Cerebral oxidative metabolism in fetal sheep with multiple-dose ethanol infusion

Cerebral oxidative metabolism in fetal sheep with multiple-dose ethanol infusion Bryan Riehardson, M.n., John Patriek, M.n.,Jaeobus Homan, B.Se ., Lesley Carmichael, B.Se., and James Brien, Ph.D. London, Ontario, Canada Cerebral oxidative metabolism and cotylendonary blood Ilow were measured in 10 unanesthetlzed letal sheep (127 t6132 days' gestation)duringa control period, after the l irst, third, and lourth inlusions 01 lour doses 01 0.5 gm 01 sthano l per kilogram 01 maternal body weight infused into the ewe during 5 hours , and 24 hours after ethanol Intuston. Preductal arteria! and sagittal vein blood sampies ware analyzed lor oxygen content, blood gases, pH, and ethanol. Cerebral and cotylendonary blood flow were rneasured with a radioactive microsphere technique. Fetal blood gases and pH chanqed Iittle with the ethanol infusions, although Pa0 2and oxygen content decreased 24 hoursafter ethanol infusion. Cotylendonary blood Ilow , which was decreased after the third and lourth ethanol infusions, did not account for these delayed hypoxemic chanqes. Similarly, cerebra! ox idative metabolism wasdecreasedwhen measured after each of the ethano l infusions, with no dose response or tolerance evident. This noted lall in letal cerebra l oxidative metabol isrn appears to be a direct depressant ellect that was maximal at rather low leta ! ethano l levels , which, il prolonged , might weil allect cerebral growth and development. Recovery 01 cerebral metabo lie lunction appeared complete by 24 hours. However , relative letal hypoxemia was evident at this time, the mechanism of which remains to be determined. (AM J OBSTET GVNEC OL 1987;157:1496-502 .)

Key words: Ethan ol, cerebral oxida tive metabolism .

Prominent among the defects noted in infants exposed to excessive matemal aleohol in ta ke are abnormalities in brain growth and structural development ' and d ysfunction of the cent ral nervou s system ,"" with an apparent d ose-resp on se relation ship for these effects. Abnormalitie s in br ain growth and development are also no ted in the ra t em bryo exposed to ethan ol, with me ch an isms in volvin g de creased protein synthesis an d cellu lar hypoplasia.' :" We have previously sh own that a sho rt-terrn in fusion of moderate amounts of ethanol to pregnant ewe s (1.0 gm . kg - ' over a l-hour period) re sults in alterations in the fet al state with th e emergence of an intermediatevolta ge el ectrocortical state and a de crease in fetal cerebral oxidative met abolism that is stilI evident I hour afte r ethan ol in fusion." We h ypothesized th at if prolon ged , th is change in fe tal state and de crease in cerebral ox ida tive metab olism migh t weil affect fet al brain development and p rovide a me ch an ism whereby

From. the R esearch Inst itute, St .joseph's Hospital, and the Department of Obstetrics and Gynecology, University of Western Oniano, and the Department of Pharmacology and T oxicology, Faculty of Med icine, Queen's University. Supported by Grants [ro m the Canadian Medica l R esearch Counci l and the R ichard and j ean Ivey Foundation. Sponsored by the Society for Gynecologic Investigation. R epri nt requests: B ryan Richardson, M.D., Department cf Obstetrics and Gynecology, St. [oseph 's H ospital, London, Ontano N6A 4V2, Canada.

