Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen F. CBCEANI, E. WHITE,E. BODACH, AND P. M. QLLEY Research Institute, The Hospital for Sick Children, Toronto, O~zt.,Canuda 1F156' 1x8
Received January 8, 1979 COCEANI, F., WIIITE,E., BODAGH, E., and OLLEY,P. M. 1979. Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen. Can. J. Physiol. Pharmacol. 57, 825-83 1 . Circular strips of ductus arteriosus from larnbs of gestational age between 90 and 144 days (term 147 days) were studied in vitro at low (8-1 6 torr (1 torr = 133.322 Pa)) and high (426-622 torr) Po,. Potassium- and oxygen-induced contractions increased with the gestational age and attained a maximum at term. At low Po,, ibuprofen, a blocker of prostaglandin synthesis,produced a dose-dependent contraction of the ductus at all ages and enhanced the potassiuminduced contraction of the immature ductus (90-124 days). Both effects were relatively greater in the 103- to 107-day gestational group. At that age, ibuprofen also potentiated the oxygeninduced contraction. These findings, while confirming that a prostaglandin is involved in ductus patency, indicate that the prostaglandin-relaxing mechanism becomes functional at an early stage of gestation and reaches maximal activity before term. The existence of an active, prostaglandin-mediated relaxation in the preterm ductus may account, in part, for the reduced responsiveness of the vessel to oxygen. It is confirmed that ibuprofen and other nonsteroidal antiinflammatory drugs are well suited for the management of the premature infant with patent ductus arteriosus. COCEANI, F., WHITE,E.: BODACH, E., et OLLEY,P. M. 1979. Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen. Can. 9. Physiol. Pharmacol. 57, 825-831. Des bandes circulaires de canal artkriel d'agneaux durant leur gestation 2gks entre 90 et 144 jours (terme a 147 jours) ont kt6 ktudiees in vitro 2 Po, basse (8-16 torr (1 torr = 133.322 Pa)) et i?i Po, ClevCe (426-622 torr). kes contractions induites par le potassium et l'oxygkne augmentent avec 1'8ge de la gestation et atteignent un maximum $I terme. A Po, faible, l'ibuprofkne, un bloqueur de la synthese de la prostaglandine, produit a tous les iiges une contraction du canal qui est dose-dependante et accentue la contraction de canaux immatures (90-124 jours), induite par du potassium. Ces deux effets sont relativement plus importants dans le groupe dont la gestation varie entre 103 et 107 jours. A cet Zige, l'ibuproftne potentiallse kgalement la contraction induite par de l'oxygtne. Ces rksultats, tout en confirmant qu9une prostaglandine est impliquke dans 190uverture du canal, indiquent que le mitcai~ismede relsiehement i?i la prostaglandine devieilt fonctionnel t6t durant la gestation et qu'il atteint une activit6 maximale avant 1e terme. L'existence d'un relkhement actif du canal, mkdik par la prostaglandine, peut en partie compter dans la reduction de la reponse des vaisseaux ii l'oxygtne. I1 est confirm6 que 1 ibuproftne ainsi que d'autres drogues anti-inflammatoires non-stkroidales conviennet bien dans la prise de soin d'enfants prkmatures ayant un canal artCriel persistant. [Traduit par le journal]
Introduction It is now thought that a PC maintains patency of the ductus arteriosus in the fetus (cf. Coceani, Olley et al. 1978). This concept is supported by experiments which show that blockers of PG synthesis, such as eicosa-5,8,11,14-tetraynoicacid and nonsteroidal antiinflammatory compounds, contract the vessel in viiro (Coceani et al. 1975) and in vivo (Sharpe et al. 1974; Olley cr ul. 1975; Sharpe et al. 1975; Iieymann and Rudolph 1976). Most of this work, however, has been performed in animals at term and the time course of the development of this PG-relaxing mechanism is unknown. ABBREVIATION: PG, prostaglandin(s) .
