- Email: [email protected]
LACK OF RELATION BETWEEN PLASMA-GROWTH-HORMONE LEVELS AND SMALL DECREMENTS IN BLOOD-SUGAR
13
LACK OF RELATION BETWEEN PLASMAGROWTH-HORMONE LEVELS AND SMALL DECREMENTS IN BLOOD-SUGAR C. S. KOH
J.
KOHN
MEDICAL STUDENT
MEDICAL STUDENT
M.D.
K. J. CATT Melb., M.R.A.C.P.
plasma H.G.H. may occur in response to small falls in blood-sugar. This was investigated by infusing increasing quantities of insulin into five normal subjects, and measuring bloodsugar and plasma-H.G.H. before, during, and after the infusion. The object of the experiment was to determine whether increases in H.G.H. during this time were causally related to preceding falls in blood-sugar. in
SENIOR LECTURER IN MEDICINE
UNIVERSITY, PRINCE HENRY’S HOSPITAL, MELBOURNE, VICTORIA, AUSTRALIA
MONASH
H. G. BURGER M.D. Melb., M.R.A.C.P. ASSOCIATE DIRECTOR, CENTRE, PRINCE HENRY’S
MEDICAL RESEARCH
HOSPITAL,
MELBOURNE
Plasma-human-growth-hormone (H.G.H.) was measured in five normal subjects given nineteen infusions with increasing doses of regular insulin. Summary
When
H.G.H.
increments greater than 3 ng. per ml. and
Methods All subjects were studied after an overnight fast between 8.30 and 11.30 A.M. Venous blood was collected into heparinised tubes from an indwelling cannula, and infusions were given into the other arm from a continuous-infusion pump. Physiological saline solution was infused for one hour, followed by insulin in saline for a further hour. Each subject was infused on four separate occasions, with 0, 0-01, 0-015, and 0-02 unit per kg. per hour of glucagon-free crystalline insulin (’Actrapid’, Nova Industri A/S, Copenhagen, Denmark). In all, nineteen infusions were performed on the five subjects (one subject was TABLE I-BLOOD-SUGAR AND PLASMA-H.G.H. DURING INSULIN INFUSIONS
blood-sugar decrements greater than 10 mg. per 100 ml. were compared, seven of the fourteen H.G.H. rises appeared to be temporally related to a small fall of blood-sugar. However, an equal number of H.G.H. elevations was observed in the absence of such a fall in blood-sugar. The data do not support the suggestion that H.G.H. is secreted in response to small changes in blood-glucose levels. Introduction IT has been suggested by Luft et al. (1966) that human growth hormone (H.G.H.) is secreted in response to small fluctuations in blood-glucose, and that the hormone is therefore a sensitive regulator of blood-glucose homoeostasis. Whether such a secretion of H.G.H. would play a significant role in glucose homoeostasis is debatable: milligramme quantities of H.G.H. are required to alter glucose and free fatty acid metabolism in normal subjects, and these raise plasma levels to a much greater extent than the changes observed by Luft et al. Before considering this aspect of the problem, it is essential to be sure that such a secretion does, in fact, occur as a response to changes in blood-sugar under normal circumstances. It has become apparent, during diagnostic use of the H.G.H. assay following insulin-induced hypoglycsemia, that moderate falls in blood-glucose may not be accompanied by a change in plasma-H.G.H. level. In fact, the interpretation of such tests is not valid unless substantial hypoglycaemia (e.g., a fall by 50% of the basal values) has been achieved (Roth et al. 1963). Furthermore, marked fluctuations in plasmaH.G.H. levels have been found in normal subjects throughout the day (Greenwood et al. 1964). Therefore, it seemed important to examine critically the proposal that changes
Adams, F. (1939) Genuine works of Hippocrates; p. 337. Baltimore. Cason, J. S., Jackson, D. M., Lowbury, E. J. L., Ricketts, C. R. (1966) Br. med. J. ii, 1288. Currence, W. W. (1952) Am. J. Dis. Child. 83, 637. Gillies, R. R., Govan, J. R. W. (1966) J. Path. Bact. 91, 339. Kass, E. H., Sossens, H. S. (1959) J. Am. med. Ass. 169, 1181. Lowbury, E. J. L. (1966) in The Therapeutic Use of Antibiotics in Hospital Practice (edited by M. Ridley and I. Phillips); p. 203. Edinburgh and London.
