The 24-hour excursion and diurnal rhythm of glucose, insulin, and C-peptide in normal pregnancy

The 24-hour excursion and diurnal rhythm of glucose, insulin, tind C-peptide in normal pregnancy L.

COUSINS

L.

RIGG*

D.

HOLLINGSWORTH

G. BRINK J. AURAND s. s.

c.

YEN

La Jolla, California A longitudinal study to quantitate the progressive effects of the second and third trjmesters of normal pregnancy on the levels of plasma glucose, immunoreactive insulin (IRI), and C-peptide (C-P) at hourly intervals throughout the 24.hour “metabolic clock” was made. Identical studies were conducted in each subject at 8 to 11 weeks post partum and these data were used as nonpregnant control values. Data analyses were made to determine the role of meal-activity-sleep cycles as physioioglc modifiers. A diurnal rhythm of plasma glucose, IRI, and C-P was demonstrated in all study periods. During meals anabolic values of plasma glircose (increments above the 24.hour mean) in response to meal Intake were remarkably small, ranging between 30 and 35 mgilO0 ml in the postpartum state, and were not sfgnificantly modified by pregnancy. The corresponding IRI levels were similarly small with a mean increase on only 31% in pregnancy. However, during the third but not the second trimester of pregnancy, the peak anabolic values for both plasma glucose and IRI were significantly (p < 0.05) increased and consequently the P-hour postprandial glucose and IRI levels were significantly elevated after meal Ingestion. When values were compared with those of the postpartum state, there was a progressive increase in the degree of catabolic excursion (decrease from 24hour mean) of plasma glucose during sleeping hours from the second to third trimester of pregnancy. This resulted in a state of relative hypogiycemia, with significantly reduced fasting {S A.M.) plasma glucose and 24-hour integrated glucose levels. This relative nocturnal hypoglycemia was associated with synchronbus IRI values but without concomitant reduction of absolute IRI levels. Consequently, the fasting, premeai, and 24-hour iRi/glucose ratios were increased. Thus, basal insulin secretion is significantly augmented relative to levels of plaSt?IS glucose, but a quantitative increase in insulin secretion following food intake is relatively small during pregnancy. These observations together with the finding of a marked diurnal rhythm of plasma glucose and relative nocturnal hypoglycemia provide important insights for the formulation of guidelines for the timing, amount, and mode of delivery of exogenous insulin necessary for the management of diabetic patients during pregnancy. (Au. J. OBSTET. GYNECOL. 136:463, 1960.)

From the Department School of Medicine,

of Reproductive Medicine (T-002), University of Calijontia, San Diego.

ALTHOUGH

homeostasis during pregnancy extensively, excursions of plasma glu-

GLUCOSE

has been studied

Supported by a Research Grant from the National FoundationlMarch of Dimes and in part by the UCSD General Clinical Research Center, National Institutes of Health/Division of Research Resources, Grant RR-00827.

Reprint requests: Dr. S. S. C. Yen, Department of Reproductive Medicine (T-002), School of Medicine, University of Cal$ornia, San Diego, La Jolla, California 92093.

Presented at the Twenty-sixth Annual Society for Gynecologic Investigation, California, March 21-24, 1979.

*Former Fellow in Reproductive Endocrinology. Current address: Department of Obstehcs-Gynecology, Washington University School Medicine, 4911 Barnes Hospital Plaza, St. Louis, Missouri 63110.

0002-9378/80/040483+06$00.60/0~

Meeting of the San Diego,

1980 The C.V.Mosby

Co.

483

484

Cousins et al

February Am. J. Obstet.

GLUCOSE

Postpartum

I

15, 1980 Gynexd.

Table I. Mean (+SEM) integrated plasma glucose (expressed as mg/ 100 ml/interval) and integrated plasma IPI (expressed as pU/ml/interval) analyzed during the 24-hour metabolic periods and in B-hour phases of the day in pregnancy and the corresponding postpartum values I I I

Glutme:

24 hr. :) N

2,250 544 765 742

24 hr. 1) b: N

921 382 370 16X

2nd Trimester

t + -t -t

45 39 23 32

2.064* + 69 742 2 20 696 rf: 33$ 62611 k 23$

2.108t 747 741 620/l

‘-t ‘2

41 19 229: 19

1,178f * 509112 479* t 189 ”

216 99 8911 35

Insulin:

Fmtiflg = 77.7k2.3

l

*

24hrMean= 85.6?2.9If

0800

1200

1600

*** I

1

I

2000

2400

0400

895 412 349 134

k 200 -+ 86 + 934 2 30

*p < 0.05 compared to post partum. +p < 0.005 compared to post partum. $p < 0.0.5 compared with different phases of the da) $p < 0.005 compared with different phases of the day. lip < 0.01 compared to post partum. Bp < 0.01 compared with different phases of the da).