Sharpe et ul. (1974, 1975) reported that indon~ethacin,although it is a potenthuctus constrictor in fetal rats at term, has no effect on the 18-day-old fetus, which implies a late development of PG function. Their data, however, are in apparent contrast with results of clinical trials in which indametkacin or acetylsalicylic acid have been used successfully to close a patent ductus in premature infants (Friedman et ul. 1976; Iieymann et al. 1976). In fact, closure of the ductus could be obtained in infzints as young as 24 weeks gestation (Heymann and Rudolph 1978). To resolve this inconsistency and gather some insight into the significance of PG in the control of muscle tone in the developing ductus, ibuprofen, a blocker of P G syilthesis lower 1974), was tested on
0008-4212/79/080825-07$01.00/0 1979 National Research Council of Canada jConseil national de recherches du Canada
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
826
CAN. J. PHYSIOL. PHARMACOL. VBL. 57, 1979
isolated ductal preparations from lambs ranging in gestation age from 90 days onwards. Ibuprofen was used even though it is less activc than other blockers, specifi cal by indornetkacin (Flower 1974). because it has low toxicity (Davies and Avery 1971) and may, therefore, prove useful therapeutically. It was found that this compound cor~tractsthe diactus at all ages suggesting that the PC2 ~nechanisr~n resporssible for patency becomes f~ancticpa~al early in gestation. A prelin~inaryaccount of this work has alrsady appeared (OJley et a/. 1976). %faterialsand h4etlaods Experiments were performed with pregnant ewes (Suffolk, Suffolk-Dorset, Sutfolk-Rambley) of known breeding dates. Fetuses were subdivided into four groups depending on thcir gestational age, viz., 90-97, 103-107, 119-1 24, and 156-144 days (term is 147 days). Circular strips of the ductus arteriosus were prepared as described previously (Coceani, Hishai ei sat!. 1978) and were mounted in individual organ baths between a stationary glass rod and an isometric tension transducer (Grass FT.OJC). The transducer was coupled with a Grass jsolygraph. While lambs froraz 119 days gestation onwards yielded two strips per ductus, only one strip was obtained from each of the younger animals. In the latter case, strips comprised the n~~idportion of the ductus or, somesilnes, virtually the whole ductus. Except for being thinner, however, immature preparations c h i not dif1c:r greatly in their width and length from mature preparations. Strips were stretcined to a passive tension of 1 g (90-97 days gestation) or 1.5 g (103 days gestation to term). Preparatioiss were perfused with Krebs-Henseleit solution (NaCl, 118; KCI, 4.7; CaC12, 2.5; K H 2 P 0 4 , 1 ; MgSQ,, 0.9 ; dextrose, 1 1.1 : NaHCQa, 25 n~anol:/L)equilibrated at 37'C with 55.1 C 0 2 in nitrogen or oxygen. To allow rapid changes in the Po,, the naediunz was preequilibrated with the appropriate gas mixture and then gassed again inside the organ bath. Po, was measured in samples of bath fluid with an Instrulnentation Laboratory gas analyzer and was 8-16 and 426-462 torr (1 torr 133.322 Pa), respectively, with the 95'8; N, - 5j; CO- and 955; O 2- 5':; COz gas mixtrrres. A solution with excess potassium (55 anhi') was prepared by replacing the NaCl with an equinaolar amount of KC1. Recordings were made under standard artificial illumination except in a Sew experiments with the 103- to 107-day gestational age group and the tern1 group where the organ bath was wrapped with black cardboard aiad the room was kept in near complete darkness. Dark-adapted preparations were used t o rule out an inhibitory effect of light on contractile responses of ductal muscle and specifically on the response to oxygen (cf. CIyn~anand Ru~lc~lph 1978). The occurrence of this astifactual factor evould have precluded any conclusion on the maturation of oxygen sensitivity,. Ibuprofe~a(CJ~?.john)was dissolved in continuously stirred warm (about 5BBc'C) Krebs rnecliunl. The final concentration was 4.8 )< !M anci this solution was diluted as recluired by the experinlental protocol. 'I'wo procedures were used for testing ilsuprofe~~ on the immature ductus (90- to 124-days gestation). In some experiinents (procedure 1): tissues were first equilibrated ira normal rrmediuin at %owPo, until a steady tension was developed ancl were then exposed to increasing drug c~ncenltrations (maxirntlra~ 4.8 X 1W4M). Once the tension developed at each dose of ibuprofen had been recoraied, the medium was gassed with 5',4 C 0 2 in oxygen and thc
-
ensuing contraction was measured. Alternatively (procedure 2), tissues were allowed to stabili~eat a low and then a high Po, in the ahencc of ibuprofen, and finally at a high Po, in tine presence of a rnaxitnal dose of ibuprofen. Only the former test procedure was uscd with the term ductus because control values for the oxygen response were obtained in a separate series of experiments (Cocear-ai,Bishai o r ~ 1 f . 1978). Witin either procedure, the contractile response of tissues t o excess potassium was measrared immediately after equilibration at low Po,. Excess potassium was sotnetimes retested on ibuprofentreated (4.8 X l W 4 :W) tissues at low Po,. Strips frcsnn the sanw ductiis were subjected t o identical tests. standard error. Each Data are expressed as the mean naean is based on the number of individual values given and is derived ikon1 2 to 19 separate experimem~ts.Statistical comparisons of two means have been madc using Student's f test. Multiple comparisons have been made with an analysis of variance and IBuncan9smultiple range test (Kramer 1956).
