Effects of Atropine and Gastric Inhibitory Polypeptide on Hepatic Glucose Uptake and Insulin Extraction in Conscious Dogs

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1 ffects of Atropine nd Gstric nhibitory Polypeptide on Heptic Glucose Uptke nd nsulin xtrction in Conscious Dogs Zvi Chp, Toshihiko shid, Jesse Chou, Robert Lewis, Crig Hrtley, Mrk ntmn, nd Jmes B. Field Dibetes Reserch Lbortory, St. Luke's piscopl Hospitl, Division ofndocrinology nd Metbolism, Bylor College ofmedicine, Houston, Texs 773; nd Section ofcrdiovsculr Sciences, Deprtment ofmedicine, Bylor College ofmedicine, Houston, Texs 773 Abstrct Previous studies compring the effects of orl, intrportl, nd peripherl venous dministrtion of glucose in conscious dogs demonstrted significnt increse in heptic extrction of insulin only fter orl glucose, but similr heptic uptke of glucose fter orl nd intrportl glucose, which ws greter thn tht fter peripherl intrvenous glucose infusion. This study evluted the effect of tropine blockde of the prsympthetic nervous system on the incresed frctionl heptic extrction of insulin nd the role of gstric inhibitory polypeptide (GP) on ugmented heptic uptke of orl glucose in conscious dogs with chroniclly implnted Doppler flow probes on the portl vein nd heptic rtery, nd ctheters in the portl nd heptic veins nd crotid rtery. Since tropine infusion decresed bsorption of glucose, nd in order to chieve comprble portl vein levels of glucose nd insulin, the dogs receiving tropine were given 1.9±.1 g/kg glucose, compred with the control dogs who received 1.1±.1 g/kg. The percentge of the glucose lod tht ws bsorbed ws greter in the dogs not given tropine (8±4 vs. 44±7%), but becuse of the different lods, the bsolute mount of glucose bsorbed ws similr in both groups (2.2±1.6 vs. 21.7±4.1 g). Although delyed by tropine, the pek portl vein glucose nd insulin concentrtions nd the mounts presented to the liver were similr in both groups. However, the incresed portl vein plsm flow nd frctionl heptic extrction of insulin observed fter orl glucose ws not observed in the dogs infused with tropine. The net heptic glucose uptke fter orl glucose ws significntly less t 1, 2, nd 45 min in the tropinetreted dogs, nd the re under the curve over the 18min period ws 44% less. However, the ltter ws not sttisticlly significnt. nfusion of GP with peripherl intrvenous glucose did not increse heptic uptke of glucose or the frctionl heptic extrction of insulin compred with peripherl intrvenous glucose lone. These results indicte n importnt role for prsympthetic innervtion in the ugmented frctionl heptic extrction of insulin, nd incresed portl vein plsm flow fter orl glucose. Although reltionship between the ugmented frctionl extrction of insulin nd the net heptic glucose uptke my exist, it does not necessrily indicte tht the former is required for the ltter. Such prsympthetic innervtion my Dr. shid's current ddress is First Deprtment of Medicine, Kgw Medicl School, Miki, Kit, Kgw 7617, Jpn. Address correspondence to Dr. Field, St. Luke's piscopl Hospitl. Receivedfor publiction 28 December 1983 nd in revisedform 24 April J. Clin. nvest. The Americn Society for Clinicl nvestigtion, nc /85/9/1174/8 $1. Volume 76, September 1985, be involved in the greter removl of glucose by the liver fter orl compred with peripherl glucose dministrtion. The ugmented heptic uptke of glucose nd frctionl heptic extrction of insulin fter orl glucose does not pper to be medited by gstric inhibitory polypeptide. ntroduction The frctionl heptic extrction of insulin incresed fter the orl dministrtion of glucose (13). Under these circumstnces, both the mount of insulin nd glucose presented to the liver lso incresed, but neither one seems to be the signl for the ugmented frctionl heptic extrction of insulin. Thus, infusion of insulin into the portl circultion, which reproduced the concentrtions chieved fter orl glucose, did not increse frctionl heptic