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ROLE OF ADRENERGIC RECEPTORS IN GLUCOSE-INDUCED INSULIN SECRETION IN MAN
301
ROLE OF ADRENERGIC RECEPTORS IN GLUCOSE-INDUCED INSULIN SECRETION IN MAN SUAD EFFENDIC
EROL CERASI ROLF LUFT
Department of Endocrinology and Metabolism, Karolinska Hospital, Stockholm 60, Sweden Administration to healthy volunteers of a &bgr;-receptor blocker (propranolol) in most instances significantly inhibited the insulin response to glucose infusion, while &agr;-receptor blocking (by phentolamine) enhanced the insulin release. The inhibition induced by the &bgr;-blocking agent was totally or partially overcome by simultaneous administration of aminophylline. These results indicate that, in man, glucose-induced insulin release is mediated by adenyl cyclase and, consequently, by the intracellular level of cyclic adenosine monophosphate.
Sum ary
INTRODUCTION
A RELATIONSHIP between adrenergic receptors and insulin release from the pancreas in man was first shown by Porte et al.1 who showed that the insulinsupressing effect of catecholamines is mediated by the a-adrenergic receptors. However, Porte2 has said that he does not know if adrenergic receptors partici-
pate in the physiological stimulation of insulin secretion. We have found that insulin release during
(a) Propranolol
(b) Propranolol
hyperglycaemia
does involve the
adrenergic receptor
system. PATIENTS AND METHODS
Tests were done on six healthy volunteers, aged 22-34, with normal intravenous glucose tolerance3 (k values 1-133.85). Plasma-insulin levels were measured during a glucose-infusion test (G.I.T.) 4 in which a priming dose of 500 mg. glucose per kg. body-weight was followed by the constant infusion, for 60 minutes, of 20 mg. of glucose per kg. per minute. Venous blood-samples for measurement of blood-glucose and plasma-insulin (double-antibody radioimmunoassay 5) were drawn at 10-minute intervals during the infusion period and at 20-minute intervals for another hour. The effect of P-receptor blockade on insulin response to glucose infusion was investigated in a second
experiment by giving 3 mg. propranolol intravenously over 5 minutes followed by a constant infusion of 0-08 mg. per minute for 85 minutes. A G.I.T. was started 30 minutes after the beginning of propranolol administration. Bloodsamples were collected during the half-hour preceding the G.I.T. The effect of a-receptor blockade was investigated by giving a phentolamine infusion (0-5 mg. per minute) during the half-hour preceding the G.I.T. and during the glucose infusion. Blood-samples were taken as in the experiments with propranolol. In a fourth series of experiments the propranolol/G.I.T. was combined with the administration of aminophylline. This drug was given 30 minutes before the 5 mg. dose of propranolol as a 200 mg. priming injection followed by 200 mg. administered as a constant infusion for 60 minutes. RESULTS
Neither
(see figure)
norblockade alone affected basal levels of blood-glucose and plasma-insulin.
(c)
a
Phentolamine
(d) Aminophylline + propranolol
Blood-glucose and plasma-insulin response to glucose-infusion test after propranolol, phentolamine, or propranolol Horizontal bars show duration of infusion of:
(1) glucose, (2) propranolol (or phentolamine),
and
plus aminophylline.