1496

chronic aleohol intake co ntribu tes to growth anornalies and dy sfunction of the central nervous system in infants exposed to aleohol in utero. It is not known, however, wh ether the decrease in fet al cerebral oxida tive metabolism is a d irect effect of the ethanol or caused by th e change in fetal sleep sta te noted , since we have recentl y demonstrated a significant fall in cerebral ox ygen con sumption in the fet al larnb with a cha nge fr om a low-voltage electrocortical state.' The ethanol dosecerebral oxid ative metab olism response relationship and time course for re covery also remain to be determined. . Therefore the purpose of the present study was to examine the effect of a multiple-dose maternal ethanol infusion on fetal cerebra l ·oxygen· co nsu m ption to determine if a dose-response relationship exists along with the time course for re covery and also to determine the extent to wh ich behavioral state changes are involved in these effects . Because fetal hyp oxi a ha s also been proposed as a me ch anism for ethan oI-induced growth anornalies," coty ledon ary blood flow was rneasured in rel ation to noted fetal blood gas chan ges. Material and methods SurgicaI proeedures. Stu d ies were performed on 10 fet al shee p of mixed bre ed between 127 and 132 d ays' ge station (te rm 147 days). Fetuses were prepared fo r study at least 3 days before initiation of all experiments. The ewes were anesthetized with 1.5 to 2.0% halothan e

Fetal cerebral oxidative metabolism wiih ethanol exposure

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1497

Table I. Mea surernents of fetal card iovasculatu re and arterial metabolites frorri experimental periods E thanol infusums First dose

Control

Ethanol (mg/ mi)

ND 7.32 :!: 0.01 22.6:!: 0.9 49.1 ± 0.8 9.5 ± 0.5 ' 46 ± 4 171 :!: 5

pH , . '

P0 2 (mm Hg ) Pc0 2 (mmHg) Hernaglobin (gm/d l) Mean blood pressur e{mm Hg) FHR (bpm)

0.8 1 7.32 24. 1 49.2 9.5 46 174

± 0.05* :!: 0.01 ± 0.8 ± 0.8 ± 0.5 :!: 4 :!: 7

I

T hird ' dose

1.84 7.33 24.1 48.1 9,9 44 163

.

'

± 0.12*

± 0.0 1 ± l.l

± ± :!: ±

0.6 0.4 4 6

I

Fou rth dose

2.37 7.33 24.1 47.6 9.7 44 158

.. ± 0.16* :!: 0.01 ± 0.8 ± 1.2 ± 0.5 ± 4 ± 5

24 hr

0.08 7.32 20.8 50.7 9.4 43 158

± 0.08

± 0.01

± ± ± ± ±

Q.9t QAt . 0.4 3 6

ND = No t detected.: Values are means ± ,SEM; n = except for 24 hours where n = 9. Mean blood pressure and FHR values we~e averaged fo~ the time during each blood flow determination and 15 minutes thereafte r, *p < 0.01. t p < 0.05 .

10

.

,

,

and 50 % oxygen to 50% nitrous oxide, and the uterus was exposed and opened th rough a lower abd ominal midline incision . Polyvinyl catheters were placed in the brach ioce phalic trunk via a fetal forelirnb ar tery for sampling preductal arterial blocid and in the femoral artery via a fetal hindlirnb artery for sampling postductal arterial blood . A catheter was pla ced in the inferior vena cava via a fetal pedal vein, and the sag ittal sinus was instrumenred and sampled as previously reported. " Tr~cheal a~d amniotidluid catheters were ~Iso placed as previously describe&9 Electrodes of stainless steel, Teflon-coated wire (C:;oo~er, Chatsworth, Ca Iiforn ia) were im planted biparietally on the dura fo r fet al elecrr oencephalographic reco rd ings, through th e o rbital r idge of the zygomati c bone of each eye for electroocular re cordings, and over the sternum for fetal heart rate ( FH R) rec ordings. A reference ele ctrode was placed in the loo se connective tissue overl ying the occipital bone of th e skulI . The catheters, which contained heparinized saline solution, and wire s were exteriorized through the flank of the ewe , and the abdomen was elosed in layers. Polyvinyl cathe ters were then placed in the maternal femo ra l artery and vein. At th e time o f surgery, 1 gm of d ihydrostreptomycin and 800,000 U of penicillin G were inje cted intramuscularly into the ewe , and after the uterus was elosed, 1,000,000 U of penicillin G were injected into both the fetal hindlimb vein and th e amniotic cavity. This an tibioti c was contin ue d daily for 2' to 3 d ays. Afte r su rger y, animals were maintained in ind ivid ua l cages suitable for continuous monitoring, with food and water available. Physiologie measurements, Eac h fetal lamb was stud ied during a co ntrol period, after th e first, thi rd, and fourth of four multiple doses of ethan ol in fused into the ewe over 5 hours, and 24 hours a fter ethanol infusion. Strain-gauge manometers (Statham Model

