Physiology&Behavior,Vol. 54, pp. 1021-1023, 1993
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Metabolic Correlates of Behaviour in the Newborn Infant G I O V A N N A M A R C H I N I , *~ B E N G T P E R S S O N * A N D K E R S T I N U V N A S - M O B E R G I "
*Department of Pediatrics KS-St. Gi~ran, Karolinska Hospital P.O. 60500 S-104 01 Stockholm, Sweden and i'Department of Pharmacology, Karolinska Institute, P.O. 60400S-104 01 Stockholm, Sweden Received 23 N o v e m b e r 1992 MARCHINI, G., B. PERSSON AND K. UVNAtS-MOBERG.Metaboliccorrelatesofbehaviourin the newborninfant. PHYSIOL BEHAV 54(5) 1021-1023, 1993.--Twenty-four infants were submitted to behavioural observation 0.5 and 3.5 h after birth. Blood sampleswere collectedfrom the umbilicalcord and from the infant immediatelyfollowingobservation,for the determination of glucose, insulin, cholecystokinin(CCK), and free fatty acids (FFA). It was found that 88% of the infants were awake and 83% performed sucking movements 0.5 h after birth; these findingswere associated to a decrease in the plasma glucose concentration (p = 0.05). Eighty-eightpercent of the infants were asleep and only 12% exhibited sucking movements 3.5 h after birth; at this time point there was an increase in the plasma concentrations of both CCK (p = 0.05) and FFA (p = 0.01). The infants' plasma insulin concentrations remained unchanged during the time course. It is suggested that the initial behavioural pattern of the newborn, characterized by the appearance of sucking movements, may be due to the rapid decrease of the circulating glucose concentration. The successiveincreasein the blood concentrations of both CCK and FFA might be two of the factors contributing to the cessation of sucking and to the establishment of a sleepingstate. Infant newborn
Feedingbehaviour
Glucose
Cholecystokinin Insulin
THE newborn infant exhibits a behavioural sequence soon after birth, characterized initially by a state of wakefulness and the appearance of spontaneous sucking movements, followed by a sleeping state and the cessation of the sucking activity after a few hours (14). Various substances are known to affect behaviour. A decrease in the circulating glucose concentration elicits hunger arousal in humans (8) and feeding behaviour in rats and rabbits (7). In contrast, exogenously administered cholecystokinin (CCK) interrupts ongoing feeding and induces a satiety behaviour and a sleeping state (1). A reduction of the feeding behaviour is also found in concomitance with an increase in the circulating concentrations of free fatty acids (FFA) elicited by heparinoid injection in rats (9). The purpose of this study was to investigate whether changes in the plasma concentrations of glucose, CCK, and FFA could be associated with different behavioural states of the newborn infant. We also measured the insulin concentration in plasma, because this hormone regulates the glucose turnover. METHOD We examined 24 infant-mother pairs. The study was approved by the Ethical Committee of Karolinska Hospital. All parents gave their consent. The mothers were in good health
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Free fatty acids
and had not taken medication: seven were primiparae and 17 were multiparae. Pregnancies and deliveries were uneventful. Seven women receiving oxytocin during labor had infusions with Rehydrex containing 25 mg/ml glucose (Kabi, Stockholm, Sweden). The maximal infusion velocity was 75 ml/h, which corresponded to 1.9 g glucose/h. The types of anesthesia given during delivery to the women were: pethidine (15), N20-O2 (5), pudendal block (7), epidural block (l). All infants were born at term: the gestational time was 40 _+ l weeks (mean _+ SD). The Apgar score at 5 rain was l0 in all infants. Eleven infants were boys and 13 were girls; their birth weight was 3605 + 415 g (mean + SD). The infants were dried and placed on the mother's chest during the first 0.5 h after birth, according to normal hospital practice. At about 1 h after birth, the mothers had the infants put to breast; all but two infants attached. The total sucking time was estimated to be approximately 5 - l 0 min. The infants were weighed and received vitamin K after the sucking period. The infants were observed for a period of 2 min to assess their behavioural state and presence/absence of spontaneous rooting/ sucking movements 0.5 and 3.5 h after birth; only changes lasting 2 min or longer were accepted as a new state. Behavioural state
1022
MARCHINI, PERSSON AND UVNJ~S-MOBER(, TABLE 1 PLASMA CONCENTRATIONS IN MOTHERS AND INFANTS
Maternal Umbilical artery Infant--0.5 h Infant--3.5 h
Glucose (mmol/I)
Insulin (mU/I)
CCK /pmol/I)
FFA tmmol/I)
5.7 +_0.9 [22] 4.1 ± 0.9 [24] 3.5 ± 1.1 [23] 3.0 ± 0.7 [24]
30.4 -+ 11.7 [21] 11.1 ± 2.9 [22] 10.9 ± 3.8 [20] 10.5 _+ 1.2 [22]
5.8 ± 0.7 [17] 42.0 ± 14.7 [17] 48.4 + 17.0 [17] 51.1 +_ 14.7 [17]
0.12 ± 0.05 [161 0.13 _+0.10115] 0.73 ± 0.31 [17]
Values are mean _+SD. --, not measured. Number of subjects are shown in brackets.
