Res. 11: 874-877 (1977)
Glucose homeostasis metabolism
neonate prematurity t r a c e r kinetics
Glucose Homeostasis in Preterm Rhesus Monkey Neonates W . GEOFFREY SHERWOOD,':"' D O N A L D E . HILL, A N D G R A I l A h l \V. CHANCE f'eri~r~jt~jl Gro1t.111 111rdD C \ , C ~ / O ~ I1'rogr(111111rc, IICII~ f < ~ ~ . s c ~Ij~r c~/.~\ t i t ~111rcI i t ~ ,I, > ~ ~ ~ ~ ~ ~ofI lI 'I ~I ~C ~~ ~I ~I ~/ Li ~l i ~ ,tir, si i~of o ~ ~. s , fo. Of~rtrrio. Crrr~rrtltr Pc3rirrrrtology, Tlre llo.\pirctl fi)r Sick C l ~ i l t i r o Toroil ~,
causes of liypcrglycemia in the neonate such as scpsis (27) and hyposi;~(2). \vliich ;ire themselves :issociatccl with increased Response to a prin~edglucose infusion (0.5 g/kg injected over mortality. hlany very low birth \\.eight neonates esperiencc hy3 niin and 8 nig/kg/r~~in infused for 3 hr) was studied in 5 tern1 pcrglyccmi;~where n o immediate etiologic factor can he inipliand I I preterni rhesus n~onkeyneonates 2-3 hr after delivery by cated. Sueti neonates represent n dilemma in clinical m:uiagccesarian section. The glucose challenge perturbed a steady state mcnt. namely. the provision o f continued nutritional support in glucose specific activity achieved in the previous 100 rnin hy a the presence of hypcrglyccnlia tvith resultant osmotic diurcsis prin~edtrace infusion of 2-[:'li]glucose (6 p C i and 0.2 pCi/nlin). and water-electrolyte imbalance. This allo~redthe dcterrrlination of changes in enclogenous gluKno\vlcdge of underlying mechanisms is esscnti:ll in order t o cose turnover in response to exogenous glucose in the in~niediate ration:rlizc the clinic;ll rnan;lgcmcnt. T h e purpose of this study nerrhorn period. \\'as t o clevclop a primate rnodel ;rncl apply :I study protocol to the \Vith glucose challenge, the 5 tern1 anin~alsand 6 of the 1 1 prematurely dclivcred rhesus monkey neon:ltc in order to invcspretern~animals developed a ilew steady state glucose concentigate postnatal glucose homeostasis utilizing radioactive tracer tration (80-100 n~l/dl).Coincident with this was a marked rekinetic methodology. duction in endogenous hepatic glucose output ancl a n~oderate increase in peripheral glucose utilization as rr~easuredby the tracer methodol(~gy.In contrast, the other five preterni monkeys developed hyperglycemia upon glucose challenge (190-210 mg/ PROCEDURES dl). All groups had siniilar glucose-stimulatctl insulin release trhich peaked after 60 niin of glucose infusion. lIowever, in O u r primate population \vas clcrivccl from the breeding colony comparison to the other groups, the group that was to develop m:iint;rined in the Psychology Department of the U~livcrsityof hyperglycemia exhibited: ( I ) lo\rer I m a l insulin and higher \Vatcrloo, Ontario, where conception was tirnccl to * I day. basal glucose values; ( 2 ) no suppression of endogenous hepatic Sixteen rhesus monkeys (i\lacrrcrr rr~rrlnrrrr)were rlelivcrcd by glucose output o r lipolysis despite glucose-stimulated insulin ccsarian section under kctanline-HCI :~ncsthcsi;~(29): 5 near release; ( 3 ) lower birth weight and gestational age, ancl incrcasccl evcntu:il n~ortality. IIypoxi:~ rv:is not cviclc~~t in i ~ n y term ( 1 58 clays) ancl I l prcm;~turcly(1 3s- 1-12) cl;~yh).Others have sho\vn that the increase in the amniotic fluicl Iccithingroup as evidenced by clinical signs and decreasing lactatel spliingomyelin ratio in rhesus nlonkeys commenced a t arounri pyruvate ratios during the glucosc infusions. 