3rd Trimester

Fasting = 7422 7 l 24hr Mean = 87 3k1.7 1 I

t 184 k 82 -r- 689: 2 40

J

0800

CLOCKHOURS Fig. 1. Excursion of plasma glucose during the 24-hour metaholic clock in six normal pregnant women studied during the second and third trimesters of pregnancy and 6 to 11 weeks post partum. Meals are indicated by 4. Data points reflect mean + SEM. Horizontal lines in postpartum, second-trimester. and third-trimester panels represent the 24-hour mean. ‘p
and C-P throughout the 24-hour period with mealactivity-sleep cycles as metabolic modulators. Identical studies were conducted at 6 to 11 weeks post partum and these data were used as a reference for the analysis of pregnancy-induced alterations in the glucose-IRI relationship. These observations represent the necessar! first step in the assessment of metabolic derangements in diabetic pregnancies.

Material and methods The study subjects consisted of six nonobese women, 18 to 32 years of age, observed from early pregnancy. All subjects had a ni-n-ma1 3-hour oral glucose tolerance test and no prenatal or postpartum complications. All infants were born at term and their weights were appropriate for gestational age. Written and informed consents were obtained. All studies were conducted in the metabolic unit of the Clinical Kesearch Center (CRC). ‘I‘he sul~ject~ arrived at the CRC shortly before 0730 hours on the das of the experiment following 10 hours of overnight fasting. A 24-inch, heparin-lock, intravenous catheter was inserted in a wrist vein. This permitted normal activity and was satisfactory for blood sampling during sleeping hours. The subjects were provided With standard hospital meals at 0800, 1200, and 1700 hours and were encouraged to maintain their normal levels of activity. Hourly plasma samples (6 ml) were obtained throughout a 24-hour period in the second (22 to 26

Volume

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24-Hour

glucose,

insulin,

and C-peptide

485

Number4

1NSLlUN

120 r

2.5

80 z 2 t

r

c-PEPTIDE

Postpartum

Postpmtum

40

Fasting = 13.0 i 3. I 0

24 hr h&-an = 3?.9+

7.7

2nd Trimester 2nd Trimester

3?d Trimester

2.5

-

2.0

3rd Trimester

1.5 1.0 0

’

1

0800

1200

1600

2000

2400

0400

I

0.5

+

0800

OL

CLOCK HOURS

0800

Fig. 2. Excursion

of plasma IRI during the 24-hour metabolic clock in the second-trimester, third-trimester, and postpartum periods. See legend to Fig. 1 for details of format.

Fig. 3. Excursion

weeks)

hour metabolic and postpartum format.

and

third

(35

to 37 weeks)

trimesters

of preg-

and again at 6 to 11 weeks after delivery. Plasma concentrations of glucose were measured by an automatic glucose oxidase method and plasma IRI levels were determined by radioimmunoassay.’ C-P immunoreactivity was measured by a radioimmunoassay kit (Calbiochem, La Jolla, California). The first antibody, raised in rabbits, to human C-P cross reacts 22% by weight with proinsulin. I1 Because proinsulin is present at 10% to 20% of the level of C-P in the plasma of normal individuals,” it contributes 2.2% to 4.4% of C-P immunoreactivity. The assay sensitivity ranges from 0.24 to 0.45 rig/ml with an interassay variation of 8% and an inn-a-assay variation of 5%. All blood samples for IRI and C-P determinations were centrifuged at cold temperatures (-2” C), separated, and frozen (-20” C) immediately until assay. Both IRI and C-P samples obtained from serial studies were determined in the same assay. Excursions of plasma glucose, IRI, and C-P values were expressed as deviations from the 24-hour mean determined from the values obtained at hourly intervals.

I

I

I

1200

1600

2000

I

I 2400

I 0400

0600

CLOCK HOURS of immunoreactive C-P during the 24clock in the second-trimester, third-trimester, periods. See legend to Fig. 1 for details of

nancy

The effect of pregnancy on integrated glucose and IRI concentrations was estimated by the calculations of areas under the curve for the 24-hour period. The effects of feeding and fasting on these values were analyzed by dividing them into three S-hour segments: daytime (D), 0700 to 1500 hours; evening (E), 1500 to 2300 hours; and night (N), 2300 to 0700 hours. Paired t tests and linear correlations were used for statistical analyses.