(3) aminophylline
302
In four
of six
experiments P-receptor blockade by propranolol significantly inhibited the insulin response to glucose. In three, this inhibition lasted throughout the period of increased insulin secretion (a); in one the initial response was preserved (b). In three out of four tests the a-receptor blocking agent phentolamine enhanced the glucose-induced release of insulin (c). In all three tests propranolol-induced inhibition of insulin release on glucose infusion was partially or totally overcome by the simultaneous administration of aminophylline (d). (Aminophylline alone, in the amounts used here, has no enhancing effect on insulin secretion in healthy individuals.6) out
DISCUSSION
Since {3-receptor blockade inhibited and oc-blockade enhanced the glucose-induced insulin release, this implies that the stimulatory action of glucose on insulin secretion is either mediated through the &bgr; receptor or is closely related to it. The variability in the effects of the blocking agents might be due to individual differences in the potency of the receptors or in their sensitivity to the drugs used.7 Robinson et al.have suggested that p-adrenergic receptors are identical with, or closely related to
adenyl cyclase. Since cyclic
A.M.P. is a key substance in the secretion of insulin 9 the inhibition of glucoseinduced insulin release byblockade may be related to a decrease in the formation of cyclic A.M.P. This assumption is supported by our finding that aminophylline counteracted the inhibitory effectof propranolol. Since aminophylline alone, at the doses used here, does not stimulate insulin release,the insulin response to glucose in the presence of both propranolol and aminophylline could not be the sum of inhibitory and stimulatory actions on insulin release. We suggest that the small doses used here of aminophylline, a competitive inhibitor of adenosine-3,5’monophosphate phosphodiesterase, could influence significantly the level of cyclic A.M.P. only when this nucleotide was formed at a lower rate than normal. Bressler et al.1O suggested that (3-receptor blockers in mice act at a locus beyond adenyl cyclase, but they used blocker doses 100 times higher than ours, and the effects may have been unspecific. Our findings suggest that, in man, glucose-induced insulin release is mediated by adenyl cyclase and, consequently, by the intracellular level of cyclic A.M.P. We thank Mr. A. Roovete, Mrs. Kerstin Waldelof, Mrs. Christina Thornqvist, Miss Gunnie Sandgren, and Miss Anette Johansson for valuable assistance. This study was supported by grants from the Swedish Medical Research Council (B 6919X-34-05 A) and Knut and Alice Wallenberg’s Foundation. Requests for reprints should be addressed to R. L. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
10.
Porte, D. Jr., Graber, A. L., Kuzuya, T., Williams, R. H. J. clin. Invest. 1966, 45, 288. Porte, D. Jr. Archs. intern. Med. 1969, 123, 252. Ikkos, D., Luft, R. Acta endocr., Copenh. 1957, 25, 312. Cerasi, E., Luft, R. ibid. 1967, 55, 278. Hales, C. N., Randle, P. J. Biochem. J. 1963, 88, 137. Cerasi, E., Luft, R. Horm. metab. Res. (in the press). Östman, J., Efendic, S. Acta med. scand. (in the press). Robinson, G. A., Butcher, R. W., Sutherland, E. W. Ann. N.Y. Acad. Sci. 1967, 139, 703. Sussman, K. E., Vaughan, G. D., Timmer, R. F. Diabetes, 1966, 15, 521. Bressler, R., Vargas Cordon, M., Brendel, K. Archs intern. Med. 1969, 123, 248.
ACETATE IN THE CORRECTION OF ACIDOSIS SECONDARY TO DIARRHŒA KHONDAKAR M. M. TOHA RICHARD A. CASH ZAHIDUL HUQ DAVID R. NALIN ROBERT A. PHILLIPS Pakistan-SEATO Cholera Research Laboratory, Institute of Public Health, Mohakhali, Dacca 12, East Pakistan
Patients with acute acidosis and dehydration due to diarrhœa were treated with rapid intravenous infusions of electrolyte solutions containing either acetate or bicarbonate, and the rate of correction of arterial pH was monitored. The final pH correction was similar with the two types of solutions, demonstrating that acetate-containing solutions are effective in the treatment of this type of metabolic acidosis.
Sum ary
INTRODUCTION
SOLUTIONS containing either bicarbonate or lactate have been used widely in the correction of the acidosis of diarrhrea.1-3 Bicarbonate, however, must be autoclaved under a high partial pressure of carbon dioxide, a procedure which makes it difficult to produce large quantities of intravenous solution. Lactate readily supports the growth of mould, can cause deterioration of certain types of glassware, and thus has a variable shelf-life. Sodium acetate is easy to autoclave, inexpensive, stable, and has a long shelf-life. This study was undertaken to determine the efficacy of intravenous infusions of solutions containing acetate and other electrolytes in the correction of the acidosis and dehydration of cholera and other acute diarrhoeal diseases. PATIENTS AND METHODS
patients were selected from severely dehydrated patients admitted to our ward with a history of acute diarrhoea. After a brief history and physical examination, an arterial blood-sample and electrocardiogram were obtained, and intravenous infusion was begun. Arterial blood-samples and electrocardiogram were repeated after each litre of replacement therapy and after rehydration was complete (as determined by clinical status and plasma sp. gr.). The compositions of the intravenous solutions used in 17
the different groups is shown in table
I.
TABLE I-COMPOSITION OF SOLUTIONS USED
(meq./l.)