Ochs, I. L. (1950) Archs Otolaryng. 52, 935. Owen, C. R. (1946) J. Bact. 52, 353. Phillips, I. (1967) J. Hyg. Camb. 65, 229. Pulvertaft, R. J. V. (1943) Lancet, ii, 341. Smith, D. T. (1924) Am. J. Dis. Child. 28, 1. Taylor, K. (1916) J. Am. med. Ass. 67, 1598.
given 0-02 and 0-025 unit
per kg. per hour). The various doses of insulin were given in random order. Blood samples were taken at intervals of fifteen minutes throughout the three-hour period of the experiment. Bloodsugar was measured in the ’Autoanalyzer ’ by the ferricyanide method. The reproducibility of standards in this method was
±2.5%. Plasma-H.G.H. was measured by the disc solid-phase radioimmunoassay procedure (Catt et al. 1967). The precision obtained by the use of plasma samples diluted 1 : 1 before assay was +15%. The change in blood-sugar was assessed by comparing the mean level during the first hour of infusion with the lowest level thereafter. Results
While the infusion of the highest insulin doses resulted in definite falls of blood-sugar, the effect of the lower doses was rather irregular (table I). In no case did the bloodsugar fall significantly during the control infusions without insulin. Infusions of 0-02 unit per kg. per hour caused a mean fall of 18 mg. per 100 ml. The changes in blood-sugar and H.G.H. were analysed
14
according to the sizes of the fall in sugar, the rise in H.G.H., and the temporal relation between these two changes. The latter analysis was necessary to take into account random changes in H.G.H. either in the absence of a change in blood-sugar (as in six infusions) or before any change in blood-sugar (as in one infusion) (see accompanying figure). A rise in H.G.H. was regarded as being " related to the fall in blood-sugar " if it occurred at any time after the commencement of infusion-i.e., in the ensuing two hours. This definition was felt to be a generous interpretation of the relation between blood-sugar and plasma-H.G.H., and may in fact slightly overestimate the degree of any such relation. To simplify the assessment of these changes, a fall in blood-sugar was regarded as a change exceeding 10 mg. per 100 ml. It is this level which Luft et al. (1966) have claimed to be adequate to evoke a rise in plasma H.G.H. Of the infusions where " no change " is said to have occurred, the fall of blood-sugar ranged from 0 to 7 mg. per 100 ml., with a mean of 1-5 mg. per 100 ml. Those with a fall greater than 10 mg. per 100 ml. ranged from 14 to 37 mg. per 100
ml., with
a mean
of 21 mg. per
100 ml.
Elevation of plasma-H.G.H. beyond 3 ng. per ml. in
two
TABLE II-SUMMARY OF RESULTS
In
one
additional subject,
a
rise in
H.G.H.
preceded the
fall in blood-sugar.
consecutive samples was regarded as a significant rise. The basal level in all subjects was close to 1 ng. per ml. The results of the study are summarised in table II. When changes in plasma H.G.H. and sugar were compared, it was observed that a rise in H.G.H. beyond 3 ng. per ml. occurred during fourteen of the nineteen infusions. Of these fourteen elevations, six occurred in the absence of a change in blood-sugar, one occurred before a fall in blood-sugar, and seven followed a decline in or more
blood-sugar. During the nine infusions in which the blood-sugar level did not fall, six subjects showed a rise in plasmaH.G.H. Of the ten infusions with a fall in blood-sugar exceeding 10 mg. per 100 ml., seven showed a rise in H.G.H. at or after the time of the nadir, and in one case a rise in H.G.H. preceded a fall in blood-sugar. Discussion
The presence of intermittent peaks of H.G.H. secretion first observed in blood samples taken from children during the night (Hunter and Rigal 1966). Such fluctuations have also been observed in normal adults, in whom several H.G.H. peaks occurred throughout a twenty-fourhour fast (Quabbe et al. 1966). These peaks were not related to changes in the blood-sugar or plasma-nonesterified-fatty-acid values, indicating that such changes are not directly responsible for H.G.H. release during fasting. Luft et al. on the other hand, postulated that minor to moderate decreases in blood glucose (6-19 mg. per 100 ml.) were responsible for an increased secretion of was
H.G.H.