P-23 ID , Could, Oxnard, California) arid a s tr ipcchart re~orde r (Model78D, Grass Instr~mem, Quinc y, M assachusetts) were used torecord pressu re sin th~ tr achea, amnioti c fluid, and the brachiocep~alic a:~te~y. Mean ar terial blood pressure was calculated as di~stolic plusO.d of systolic minusdiastolic pres~ur.~ : Ele~trlcal signals were processed with a common .mode rejectiori prearnplifier (Model 7 P5~ IJ , Grass .In strumentr.EHk was measured by means of a cardiotachometer (Model 7P44B). Fetalelectrocortical and electrooc ular potentials were di splayed directly on the chart re corder after pass ingthrough a passive band-pass Eiter, 0:3 to 3Ö Hz , o n the prearnplifier. ' Com in uous recordings of electrocortical, electroocula~, tr~cheaIpr~ssure , amriiotic fluid pressure, fetal arterial blood pressure, and FHR were be gun 24 hours beforeethanol infusion . Approximatel y 1 hour :before e thanol infusio n and dur ing a- pe riod of h igh volta ge ele ctrocortical ~vith ele ctroocular activityabsent, r~dionuclide-Iabeled microspheres ~ere inj ected i~tö the fetal in ferior vena cava for deterrnination of regional blood flow distribution. This procedurewas followed immediately by two pa ired blood sarn ples , 5 rninutes apart, wh ich were drawn simultaneo usly fr om the brach iocephalic artery and the sagittal vein . FOl;1r d oses' ofO .5 gm ethanol per kilogram of maremal body weight were then in fu sed into the maternal vena cava of each ewe over a 5-hour period. Each d ose , as a 40 % . vlv solut ion o f et hanol (Alcool, Liqu or Control Board o f Ontario), was administered by an infu sion pump over 30 minutes, with a l-hour interva l betw een each dose to allow ex travascular di str ibution of ethanol in the maternal and fetal compartments before each successive d ose." After the first, third, and fourth ethan ol doses and again 24 hours after etha nol infus ion, rnicrosphere injections were agai n performed, followed by a paired blood sampling from the brachiocephalic

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Richardson et a l,

December 1987 Am J Obstet Gynecol

Table H. Cerebral metabolic measurements Ethanol infusions

M easurements

CAO. (rnmol/L)

Blood flow : (ml : 100 gm" min- I ) Oxygen delivery (u mol . 100 g~- l . min ") Oxygen constimption (urnol - 100 gm- I . min- I ) Ox ygen fractional extraction Arteriovenous ethanol difference (mg/rnl)

First dose

Control

I

Third dose

I

Fourth dose

24 hr

2 .9 :t 0.2 157 :t 15

2.9 :t 0.2 114:t Il t

2.9 :t 0.2 115 :t ISt

2.7 ± 0.2 124 :t 7

2.2 :t 0.1 (9)* 190 :t 19 (7)

441 :t 35

321 :t 20t

317 :t 35t

320 :t 29t

393 :t 17 (7)

127 :t 9 (8) 0.31 :t 0.01 (8) ND

98 :t 7 (8)*

98 :t 8 (8)*

98 :t 9 (7)t

115:t 12 (6) .

