Silverberg AD, Shah SD, Haymond MW, Cryer PE. 1978 Norepinephrine: hormone and neurotransmitter in man. Am J Physiol. 234:E252âE256. 21. Cotterill AM ...
0021-972X/97/$03.00/0 Journal of Clinical Endocrinology and Metabolism Copyright © 1997 by The Endocrine Society
Vol. 82, No. 8 Printed in U.S.A.
Influence of Circulating Epinephrine and Norepinephrine on Insulin-Like Growth Factor Binding Protein-1 in Humans EVA FERNQVIST-FORBES, AGNETA HILDING, KARIN EKBERG, KERSTIN BRISMAR
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Department of Surgical Sciences, Division of Clinical Physiology (E.F-F., K.E.); and Department of Molecular Medicine, Endocrine and Diabetes Unit (A.H., K.B.) Karolinska Hospital, Stockholm, Sweden ABSTRACT The aim of the present study was to investigate the influence of circulating epinephrine (Epi) and norepinephrine (Norepi) on serum insulin-like growth factor binding protein-1 (IGFBP-1) concentrations. Healthy men received 0.3 nmolzkgzmin Epi iv (n 5 6), 0.5 nmolzkgzmin Norepi iv (n 5 7), or saline (n 5 5) during 30 min. Arterial blood samples were obtained before, during, and 120 min after infusion. During the catecholamine infusion arterial Epi and Norepi plasma concentrations reached 6.35 6 0.53 and 15.65 6 2.71 nmol/L,
respectively, which resulted in significant increases in glucose concentrations. When Epi was infused, IGFBP-1 increased from 45 6 6 mg/L to 76 6 10 mg/L (P , 0.05) 60 min after the infusion. Epi was also followed by increases in insulin, C-peptide, and glucagon. Norepi resulted in a slight increase in circulating IGFBP-1 (43 6 6 to 54 6 8 nmol/L, NS). The findings suggest that Epi, at plasma concentrations similar to those reached during physical stress, stimulates the production of IGFBP-1 in humans. (J Clin Endocrinol Metab 82: 2677–2680, 1997)
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circulating Epi and Norepi, at levels found during physical stress, influence the serum levels of IGFBP-1.
HE INSULIN-LIKE growth factors I and II (IGF-I and IGF-II) are primarily circulating bound to binding proteins (IGFBP 1– 6), and less than 1% circulate in free form. The half-life of free IGF-I is less than 10 min. A majority of IGF-I binds to IGFBP-3 and an acid-labile subunit, thereby prolonging the half-life of IGF-I to more than 16 h (1, 2). IGFBP-1 is known to undergo rapid changes in serum concentration (3–5) and has been shown to be inversely related to free IGF-I (6). Thus, IGFBP-1 may play an important role in the regulation of the bioavailability of IGF-I and consequently its insulin-like effects (7, 8). IGFBP-1 is produced by the liver. Insulin inhibits IGFBP-1 production (4) at the transcriptional level (9, 10). Insulin also increases the turnover rate of IGFBP-1 by enhancing its transport through the endothelium wall (11). Glucagon stimulates IGFBP-1 production in vivo (12, 13) and in vitro (14, 15), probably partly via a cAMP mechanism (16 –18). Epinephrine (Epi) and norepinephrine (Norepi) are also known to act via cAMP. Thus, they may also affect the IGFBP-1 production. Epi and Norepi plasma concentrations increase in response to physical stress (19, 20), e.g. during insulin-induced hypoglycemia and profound physical exercise. An increase in circulating IGFBP-1 has likewise been demonstrated after hypoglycemia (21–24) and long-term physical exercise (25, 26). The aim of the present study was to investigate whether Received December 18, 1996. Revised May 2, 1997. Accepted May 12, 1997. Address all correspondence and requests for reprints to: Eva Fernqvist-Forbes, Division of Clinical Physiology, Karolinska Hospital, S-171 76 Stockholm, Sweden.
Subjects and Methods Subjects Eight healthy males, with a mean age of 26 6 1 yr (range 22–31) and mean body mass index of 23.7 6 0.9 kg/m2 (range 21.1–27.7) participated in the study. Five of them were studied at three different occasions, at least 2 weeks apart, when Epi, Norepi or saline was given, respectively. One additional subject was added to the Epi group and another two to the Norepi group. The subjects were informed of the nature, purpose, and possible risks before giving their consent to participate in the study. The study protocol was approved by the Local Ethics Committee at Karolinska Hospital.
Study design The investigations started at 0730 h after an overnight fast. For blood sampling and blood pressure measurements a thin Teflon catheter was inserted percutaneously into a brachial artery under local anesthesia. For infusion another catheter was placed in an ipsilateral vein. Blood pressure and heart rate were measured at timed intervals. After 40 min of resting in supine position (time 5 0 min), the subjects received either Epi (0.3 nmolzkgzmin; n 5 6), Norepi (0.5 nmolzkgzmin; n 5 7) or saline (0.9%; n 5 5) iv for 30 min. No subjective symptoms or side effects were noted during the infusions. Arterial blood for determination of catecholamines, immunoreactive insulin (IRI), C-peptide, glucose, IGF-I, IGFBP-1, and glucagon were drawn at the time points indicated in the figures.
