Adrenal Response to Tolbutamide-Induced Hypoglycemia in High Altitude Dwellers ENRIQUE URDANIVIA,1 FAUSTO GARMENDIA, JOSE TORRES, MARIO ZUBIATE, AND RAUL TAMAYO2
ABSTRACT. Adrenal response to tolbutamideinduced hypoglycemia was studied in 23 normal men born and living at high altitude (Morococha, Peru, 4,540 m) and compared to 23 men born and living near sea level. Fasting blood sugar was significantly lower in the high altitude dwellers (HAD) and this difference persisted throughout the test period. The blood
W
HILE adrenal output dramatically increases with acute exposure to high altitude, the chronic high altitude dweller does not respond in this manner. Plasma corticoids, basal urinary 17-hydroxy and 17 ketosteroids, cortisol secretion rates, response to Metapyrone administration and the suppressive effects of dexamethasone are all similar in high altitude dwellers (HAD) to those found in sea level inhabitants (1-7). Adrenal stimulation with from 1-5 U of ACTH, however, produces significantly lower responses in the HAD, and it has been postulated that endogenous ACTH levels are increased in HAD in order to explain this diminished sensitivity to exogenous ACTH (3,8). To evaluate the hypothalamic-hypophysealadrenocortical axis, serum cortisol responses to tolbutamide-induced hypoglycemia were measured in a group of HAD.
Materials and Methods Tolbutamide, 15 mg/kg, was administered by rapid intravenous injection to 23 normal men, born and living in a high altitude (Morococha, Peru, alt = 4,540 m), and to 23 normal men living at sea level (Lima, Peru, alt = 150 m). After an overnight fast, an indwelling catheter was placed in an antecubital vein and the subjects were allowed to rest for 30 min in a recumbent position. Tolbutamide was injected imReceived January 23, 1974. Supported by a grant from Instituto Hipolito UnanueLima-Peru. 1 Present address: The Grace Hospital, Wayne State University, Detroit, Michigan. 2 Present address: Sinai Hospital, Detroit, Michigan.
glucose decrement at 30 min was significantly less in the HAD. Plasma cortisol response was significantly higher at 30 and 60 min in the HAD. Peak cortisol level occurred earlier in the HAD than in men living at sea level. The absolute cortisol increment at 30 min was significantly greater in the HAD. (J Clin Endocrinol Metab 40: 717, 1975) mediately after drawing basal samples, and blood was obtained at 3, 6, 10, 20, 30, 60, and 90 min following injection. Sera were frozen at -20 C until assayed. Cortisol content was determined in duplicate assays of each sample-by the technique of Nugent and Mayes (9). 3H-Cortisol was purified through a column of Sephadex LH-20, as described by Murphy (10). Whole blood glucose was measured by the Somogyi-Nelson method (11-13) in all samples; specimens from both groups were done at the same time. Statistical analyses were performed using the Student's t test and the coefficient of correlation.
Results Fasting blood sugar was significantly lower in the high altitude group (Fig. 1), and this difference persisted throughout the test period. The latter finding appears to be related to the difference in the basal glucose concentration, since shape of the curves was almost identical in both groups. The calculated absolute glucose fall was also similar in both groups (Fig. 2), except that the blood glucose decrement at 30 min was significantly less in the HAD. Plasma cortisol response was significantly higher at 30 and 60 min in the groups living at high altitude. Peak cortisol levels occurred at 60 min in the HAD and at 90 min in the groups living at sea level. The absolute cortisol increment was significantly greater at 30 min in the HAD. No correlation was found between the glucose nadir and the cortisol changes at 60 and 90 min.
Discussion It is well known that the HAD has a significantly lower basal blood glucose which is 717
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
Institute de Biologia Andina and Institute de Investigaciones Clinicas, Universidad Nacional Mayor de San Marcos, Lima, Peru
COMMENTS
718 30 28 26 24
I.V. TOLBUTAMIOE 19mg/Kg b.w.