was defined as: state 1 = eyes closed, no/few movements; state 2 = eyes open, calm, few movements; state 3 = eyes open, gross movements; state 4 = eyes open/closed, crying. The umbilical cord was double clamped at the placental and at the infant end within 5 s after birth. Umbilical arterial blood was collected from the intermediate cord segment. Venous blood samples were also collected from the infant immediately following the observations 0.5 and 3.5 h after birth, with an openneedle technique from a vein on the back of the hand or from the antecubital vein. The infant was placed on an open bed incubator for that purpose and care was taken to keep the infant warm. One blood sample was also collected from the mother from the antecubital vein, within 10 rain of delivery. Blood sampies were collected into ice-chilled plastic tubes containing 10 U heparin (Kabi AB, Stockholm, Sweden) and 500 IU aprotinin (Trasylol, Bayer AB, Stockholm, Sweden)/ml blood. Plasma samples were obtained after centrifugation at +4°C for 10 min and were stored at - 7 0 ° C until assayed. Glucose concentration was determined using an enzymatic method (Merck, Darmstadt, Germany). Insulin concentration was determined in plasma by radioimmunoassay (RIA) (Novo Research Institute, Bagsvaerd, Denmark). Cholecystokinin immunoreactivity in plasma was measured by radioimmunoassay after purification of samples on Sep-Pak C 18 cartridges (Water Associates, Milford, MA). The cartridge was coated with 5 ml 0.1% acetic acid containing polypep 1 mg/ml (Sigma Chemical Co., ST. Louis, MO) and washed with 10 ml acetonitrile followed by 10 ml 0.1% acetic acid before the application of 0.5 ml plasma samples. After washing with 5 ml 0.1% acetic acid, CCK was eluted with 6 ml of a mixture of one volume of acetonitrile and one volume of 0.05% acetic acid. The eluate was evaporated to dryness in vacuo and later reconstituted in 250 ul of the assay TABLE 2 BEHAVIOURAL STATE AND PRESENCE OF SPONTANEOUS SUCKING MOVEMENTS IN 24 INFANTS AFTER BIRTH
State
Presenceof Sucking In Percentageof Infants (%) (%)
0.5 h State 1 State 2 State 3 State 4 3.5h State 1 State 2
12 71 4 13
100 88 100 33
88 12
10 33
buffer (0.03 M Na phosphate buffer, pH 7.4) and subjected to R1A. Aliquots of 100 ~zlwere assayed in duplicate. The antiserum used is directed against the amino-terminal of sulphated CCK8 (Otsuka Pharmaceutical Co., Ltd., Tokushima, Japan) (6), and recognizes sulphated CCK-8, CCK-33, and CCK-39 to 100%, whereas sulphated gastrin- 17, unsulphated gastrin- 17, and gastrin-34 is recognized to less than 0.1%. Synthetic sulphated CCK-8 (Cambridge Research Biochemicals, Kartson, Cambridgeshire, UK) served as standard and [125I]CCK-39 (Otsuka Pharmaceutical Co., Ltd.) was used as tracer. The detection limit of the assay was 2 pmol/1 (the concentration of the samples is taken into consideration). Free fatty acids were determined in plasma using an enzymatic colorimetric method (NEFAC, Wako Chem., Neuss 1, Germany).
Statistics Clinical and demographic data of mothers and their infants, as well as all hormone and metabolite concentrations, are given as mean + SD. Postnatal changes of hormone and metabolite concentrations were analyzed by one-way analysis of variance followed by Duncans' multiple range test. Maternal and umbilical cord hormone and metabolite concentrations were compared by paired or t-test. The degree of correlation between two variables was calculated with Spearman's test. RESULTS
There was a significant decrease (p = 0.05) in the glucose concentration from 4.1 + 0.9 mmol/l in the cord blood to 3.5 +__ 1.1 mmol/l in the infants' venous blood at 0.5 h after birth; no further significant decrease occurred at 3.5 h after birth. The insulin concentration remained unchanged (p = 0.4) during the time course. The plasma CCK and FFA concentrations increased significantly 3.5 h after birth (p = 0.05 and p = 0.01, respectively). Hormone and metabolite concentrations are summarized in Table 1. There was a significant relationship between the infants' FFA and log~0 CCK concentrations 3.5 h after birth (Rs = 0.45, n = 16, p = 0.04), but not at the other time points studied. Maternal glucose infusion did not significantly influence the glucose or insulin concentrations, either in maternal (p = 0.1 and p = 0.8, respectively), or in cord blood (p = 0.4 and p = 0.3, respectively) (Student's t-test).