On the basis of the results reported here, it is difficult sustain a relation between H.G.H. secretion and falls of blood-sugar in the 10-20 mg. per 100 ml. range. Although a rise in plasma H.G.H. was observed in 78% of infusions accompanied by a fall in blood-sugar, the same observation was made in 70% of infusions in which no change in sugar levels occurred. The results may be alternatively stated to show that, of all fourteen elevations in plasma-H.G.H., only 50% occurred in temporal relation to a fall in bloodsugar. The equal frequency of H.G.H. elevations in the control infusions indicates that similar fluctuations following small changes in blood-sugar cannot be regarded as responses to these changes. to
Three patterns of change in blood-sugar and plasma-H.G.H. during infusion of small doses of insulin.
The period of infusion is indicated by the horizontal black bar (0-60 minutes). Upper panel: A rise in H.G.H. preceding a fall in blood-sugar,
observed on one occaston. Add/s panel: A rise in H.G.H. occurring in the absence of a change in blood-sugar, observed on six occasions. Loz;:er panel: A rise in H.G.H. occurring in relation to a fall in bloodsugar, observed on seven occasions. Of the remaining five infusions, three showed no change in either blood-sugar or H.G.H., and two showed a fall in blood-sugar but no
change
in
H.G.H.
This work was supported by a grant from the Australian Research Grants Committee to two of us (K. J. C. and H. G. B.). Requests for reprints should be addressed to H. G. B. REFERENCES
Catt, K. J., Niall, H. D., Tregear, G. W. (1967) J. Lab. clin. Med. 70, 820. Greenwood, F. C., Hunter, W. M., Marrian, V. J. (1964) Br. med. J. i, 25. Hunter, W. M., Rigal, W. M. (1966) J. Endocr. 34, 147. Luft, R., Cerasi, E., Madison, L. L., von Euler, U. S., Della Casa, L., Roovette, A. (1966) Lancet, ii, 254. Quabbe, H. J., Schilling, E., Helge, H. (1966) J. clin. Endocr. 26, 1173. Roth, J., Glick, S. M., Yalow, R. S., Berson, S. A. (1963) Science, N.Y. 140, 987.
LACK OF RELATION BETWEEN PLASMAGROWTH-HORMONE LEVELS AND SMALL DECREMENTS IN BLOOD-SUGAR C. S. KOH
J.
KOHN
MEDICAL STUDENT
MEDICAL STUDENT
M.D.
K. J. CATT Melb., M.R.A.C.P.
plasma H.G.H. may occur in response to small falls in blood-sugar. This was investigated by infusing increasing quantities of insulin into five normal subjects, and measuring bloodsugar and plasma-H.G.H. before, during, and after the infusion. The object of the experiment was to determine whether increases in H.G.H. during this time were causally related to preceding falls in blood-sugar. in
SENIOR LECTURER IN MEDICINE
UNIVERSITY, PRINCE HENRY’S HOSPITAL, MELBOURNE, VICTORIA, AUSTRALIA
MONASH
H. G. BURGER M.D. Melb., M.R.A.C.P. ASSOCIATE DIRECTOR, CENTRE, PRINCE HENRY’S
MEDICAL RESEARCH
HOSPITAL,
MELBOURNE
Plasma-human-growth-hormone (H.G.H.) was measured in five normal subjects given nineteen infusions with increasing doses of regular insulin. Summary
When
H.G.H.