1-10 days of gestation (1 1). All of o u r preterm neon;itcs eshihitcd clinical signs of pulmonary immaturity. 'The mothers Speculation were ci~loriedcprived overnight hut allo\vcd water rirl 1iDitutl1. During :inestlicsia. a slo\v intravenous infusion of 0 . 9 % sodium The inability of cert:~in preternl rhesus rnonkeys to niaintain chloride solution \vas administered. l'hc iiveritgc time from initinormoglycen~ia,but rather to develop hyperglycemia in the face ation of n1atcrn:rl anesthesia to delivery was 20-35 1iii11. of a glucose infusion niight I)e related to inappropriate adrenerIJmhilical arterial ;rncl venous catheters (30) were pl;iccd and gic activity unrelated to either hypoxia o r hypothermic stress. secured in all the ncon;ltes immediately after delivery. All of thc This represents an aninial n~odelfor the further stucly o f hyperpretcrm newborns underwent enclotrache:~l i11tuh;ition \vitIi auitglyccniia seen in certain hurnan pretern~neonates. ably sized tuhcs ( 3 1). Ventilatory support \v:is provided in order t o maintain good clinical oxygenation ;IS indicated by pink bucci~l T h e development of metabolic control of postnatal energy mucosac. This was achicvecl by :111 incrc;~seclinspirntory oxygen concentration (FI,,,,)in the range of 0.3-0.5 and the application hon~eostasisremains an enigmatic area in perinatal medicine. Neonatal hypoglycemia has received much attention because of o f continuous :iir\vays distending pressure in the rangc of 5-8 crn its association with neurologic aymptomntology and conscqucnt water. I n those prcterm ncon;ltcs who exhibited some irrcgularcerebral danlagc. A s a result of technologic advances vcry lo\\, ity in respiratory pirttcrn \vith a tendency to\vards periods of birth weight neonates arc surviving in increasing nunil>crs. A apne;i. prophylactic intermittent positive pressure ventilation high incidence of hyperglyccmi;~(hlood glucose values greater \\,as provieled (33). This ivas recluired only during the first 2 hr of than 125 n1g/100 n ~ l has ) been reported when glucosc is adminislife. Adccluatc rib cage movement was achieved wit11 inspiratory tered either orally o r intravenously in clu;intitics that \vould he pressure in the rangc of 30-25 c11i \\later and inspiratory rate in \vcll tolerated and maintain cuglycemia in most neonates ( 5 , 6). the rangc of -10-SO/min. T h e small hlood volume of these neoEthicill, rather than technical, considerations rightly prevent nates prohibited intermittent nlonitoring of hlood pH. pO,. and comprehensive investigation of the m;~turationof glucosc homcpCO,. Cathcteriz;~tionancl intubation were complctccl \vitliin 5 ostasis in these infants. min of severance of the umbilical cord. T h e catheters were Reports of hypcrglycemia in vcry lo\\, birth \vcight neonates maintained patent with a slo\v saline infusion dclivcred hy conindicate a nonspecific :lssociation \vith increased mortality (-1. 6, st:int infusion pump. These procedures \Yere pcrfurniccl under an 9, 2 2 , 28). Ho\vever, few series have escluclcd the recognized infrared racliant heat \varmer. T h e nc\vborrls were then pl:iccd