uptke of insulin (4). n ddition, infusion ofglucose into the portl vein to mtch the portl vein glucose concentrtion obtined fter orl glucose did not ugment frctionl heptic extrction of insulin (3). n these ltter studies, the net heptic uptke of glucose ws similr whether the glucose ws given orlly or infused into the portl vein, confirming the erlier results of Bergmn et l. (5). However, such net heptic uptke ofglucose ws greter thn when n equivlent mount ofglucose ws infused into peripherl vein (3). The present studies exmined the role of the prsympthetic nervous system on the ugmented frctionl heptic extrction of insulin nd heptic glucose uptke fter orl glucose. The possibility tht gstric inhibitory polypeptide (GP)' ws responsible for the greter heptic glucose uptke fter orl compred with peripherl intrvenous glucose dministrtion ws tested by portl infusion of GP nd peripherl infusion of glucose. Methods Animls nd surgery. Helthy, dult mle nd femle mongrel dogs, weighing 236 kg, were prepred with ctheters in the portl vein, left common heptic vein, nd crotid rtery, nd Doppler flow probes on the portl vein nd heptic rtery s previously described (3). The tip of the ctheter in the portl vein ws positioned immeditely below the portl vein bifurction. Postopertively, the dogs were fed one cn of KenL Rtion (Rlston Purin Co., St. Louis, MO) ech dy, nd the ctheters were flushed with 2 ml heprinized sline (5 U/ml) dily to prevent thrombosis. xperiments were done in overnight fsted, conscious, nd unrestrined nimls t lest 2 wk fter recovery from surgery. xperiments were done on nimls whose hemtocrits were >3%, who ppered in helthy condition, nd hd good ppetite with norml stools. During the experiments, phsic nd men control blood pressure ws mesured using Stthm P23 db pressure trnsducer tht ws connected to the rteril ctheter. xcept for n initil increse ssocited with ingestion of glucose, the blood pressure did not chnge significntly 1. Abbrevition used in this pper: GP, gstric inhibitory polypeptide Z. Chp, T. shid, J. Chou, R. Lewis, C. Hrtley, M. ntmn, nd J. B. Field

2 throughout ech experiment. Blood smples for glucose, insulin, glucgon, nd GP were collected simultneously from the portl vein, heptic vein, nd crotid rtery in chilled tubes contining 5 U Trsylol (FBA Phrmceuticls, nc., New York, NY) nd 1.2 mg DTA/ml of blood. Blood flows in the portl vein nd heptic rtery were mesured continully (3). They were corrected to plsm flow bsed on hemtocrits obtined every 3 min, since glucose nd insulin were mesured in plsm. Sline ws infused into the cephlic vein to compenste for blood loss S U1 j& 8 * Orl Glucose xi2t1.z.lzi j 2 OPortl Vein Or OHeptic Vein &,Heptic Artery Men+SM i mp<.5 ~ 24' C. 16 U co C~ 8 U Atropine.314g/kg/min Orl Glucose lin r i coportl Vein OHeptic Vein &Heptic Artery i Men±SM ' 24 8 t 2 J 16 Orl Glucose oportl Vein cheptic Vein 6&Heptic Artery Men±SM n =7 *uhp<.5 vs. Bsl 24 2 (D.' 16 D :! 12' U Atropine.3Mg/kg/min * Orl Glucose coportl Vein o'oheptic Vein Artery Men+SM *UAP<.5 vs. Bsl OOC P<.5 vs. Bsl ( 8 3 3o o c OR1 1 8._C 6 4 co 2 z Atropine.3 hg/kg/min U Orl Glucose 'V A lrl^~~ ' ooheptic Blnce oosplnchnic Blnce Men±SM * mp<.5 vs. Bsl OOP<.5 vs. Bsl g Figure 1. ffect of orl glucose with (right pnels) nd without (left pnels) tropine infusion on portl vein, heptic vein, nd heptic rtery plsm flow (upper pnels), plsm glucose concentrtions in the bo i9 1 2 i 1i portl vein, heptic vein, nd crotid rtery (middle pnels), nd net heptic nd splnchnic glucose blnce (lower pnels). Regultion ofheptic Glucose nd nsulin Uptke in Conscious Dogs 1175