increments greater than 3 ng. per ml. and
Methods All subjects were studied after an overnight fast between 8.30 and 11.30 A.M. Venous blood was collected into heparinised tubes from an indwelling cannula, and infusions were given into the other arm from a continuous-infusion pump. Physiological saline solution was infused for one hour, followed by insulin in saline for a further hour. Each subject was infused on four separate occasions, with 0, 0-01, 0-015, and 0-02 unit per kg. per hour of glucagon-free crystalline insulin (’Actrapid’, Nova Industri A/S, Copenhagen, Denmark). In all, nineteen infusions were performed on the five subjects (one subject was TABLE I-BLOOD-SUGAR AND PLASMA-H.G.H. DURING INSULIN INFUSIONS
blood-sugar decrements greater than 10 mg. per 100 ml. were compared, seven of the fourteen H.G.H. rises appeared to be temporally related to a small fall of blood-sugar. However, an equal number of H.G.H. elevations was observed in the absence of such a fall in blood-sugar. The data do not support the suggestion that H.G.H. is secreted in response to small changes in blood-glucose levels. Introduction IT has been suggested by Luft et al. (1966) that human growth hormone (H.G.H.) is secreted in response to small fluctuations in blood-glucose, and that the hormone is therefore a sensitive regulator of blood-glucose homoeostasis. Whether such a secretion of H.G.H. would play a significant role in glucose homoeostasis is debatable: milligramme quantities of H.G.H. are required to alter glucose and free fatty acid metabolism in normal subjects, and these raise plasma levels to a much greater extent than the changes observed by Luft et al. Before considering this aspect of the problem, it is essential to be sure that such a secretion does, in fact, occur as a response to changes in blood-sugar under normal circumstances. It has become apparent, during diagnostic use of the H.G.H. assay following insulin-induced hypoglycsemia, that moderate falls in blood-glucose may not be accompanied by a change in plasma-H.G.H. level. In fact, the interpretation of such tests is not valid unless substantial hypoglycaemia (e.g., a fall by 50% of the basal values) has been achieved (Roth et al. 1963). Furthermore, marked fluctuations in plasmaH.G.H. levels have been found in normal subjects throughout the day (Greenwood et al. 1964). Therefore, it seemed important to examine critically the proposal that changes
Adams, F. (1939) Genuine works of Hippocrates; p. 337. Baltimore. Cason, J. S., Jackson, D. M., Lowbury, E. J. L., Ricketts, C. R. (1966) Br. med. J. ii, 1288. Currence, W. W. (1952) Am. J. Dis. Child. 83, 637. Gillies, R. R., Govan, J. R. W. (1966) J. Path. Bact. 91, 339. Kass, E. H., Sossens, H. S. (1959) J. Am. med. Ass. 169, 1181. Lowbury, E. J. L. (1966) in The Therapeutic Use of Antibiotics in Hospital Practice (edited by M. Ridley and I. Phillips); p. 203. Edinburgh and London.
Ochs, I. L. (1950) Archs Otolaryng. 52, 935. Owen, C. R. (1946) J. Bact. 52, 353. Phillips, I. (1967) J. Hyg. Camb. 65, 229. Pulvertaft, R. J. V. (1943) Lancet, ii, 341. Smith, D. T. (1924) Am. J. Dis. Child. 28, 1. Taylor, K. (1916) J. Am. med. Ass. 67, 1598.
given 0-02 and 0-025 unit
per kg. per hour). The various doses of insulin were given in random order. Blood samples were taken at intervals of fifteen minutes throughout the three-hour period of the experiment. Bloodsugar was measured in the ’Autoanalyzer ’ by the ferricyanide method. The reproducibility of standards in this method was
±2.5%. Plasma-H.G.H. was measured by the disc solid-phase radioimmunoassay procedure (Catt et al. 1967). The precision obtained by the use of plasma samples diluted 1 : 1 before assay was +15%. The change in blood-sugar was assessed by comparing the mean level during the first hour of infusion with the lowest level thereafter. Results
While the infusion of the highest insulin doses resulted in definite falls of blood-sugar, the effect of the lower doses was rather irregular (table I). In no case did the bloodsugar fall significantly during the control infusions without insulin. Infusions of 0-02 unit per kg. per hour caused a mean fall of 18 mg. per 100 ml. The changes in blood-sugar and H.G.H. were analysed
14
according to the sizes of the fall in sugar, the rise in H.G.H., and the temporal relation between these two changes. The latter analysis was necessary to take into account random changes in H.G.H. either in the absence of a change in blood-sugar (as in six infusions) or before any change in blood-sugar (as in one infusion) (see accompanying figure). A rise in H.G.H. was regarded as being " related to the fall in blood-sugar " if it occurred at any time after the commencement of infusion-i.e., in the ensuing two hours. This definition was felt to be a generous interpretation of the relation between blood-sugar and plasma-H.G.H., and may in fact slightly overestimate the degree of any such relation. To simplify the assessment of these changes, a fall in blood-sugar was regarded as a change exceeding 10 mg. per 100 ml. It is this level which Luft et al. (1966) have claimed to be adequate to evoke a rise in plasma H.G.H. Of the infusions where " no change " is said to have occurred, the fall of blood-sugar ranged from 0 to 7 mg. per 100 ml., with a mean of 1-5 mg. per 100 ml. Those with a fall greater than 10 mg. per 100 ml. ranged from 14 to 37 mg. per 100
ml., with
a mean
of 21 mg. per
100 ml.