0.32 :t 0.03 (8) 0.02:t 0.02 (8)

0.35 :t 0.03 (8) 0.02 :t 0.03 (8)

0.34 :t 0.03 (7) 0.08 :t 0.05 (8)

0.29 :t 0.02 (6) 0.01 :t 0.01 (6)

ND = Not detected; CAO. = arterial oxygen concentration. Values are means :t SEM ; n = 10 except where otherwise indicated; significance based on paired data. *p < 0.01. tp < 0.02. tp< 0.05.

artery arid sagittal vein . Fetal monirering was continued throughout this time. Although the fetal state was not controlled for, in 25 of the 30 measurements after ethanol infusion andin eight of the riine meas urements at 24 hours, the fetus was either in the high-voltageor an intermediate-voltage electrocortical state. .Each blood sam pIe was analyzed for oxygen content, pH, Po.; Pco., and ethanol. Results were averaged for the two control period samples 10 obtain a mean vaiue . With each paired blood sample, approximately 1 ml of arterial blood and I ml of venous blood were withdrawn. Oxygen conterit was determined in triplicate by rneans of a Le x-Os-Con (Lexi ngton Instruments, Waltham, Massachusetts) blood gas analyzer. Blood pH, Po 2 , and Pco, were analyzed on an ABL-3 biood gas analyzer with temperature corrected to 39 0 C (Radiometer, Copenhagen, Denmark). Blood ethanol concentrauen was meas~red by gas-liquid chromatography with the use of headspace analysis as previously described." . Regional blood flow was measured with 15 JLm diarneter microspheres (New England Nuclear, Boston, Massachusetts, and 3M, New Brighton, Minnesota) labeled with one of five different radioisotopes (Cerium 141, chrornium st. strontium 85, niobium 95, or scandium 46) by means of methods previously published,? Reference sam pies were withdrawn from both the brachiocephalic and femoral arteries at a rate of 2.40 ml/min via a Harvard infusiori withdrawal pump (Harvard Apparatus, Dover, Massachusetts). At the completion of each microsphere injection and subsequent blood sampling, estimated fetal blood loss was replaced with maternal blood. On completion of the studies, the ewe and fetus were

killed, and an autopsy was performed on the fetus to validate catheter placement, The fetal brain was weighed and dissecred into the following regions: right and left cerebra l hemispheres, subcortical structures (thalarnus, epithalarnus, hypothalamus, corpus striaturn, and rnidbrain), cerebellurn, pons, and medulla. The fetal cotyledons were dissected free of the myometrial tissue and fetal membranes were trimmed. All tissues were weighed separately and analyzed for radioactivity (Compugamma Model 1282, LkB Wallac Oy, Turku, Finland). Blood flow to these tissues was then calculated as previously described by Makowski et al. l 1 Data analysis. Results obtained from the 10 animals for control, ethanol infusion, and postethanol infusion periods are presented as grouped means ± SEM. One fetal lamb, with normal blood gases and pH during the control period, Pa0 2 18.7 and pH 7.35 , developed progressive metabolic acidosis after the fourth ethanol dose, with fetal dernise occurring approximately 18 hours after ethanol infusion . In sorne experiments catheter failure prevented the completion of alI studies in each fetus. Cerebral oxygen consumption values were calculated as the product of arteriovenous clifference and ce~ebral blood flow. Cerebral blood flow on ly included flow to the cerebral hemispheres, since this is the region drained primarily by the sagittal sinus . Cerebral oxygen delivery was calculated as the product of arterial oxygen content and hernispheric blood flow. Cerebral fra ctional extraction of oxygen was calculated from thc arteriovenous difference divided by arterial oxygen content, Electrocortical activit y was assessed by visual analysis into periods of high voltage (100 to 200 JLV), low-voltage «50 JLV), and intermediate-voltagc electro cortical (50 to 100 JLV). The data reported in Ta-

Fetal cerebral oxidative metabolism with ethanol exposure

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1499

Table III. Changes in blood flow to specific regions of the fetal brain Ethanol infusio ns R egions

Cerebral hemisphere Subcortex Cerebellum Pons Medulla

Gontrol

157 204 197 217 245

± 15 ± 15 ± 16 :!:

19

± 24

First

dose

114 162 172 188 214

± ± ± ± ±

11* 18t 17 23 23

I

Third

dose

115 192 198 240 272

:!:

± ± ± ±

15t 30 21 40 36

I

Fourth

dose

124 :!: 7 190 ± 18 219 ± 28 229 :!: 29 290 ± 30

24 hr

190 307 263 332 336

:!:

± ± ± ±

19 28:1: 24t 35t 27*

VaIues are means (mI · 100 gm -I . rnin" ) ± SEM; n = 10 except for 24 hours where n = 7; significance based on paired data, *p < 0.02. tp < 0.05. :l:p< 0.01.

bles I to III were examined by analysis of variance for repeated measurements followed by the Newm an-Keuls test if a significant F ratio was obtained (p < 0.05) . Fetal breathing movements, electrooocular activity, and electrocortical activity, which were monitored continuously both be fore and after ethanol infusion , are reported separately," as is the pharmacokinetics and pharmacodynamics of ethanol in the maternal fetal unit. 13

Results During the experiments ewes did not exhibit unusual agitation; however, during the mu ltiple-d öse ethano l infusions, the sheep appeared to have impairment of balance and spent a greater part of the time lying down. They returned to regular activity within 6 hours after ethanol infusion with no apparent ill effect. Fetal cardiovascular and arterial metabolie rneasurements from the experimental periods are shown in Table I. The 5-hour mu ltiple-dose ethanol infusion re sulted in a stepwise increase in ethanol concentrations of fetal arterial blood to a maximum of 2.37 mg/m i after the fourth ethanol infusion. Although feta l ar- ' terial blood gases changed little during ethanol infusions, 24 hours after infusion , Po. significantly de creased (p < 0.05), whereas Pco, significantly increased (p < 0.05). No significant differences were no ted in fetal hemoglobin concentration or in mean arterial blood pressure or FHR measured at the time of blood flow deter minat ions. Maternal arterial pH declined progressively during multiple-dose ethanol infusions from a control value of 7.44 ± 0.01 to 7.38 ± 0.01 after the fourth ethano l infusion (p < 0.01). Maternal arterial pH increased significantly 24 hours after infusion, 7.47 ± 0.01 , when compared with control values (p < 0.05). These pH changes were largely metabolie in nature, since the base excess also showed a progressive decline from 0.6 ± 0.9 to -4.8 ± 0.7 mmollL after the fourth ethanol infusion (p< 0.01) and then increased to 1.8 ± 0.9 mmol/L, although not significantly, when

measured 24 hours after infusion. Maternal arterial Po. and Pco, changed little throughout the study whe n compared with control value s, 101.4 ± 2.8 and 36. 1 ± 0.5 mm Hg, respectively. Cereb ral oxygen delivery. Fetal arterial oxygen content, although unchanged during ethanol infusions, also significantly decreased when measured 24 hours after ethanol infusion (p < 0.01; Table II ). Blood flow to the cerebral hemispheres was significantly decreased after both the first and third doses of ethanol (p < 0.02 and p < 0.05, respectively), and although still decreased after the fourth dose, it was not significant (Table II) . The decrease in cerebral hemispheric blood -fiow with little change in arterial oxygen content resulted in a significant decrease in cerebral oxygen delivery after each of the ethanol infusions where measured (Table II ). Cerebral ox ygen consumption. Cerebral oxygen consumption was 127 ± 9 p.mol : 100 gm -I. min " during the control period and de creased significantly where measured after eac h of the ethanol infusions (Table II), with a related fall in cerebral blood flow; the arteriovenous oxygen difference remaining little changed. Cerebral oxygen consumption returned to control values when measured 24 hours after ethanol infusion. The cerebral fractional extraction of oxygen, as a measure of the ox ygen consumed as a fraction of that delivered, remained little changed throughout the study (Table II). There was no measured consumption of ethanol by the brain, since the cerebral arteriovenous ethanol difference was negli gible both with the infusions and 24 hours after infusion (Table II) . Regional blood ßow. Control blood flows were de termined during an episode of a high-voltage electrocortical state whereas subsequently c1ectrocortical states were variable during blood flow determinations but again were usually of high or int ermediate voltage. Changes in blood flow to specific regions of the fetal brain are presented in Table III and Fig. I. Regional

1500

Richardson et al.