3 xperimentl procedures Orl glucose dministrtion. After 3min control period, seven dogs consumed glucose (1.1±.1 g/kg per body weight) s 1% glucose solution in 2 min. Blood smples were obtined t 3, 2,,, O1, 2, 3, 45, 6, 75, 9, 15, 12, 15, nd 18 min. n nother seven dogs fter 3min control period (63 min), tropine ws infused into the jugulr vein from 3 to 18 min t rte of.38 mg/h fter bolus injection (1 fig) t 3 min. Glucose (1.9±.1 g/kg body weight) ws given s 1% solution orlly t zero time nd consumed in 2 min. Since tropine delyed nd reduced glucose bsorption, the glucose lod ws incresed in order to mtch the portl vein glucose nd insulin con centrtions tht were chieved fter orl glucose without tropine. Blood smples were obtined every 1 min from 6 to min, nd then t the sme times s in the experiments with orl glucose without tropine. Peripherl intrvenous glucose dministrtion with GP. After 3 min control period (3 min), GP obtined from the Ntionl nstitute of Arthritis, Dibetes, Digestive nd Kidney Diseses ws infused into the superior mesenteric vein in eight dogs from to 6 min t rte of 2 ng/kg per min. Glucose (5% in wter) ws lso infused into the jugulr vein t the following rtes:.8 mg/kg per min from to 1 min, 1.3 mg/kg per min from 1 to 6 min,.8 mg/kg per min from 6 to 75 min,.4 mg/kg per min from 75 to 9 min, nd.3 mg/kg per Orl Glucose 2 Portl Vein o.oheptic Vein &Artery i Men±SM * *AP< W ooportl Vein.OHeptic Vein 66Artery Men! SM *P<.5 i 1 c 1Q m C 5 4..i ' ' 1. Orl Glucose ooto Liver.OFrom Liver Men±SM n =7 * up<.5 vs. Bsl :3 6 j )4 r ) X 2 co U * Orl Glucose oto Liver O.OFrom Liver i Men±SM n = 7 * P<.5 vs. Bsl 3 3 6P Orl Glucose Men±SM * P<.5 vs. Bsl 6 Men±SM n =7 * P<.5 vs. Bsl 6! x.2 D x 4 2 wx: 4' Figure 2. ffect of orl glucose with (right pnels) nd without (left pnels) tropine infusion on plsm insulin concentrtions in the portl vein, heptic vein, nd crotid rtery (upper pnels), insulin bl nce cross the liver (middle pnels), nd frctionl heptic extrction of insulin (lower pnels) Z. Chp, T. shid, J. Chou, R. Lewis, C. Hrtley, M. ntmn, nd J. B. Field

4 min from 9 to 12 min. This rte ws the sme s tht infused intrportlly to mtch the portl vein glucose concentrtions fter orl glucose s previously reported (3). The control experiments for the dogs infused with GP nd peripherl glucose hve been published (3), but re included for esier comprison. Blood smples were obtined t the sme times s fter orl glucose. nsulin (3), glucgon (3), nd GP (6) were ssyed by previously reported methods. The flux of glucose nd hormone in ech vessel ws obtined by multiplying the plsm concentrtion by the plsm flow in tht vessel. Heptic vein plsm flow ws the sum of the portl vein nd heptic rtery plsm flows. The mount of glucose nd insulin presented to the liver ws the sum of the contribution from the portl vein nd heptic rtery (concentrtion times flow). The mount leving the liver ws theproduct of heptic vein plsm flow nd heptic vein concentrtion. The frctionl heptic extrction of insulin ws clculted s follows: (insulin presented to the liver insulin leving the liver)/(insulin presented to the liver) X 1%. The net heptic blnce of glucose ws obtined by subtrcting the mount ofglucose presented to the liver from the mount leving tht orgn. Positive vlues indicte net heptic glucose output, while negtive numbers represent net heptic glucose uptke. n some cses, these vlues hve been integrted over time s the re under the curve. The net bsorption of glucose ws clculted by multiplying the portl veinrteril glucose concentrtion by the portl vein plsm flow. The dt re presented s mens±sm. The bsl vlue ws the men±sm of the four vlues obtined from 3 to min. Pired t test ws employed for sttisticl nlyses of the chnge from the bsl vlue within group. Differences in men vlues between groups were detected by unpired t test. P vlues <.5 were considered to be significnt. Results Atropine infusion before the dministrtion of orl glucose hd no effect on bsl portl vein plsm flow (Fig. 1, upper right pnel). However, it significntly incresed net heptic glucose production fter 1 nd 3 min of infusion, which resulted in significnt increse in plsm glucose concentrtion in ll three vessels (Fig. 1, middle right pnel). There ws no significnt chnge in the bsl portl vein insulin concentrtion (Fig. 2, upper