+
Results
Response to Oxygen a d Putcrs\ilan Under rsormal room illumination, ductal strips fro111 all animals began to contract after being mounted in Krcbs medium preeq~lilibrated with 95'& N 2 - 5C';1 C:O2 (Pa,:,8-1 6 torr). 'I-his contraction was slow and, with any age group. rsquired 1-4 11 to reach a maximurn. Maximal tensiorn output, howcver, was greater in ternn than in preterm animals (Figs. 1 and 2). kikcwise, eflects of oxygen (Po2 326-662 torr) and excess potassium were age related (Figs. 1 and 2), the contractile tensiors dcvcloped at the 90-to 107day gestational age being approximately one-third of that at term. Besides being weaker. the response of the immature ductus to oxygsn was at times discontinuous and consisted of two or three ccsit~secutive contractions sf increasirsg strength. linnrnat~ircpreparations (103-107 days gestational gsoaap) kept in the dark developed greater tension than those exposed to light both in the absence and the presence of excess potassiunl at low P O 2 . By contrast, in mature preparations the absence of light had no etyect on the potassiunl response and caused only little increase of the tension output at low Po,. 'Thc oxygen-induccd comtracticm exhibited a difkrent ~Pependence011 soon1 illumination. While the contraction of rhe immature ductus showed no obvious change with room illumination, the contraction of the snat~areductus was smaller in the dark than in the light. This notwithstanding, in the dark as in the Bight mature and immature ductuses differed in their response to high 4'02. Tablc 1 sun~marizesthe findings with dark- vs. light-adapted preparations. E'ec t 0f' Iisuprqftm Ibuprofen contracted the hypoxie ductus at all stages of gestation (Figs. I and 2). Its threshold concentration was around 18-" M and responses were
827
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
COCEANI ET AL.
FETAL AGE (days)
FIG.1. Isolated ductus arteriosus from Iambs at difyerent stages of gestation. Muscle tension at low (A) and high (M) Po, and potassi~rrn-inducedcontractioll at low Po, ( C ) before (open colun~n) and after (solid colurnm) treahmerat with ibuprofen (4.8 X 1V.f) ira nornizrl rocptml illumination. Hn those instances where the oxygen response was discontinuous (see text), values apply to maximal tension output. Values are nleans i SE for the nuntber of preparations given on top of each column and are corrected for the tcnsion applied at the start of the experiment.