Elevation of plasma-H.G.H. beyond 3 ng. per ml. in
two
TABLE II-SUMMARY OF RESULTS
In
one
additional subject,
a
rise in
H.G.H.
preceded the
fall in blood-sugar.
consecutive samples was regarded as a significant rise. The basal level in all subjects was close to 1 ng. per ml. The results of the study are summarised in table II. When changes in plasma H.G.H. and sugar were compared, it was observed that a rise in H.G.H. beyond 3 ng. per ml. occurred during fourteen of the nineteen infusions. Of these fourteen elevations, six occurred in the absence of a change in blood-sugar, one occurred before a fall in blood-sugar, and seven followed a decline in or more
blood-sugar. During the nine infusions in which the blood-sugar level did not fall, six subjects showed a rise in plasmaH.G.H. Of the ten infusions with a fall in blood-sugar exceeding 10 mg. per 100 ml., seven showed a rise in H.G.H. at or after the time of the nadir, and in one case a rise in H.G.H. preceded a fall in blood-sugar. Discussion
The presence of intermittent peaks of H.G.H. secretion first observed in blood samples taken from children during the night (Hunter and Rigal 1966). Such fluctuations have also been observed in normal adults, in whom several H.G.H. peaks occurred throughout a twenty-fourhour fast (Quabbe et al. 1966). These peaks were not related to changes in the blood-sugar or plasma-nonesterified-fatty-acid values, indicating that such changes are not directly responsible for H.G.H. release during fasting. Luft et al. on the other hand, postulated that minor to moderate decreases in blood glucose (6-19 mg. per 100 ml.) were responsible for an increased secretion of was
H.G.H.
On the basis of the results reported here, it is difficult sustain a relation between H.G.H. secretion and falls of blood-sugar in the 10-20 mg. per 100 ml. range. Although a rise in plasma H.G.H. was observed in 78% of infusions accompanied by a fall in blood-sugar, the same observation was made in 70% of infusions in which no change in sugar levels occurred. The results may be alternatively stated to show that, of all fourteen elevations in plasma-H.G.H., only 50% occurred in temporal relation to a fall in bloodsugar. The equal frequency of H.G.H. elevations in the control infusions indicates that similar fluctuations following small changes in blood-sugar cannot be regarded as responses to these changes. to
Three patterns of change in blood-sugar and plasma-H.G.H. during infusion of small doses of insulin.
The period of infusion is indicated by the horizontal black bar (0-60 minutes). Upper panel: A rise in H.G.H. preceding a fall in blood-sugar,
observed on one occaston. Add/s panel: A rise in H.G.H. occurring in the absence of a change in blood-sugar, observed on six occasions. Loz;:er panel: A rise in H.G.H. occurring in relation to a fall in bloodsugar, observed on seven occasions. Of the remaining five infusions, three showed no change in either blood-sugar or H.G.H., and two showed a fall in blood-sugar but no
change
in
H.G.H.
This work was supported by a grant from the Australian Research Grants Committee to two of us (K. J. C. and H. G. B.). Requests for reprints should be addressed to H. G. B. REFERENCES
Catt, K. J., Niall, H. D., Tregear, G. W. (1967) J. Lab. clin. Med. 70, 820. Greenwood, F. C., Hunter, W. M., Marrian, V. J. (1964) Br. med. J. i, 25. Hunter, W. M., Rigal, W. M. (1966) J. Endocr. 34, 147. Luft, R., Cerasi, E., Madison, L. L., von Euler, U. S., Della Casa, L., Roovette, A. (1966) Lancet, ii, 254. Quabbe, H. J., Schilling, E., Helge, H. (1966) J. clin. Endocr. 26, 1173. Roth, J., Glick, S. M., Yalow, R. S., Berson, S. A. (1963) Science, N.Y. 140, 987.