Assays Whole blood glucose was analyzed enzymatically (27). All peptide hormones, except glucagon, were determined in serum by RIA as described elsewhere (5). C-peptide was determined with a commercial kit (Hoechst Behringwerke, Frankfurt, Germany). In plasma samples from the Epi and saline studies, glucagon was analyzed by RIA using a 30K antibody according to method of Faloona and Unger (28). Glucagon from the Norepi study was assessed by a commercial kit (Eurodiag-
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nostica AB, Malmo¨, Sweden). Arterial plasma catecholamines were determined with high-performance liquid chromatography and electrochemical detection (29).
Statistical analyses Results are presented as mean values 6 sem. Basal levels were calculated from the mean of three samples before the start of the infusion. Comparisons are performed only within study occasions, by Student’s paired t-test, and P , 0.05 was considered significant. For the purpose of calculation, undetectable insulin concentrations were assigned to 57 pmol/L.
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8.81–23.95) at 15 min of Norepi infusion (Fig. 2). Thirty minutes after cessation of the infusions, concentrations were restored to basal levels. During the control day (saline infusion), the basal Epi or Norepi concentrations were in the same range as above, and no alterations were observed during the study (data not shown). Blood glucose
Basal arterial Epi concentration was 0.34 6 0.08 nmol/L and rose to 6.35 6 0.53 nmol/L (range 5.07– 8.29) at 15 min of Epi infusion (Fig. 1). Basal Norepi concentration was 0.62 6 0.07 nmol/L and rose to 15.65 6 2.71 nmol/L (range
Basal blood glucose was 4.75 6 0.14 mmol/L and increased significantly to 6.92 6 0.14 mmol/L (P , 0.001, Fig. 1) at 30 min of Epi infusion, followed by a normalization at 90 min (4.99 6 0.10 mmol/L). During Norepi infusion, blood glucose rose significantly from 5.08 6 0.16 to 6.33 6 0.36 mmol/L at 30 min of infusion (P , 0.05, Fig. 2). During the control day, basal blood glucose was 5.45 6 0.34 mmol/L, and no significant alteration during or after the saline infusion was seen.
FIG. 1. Arterial plasma Epi (A), arterial blood glucose (B), arterial serum insulin (C), and arterial serum IGFBP-1 (D) in six healthy males before, during (30 min), and after 0.3 nmolzkgzmin Epi infusion. Mean 6 SEM are presented. *, P , 0.05; ***, P , 0.001.
FIG. 2. Arterial plasma Norepi (A), arterial blood glucose (B), arterial serum insulin (C), and arterial serum IGFBP-1 (D) in seven healthy males before, during (30 min), and after 0.5 nmolzkgzmin Norepi infusion. Mean 6 SEM are presented. *, P , 0.05.
Results Plasma catecholamines
EPINEPHRINE STIMULATES IGFBP-1 PRODUCTION Serum IRI and C-peptide
Basal IRI concentrations were 64.6 6 7.2 and 71.8 6 7.2 pmol/L at Epi (Fig. 1) and Norepi (Fig. 2) infusion days, respectively. After the Epi infusion, IRI rose at 60 min to 122 6 14 pmol/L (P , 0.05 vs. basal), followed by a decline to basal level at 120 min. When Norepi infusion was given, a nonsignificant increase in IRI was observed at 60 min (86.1 6 7.2 pmol/L). During the control day, basal insulin concentration was similar and stayed constant during the study. Following Epi infusion, C-peptide increased from 0.50 6 0.06 to 0.91 6 0.09 nmol/L at 60 min (P , 0.001) and returned to basal at 120 min. C-peptide was not analyzed during the Norepi and the control days. Serum IGFBP-1 and IGF-I
Basal IGFBP-1 was 45 6 5 and 43 6 6 mg/L on the Epi (Fig. 1) and Norepi (Fig. 2) infusion days, respectively. After Epi infusion, IGFBP-1 rose to 76 6 10 mg/L (P , 0.05) at 90 min, corresponding to a 74 6 22% increase. Thereafter, IGFBP-1 gradually decreased to the basal level. Following the Norepi infusion, IGFBP-1 concentrations increased in five out of seven individuals, whereas it was unaltered in one and decreased in one. Thus, IGFBP-1 was 54 6 8 mg/L at 90 min, corresponding to an 28 6 13% increase above basal (NS). During the control day, basal IGFBP-1 concentration was 42 6 9 mg/L, without any change during or after the saline infusion. IGF-I levels were 198 6 23 and 213 6 23 mg/L at basal the Epi and Norepi study days, respectively. Similar concentrations were found during the control day. No significant alterations were found in the IGF-I levels during any of the studies. Plasma glucagon
Basal glucagon concentrations were 364 6 127, 371 6 162, and 587 6 168 ng/L at the Epi, Norepi, and control day, respectively. After 30 min of Epi infusion, glucagon increased 40 6 8% above basal (P , 0.01), followed by a decline to basal level at 60 min. During Norepi infusion, a slight but not significant increase (15 6 5%) was seen. During saline infusion glucagon decreased 14 6 2%. Heart rate and blood pressure