20 18 16 14 12 10 8
100 90 80 70 60 90 40 90 20 10
odi
.005
N.5.
m • SEA LEVEL * - . . « HIGH ALTITUDE
Hypoglycemia is generally considered to be of value in assessing hypothalamic-hypophyseal-adrenocortical function; the response to insulin-induced hypoglycemia is dependent on the degree and duration of the hypoglycemia, and on the integrity of the axis (19). Thus this axis appears to be intact in the HAD. The changes in cortisol production during tolbutamide-hypoglycemia found in this study are consistent with changes reported in other hormones during hypoglycemia in the HAD (i.e., growth hormone and catecholamines). The findings suggest that these endocrine alterations may counteract the increased sensitivity to endogenous insulin which occurs in the chronic HAD. Acknowledgments The authors are grateful to Dr. Margo P. Cohen and Dr. Carl B. Lauter for helpful criticisms to the manuscript and to Elva Fernandez, Sara Vicuna and Elizabeth Espejo for their excellent technical assistance.
JX* XX*
003
OO3
03610 20 30
.01
60
.001 90
MINUTES FIG. 1. Concentration of cortisol and glucose in normal individuals at sea level and high altitude after an intravenous tolbutamide test.
not entirely dependent on the higher hematocrit values in these individuals; this subject has been discussed in recent reviews (14,15). In studies performed in the same men participating in the present investigation, we have found that although free fatty acid levels are increased and the fasting blood sugar is decreased in the HAD, the basal immunoreactive insulin concentrations are similar to those found in men living at sea level (16). This suggests that sensitivity to endogenous insulin is increased in the HAD. Other investigations have reported increased basal growth hormone levels (17), and increased catecholamine responses to insulin-induced hypoglycemia (18) in the HAD. These reports are of particular interest in view of the present findings which demonstrate that the blood glucose decrement at 30 min is less in HAD than in men living at sea level, and that the cortisol response to tolbutamide-induced hypoglycemia is greater in the former group.
1 h
+ 16 + 14 + 12 + 10 + 8 + 6 + 4 + 2 0
J, I.V. TOLBUTAMIDE 15 mg/Kg b.w.
-10 -20 -30 SEA LEVEL o — o HIGH ALTITUDE
!u - 4 0 -50PKNS KS"* I
I I
I
N
-S. X323
i
N.S.
N.S.
60
90
i
03610 20 30
MINUres FIG. 2. Absolute cortisol increment and glucose fall at sea level and high altitude after an intravenous tolbutamide test.
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
22
JCE & M • 1975 Vol 40 • No 4
COMMENTS References 11. 12. 13. 14. 15. 16.
17.
18. 19.
ing, Karolinska Symposia on Research Methods in Reproductive Endocrinology, Geneve, 1970, pp. 37-60. Somogyi, M.J Biol Chem 86: 655, 1930. Nelson, N. A., J Biol Chem 153: 375, 1944. Somogyi, M . J Biol Chem 195: 19, 1952. Picon-Reategui, E., Arch lnst Biol Andina 1: 255, 1966. Garmendia, F., J. Arroyo, and M. Muro, Arch lnst Biol Andina 3: 209, 1970. , J. Torres, R. Tamayo, and E. Urdanivia, Abstract no. 262, 8th International Diabetes Federation Congress, Brussels, Excerpta Medica Foundation, International Congress, Series no. 280, 1973. Sutton, J., J. D. Young, L. Lazarus, J. B. Hickie, F. Garmendia, and T. Velasquez, Lancet 2: 1194, 1970. Moncloa, F., M. Gomez, and A. Hurtado, J Appl Physiol 20: 1329, 1965. Landon, J., V. Wynn, and V. T. H. James, J Endocrinol 27: 183, 1963.