dose-related over a range ~ a pto 4.8 X 1Qd4 1W (Fig. 3). At a n j dose, ibuprofen contraction began after a few nainutes delay and progressed slowly to a stable platea~a.The time to peak s7as quite variable and ranged between 23 and 116 miw. Maximnal tension output following ibuprofen increascd with advancing gestation; however, the increase of tension over control values was relatively greater with the 103- to 107-day gestational group. TABLE 2 . Tension output
(9f
103-107
Light
On Off
These results demonstrate that ibuprofen contracts the fetal lamb ductus throtaghsut the last third of gestation implying an early development of the FG n~echanisrnresponsible for paterncy. Zw fact, judging
dark- vs. light-adapted preparations of lamb ductus arterissus 95''l;
Gestation age , days
With the exception of ductuses a t 103-107 days gestation ibuprofen failed to enhance the oxygeninduced contraction (Figs. 1 and 2). At that age, the oxygen response, which is normally little developed, increascd on the average twofold. The time course of ibuprofen contraction at a higir Poz resembled that observed a t low P o 2 . Whether or not increased in magt~ituide,however, the oxygen response following ibuprofen diRered from controls. As shown in Fig. 4, ibuprofen-treated tissues relaxed before contracting upon transfer from a low to a high oxygen elsvirsnment. Maximal loss of tension ranged between 0.2 and 0.9 g, and w7as c~ccasionallygreater (nnaximum 2 g). Oxygen-induced relaxation occurred in all but one preparatioia from 119 days gestation onwards and in about 6076 crf the younger preparations. When present, however, this response showed no c~lavlious change in magnitude with the age of the animal. The contractile response ofthe immature ductus t o excess potassium was also enhanced following cxpowre t o ibuprofen (Figs, 1 and 2). Ibuprofen action was relatively greater at a gestatic~nalage between 203 and 107 d a j s anmd tlne resulting contracticsra did not dlitfer significantly from that observed in the untreated, term duct~rs.By contrast, ibuprofen had no effect 811 the potassium-induced contraction at term. fbuprofen also contracted preterm 103-1107 gestation days) and tcrrn ductuses kept in the dark and its action was similar to that observed in the light. liowever, following treatment with ibuprofen lightand dark-adapted tissues differed in%that the latter exlmibited a greater relaxant component (range. 1.2-3.6 g) in their response to oxygen (Fig. 4).
N z - 5'1; COn
Normal medium
Excess potassium, 55 mikg
0.44iO.B1 (14) 1.30+0.20B3)G
2.28-tO.23 (10) 3.96+0.48(%)a
95'&
0 2
- 5 5 1COZ
2 -68 k0.64 ( 5 ) 2.5: 3.7
ap < 0.01 (nonpaired F test). bp < 0.05 (ii~onpairedt test). Narc: Values (grams) arc means rl: SE for the number of prcparatio~isgiven in parentheses cscept for one experimental group (immature dark-adapted prepclratiorrs at high Por) wherc values apply to illdivideral experirnenta. Values for light-atlapied preparations are taken from Fig. 1. All figures are corrected for the applied tension.
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
CAW. 9. PHYSIOL. PHARMACOL. VOL. 57, 1979
P
Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen F. CBCEANI, E. WHITE,E. BODACH, AND P. M. QLLEY Research Institute, The Hospital for Sick Children, Toronto, O~zt.,Canuda 1F156' 1x8
Received January 8, 1979 COCEANI, F., WIIITE,E., BODAGH, E., and OLLEY,P. M. 1979. Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen. Can. J. Physiol. Pharmacol. 57, 825-83 1 . Circular strips of ductus arteriosus from larnbs of gestational age between 90 and 144 days (term 147 days) were studied in vitro at low (8-1 6 torr (1 torr = 133.322 Pa)) and high (426-622 torr) Po,. Potassium- and oxygen-induced contractions increased with the gestational age and attained a maximum at term. At low Po,, ibuprofen, a blocker of prostaglandin synthesis,produced a dose-dependent contraction of the ductus at all ages and enhanced the potassiuminduced contraction of the immature ductus (90-124 days). Both effects were relatively greater in the 103- to 107-day gestational group. At that age, ibuprofen also potentiated the oxygeninduced contraction. These findings, while confirming that a prostaglandin is involved in ductus patency, indicate that the prostaglandin-relaxing mechanism becomes functional at an early stage of gestation and reaches maximal activity before term. The existence of an active, prostaglandin-mediated relaxation in the preterm ductus may account, in part, for the reduced responsiveness of the vessel to oxygen. It is confirmed that ibuprofen and other nonsteroidal antiinflammatory drugs are well suited for the management of the premature infant with patent ductus arteriosus. COCEANI, F., WHITE,E.: BODACH, E., et OLLEY,P. M. 1979. Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen. Can. 9. Physiol. Pharmacol. 57, 825-831. Des bandes circulaires de canal artkriel d'agneaux durant leur gestation 2gks entre 90 et 144 jours (terme a 147 jours) ont kt6 ktudiees in vitro 2 Po, basse (8-16 torr (1 torr = 133.322 Pa)) et i?i Po, ClevCe (426-622 torr). kes contractions induites par le potassium et l'oxygkne augmentent avec 1'8ge de la gestation et atteignent un maximum $I terme. A Po, faible, l'ibuprofkne, un bloqueur de la synthese de la prostaglandine, produit a tous les iiges une contraction du canal qui est dose-dependante et accentue la contraction de canaux immatures (90-124 jours), induite par du potassium. Ces deux effets sont relativement plus importants dans le groupe dont la gestation varie entre 103 et 107 jours. A cet Zige, l'ibuproftne potentiallse kgalement la contraction induite par de l'oxygtne. Ces rksultats, tout en confirmant qu9une prostaglandine est impliquke dans 190uverture du canal, indiquent que le mitcai~ismede relsiehement i?i la prostaglandine devieilt fonctionnel t6t durant la gestation et qu'il atteint une activit6 maximale avant 1e terme. L'existence d'un relkhement actif du canal, mkdik par la prostaglandine, peut en partie compter dans la reduction de la reponse des vaisseaux ii l'oxygtne. I1 est confirm6 que 1 ibuproftne ainsi que d'autres drogues anti-inflammatoires non-stkroidales conviennet bien dans la prise de soin d'enfants prkmatures ayant un canal artCriel persistant. [Traduit par le journal]
Introduction It is now thought that a PC maintains patency of the ductus arteriosus in the fetus (cf. Coceani, Olley et al. 1978). This concept is supported by experiments which show that blockers of PG synthesis, such as eicosa-5,8,11,14-tetraynoicacid and nonsteroidal antiinflammatory compounds, contract the vessel in viiro (Coceani et al. 1975) and in vivo (Sharpe et al. 1974; Olley cr ul. 1975; Sharpe et al. 1975; Iieymann and Rudolph 1976). Most of this work, however, has been performed in animals at term and the time course of the development of this PG-relaxing mechanism is unknown. ABBREVIATION: PG, prostaglandin(s) .
Sharpe et ul. (1974, 1975) reported that indon~ethacin,although it is a potenthuctus constrictor in fetal rats at term, has no effect on the 18-day-old fetus, which implies a late development of PG function. Their data, however, are in apparent contrast with results of clinical trials in which indametkacin or acetylsalicylic acid have been used successfully to close a patent ductus in premature infants (Friedman et ul. 1976; Iieymann et al. 1976). In fact, closure of the ductus could be obtained in infzints as young as 24 weeks gestation (Heymann and Rudolph 1978). To resolve this inconsistency and gather some insight into the significance of PG in the control of muscle tone in the developing ductus, ibuprofen, a blocker of P G syilthesis lower 1974), was tested on
0008-4212/79/080825-07$01.00/0 1979 National Research Council of Canada jConseil national de recherches du Canada
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
826
CAN. J. PHYSIOL. PHARMACOL. VBL. 57, 1979
isolated ductal preparations from lambs ranging in gestation age from 90 days onwards. Ibuprofen was used even though it is less activc than other blockers, specifi cal by indornetkacin (Flower 1974). because it has low toxicity (Davies and Avery 1971) and may, therefore, prove useful therapeutically. It was found that this compound cor~tractsthe diactus at all ages suggesting that the PC2 ~nechanisr~n resporssible for patency becomes f~ancticpa~al early in gestation. A prelin~inaryaccount of this work has alrsady appeared (OJley et a/. 1976). %faterialsand h4etlaods Experiments were performed with pregnant ewes (Suffolk, Suffolk-Dorset, Sutfolk-Rambley) of known breeding dates. Fetuses were subdivided into four groups depending on thcir gestational age, viz., 90-97, 103-107, 119-1 24, and 156-144 days (term is 147 days). Circular strips of the ductus arteriosus were prepared as described previously (Coceani, Hishai ei sat!. 1978) and were mounted in individual organ baths between a stationary glass rod and an isometric tension transducer (Grass FT.OJC). The transducer was coupled with a Grass jsolygraph. While lambs froraz 119 days gestation onwards yielded two strips per ductus, only one strip was obtained from each of the younger animals. In the latter case, strips comprised the n~~idportion of the ductus or, somesilnes, virtually the whole ductus. Except for being thinner, however, immature preparations c h i not dif1c:r greatly in their width and length from mature preparations. Strips were stretcined to a passive tension of 1 g (90-97 days gestation) or 1.5 g (103 days gestation to term). Preparatioiss were perfused with Krebs-Henseleit solution (NaCl, 118; KCI, 