pnels) or frctionl heptic extrction of insulin (Fig. 2, lower pnels). However, infusion of tropine inhibited the significnt rise in portl vein plsm flow, which ws observed fter orl glucose (Fig. 1, upper pnels). The increse nd pek glucose concentrtion in the portl vein ws similr in both groups, but ws slightly, but not sttisticlly delyed nd more prolonged in the dogs infused with tropine (Fig. 1, middle pnels). The mount of glucose bsorbed into the portl system ws similr 51. cl z.5 J c ci u.s 1 cm Atropine.3 pg/kg/min f U Orl Glucose.O c l. z 3 so 9 Figure 3. ffect of orl glucose with (bottom) nd without (top) tropine infusion on net glucose bsorption. The method of clcultion of net glucose bsorption is given in the Methods section. (Top)., Men+SM, n = 7;., P <.5 vs. bsl. P <.5 vs. bsl. Other symbols sme s top. J. CL CD Figure 4. ffect of orl glucose with (bottom) nd without (top) tropine infusion on portl vein nd rteril glucgon concentrtions. o, Portl vein; A, rtery; l, men±sm, n = 6 (top), n = 7 (bottom);.,., P <.5 vs. bsl. Regultion ofheptic Glucose nd nsulin Uptke in Conscious Dogs 1177

5 l in both groups of dogs (2.2±1.6 g in control nd 21.7±4.1 g in tropine dogs) (Fig. 3). This ws chieved by dministering lrger mount of glucose to the dogs receiving the tropine infusion. Thus, while 8±4% of the 1.1±.1 g/kg glucose given to the control dogs ws ccounted for in the portl system, only 44±7% of the 1.9±.1 g/kg glucose dministered to the tropine dogs ws found in the portl system over the 3h period. The net heptic glucose uptke ws significntly less t 1, 2, nd _ T15 Glucose _ f ntrvenous Glucose nfusion (mg/kg/mln) 1711 ooportl Vein 2 &.ehoptic Vein eartery.1. f T1 Glucose 14 1 ~~~~~(mg/kglmln) ntrvenous Glucose infusion 1=11 *To Liver ), (1, oofrom Liver Q 8 4) cmt,% 2 c 2 m 4 o ; r l ntrvenous Glucose nfusion o~~~~115 Glucose n = 1 1 i l Figure 5. ffect of intrportl GP nd peripherl intrvenous glucose infusion on plsm glucose (upper pnels), glucose blnce cross the liver (middle pnels), nd net heptic glucose blnce (lower pnels). 45 min in the dogs infused with tropine compred with the control dogs (Fig. 1, lower pnels), while the splnchnic glucose output ws similr in both groups. Although the shpe of the curve ws different, net glucose uptke s ssessed by the re under the curve over 18 min ws not sttisticlly different in the two groups (5.6±1 vs. 3.2±.9 g). After orl glucose, glucose uptke ws greter nd ws no longer present fter 9 min, while fter tropine it persisted for the reminder of the experiment. 1= 2 o 1 _1,4 1 )F 1,2 C.) S.. 1., c4 1._.i or ) f.7( GP 2 ng/kg/min F 1 15 Glucose 17 T O (m9/kgimin) ntrvenous Glucose nfusion n41 oop~rtsl Vein...Hepetic Veil.Artery GP 2 ng/kg/min T15 Glucose 1 (mg/kg/mmn) ntrvenous Glucose nfusion ns *.To Liver cofrom Liver F GP 2 ng/kg/min L 1 15 Glucose ntrvenous Glucose infusion 17= The dt from the nimls infused with glucose without GP (left pnels) hve been published previously (3) Z. Chp, T. shid, J. Chou, R. Lewis, C. Hrtley, M. ntmn, nd J. B. Field

6 nfusion of tropine ws ssocited with dely in the increse in portl vein insulin concentrtions compred with orl glucose lone (Fig. 2, upper pnels), but the vlues eventully chieved were greter thn fter glucose lone. The dely in the rise in portl vein insulin concentrtions reflected the slower increse in rteril glucose vlues fter tropine nd orl glucose. The insulin concentrtions in the heptic vein t 6 nd 75 min nd rtery t 6 min were significntly greter in the tropine dogs compred with the controls (Fig. 2, upper pnels). Bsl frctionl heptic extrction ofinsulin ws similr in both groups of dogs nd ws not influenced by tropine infusion (Fig. 2, lower pnels). Orl dministrtion ofglucose ws ssocited with significnt incresed frctionl heptic extrction of insulin, in confirmtion of previous results (13). n contrst, despite similr mounts of insulin nd glucose presented to the liver fter orl glucose nd infusion oftropine, no