The bicarbonate solution and acetate-2 were prepared at our laboratory. Acetate-1 (’ Isolyte E McGaw Laboratories, Milledgeville, Georgia) was supplied by the U. S. Agency for International Development.
The blood-samples were analysed for pH, carbon dioxide, electrolytes, hasmatocrit, and plasma sp. gr. The carbondioxide content was determined by Van Slyke manometric method. Sodium and potassium were determined on a Baird atomic flame photometer; calcium and magnesium on a Perkin-Elmer atomic absorption spectrophotometer, and pH on a Corning 12-B meter. RESULTS
Of the 17 patients, 9 received a solution containing acetate and 8 received a solution containing bi-
ROLE OF ADRENERGIC RECEPTORS IN GLUCOSE-INDUCED INSULIN SECRETION IN MAN SUAD EFFENDIC
EROL CERASI ROLF LUFT
Department of Endocrinology and Metabolism, Karolinska Hospital, Stockholm 60, Sweden Administration to healthy volunteers of a &bgr;-receptor blocker (propranolol) in most instances significantly inhibited the insulin response to glucose infusion, while &agr;-receptor blocking (by phentolamine) enhanced the insulin release. The inhibition induced by the &bgr;-blocking agent was totally or partially overcome by simultaneous administration of aminophylline. These results indicate that, in man, glucose-induced insulin release is mediated by adenyl cyclase and, consequently, by the intracellular level of cyclic adenosine monophosphate.
Sum ary
INTRODUCTION
A RELATIONSHIP between adrenergic receptors and insulin release from the pancreas in man was first shown by Porte et al.1 who showed that the insulinsupressing effect of catecholamines is mediated by the a-adrenergic receptors. However, Porte2 has said that he does not know if adrenergic receptors partici-
pate in the physiological stimulation of insulin secretion. We have found that insulin release during
(a) Propranolol
(b) Propranolol
hyperglycaemia
does involve the
adrenergic receptor
system. PATIENTS AND METHODS
Tests were done on six healthy volunteers, aged 22-34, with normal intravenous glucose tolerance3 (k values 1-133.85). Plasma-insulin levels were measured during a glucose-infusion test (G.I.T.) 4 in which a priming dose of 500 mg. glucose per kg. body-weight was followed by the constant infusion, for 60 minutes, of 20 mg. of glucose per kg. per minute. Venous blood-samples for measurement of blood-glucose and plasma-insulin (double-antibody radioimmunoassay 5) were drawn at 10-minute intervals during the infusion period and at 20-minute intervals for another hour. The effect of P-receptor blockade on insulin response to glucose infusion was investigated in a second
experiment by giving 3 mg. propranolol intravenously over 5 minutes followed by a constant infusion of 0-08 mg. per minute for 85 minutes. A G.I.T. was started 30 minutes after the beginning of propranolol administration. Bloodsamples were collected during the half-hour preceding the G.I.T. The effect of a-receptor blockade was investigated by giving a phentolamine infusion (0-5 mg. per minute) during the half-hour preceding the G.I.T. and during the glucose infusion. Blood-samples were taken as in the experiments with propranolol. In a fourth series of experiments the propranolol/G.I.T. was combined with the administration of aminophylline. This drug was given 30 minutes before the 5 mg. dose of propranolol as a 200 mg. priming injection followed by 200 mg. administered as a constant infusion for 60 minutes. RESULTS
Neither
(see figure)
norblockade alone affected basal levels of blood-glucose and plasma-insulin.
(c)
a
Phentolamine
(d) Aminophylline + propranolol
Blood-glucose and plasma-insulin response to glucose-infusion test after propranolol, phentolamine, or propranolol Horizontal bars show duration of infusion of:
(1) glucose, (2) propranolol (or phentolamine),
and
plus aminophylline.