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
1. San Martin, M., Y. Prato, and L. Fernandez, Rev San Poliria 13: 110, 1953. 2. , , and , Ann Fac Med Lima 37: 736, 1954. 3. Subauste, C , R. Aliaga, C. Silva, J. Correa, and F. Moncloa, School of Aviation Medicine USAF, Randolph Field Report 58-95-1958. 4. Moncloa, F., E. Pretell, and K. Correa, Proc Soc Exp Biol Med 108: 336, 1961. 5. Garmendia, F., M. Valdivieso, C. Umezaki, and E. Marticorena, Arch lnst Biol Andina 2: 111, 1967. 6. Moncloa, F., and E. Pretell, J Clin Endocrinol Metab 24: 915, 1964. 7. , Pan American Health Organization, Scientific Publication No. 140, 1966, p. 36. 8. Correa, J., R. Aliaga, and F. Moncloa, School of Aviation Medicine USAF, Randolph Field Report 56-101, 1966. 9. Nugent, C. A., and D. M. Mayes,/ Clin Endocrinol Metab 26: 1116, 1966. 10. Murphy, B. E. P., Steroid Assay by Protein Bind-
719
ABSTRACT. Adrenal response to tolbutamideinduced hypoglycemia was studied in 23 normal men born and living at high altitude (Morococha, Peru, 4,540 m) and compared to 23 men born and living near sea level. Fasting blood sugar was significantly lower in the high altitude dwellers (HAD) and this difference persisted throughout the test period. The blood
W
HILE adrenal output dramatically increases with acute exposure to high altitude, the chronic high altitude dweller does not respond in this manner. Plasma corticoids, basal urinary 17-hydroxy and 17 ketosteroids, cortisol secretion rates, response to Metapyrone administration and the suppressive effects of dexamethasone are all similar in high altitude dwellers (HAD) to those found in sea level inhabitants (1-7). Adrenal stimulation with from 1-5 U of ACTH, however, produces significantly lower responses in the HAD, and it has been postulated that endogenous ACTH levels are increased in HAD in order to explain this diminished sensitivity to exogenous ACTH (3,8). To evaluate the hypothalamic-hypophysealadrenocortical axis, serum cortisol responses to tolbutamide-induced hypoglycemia were measured in a group of HAD.
Materials and Methods Tolbutamide, 15 mg/kg, was administered by rapid intravenous injection to 23 normal men, born and living in a high altitude (Morococha, Peru, alt = 4,540 m), and to 23 normal men living at sea level (Lima, Peru, alt = 150 m). After an overnight fast, an indwelling catheter was placed in an antecubital vein and the subjects were allowed to rest for 30 min in a recumbent position. Tolbutamide was injected imReceived January 23, 1974. Supported by a grant from Instituto Hipolito UnanueLima-Peru. 1 Present address: The Grace Hospital, Wayne State University, Detroit, Michigan. 2 Present address: Sinai Hospital, Detroit, Michigan.
glucose decrement at 30 min was significantly less in the HAD. Plasma cortisol response was significantly higher at 30 and 60 min in the HAD. Peak cortisol level occurred earlier in the HAD than in men living at sea level. The absolute cortisol increment at 30 min was significantly greater in the HAD. (J Clin Endocrinol Metab 40: 717, 1975) mediately after drawing basal samples, and blood was obtained at 3, 6, 10, 20, 30, 60, and 90 min following injection. Sera were frozen at -20 C until assayed. Cortisol content was determined in duplicate assays of each sample-by the technique of Nugent and Mayes (9). 3H-Cortisol was purified through a column of Sephadex LH-20, as described by Murphy (10). Whole blood glucose was measured by the Somogyi-Nelson method (11-13) in all samples; specimens from both groups were done at the same time. Statistical analyses were performed using the Student's t test and the coefficient of correlation.
Results Fasting blood sugar was significantly lower in the high altitude group (Fig. 1), and this difference persisted throughout the test period. The latter finding appears to be related to the difference in the basal glucose concentration, since shape of the curves was almost identical in both groups. The calculated absolute glucose fall was also similar in both groups (Fig. 2), except that the blood glucose decrement at 30 min was significantly less in the HAD. Plasma cortisol response was significantly higher at 30 and 60 min in the groups living at high altitude. Peak cortisol levels occurred at 60 min in the HAD and at 90 min in the groups living at sea level. The absolute cortisol increment was significantly greater at 30 min in the HAD. No correlation was found between the glucose nadir and the cortisol changes at 60 and 90 min.
Discussion It is well known that the HAD has a significantly lower basal blood glucose which is 717
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
Institute de Biologia Andina and Institute de Investigaciones Clinicas, Universidad Nacional Mayor de San Marcos, Lima, Peru
COMMENTS
718 30 28 26 24
I.V. TOLBUTAMIOE 19mg/Kg b.w.
20 18 16 14 12 10 8
100 90 80 70 60 90 40 90 20 10
odi
.005
N.5.
m • SEA LEVEL * - . . « HIGH ALTITUDE
Hypoglycemia is generally considered to be of value in assessing hypothalamic-hypophyseal-adrenocortical function; the response to insulin-induced hypoglycemia is dependent on the degree and duration of the hypoglycemia, and on the integrity of the axis (19). Thus this axis appears to be intact in the HAD. The changes in cortisol production during tolbutamide-hypoglycemia found in this study are consistent with changes reported in other hormones during hypoglycemia in the HAD (i.e., growth hormone and catecholamines). The findings suggest that these endocrine alterations may counteract the increased sensitivity to endogenous insulin which occurs in the chronic HAD. Acknowledgments The authors are grateful to Dr. Margo P. Cohen and Dr. Carl B. Lauter for helpful criticisms to the manuscript and to Elva Fernandez, Sara Vicuna and Elizabeth Espejo for their excellent technical assistance.