4.7; CaC12, 2.5; K H 2 P 0 4 , 1 ; MgSQ,, 0.9 ; dextrose, 1 1.1 : NaHCQa, 25 n~anol:/L)equilibrated at 37'C with 55.1 C 0 2 in nitrogen or oxygen. To allow rapid changes in the Po,, the naediunz was preequilibrated with the appropriate gas mixture and then gassed again inside the organ bath. Po, was measured in samples of bath fluid with an Instrulnentation Laboratory gas analyzer and was 8-16 and 426-462 torr (1 torr 133.322 Pa), respectively, with the 95'8; N, - 5j; CO- and 955; O 2- 5':; COz gas mixtrrres. A solution with excess potassium (55 anhi') was prepared by replacing the NaCl with an equinaolar amount of KC1. Recordings were made under standard artificial illumination except in a Sew experiments with the 103- to 107-day gestational age group and the tern1 group where the organ bath was wrapped with black cardboard aiad the room was kept in near complete darkness. Dark-adapted preparations were used t o rule out an inhibitory effect of light on contractile responses of ductal muscle and specifically on the response to oxygen (cf. CIyn~anand Ru~lc~lph 1978). The occurrence of this astifactual factor evould have precluded any conclusion on the maturation of oxygen sensitivity,. Ibuprofe~a(CJ~?.john)was dissolved in continuously stirred warm (about 5BBc'C) Krebs rnecliunl. The final concentration was 4.8 )< !M anci this solution was diluted as recluired by the experinlental protocol. 'I'wo procedures were used for testing ilsuprofe~~ on the immature ductus (90- to 124-days gestation). In some experiinents (procedure 1): tissues were first equilibrated ira normal rrmediuin at %owPo, until a steady tension was developed ancl were then exposed to increasing drug c~ncenltrations (maxirntlra~ 4.8 X 1W4M). Once the tension developed at each dose of ibuprofen had been recoraied, the medium was gassed with 5',4 C 0 2 in oxygen and thc
-
ensuing contraction was measured. Alternatively (procedure 2), tissues were allowed to stabili~eat a low and then a high Po, in the ahencc of ibuprofen, and finally at a high Po, in tine presence of a rnaxitnal dose of ibuprofen. Only the former test procedure was uscd with the term ductus because control values for the oxygen response were obtained in a separate series of experiments (Cocear-ai,Bishai o r ~ 1 f . 1978). Witin either procedure, the contractile response of tissues t o excess potassium was measrared immediately after equilibration at low Po,. Excess potassium was sotnetimes retested on ibuprofentreated (4.8 X l W 4 :W) tissues at low Po,. Strips frcsnn the sanw ductiis were subjected t o identical tests. standard error. Each Data are expressed as the mean naean is based on the number of individual values given and is derived ikon1 2 to 19 separate experimem~ts.Statistical comparisons of two means have been madc using Student's f test. Multiple comparisons have been made with an analysis of variance and IBuncan9smultiple range test (Kramer 1956).
+
Results
Response to Oxygen a d Putcrs\ilan Under rsormal room illumination, ductal strips fro111 all animals began to contract after being mounted in Krcbs medium preeq~lilibrated with 95'& N 2 - 5C';1 C:O2 (Pa,:,8-1 6 torr). 'I-his contraction was slow and, with any age group. rsquired 1-4 11 to reach a maximurn. Maximal tensiorn output, howcver, was greater in ternn than in preterm animals (Figs. 1 and 2). kikcwise, eflects of oxygen (Po2 326-662 torr) and excess potassium were age related (Figs. 1 and 2), the contractile tensiors dcvcloped at the 90-to 107day gestational age being approximately one-third of that at term. Besides being weaker. the response of the immature ductus to oxygsn was at times discontinuous and consisted of two or three ccsit~secutive contractions sf increasirsg strength. linnrnat~ircpreparations (103-107 days gestational gsoaap) kept in the dark developed greater tension than those exposed to light both in the absence and the presence of excess potassiunl at low P O 2 . By contrast, in mature preparations the absence of light had no etyect on the potassiunl response and caused only little increase of the tension output at low Po,. 'Thc oxygen-induccd comtracticm exhibited a difkrent ~Pependence011 soon1 illumination. While the contraction of rhe immature ductus showed no obvious change with room illumination, the contraction of the snat~areductus was smaller in the dark than in the light. This notwithstanding, in the dark as in the Bight mature and immature ductuses differed in their response to high 4'02. Tablc 1 sun~marizesthe findings with dark- vs. light-adapted preparations. E'ec t 0f' Iisuprqftm Ibuprofen contracted the hypoxie ductus at all stages of gestation (Figs. I and 2). Its threshold concentration was around 18-" M and responses were
827
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
COCEANI ET AL.