Results The mean (*SE) fasting, 24-hour mean, and excursions of plasma glucose are depicted in Fig. 1. Mean fasting glucose levels were significantly reduced during the second (p < 0.01) and third (p < 0.05) trimesters of pregnancy compared to the postpartum control values. The mean 24-hour glucose concentrations were also significantly reduced during the second (p < 0.01) and the third (p < 0.005) trimesters of pregnancy (Fig. 1).

486

Cousins I it~ *il r

Table 11. Anal~srs of the ratio of insulin (@J/ml) and plasma glucose (mg/lOO ml) during (premeaf) and t&ding phase (l- and P-hour postprandial values) as well as the integrated pregnancy as compared to the postpartum period (mean 2 SE) PO>/pnri11m Fasting 24-lwunf'rcnwal

tr,(';tn

I -hvur 1,ostprandial ;I-hour postprandial --

Sucortd trimestr?

0.153 _t 0.039

0.241 c!z0.077

0.394 0.266 0.694 0.tiI-l

0.394 0.302 0.746 0.565

+ t 2 2

0.044 0.049 0.071 0.072

Gluc,ose cx< \rl-sions in response to meals during the clay and evening hours were not significantly modified during the srrond trimester of pregnancv. However. a significant elevatirm of‘ the Z-hour postprandial value was c-leaI-Iv csvitlcttl in rhe third trimester compared to h(Jth SP~~Otl~~-~l~II~l~S~~I (p < 0.05) ;317d postpartum valLIPS ‘p .:C0.0 1 ) 1Fig. I ). Ttierc was no significant alteration of’ the integrated ~ILIUW values during day and evening haul-c iTable I). The downward excursion of ftlasma glucose during sleeping hours revealed a progressive deviation f’rom thy nonpregnant state (post pat-and ILI~) a~ compared 10 tht qec-ond (not significant) third (p < 0.03) trimesters ot pregnant? (Fig. 1). Thus, the significanr decrease in 24hour integrated glucose concentration during the second half of pregnancy can be ,+ccortttred !or h!- the significant reduction of’ integratecf glucocr~ .11‘cas (luring rhe sleeping segment of the metahohc cloc~k Cl ;jblr I!. ‘l-lie corrt~sf~~ndittg changes in IRI concentrarions ,rr‘e shown III tip. :! ,tttd ~l‘able I. l-her-e \sas a progressive increast, iri lasting if<1 Icvels during the second inol siqriiiic,itir i and the thtrd trimesters (p < 0.05) ot pregt1k.y from the postpartum level. The IRI increments at 1 ttoltt after each meal were not changed dul-ing Ihe second ,ind tltir-d trimesters of‘ pregnattc! (Fig. 2). H0weve1 . Ihr 9,-hour pos’prattdial IRI increments during the third trimester of pregnancy appeared to be mot-c susrairtcd. and consequently the magnitude of IRI excursior; was significantly greater (p < 0.05) at 2 looters after cw h meal in the third trimester than in the second trimlt”\ittt ;th well as in th
* ? + iz

0.047 0.058 0.078 0.075

the fasting phase 24-hour values in Third tnnlerlrr 0.305 0.516 0.400 0.790 0.8 10

ir -i+ t t

0.07 1* 0.051t 0.077* 0.073 0.069

second-trimester and postpartum values (Fig. 2). -1‘his increased IRI excursion during sleeping hours in late pregnancy is not accompanied by a reduction of absolute IRI secretion as reflected by the unchanged integrated IRI values during the sleep segments of’the da) (Tat& I). The relative change in the insulinogenic response to mixed meals and fasting were analyzed. The relationship between IRI and glucose concentrations during lasting phases (before and during sleeping hours), cxpressed as the fRI/glucose ratio, was significantf) < 0.05). premeal (11 < 0.05). greater at H A.M. tasting (p and 24-hour mean (p < 0.005) values in the third rrimcster compared to the postpartum period (Table 11). However, analyses of I- and ‘L-hour postprandial IRI/glucose ratios revealed no significanr difference be&en increments during pregnant) and the postpartum period (Table II). As expected, the C-P excursions fhllowed closely those of IRI (Fig. 3). The correlation coefficients for IRI and C-P were highly significant for all study periods (r = 0.793 for the postpartum period, r = 0.868 for the second trimester. and r = 0.972 for the third rrimester).