significnt increse in the frctionl heptic extrction of insulin ws observed, nd, in fct, the vlues t 1 nd 6 min were significntly less thn the control. During the infusion of tropine lone, there ws significnt (P <.5) increse in the plsm glucgon concentrtions when the verge vlue during tropine ws compred with tht before its infusion (Fig. 4). Atropine did not modify the decline of plsm glucgon levels induced by orl glucose (Fig. 4). Peripherl infusion of glucose produced similr rteril nd heptic vein glucose concentrtions to those chieved fter orl glucose, but the portl vein glucose concentrtions were significntly less in the former sitution (3) (Fig. 1, middle left pnel, nd Fig. 5, upper left pnel). However, infusion of GP into the portl system to mimic the increse observed fter orl glucose (Fig. 6) hd no pprent effect on the glucose concentrtion in the three vessels during peripherl intrvenous infusion ofglucose (Fig. 5, upper right pnel). As reported previously (3), the net heptic glucose uptke ws significntly less fter peripherl intrvenous glucose dministrtion compred with orl glucose (Fig. 1, lower left pnel, nd Fig. 5, lower left pnel), nd ws not incresed by the concomitnt infusion ofgp into the portl circultion. Although GP did not modify net heptic uptke of glucose fter its peripherl intrvenous dministrtion, it did hve biologic effect, in tht it ugmented pncretic insulin 2,4 ~ 2$1,6 3.. CD o , Figure 6. Portl vein GP concentrtions fter orl glucose compred with those chieved with intrportl GP nd peripherl vein glucose infusion. o, Orl glucose; o, intrvenous glucose plus GP; *, men+sm, n = 6;.,., P <.5 compred with bsl. secretion in response to the hyperglycemi (Fig. 7, upper pnels). Thus, fter GP, the mount of insulin delivered to the liver incresed to 95±23 mu/min t 6 min, compred to 6±4 mu/ min with peripherl intrvenous infusion of glucose without GP. GP did not modify the suppression of glucgon fter the intrvenous infusion of glucose (Fig. 7, middle pnels), nd hd no effect on the frctionl heptic extrction of insulin (Fig. 7, lower pnels). Discussion The mechnism for the ugmented frctionl heptic extrction of insulin fter orl glucose (13) compred with peripherl intrvenous glucose infusion (3) is not known. We hve previously discussed the reltionship between the mount of glucose presented to the liver nd frctionl heptic extrction of insulin nd the evidence tht the former does not determine the ltter (3). The present results with tropine provide dditionl support for this conclusion. Thus, despite equivlent mounts of glucose reching the liver fter orl glucose in the two experiments, tropine inhibited the expected incresed frctionl heptic extrction of insulin (Fig. 2, lower pnels). Since tropine delyed nd decresed the bsorption of glucose, it ws necessry to dminister significntly lrger mount of glucose to these dogs to chieve comprble portl vein concentrtions of glucose in the two groups (Fig. 1, middle pnels). This ws chieved s indicted both by the ctul glucose concentrtions in the portl vein s well s by the mount of glucose bsorbed over the 3h experimentl period (Fig. 3). Since the rte t which the portl vein glucose concentrtion incresed ws more rpid without tropine, it is possible tht this could be n importnt fctor in the ugmented frctionl heptic extrction of insulin. However, our previous experiments in which orl nd intrportl glucose were dministered mke this less likely (3). Thus, despite the sme mounts nd rtes of glucose presented to the liver, incresed frctionl heptic extrction ofinsulin ws observed only fter orl glucose. Since tropine infusion did not decrese, nd my hve ctully incresed the insulin response to orl glucose (Fig. 2, middle pnels), it is unlikely tht chnges in the mount of insulin presented to the liver re importnt in the ugmented frctionl heptic extrction of insulin fter orl glucose. xperiments in which different mounts of insulin were infused into the portl