December 1987 Am J Obstet Gynecol

~

400

0

~

Cl

0 0

...J

lD

Z

~

lD

...J

~

0 (3

W

0:::

,...... c:

'E <,

300

Cl 0 0

-E

200

-

-(...,~

• •• 0

CONTROL

0

0.8 2.0

<,

100

0

CEREBRAL

SUBCORTEX

PONS

MEDUllA

CEREBEllUM

CORTEX

Fig. 1. Mean (± SEM) blood flows to the different brain regions during the control period , after the first , third, and fourth ethanol infusions, and 24 hours after ethanol infusi on.

differences in the effect of ethanol on blood flow to the brain were evident. with flow to the cerebral hemispheres significantly decreased after both the first and third ethanol infusions (a 27 % decrease), flow to the subcortical tissues significantly decreased after only the first ethanol infusion (a 20% decrease) , and flow to the other brain tissues showing no significant change. Twenty-four hours after ethanol infusion , blood flow significantly increased in all regions of the brain except the cerebraI hemispheres, with the increase most pronounced in the subcortex (a 50 % increase) and the pons (a 53 % increase). Blood flow to the fetal cotyled ons was deterrnined during the control and ethanol infusion periods in seven of the study animals and 24 hours after ethanol infusion in five of the study animals. Cotyledonary blood flow was 193 ± 26 m l : kg " . min- l dur ing the control period and decreased significantly after both the third, 144 ± 23 ml- kg- 1 • min- I (p < 0.01) and the fourth, 136 ± 21 ml . kg -' . min- 1 (p < 0.01) ethanol infusions . Twenty-four hours after infusion, cotyledonary blood flow returned to control values, 178 ± 23 ml . kg " . min" '. Comment

The regimen of four doses of 0.5 gm ethanol per kilogram of maternal body weight administered over a 5-hour period, with each dose infused over 30- minutes. and a I-hour interval between each successive dose, was selected in an attempt to mimic abinge-rype drinking episode. This multiple-dose infusion resulted in a stepwise increase in peak fetal arterial blood ethanol con- . centration to 2.37 ± 0.16 mg/mi reached at the end of the fourth ethanol infusion, which is higher than that reported in other studies involving the fetal larnb. " :" In the present study, fet al arterial blood gases and pB changed little during the ethanol infusions; however, 24 hours later, arterial Po. significantly decreased,

whereas arterial Pco, significantly increased . As noted, one fetal lamb developed progressive metabolic acidosis, with fetal death occurring approximately 18 hours after ethanol infusion. Most other studies investigating the effects of ethanol have also noted little change in fetal blood gases and pB during the ethanol infusion. l':" but all have involved infusions of, at most, out to 3 hours, with postinfusion measurements only out to 5 hours. The fetal blood gas changes noted here at 24 hours must invol ve either a decrease in oxygen delivery and carbon dioxide excretion, for example, those involving a decrease in uterine blood flow or placental exchange mechanisms or an increase in feta l oxidative metabolism and carbon dioxide production. H owever, these changes in fetal blood gas could not be accounted for by corresponding ch anges in maternal blood gas or a fall in fetal cotyledonary blood flow, which changed little from con trol values when measured at 24 hours . Maternal arterial pB fell progressively during the multiple-dose ethanol infusion, which reflects a developing metabolie acidosis as indicated by the corresponding decline in the base excess. This finding has been reported in other stud ies in which there was lower maternal ethanol exposure"" and may represent lactic acidosis since the redox changes associated with the oxidation of ethanol result in a shift of pyruvate to Iactate . I" Feta l cerebral uptake of oxygen decreased 22% from the control value when measured after the first maternal ethanol infusion and remained similarly depressed when me asured after the third and fourth infusion s despite the stepwise increase in fetal ar terial ethanol levels. Thus a dose-response relationship was not evident, with cerebral oxidative metabolism maximally depressed after the first ethanol infusion. Studies in ad ult humans'"su p port the theory that dose responsiveness may aiso depend on th e level of consciousness, since