JX* XX*
003
OO3
03610 20 30
.01
60
.001 90
MINUTES FIG. 1. Concentration of cortisol and glucose in normal individuals at sea level and high altitude after an intravenous tolbutamide test.
not entirely dependent on the higher hematocrit values in these individuals; this subject has been discussed in recent reviews (14,15). In studies performed in the same men participating in the present investigation, we have found that although free fatty acid levels are increased and the fasting blood sugar is decreased in the HAD, the basal immunoreactive insulin concentrations are similar to those found in men living at sea level (16). This suggests that sensitivity to endogenous insulin is increased in the HAD. Other investigations have reported increased basal growth hormone levels (17), and increased catecholamine responses to insulin-induced hypoglycemia (18) in the HAD. These reports are of particular interest in view of the present findings which demonstrate that the blood glucose decrement at 30 min is less in HAD than in men living at sea level, and that the cortisol response to tolbutamide-induced hypoglycemia is greater in the former group.
1 h
+ 16 + 14 + 12 + 10 + 8 + 6 + 4 + 2 0
J, I.V. TOLBUTAMIDE 15 mg/Kg b.w.
-10 -20 -30 SEA LEVEL o — o HIGH ALTITUDE
!u - 4 0 -50PKNS KS"* I
I I
I
N
-S. X323
i
N.S.
N.S.
60
90
i
03610 20 30
MINUres FIG. 2. Absolute cortisol increment and glucose fall at sea level and high altitude after an intravenous tolbutamide test.
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
22
JCE & M • 1975 Vol 40 • No 4
COMMENTS References 11. 12. 13. 14. 15. 16.
17.
18. 19.
ing, Karolinska Symposia on Research Methods in Reproductive Endocrinology, Geneve, 1970, pp. 37-60. Somogyi, M.J Biol Chem 86: 655, 1930. Nelson, N. A., J Biol Chem 153: 375, 1944. Somogyi, M . J Biol Chem 195: 19, 1952. Picon-Reategui, E., Arch lnst Biol Andina 1: 255, 1966. Garmendia, F., J. Arroyo, and M. Muro, Arch lnst Biol Andina 3: 209, 1970. , J. Torres, R. Tamayo, and E. Urdanivia, Abstract no. 262, 8th International Diabetes Federation Congress, Brussels, Excerpta Medica Foundation, International Congress, Series no. 280, 1973. Sutton, J., J. D. Young, L. Lazarus, J. B. Hickie, F. Garmendia, and T. Velasquez, Lancet 2: 1194, 1970. Moncloa, F., M. Gomez, and A. Hurtado, J Appl Physiol 20: 1329, 1965. Landon, J., V. Wynn, and V. T. H. James, J Endocrinol 27: 183, 1963.
Downloaded from https://academic.oup.com/jcem/article-abstract/40/4/717/2685027 by Duke University user on 11 January 2019
1. San Martin, M., Y. Prato, and L. Fernandez, Rev San Poliria 13: 110, 1953. 2. , , and , Ann Fac Med Lima 37: 736, 1954. 3. Subauste, C , R. Aliaga, C. Silva, J. Correa, and F. Moncloa, School of Aviation Medicine USAF, Randolph Field Report 58-95-1958. 4. Moncloa, F., E. Pretell, and K. Correa, Proc Soc Exp Biol Med 108: 336, 1961. 5. Garmendia, F., M. Valdivieso, C. Umezaki, and E. Marticorena, Arch lnst Biol Andina 2: 111, 1967. 6. Moncloa, F., and E. Pretell, J Clin Endocrinol Metab 24: 915, 1964. 7. , Pan American Health Organization, Scientific Publication No. 140, 1966, p. 36. 8. Correa, J., R. Aliaga, and F. Moncloa, School of Aviation Medicine USAF, Randolph Field Report 56-101, 1966. 9. Nugent, C. A., and D. M. Mayes,/ Clin Endocrinol Metab 26: 1116, 1966. 10. Murphy, B. E. P., Steroid Assay by Protein Bind-
719
