI~:L$ER, and V . MIRKOVITCH, J . Burg . ses . ~, 150 (1965) "