Volume 157 Number 6

mild ethanol intoxication is reported to cause Iiaie change in cerebral oxidative metabolism, whereas more severe intoxication with stupor is associated with depressed cerebral oxidative metabolism. Hemmingsen and Barry" have also noted a significant decrease in cerebral oxygen consumption with severe ethanol intoxication in acute adult rat studies. In a previous study during which control measurements were made in the low-voltage electrocortical state and ewes were subsequently given a l-hour infusion of ethanol at 1.0 gm' kg" over a I-hour period, we noted a 35 % decrease in the cerebral oxidative rnetabolism but with an associated change to a high- or interrnediate-voltage electrocortical state in most animals," Because we have also reported a significant fall in cerebral oxidative metabolism in the fetal larnb with a change from a low-voltage electrocortical state to a high-voltage electrocortical state,? the reported decrease in cerebral oxidative metabolism may have been, at least in part, an indirect effect caused by a change in the fetal sleep state. In the present study all control metabolie measurements were made du ring an episode of high-voltage electrocortical potential in which rapid eye movements were absent, whereas after each of the ethanol infusions, the fetal lambs were usually either still in a high-voltage electrocortical state or in a voltage state in between that ofhigh and low voltage. Although the significance of this intermediate-voltage state is unknown, the decrease in cerebral oxidative metabolism noted in the present study suggests a more direct effect of ethanol on cerebral metabolie function and is in keeping with abnormal brain growth and development involving decreased protein and deoxyribonucleic acid synthesis reported with ethanol exposure in other an imal studies.vvThe lack ofa dose-response relationship noted here indicates that the direct effects of ethanol on cerebral metabolie function are maximal at rather low fetal ethanol levels, which suggests that the degree of abnormal brain growth and development reported for both the animal model' and human infant' will be a function of the duration of maternal alcohol exposure rather than the intensity of acute exposure. In the present study cerebral oxygen consumption had returned to controllevels by 24 hours at a time when fetal ethanol levels were again almost negligible, indicating no discernible continued direct effects of ethanol on cerebral metabolie function. Blood flow to the cerebral hemispheres was decreased 27 % after the first and third ethanol in fusions and 21% after th e fourth ethanol infusion. If this de crease were caused by a direct vasoconstrictive effect of ethanol, an increase in the extraction of oxygen might be expected, since cerebra! arteriovenous oxygen difference has bcen found to vary inversely with changes in cerebra! blood flow under conditions in