Behavioural Observations At 0.5 h after birth, 88% of the infants were in a state of wakefulness, and 83% exhibited sucking movements. At 3.5 h after birth, 88% of the infants were in a sleeping state, and only 12% performed rooting and/or sucking movements (for details, see Table 2).
INFANT BEHAVIOUR
1023 DISCUSSION
The findings of this work are the observations of an association of a) a fall in the blood glucose concentration, a state of wakefulness, and also the presence of spontaneous sucking movements, and b) an increase in the blood concentration of both CCK and FFA, and a sleeping state as well as the absence of sucking activity in newborn infants. The glucose concentration in cord blood was in the same range as that reported by others (5). The significant decrease of the infants' blood glucose concentrations observed 0.5 h after birth is most probably due to the interruption of the feto-maternal circulation at delivery. The infant's capacity to compensate rapidly for this fuel withdrawal, by utilizing stored lipid, is not yet fully achieved so soon after birth, as indicated by the low plasma concentration of FFA (see Table 1). The blood glucose decrease was associated with a state of wakefulness and with the presence of spontaneous sucking movements in 88% and 83% of the infants, respectively. A drop in the circulating glucose concentration precedes the appearance of feeding behaviour in free-fed rats (11). Furthermore, glucose analogues elicit feeding in a variety of species (7); the effect is probably mediated by stimulation of the glucoreceptors in the lateral hypothalamus (2). Thus, the appearance of spontaneous sucking activity in newborn infants might be related to the decrease in plasma glucose concentration. The infants' plasma insulin concentrations did not change significantly after birth, confirming earlier findings (13). Another finding of this study is the demonstration of a gradual increment in the plasma concentration of CCK during the first 3.5 h after birth. The cord concentration of the hormone was seven times higher than the maternal hormone concentration. The reasons for the high and increasing CCK concentration in infants are not known. However, the origin of the hormone is most probably the small intestine, since circulating CCK derives mainly from this site (3). Eighty-eight percent of the infants showed no sucking activity and the same percentage of infants were in a sleeping state 3.5 h after birth. In rats, intraperitoneal administration of CCK elicits
a behavioural sequence characterized by the cessation of the feeding behaviour and the establishment of a rest and sleeping state (1). Cholecystokinin has been suggested to exert a physiological action as a satiety signal, and it has recently been shown that a specific CCK receptor antagonist induces hunger in humans (15). Thus, the significant increase in the blood concentration of CCK, which takes place 3.5 h after birth, might be one of the factors contributing to the cessation of the spontaneous sucking activity and to the establishment of a sleeping state in the newborn infant. One interesting aspect of this study is that it describes spontaneous behavioural and humoral changes not associated with food intake. Indeed, the infants were put to the mothers' breast at about 1 h after delivery, according to hospital practice. However, it is reasonable to assume that the infants on that occasion did not ingest volumes of milk capable of affecting the circulating hormone concentration, especially considering that lactation is established first on the fourth day after delivery (12). Furthermore, an increase in the plasma hormone concentration was also demonstrated in the two infants who did not attach to the mothers' breast (data not shown). There was a sixfold increase in the infants' plasma FFA concentrations 3.5 h after birth, in accordance with previous findings (5), indicating an intense lipolytic activity. Le Magnen and Devos have found that a sleeping state and a reduced feeding activity during daytime were associated with lipolysis in free-fed rats; the pharmacological or hormonal inhibition of this diurnal lipolysis induced an immediate increase in food intake (10). Furthermore, the postinsulin hypophagia was accompanied by lipolysis and increased plasma levels of FFA in the same experimental animal (4). It has also been found that during the first 2 postnatal days, when lipolysis was maximal, the breast feeding frequency was lower and the meal-to-meal interval longer than later on, in infants (12). These findings suggests that lipolyses may be another factor, besides CCK, that participates in the reduction of the sucking behaviour in newborn infants 3.5 h after birth. The reasons for the positive relationship between CCK and FFA concentrations remain to be established.
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