immediately in :I prewnrnied incubator in \vliich the t c ~ n p e r : ~ t u r e Grorrp I', sho\ved a significantly lo\\,cr level, 4 t 3 pU/rnl (I' < was maintained a t 30'. Neither core nor skin temperature was 0 . 0 0 1 ) . In all groups, tlie glucose-stimulated insulin release peaked to similar levels 6 0 rnin ; ~ f t c rcommencement of the directly monitored. primed glucose infusion. T h e peak levels ~ v e r e6 8 ? 4 , 6 7 1 10, and 4 7 + 7 p U / m l in,qrorrps PI, T, and I',. respectively (NS). S T U D Y I'ROTOCOL I he ne\vborns \vcre :~llo\vedto achieve clinic:~lst;~t>ilityfor 3-3 h r . T l i c ~ i:I primed infusion of 3-[:'lI]glucose of high specific activity ( 6 p C i follo\ved by 0 . 2 pCi/min) (33) in normal saline was aclministcrecl via the umbilical venous catheter. After 1 0 0 niin of isotope infusion. a primed infusion of "cold" glucose was added t o the intr:~venousndministr;~tio~i.. Glucose dosage \\,as 9 . 5 g/kg injected over 3 min follo\ved immccli:~tely by 8 mg/kg/ rnin infusecl for 180 min. ~l'hroi~gliout, the rate of fluid aclministcrcd was maintained in the range of 80-130 ml/kg/34 hr (3.35.0 ml/kg/lir). Heparinized blood samples \yere obt;liricd serially from the umbilical artery catheter. T h e total hlood volume was depeletcd I>y less than 5 % during any single study. 7
1NTERhfEDIA.I'E h1ETABOLITE D A T A (FIG. 2 )
Tlic two groups of preterm neonates, I', and P,, ivcre comp ; ~ e din terms of free fatty acid and P-hydrosybutyrate levels. I n the I':! group the basal frcc fatty acid levels were higher, 0 . 5 8 + 0 . 0 9 versus 0 . 3 0 t 0 . 0 8 mhl (I' < 0 . 0 5 ) . anel \verc not suppressed despite glucose-stimul:~ted insulin release. l ' h e levels rose margin;~lly to 0 . 6 4 + 0 . 0 7 mhl after 6 0 rnin of glucose infusion i n g r o u p p 2 . Similar trends were found in the 3-hydrosyhutyr;~te levels. T h e corresponding v ~ ~ l u efor s g r o u p 7' tvcre similar to those for grorcp I',. Tlie hasal lactate values of grolrps PI a n d I', \Yere 1 .I + 0.4 mhl and 1.7 t 0 . 7 m h l , respectively. T h e corresponding blood pyruvate levels \\,ere 0 . 0 3 8 + 0 . 0 0 7 a n d 0 . 0 3 7 + 0 . 0 0 6 m h l ; tlie
L A B O R A T O R Y hlE'I'l1ODS
Each sample was assayed for hlood glucose (14). pli~srna insulin (76). ~ I ; I S I I ~ ; I free fatty ;~cids(16), h100cI I:rctatc, pyruvatc. and 3-I1yclroxyhutyratc (3). G l u c o ~xpccific ilctivity \vas nic:~surcd in :I 100-p1 :~liquotof the filtrate ohtained by dcproteinizing and ec~uivolunicof \\hole hloocl \\,it11 0 . 6 hl perchlosic acid. rl'lie aliquot \v:~s evaporatecl to dryness irr \3rcclto. 7'hc residue was reclissolvccl in 100 p1 distilletl water. 11r;~y'ssolution was aclclccl hefore counting in :I Beckman liquid scintillation counter. Appropriate hlanks anel stanclarcls \vere run for each study in o r d e r to allow for cluench correction. CALCULATIONS
With krio\vlcdgc o f tracer infusion rate a n d glucosc specific activity. glucose turnover rate was calculated by tlie method of Stcclc (15. 7 5 ) for the basal situ;~tionancl a t hourly intcrv:~ls during the glucose-stimulated situ:~tion.It was expressed as endogenous hepatic glucose output o r R,, anel peripheral glucose utilization o r R,, in the units of rnilligrarns of glucosc per kg per min.
Throughout this section. tlie results arc presented ;IS mean + I S E . There are no significant differences bct\vccn gro1rp.s I', ;Inel T for bloocl glucose, insulin. internicdiary mctaholite. tracer kinetic. o r corcl hloocl d a t a . Significant differences (I' values), :I\ cleterminecl by S t ~ ~ c l c n tI-test. 's arc presented for the I', group in comparison t o the I', group. T h e rctrospectivc separation within the psetcrm ne\vl>orn is h:~sed on the ohscrvation of t\vo very cliffercnt glycernic responses to prirnecl glucose infusions. -1'hat tliffcrencc is cxtrcmcly significant.