Fetal cerebral oxidalive metabolism with ethanol exposure

1501

which cerebral oxidative metabolism remains unchanged." However, with the decrease in cerebral oxidative metabolism measured in this study, the significant fall in blood flow is consistent with reports of a close coupling of regional brain blood flow to rnetabolic rate." A direct vasoconstrictive effect of ethanol is also possible and is supported by in vitro studies on canine cerebral arterioles where local application of ethanol results in a graded constriction that can be blocked by calcium antagonists." When measured 24 hours after ethanol infusion, cerebral blood fiow increased abo ve control values, although not significantly, which is in keeping with the normal regulatory response to a drop in arterial oxygen content noted at this time ; the fractional oxygen extraction thus remained relatively unchanged. Regional differences in the effect of ethanol on brain blood flow were evident, with fiow to the cerebral hemispheres significantly decreased after both the first and third ethanol infusions (a 27% decrease), flow to the subcortical tissues significantly decreased after onl y the first ethanol infusion (a 20% decrease), and flow to the other brain tissues showing no signifi cant change. In our previous stud y," the fall in brain blood flow with ethanol exposure was most pronounced in the subcortex and pons, findings similar to those we have reported with a change from a low- to a high-voltage electrocortical state ? and that further support an alteration in fetal state as an indirect mechanism whereby ethanol alters cerebral oxidative metabolism. In the present study regional blood How changes suggest that the direct depressant effect of ethanol on oxidative metabolism is largely confined to the cerebral hemispheres, given the close coupling of blood flow to metabolism in the brain. This finding su pports a decrease in protein and deoxyribonueleic acid synthesis to this area of the brain with ethanol exposure during fetal development and is consistent with reports whereby abnormalities in brain growth and function are largely confined to cortical structures." Regional blood flow changes at 24 hours are again in keeping with the normal fetal re sponse to hypoxemia whereby the greatest increase occurs to the br ainstem and deep cerebral structures." B100d flow to the fetal cotyledons was decreased during the time of ethanol exposure-25 % after the third infusion and 30% after the fourth infusion- with a return to control values when measured 24 hours after ethanol infusion . The control values reported here are similar to those reported by other investigators using the chronically catheterized fetal lamb preparation ;" however we could find no reports o n th e effects of ethanol exposure. Erskine and Ritchie 26 have shown that the impedancc of the um bilical ar tery was unchanged in mothers exposed to alcohol bctween 34 and 36 week's gestation, suggesting little effect on vascular

1502 Richardson et al,

resistance ; however, maternal a1cohol levels were much less than in the present study. Because mean arterial blood pressure changed little with the ethanol infusions, the fall in cotyledonary blood flow noted here must have involvedan increase in umbilical vascular resistance, presuming the central venous pressure changed little . This decrease in cotyledonary blood flow would be expected to result in a decrease in fetal ox ygen delivery, and thus oxygen levels and may have contributed to the small fall in arterial oxygen content noted after the fourth ethanol infusion. The lack of a more pronounced fall in fetal arterial oxygen levels might be explained by a decrease in overall fetal metabolie rate and thus oxygen consumption with the ethanol exposure. Thus the decrease in fetal cerebral oxidative metabolism with maternal ethanol intoxication is both a direct depressant effect, possibly involving decreased protein and deoxyribonucleic acid synthesis, and an indirect effect involving a change in fetal state. The direct depressant effect is maximal at rather low fetal ethanol levels with no dose response evident and no evidence of tolerance developing at least during the 5 hours of ethanol exposure studied. Recovery of cerebral metabolie function appears complete by 24 hours. However, relative fetal hypoxernia is now evident, the cause of which remains to be determined, but mayaiso contribute to the growth anomalies of infants exposed to alcohol in utero. We thank Mr. G. Srnith, D. Clarke, and Dr. P. Harding for their interest in this work, and V. Ramsay for her excellent technical assistance. REFERENCES I. Clarren SK, Alvord EC, Sumi SM, Streissguith AP, Smith

2. 3. 4.

5. 6. 7.

DW. Brain mal formations related to prenatal exposure to ethanol. j Pediatr 1978;92 :64 . Jones KL, Smith DW. Recognition of the fetal alcohol syndrome in early infancy. Lancet 1973 ;2:999 . LittIe RE, Streissguth AP. Effects of a1cohol on the fetus: impact and prevention. Can Med Assocj 1981;125:159. Rawat AK. Ribosomal protein synthesis in the fetal and neonatal rat brain as infiuenced by maternal ethanol consumption. Res Commun Chem Pathol Pharmacol 1975; 12:723 . Brown NA, Goulding EH, Fabro S. Ethanol embryotoxicity: direct effects on mammalian embryos in vitro. Seience 1979;206:573. Richardson BS, Patrick JE, Bousquet j, Homan j, Brien JF. Cere bral metabolism in fetal lamb after maternal infusion of ethanol. Am J Physiol 1985 ;249 :R505. Richardson BS, Patrick JE, Abduljabbar H. CerebraI oxidative metabolism in the fetal lamb: relationship to electrocortical state. AMJ OBSTETGVNECOL 1985;153:426.

December 1987 Am J Obstet Gynecol

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