FETAL AGE (days)
FIG.1. Isolated ductus arteriosus from Iambs at difyerent stages of gestation. Muscle tension at low (A) and high (M) Po, and potassi~rrn-inducedcontractioll at low Po, ( C ) before (open colun~n) and after (solid colurnm) treahmerat with ibuprofen (4.8 X 1V.f) ira nornizrl rocptml illumination. Hn those instances where the oxygen response was discontinuous (see text), values apply to maximal tension output. Values are nleans i SE for the nuntber of preparations given on top of each column and are corrected for the tcnsion applied at the start of the experiment.
dose-related over a range ~ a pto 4.8 X 1Qd4 1W (Fig. 3). At a n j dose, ibuprofen contraction began after a few nainutes delay and progressed slowly to a stable platea~a.The time to peak s7as quite variable and ranged between 23 and 116 miw. Maximnal tension output following ibuprofen increascd with advancing gestation; however, the increase of tension over control values was relatively greater with the 103- to 107-day gestational group. TABLE 2 . Tension output
(9f
103-107
Light
On Off
These results demonstrate that ibuprofen contracts the fetal lamb ductus throtaghsut the last third of gestation implying an early development of the FG n~echanisrnresponsible for paterncy. Zw fact, judging
dark- vs. light-adapted preparations of lamb ductus arterissus 95''l;
Gestation age , days
With the exception of ductuses a t 103-107 days gestation ibuprofen failed to enhance the oxygeninduced contraction (Figs. 1 and 2). At that age, the oxygen response, which is normally little developed, increascd on the average twofold. The time course of ibuprofen contraction at a higir Poz resembled that observed a t low P o 2 . Whether or not increased in magt~ituide,however, the oxygen response following ibuprofen diRered from controls. As shown in Fig. 4, ibuprofen-treated tissues relaxed before contracting upon transfer from a low to a high oxygen elsvirsnment. Maximal loss of tension ranged between 0.2 and 0.9 g, and w7as c~ccasionallygreater (nnaximum 2 g). Oxygen-induced relaxation occurred in all but one preparatioia from 119 days gestation onwards and in about 6076 crf the younger preparations. When present, however, this response showed no c~lavlious change in magnitude with the age of the animal. The contractile response ofthe immature ductus t o excess potassium was also enhanced following cxpowre t o ibuprofen (Figs, 1 and 2). Ibuprofen action was relatively greater at a gestatic~nalage between 203 and 107 d a j s anmd tlne resulting contracticsra did not dlitfer significantly from that observed in the untreated, term duct~rs.By contrast, ibuprofen had no effect 811 the potassium-induced contraction at term. fbuprofen also contracted preterm 103-1107 gestation days) and tcrrn ductuses kept in the dark and its action was similar to that observed in the light. liowever, following treatment with ibuprofen lightand dark-adapted tissues differed in%that the latter exlmibited a greater relaxant component (range. 1.2-3.6 g) in their response to oxygen (Fig. 4).
N z - 5'1; COn
Normal medium
Excess potassium, 55 mikg
0.44iO.B1 (14) 1.30+0.20B3)G
2.28-tO.23 (10) 3.96+0.48(%)a
95'&
0 2
- 5 5 1COZ
2 -68 k0.64 ( 5 ) 2.5: 3.7
ap < 0.01 (nonpaired F test). bp < 0.05 (ii~onpairedt test). Narc: Values (grams) arc means rl: SE for the number of prcparatio~isgiven in parentheses cscept for one experimental group (immature dark-adapted prepclratiorrs at high Por) wherc values apply to illdivideral experirnenta. Values for light-atlapied preparations are taken from Fig. 1. All figures are corrected for the applied tension.
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Queensland on 11/12/14 For personal use only.
CAW. 9. PHYSIOL. PHARMACOL. VOL. 57, 1979
P