Fig. I . Sciluential changes in I.rlood glucoxc and serum insulin values hefore ;md during prirncd glucosc infu\ion. T: term newborn (158 days); I', and P,: preternl neonate5 (around I40 days).
Tlie patterns of blood glucosc response t o primed glucose infusion inilic:itc that the I I pretcrni ne\vlx)rn\ f;~ll into two categories. Five. clesignatcd 1', responded in a manner s i m i l ~ to ~r five term nc\vborns. elcsignatcd 7'. 'Ilic hasal glucose conccntrations \\ere simil:~r61 t S mglcll a n d 5 5 + 6 mg/dl, rcspcctivcly. a n d both groups developed :I ne\v glucose steady state glucosc concentration in the range of 80-100 mg/dl aftcr a n initial peak f o l l o ~ i n gthe p r i ~ n i n gdose of glucose. Tlic o t h e r six preterm ne\vhorns, designated I',. eshihitecl a higher basal glucose level. 8 0 + I mg/dl (I' < 0.005). and cleveloped a new stcatly state glucose concentration in the range 190-3 10 nig/cII (I' < 0.005).
I'LAShlA INSUL-IN D A T A (FIG. I )
ch;lngc\ in serum frcc fatty acids ( F I : / t ) .3-hydrosyFig. 7 . Secluc~~tial hutyr;~te(3llOB). I;lct;~te pyruvatc, ;uid lactatelpyruvatc (LII') ratio 'fhe hasal insulin values for Srolcps I', ancl T were not significantly different. 16 t 4 and 7 7 + 1 3 pU/niI. respecti\~cly. hcforc a n d during primcd glucose infusion.
SHER\VOOD. HIL.L, AND CHANCE
corresponding lactate/pyruvate nlolar ratios wcrc 31 t 6 and 4 7 t 7. During the glucosc challenge, the ratio progrcssivcly fell in all groups t o a range of 15-20 as the blood lact:rte and blood pyruvate values rose. T h c corresponding values f o r g r o ~ r pT \\ere similar to those for grorrp p , . TRACER KINETIC DATA
RD o 5
In the basal stezrdy state situation, the endogenous hepatic glucose output rate, R , , \\,as cclual to the peripheral glucosc utilization ratc, R,). For grolrps T. P,, and P,, the basal glucose turnovcr ratcs were not statistically different; 5 . 4 2 0.9. 6 . 7 2 0 . 7 , and 7.3 + 0 . 6 mg/kg/min. I n all groups, R I ,increased to the range 9-12 n~g/kg/niinduring the glucosc infusion. In grolrps T and P I , R , \\,as diminished to negligible amounts during the glucosc infusion. tIo\\'cvcr, in grolrp I':! there \\,as n o significant diminution of R,\.
CORD 13I.OOD DATA
T h e cord lactate values for groirps T, I',, and P, were 2.88 + 0.44. 1.5 + 0.17, and 7 . 6 + 0.67 m h l , respectively. .I'hc corrc5ponding pyruvate value\ \\'ere 0.077 + 0.070, 0.018 + 0 . 0 18. and 0.111 + 0 . 0 3 0 n ~ h l . STUDY
Retrospective analysis of the netvborns studied shotved that the "hyperglycemic" preterm group (P,) esliibitcd a lo\ver hirth weight ( P < 0.05). shorter gestational period ( P < 0.05). and higher eventual niortality (NS) when compared to the other prctcrnl group ( P , ) . Characteristics for the full term control group ( T ) are given for comparison.
Fig. 3 . Sequential changes in endogenous hcp:~ticglucose output (R,,) and peripheral utilization ratc of glucosc (Irith \vcight ncon;lte. 32. P u r i t : ~I3ennctt ~~ 1'11 2 vcntil:~tor. Linclly 1o;lncd hy Purit;~nI3ennctt Conip;lliy Ltd.. i c : ~ I ~ no. TI