Comment The present longitudinal stud! in normal \vomert demonstrates the effect of pregnancy on diurnal variations of’ plasma glucose, IRI. and C-P levels. The metabolic excursions during mixed-meal teeding and fasting phases of the 24-hour dav are modified bk pregnancy. The most notable feature of the diurnal profile in pregnancy is the progressive decrease of plasnl;~ glucose. I RI, and (1-P during sleeping hours f ram t ttc second to the third trimester (Figs. 1 ro 3 and Table I). This decrease f’rom the 24-hour mean concrnlration reflects a state of t-elati\rr hypoglycemia during nocturnal fasting and became significantly greater tn the last trimester of pregnancy without concomirant nocturnal hypoinsulinism (Table I). This finding. t~ndct. wat-

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physiologic conditions, is in agreement with the observation of exaggerated hypoglycemia found in midpregnancy during prolonged starvation studies.t2* ‘s Feligr4 has shown that the exaggerated fasting hypoglycemia of pregnancy results from substrate limitation of amino acids, particularly alanine. for gluconeogenesis. The continuous withdrawal of glucose and amino acids from mother to fetus would be additive in the genesis of relative hypoglycemia during nocturnal and early morning hours (Fig. 1). However, the counterregulatory hormone response of catecholamines, placental lactogen, steroids, cortisol. and glucagonl* i4-*0 during nocturnal hypoglycemia in pregnancy remains to be determined. The anabolic glucose excursions (maximal increments above the 24-hour mean) during the feeding hours of the day are remarkably small, ranging between 30 and 35 mg/ 100 ml in the postpartum state, and are not significantly modified by pregnancy (Fig. 1). Similarly, the catabolic excursions of plasma glucose (below the 24-hour mean) that occur between meals are not significantly changed during pregnancy (Fig. 1). The maximal excursions of IRI in response to the increments of plasma glucose following each meal are similarly unchanged at midpregnancy (Fig. 2). However, a subtle but important change in the pattern of mixed-meal-induced glucose and IRI excursion occurs in the third trimester when the P-hour postprandial glucose and IRI levels are significantly greater than the second-trimester (p < 0.05), and postpartum values (p < 0.05). This results in a more sustained glucose and IRI curve evident in Figs. 1 and 2. Thus, the synchronous glucose and IRI curves observed in women during the third trimester reflect sustained insulinogenic responses to glucose stimulation following the ingestion of mixed meals. This is consistent with the unaltered IRI/glucose ratio increments observed at 1 and 2 postprandial hours in both trimesters of pregnancy

REFERENCES

1.

2. 3.

4.

5.

Burt, R. L., and Davidson, I. W.: Insulin half-life and utilization in the normal pregnancy, Obstet. Gynecol. 43:161. 1974. Spellacy, W. N., and Coetz, F. C.: Plasma insulin in norma1 late pregnancy, N. Engl. J. Med. 268:988, 1963. Bleicher, S. J., O’Sullivan, J. B., and Freinkel, N.: Carbohydrate metabolism in pregnancy. V. The inter-relationship of glucose, insulin, and free fatty acids in late pregnancy and postpartum, N. Engl. J. Med 271:866, 1964. Freinkel, N., and Metzger, B. E.: Some consideration of fuel economy in the fed state during late human pregnancy, in Camerini, R. A., and Cole, H. S., editors: Early Diabetes in Early Life, New York, 1975, Academic Press, Inc., p. 289. Yen, S. S. C., Tsai, C. C., and Vela, P.: Gestational

24-Hour

glucose,

insulin,

and C-peptide

487

(Table II). These findings differ from previous reports describing marked (80% to 300%) hyperresponsiveness of IRI to an intravenous glucose challenge during the third trimester of pregnancy.*, 3, 5* I* In our studies the physiologic stimulus of mixed meals elicited only a small (3 1%) increase in IRI secretion in third-trimester pregnancy as compared to the postpartum state (the 4 hour postprandial integrated IRI area was 844 pU/ml versus 644 pU/ml in the third trimester and post parturn, respectively). Thus, the quantitative increase in insulin in response to food intake in pregnancy is relatively small. The mean fasting (8 A.M.) and integrated 24-hour glucose concentrations are significantly decreased during the second and third trimesters of pregnancy. These changes are principally due to the nocturnal reduction of glucose levels without changes in the absolute IRI values (Table I). Moreover, basal insulin secretion is significantly elevated during fasting phases of the day (i.e., 8 A.M. fasting and premeal levels) as reflected by the increased IRI/glucose ratio (Table II). These observations of significant nocturnal hypoglycemia without a concomitant decrease in absolute IRI levels and the elevated IRI levels in fasting phases of the day suggest that hyperactivity of p-cells in pregnancy may not be solely dependent on levels of plasma glucose. These observations are consistent with the well-known pregnancy effect of hypersecretion of and peripheral resistance to insulin.i4 The high degree of correlation between IRI and C-P is in agreement with previous studies*‘~ ** and serves as a reliable reference for evaluation of /?-cell function in diabetic women who have received insulin therapy. This longitudinal study in normal pregnant women will be helpful in the assessment of the metabolic abnormalities of diabetic pregnancies and their management by conventional methods or with a p-cell simulator.23