circultion lso indicted tht insulin ws not n importnt determinnt of its frctionl heptic extrction (4). Severl other possibilities must be considered to explin the inhibition by tropine of the incresed frctionl heptic extrction of insulin. These include the role of incresed portl vein plsm flow nd the secretion of gut fctors. Since tropine inhibited both the incresed portl vein plsm flow (Fig. 1, upper pnels) nd ugmented frctionl heptic extrction of insulin fter orl glucose (Fig. 2, lower pnels), the former my be n importnt determinnt of the ltter. Such reltionship is consistent with our previous observtion tht ingestion of met incresed both portl vein plsm flow nd frctionl heptic extrction ofinsulin (7). However, infusion ofrginine nd cholecystokinin lso significntly incresed portl vein plsm flow, but ws ssocited with significnt decrese in frctionl heptic extrction of insulin (8). Conflicting results hve been obtined in the isolted perfused liver regrding the effect of flow on heptic extrction of insulin (9, 1). Although the present experiments do not permit conclusion concerning the role of portl vein plsm flow in frctionl heptic extrction of insulin, they Regultion ofheptic Glucose nd nsulin Uptke in Conscious Dogs 1179

7 c ) ) m CL x 4 g ntrvenous Glucose infusion 1 Glucose (mg/kg/min) 17=11 o Portl Vein in*heptic Vein e Artery 15 Glucose o (mg/kg/min) ntrvenous Glucose nfusion =1 1 ooportl Vein * l*heptic Vein _ Artery Glucose (mg/kg/min) ntrvenous Glucose nfusion n=11 * nsulin 11 oglucgon :i, %w 4.i C r cm A ' C ' L 6 o 5 x 4 w vw To ~~~~~(mg/kg/mmn) GP 2 ng/kg/min 15 Glucose X7 T (mg/kg/min) ntrvenous Glucose nfusion nz8 oo Portl Vein *4Heptlc Vein * Artery GP 2 ng/kg/min 18 GP 2 ng/kg/min cs15 Glucose ntrvenous Glucose nfusion m8 nsulin T T T T oo oglucgon T15 Glucose (mg/kg/min) ntrvenous Glucose nfusion n=8 oo Portl Vein Figure 7. ffect of intrportl GP nd peripherl intrvenous glucose infusion on plsm insulin (upper pnels), plsm glucgon (middle pnels), nd frctionl heptic extrction of insulin (lower pnels). The dt from the nimls infused with glucose without GP (left pnels) hve been published previously (3). provide informtion relted to the mechnism of such incresed plsm flow fter orl glucose. ncresed portl vein flow does not directly reflect the portl vein hyperglycemi or the mount of glucose bsorbed, since these were similr in both groups of dogs. The present studies, however, cnnot exclude the rte of bsorption s being importnt, since this ws delyed by tropine (Fig. 3). nhibition of the incresed portl flow by tropine suggests tht it is dependent upon n intct muscrinic prsympthetic innervtion. t could be direct prsympthetic effect, or it could be medited by relese of gut fctors in response to ingestion of nutrients. The filure of portl infusion of GP with peripherl infusion ofglucose to increse frctionl heptic extrction of insulin (Fig. 7, lower right pnel, compred with Fig. 2, lower left pnel) confirm the previous results of Polonsky et l. ( 11) nd indicte tht this gut hormone is not involved in tht phenomenon. The portl vein GP levels obtined during its infusion were ctully greter thn those chieved fter orl glucose (Fig. 6), nd the biologic effectiveness of the GP is in 118 Z. Chp, T. shid, J. Chou, R. Lewis, C. Hrtley, M. ntmn, nd J. B. Field

8 dicted by its potentition of insulin secretion fter peripherl intrvenous infusion of glucose (Fig. 7, upper pnels). These results do not preclude the involvement of other gut hormones in the incresed frctionl heptic extrction of insulin. The present results provide dditionl informtion concerning the greter heptic glucose uptke fter orl nd intrportl glucose compred with peripherl intrvenous glucose (3). t seems unlikely tht the greter uptke of glucose by the liver fter orl glucose (Fig. 1, lower pnels) is due to the ugmented frctionl heptic extrction of insulin (3). Thus, heptic glucose uptke ws similr fter both orl nd intrportl glucose dministrtion (3, 5), but only the former ws ssocited with incresed frctionl heptic extrction ofinsulin. Whether tropine decresed the greter heptic glucose uptke fter orl glucose depends upon how the dt is evluted. t significntly diminished it t 1, 2, nd 45 min, while there ws no significnt difference when it ws clculted s the re under the curve. f tropine does not decrese the heptic uptke of glucose, yet inhibited the frctionl heptic extrction of insulin, it indictes tht the ltter is not necessry for the greter heptic uptke fter orl glucose. However, if tropine did decrese the heptic uptke of glucose, it still does not necessrily prove tht the two re relted. The different shpes of the curves of net heptic glucose uptke with nd without tropine my reflect severl fctors. First, tropine itself incresed heptic glucose production (Fig. 1, lower pnels), nd trnsient continution of this effect might ffect net heptic blnce. This lmost certinly reflects the increse of glucgon in the portl vein during tropine infusion lone (Fig. 4). Secondly, the rte of glucose bsorption ws slower fter tropine. However, these differences my not fully explin the significntly greter net heptic glucose uptke fter orl glucose during the first hour s compred with the uptke with tropine infusion; this is especilly true since the pek levels of glucose in the portl vein occurred during this time. Gut (1215) or neurogenic fctors, especilly prsympthetic (16, 17), my be importnt in the control of heptic glucose uptke. Thus, the inhibition by tropine of the ugmented net heptic glucose uptke during the first hour fter orl glucose could reflect inhibition ofneurogenic or gut fctors. t is unlikely tht GP is responsible for the ugmented heptic uptke of glucose, since its dministrtion (which resulted in portl vein GP concentrtions greter thn fter orl glucose [Fig. 6]) with peripherlly infused glucose did not increse heptic uptke of glucose or reproduce the effect obtined with orl or intrportl glucose (3). A role for the prsympthetic nervous system is lso suggested by the results of Mondon nd Burton (16), who reported tht phrmcologic mounts of cetylcholine in the presence of insulin mrkedly enhnced the uptke of glucose by the isolted perfused rt liver. n ddition, electricl stimultion ofthe prsympthetic nerves isolted from round the common heptic rtery rpidly suppressed heptic glucose output (17). Our finding tht tropine significntly reduced the net heptic glucose uptke fter orl glucose during the first hour suggests the possibility tht muscrinic prsympthetic ction is responsible for this chnge in heptic glucose metbolism. Acknowledgments The uthors re indebted to the stff of the Crdiovsculr Sciences Section for their superb help in the execution of these experiments. Dr. Thoms O'Dorisio nd Dr. Smuel Ctlnd, Deprtment of Medicine, Ohio Stte University School of Medicine, Columbus, OH, kindly provided the ssys ofgp. We would lso like to thnk Mrs. Shelley Dering nd Ms. Brbr Sims for their outstnding ssistnce in the preprtion of this mnuscript. This work ws supported by U. S. Public Helth Service grnts AM nd AM from the Ntionl nstitutes of Helth. References 1. Kden, M., P. Hrding, nd J. B. Field ffect of intrduodenl glucose dministrtion on heptic extrction of insulin in the nesthetized dog. J. Clin. nvest. 52: Jspn, J., nd K. Polonsky Glucose ingestion in dogs lters the heptic extrction of insulin. n vivo evidence for reltionship between biologic ction nd extrction of insulin. J. Clin. nvest. 69: shid, T., Z. Chp, J. Chou, R. Lewis, C. Hrtley, M. ntmn, nd J. B. Field Differentil effects of orl, peripherl intrvenous nd intrportl glucose on heptic glucose uptke nd insulin nd glucgon extrction in conscious dogs. J. Clin. nvest. 72: Hrding, P., G. Bloom, nd J. B. Field ffect of infusion ofinsulin into portl vein on heptic extrction ofinsulin in nesthetized dogs. Am. J. Physiol. 228: Bergmn, R. N., J. 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