During the catecholamine infusions there were expected changes in heart rate and blood pressure. Thus, during the Epi infusion, heart rate increased 15 6 3 beats/min (P , 0.001), the arterial systolic blood pressure rose 11 6 5 mm Hg (NS), and the diastolic blood pressure fell 15 6 2 mm Hg (P , 0.001). During the Norepi infusion, heart rate decreased 4 6 5 beats/min (NS), the systolic blood pressure increased 18 6 4 mm Hg (P , 0.01), and the diastolic blood pressure increased 7 6 2 mm Hg (NS). Discussion
In the present study circulating Epi, in plasma concentrations comparable with levels seen during physical stress, significantly increased the IGFBP-1 serum concentration in humans. The stimulatory effect of Epi was evident despite a
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preceding increment in insulin concentration. IGFBP-1 and insulin are known to have a close inverse relationship (21, 30 –33), and insulin administration decreases IGFBP-1 concentration in vivo when normo- or hyperglycemia is maintained (4, 30, 33), partly because of decreased hepatic production of IGFBP-1 (4). The effect of insulin on IGFBP-1 is delayed 60 –90 min (4, 10). In the present study the insulin peak was seen 30 min before the IGFBP-1 peak, and no relation between the rise in IGFBP-1 and insulin could be demonstrated. The effect of Epi on IGFBP-1 levels was observed 60 min after the 30 min of Epi infusion, suggesting a direct effect on hepatic production of IGFBP-1 rather than an effect on the clearance of IGFBP-1 from the circulation. Furthermore, both Epi and Norepi act via a cAMP-dependent pathway, and the hepatic production of IGFBP-1 is stimulated by cAMP, as shown in several in vitro studies (16 –18). In addition, it has previously been shown that infusion of Epi and Norepi increases IGFBP-1 messenger RNA in fetal sheep liver (34). Contrary to our findings, Cotterill and associates (23) could not demonstrate any effect of Epi infusion on circulating IGFBP-1. However, the Epi concentration in plasma was not described, and no effect on blood glucose concentration was reported. Furthermore, the IGFBP-1 level was already elevated before the start of the Epi infusion, making a further increase less likely. An alternative explanation to the increased IGFBP-1 concentrations found in the present study could be the rise in glucagon concentration following the infusion of catecholamine. Glucagon in vitro stimulates the secretion of IGFBP-1 in human fetal liver explants (14) and in Hep G2 cells (15), and in vivo glucagon injected iv caused an increment in serum IGFBP-1 concentration 90 min after administration (12, 13). In the present study the IGFBP-1 peak occurred 60 min after the maximum glucagon level. In spite of the relatively modest increase in glucagon concentration obtained, it might contribute to the IGFBP-1 increment. The doses of Epi and Norepi were chosen to result in plasma concentrations within the physiological range (35, 36), similar to levels attained during physical stress such as exercise (37). The infusion of Epi was more potent in producing effects on the metabolic and hemodynamic variables measured. However, it is well known that the threshold for various circulatory and metabolic effects are substantially higher for Norepi compared with Epi (19, 20). Furthermore, the more pronounced effect of Epi on IGFBP-1 levels may be related to the main expression of b2- rather than b1-adrenergic receptors in hepatocytes, because Epi acts mainly via b2-receptors and Norepi via b1-receptors (38). IGFBP-1 may be important for glucose homeostasis, because of its capacity to block the free fraction of IGFs. Administration of IGFBP-1 to rats results in an increase of blood glucose (6) and inhibition of the hypoglycemic effect of IGF-I (7). Moreover, in transgenic mice overexpressing IGFBP-1, the blood glucose levels are elevated (39). In the present study no alterations in IGF-I serum concentration were observed. However, an increase in IGFBP-1 may reduce free IGF-I independently of total IGF-I concentration. Therefore, during stress the catecholamine release may play a role in preventing the hypoglycemic effects of the IGFs by influ-
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encing their bioavailability via the stimulation of IGFBP-1 production. In the present study circulating Epi, in concentrations seen in connection with physical stress, increased IGFBP-1 serum concentration. Apart from the well-known effect of catecholamines on carbohydrate metabolism, the stimulatory effect of Epi on IGFBP-1 could be an additive factor behind the prolonged hyperglycemic response seen during various kinds of physical stress. Acknowledgments We thank Eva-Lena Olausson, Berit Rydlander, and Yvonne Stro¨mberg for excellent technical assistance. This work was supplied by Grants from the Swedish Medical Research Council (Grant No. 4224), the Swedish Diabetes Association, The Novo Nordisk Foundation, and Tore and Ragnar So¨derbergs Foundation.
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18. 19. 20. 21. 22. 23.
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