diagetogenesis: quantitative analyses of glucose-insulin interrelationship between normal pregnancy and pregnancies with gestational diabetes, AM. J. OBSTET. GYNECOL. 111:792, 1971. Metzger, B. E., Unger, R. H., and Freinkel, N.: Carbohydrate metabolism in pregnancy. XIV. Relationships between circulating glucagon, insulin, glucose and amino acids in response to a “mixed meal” in late pregnancy, Metabolism26:151, 1977. Persson, B., and Lunell, N. 0.: Metabolic control in diabetic pregnancy: Variations in plasma concentrations of glucose, free fatty acids, glycerol, ketone bodies, insulin, and human chorionic somatomammotropin during the last trimester, AM. J. OBSTET. GYNECOL. 122:737, 1975. Lewis, S. B., Wallin, J. D., Kuzuya, W. H., Murray, W. R., Coustan, D. R., Doane, T. A., and Rubenstein, A. H.:

488

9.

10. 1 I. 12.

13.

14. 15.

16.

Cousins

February Am. ,I. Obstet.

et al.

Circadian variation of serum glucose, C-peptide immunoreactivity and free insulin in normal and insulin treated diaheric pregnant subjects. Diabetologia 12:343, 1976. Gillmer, M. D. G., Beard, R. W., Brooke, F. M., et al.: Carbohydrate metabolism in pregnancy. Part 1. Diurnal plasma glucose profile in normal and diabetic women, Br. Med. J. 3:399. 1975. Morgan, C. R., and Lazarow, A.: Immunoassay of insulin: a two antibody stem, Diabetes 12: 115, 1963. Horowitz, D. A.. Kuzuya. H., and Rubenstein, A. H.: Circulatingserum C-peptide, N. Engl. J, Med 295:207, 1976. Fe&, P., and Lynch, V.: Starvation in human pregnancy: Hypoglycemia, hypoinsulinemia and hyperketonemia, Science 170:990, 1970. Tyson, J. E.. Austin, K.. Farinholt, J., and Fiedler, J.: Endocrine-metabolic response to acme starvation in human gestation, AM. J. OBSTET. GYNECOL. 125:1073, 1976. Felig, P.: Body fuel metabolism and diabetes mellitus in pregnancy, Med. Clin. North Am. 61:43. 1977. DeFronzo, R.A., Andres, R., Bledsoe, T. A., Boden G., Faloona, G. A., and Tobin, J. D.: A test of the hypothesis that the rate of fall in glucose concentration triggers counterregulatorv hormonal responses in man, Diabetes 2&445, 1977. Yen. S. S. (Z.: Endocrine regulation of metabolic homeo-

17.

18.

19.

20.

21.

22.

23.

15, 1980 Gynecol.

stasis during pregnancy, Clin. Obstet. Gynecol. 16: 130. 1973. Kalkoff, R., Richardson, B. L., and Beck, P.: Relative effects of pregnancy, human placental lactogen, and prednisolone on carbohydrate tolerance in normal subclinical diabetic subjects, Diabetes 18: 133, 1969. Samaan, N., Yen, S. S. C., Gonzalez, D., and Pearson, 0. H.: Metabolic effects of placental lactogen (HPL) in man, J. Clin. Endocrinol. Metab. 28:485, 1968. Beck, P.: Progestm enhancement of the plasma insulin response to glucose in rhesus monkeys, Diabetes 16: 146, 1969. Kalkoff, R., Jacobson, R. K., and Lemper, D.: Progesterone, pregnancy and the augmented plasma insulin response, J. Clin. Endocrinol. Metab. 31:24, 1970. Block, M. B., Mako, M. E., Steiner, D. F., and Rubenstein, A. H.: Circulating C-peptide immunoreactivity studies in normals and diabetic patients, Diabetes 21:1013, 1972. Horowitz, D. L., Star, J. I., Mako, M. E.. Blackard, W. C., and Rubenstein, A. H.: Proinsulin, insulin, and C-peptide concentrations in human portal and peripheral blood, J. Clin. Invest. 55:1278, 1975. Santiago, J. V., Clark, W. L., and Arias, F.: Studies with a pancreatic beta cell simulator in the third trimester of pregnancy complicated by diabetes. AM. J. OBSTET. GYNECOL. 132:455, 1978.