(3) aminophylline
302
In four
of six
experiments P-receptor blockade by propranolol significantly inhibited the insulin response to glucose. In three, this inhibition lasted throughout the period of increased insulin secretion (a); in one the initial response was preserved (b). In three out of four tests the a-receptor blocking agent phentolamine enhanced the glucose-induced release of insulin (c). In all three tests propranolol-induced inhibition of insulin release on glucose infusion was partially or totally overcome by the simultaneous administration of aminophylline (d). (Aminophylline alone, in the amounts used here, has no enhancing effect on insulin secretion in healthy individuals.6) out
DISCUSSION
Since {3-receptor blockade inhibited and oc-blockade enhanced the glucose-induced insulin release, this implies that the stimulatory action of glucose on insulin secretion is either mediated through the &bgr; receptor or is closely related to it. The variability in the effects of the blocking agents might be due to individual differences in the potency of the receptors or in their sensitivity to the drugs used.7 Robinson et al.have suggested that p-adrenergic receptors are identical with, or closely related to
adenyl cyclase. Since cyclic
A.M.P. is a key substance in the secretion of insulin 9 the inhibition of glucoseinduced insulin release byblockade may be related to a decrease in the formation of cyclic A.M.P. This assumption is supported by our finding that aminophylline counteracted the inhibitory effectof propranolol. Since aminophylline alone, at the doses used here, does not stimulate insulin release,the insulin response to glucose in the presence of both propranolol and aminophylline could not be the sum of inhibitory and stimulatory actions on insulin release. We suggest that the small doses used here of aminophylline, a competitive inhibitor of adenosine-3,5’monophosphate phosphodiesterase, could influence significantly the level of cyclic A.M.P. only when this nucleotide was formed at a lower rate than normal. Bressler et al.1O suggested that (3-receptor blockers in mice act at a locus beyond adenyl cyclase, but they used blocker doses 100 times higher than ours, and the effects may have been unspecific. Our findings suggest that, in man, glucose-induced insulin release is mediated by adenyl cyclase and, consequently, by the intracellular level of cyclic A.M.P. We thank Mr. A. Roovete, Mrs. Kerstin Waldelof, Mrs. Christina Thornqvist, Miss Gunnie Sandgren, and Miss Anette Johansson for valuable assistance. This study was supported by grants from the Swedish Medical Research Council (B 6919X-34-05 A) and Knut and Alice Wallenberg’s Foundation. Requests for reprints should be addressed to R. L. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
10.
Porte, D. Jr., Graber, A. L., Kuzuya, T., Williams, R. H. J. clin. Invest. 1966, 45, 288. Porte, D. Jr. Archs. intern. Med. 1969, 123, 252. Ikkos, D., Luft, R. Acta endocr., Copenh. 1957, 25, 312. Cerasi, E., Luft, R. ibid. 1967, 55, 278. Hales, C. N., Randle, P. J. Biochem. J. 1963, 88, 137. Cerasi, E., Luft, R. Horm. metab. Res. (in the press). Östman, J., Efendic, S. Acta med. scand. (in the press). Robinson, G. A., Butcher, R. W., Sutherland, E. W. Ann. N.Y. Acad. Sci. 1967, 139, 703. Sussman, K. E., Vaughan, G. D., Timmer, R. F. Diabetes, 1966, 15, 521. Bressler, R., Vargas Cordon, M., Brendel, K. Archs intern. Med. 1969, 123, 248.
ACETATE IN THE CORRECTION OF ACIDOSIS SECONDARY TO DIARRHŒA KHONDAKAR M. M. TOHA RICHARD A. CASH ZAHIDUL HUQ DAVID R. NALIN ROBERT A. PHILLIPS Pakistan-SEATO Cholera Research Laboratory, Institute of Public Health, Mohakhali, Dacca 12, East Pakistan
Patients with acute acidosis and dehydration due to diarrhœa were treated with rapid intravenous infusions of electrolyte solutions containing either acetate or bicarbonate, and the rate of correction of arterial pH was monitored. The final pH correction was similar with the two types of solutions, demonstrating that acetate-containing solutions are effective in the treatment of this type of metabolic acidosis.
Sum ary
INTRODUCTION
SOLUTIONS containing either bicarbonate or lactate have been used widely in the correction of the acidosis of diarrhrea.1-3 Bicarbonate, however, must be autoclaved under a high partial pressure of carbon dioxide, a procedure which makes it difficult to produce large quantities of intravenous solution. Lactate readily supports the growth of mould, can cause deterioration of certain types of glassware, and thus has a variable shelf-life. Sodium acetate is easy to autoclave, inexpensive, stable, and has a long shelf-life. This study was undertaken to determine the efficacy of intravenous infusions of solutions containing acetate and other electrolytes in the correction of the acidosis and dehydration of cholera and other acute diarrhoeal diseases. PATIENTS AND METHODS
patients were selected from severely dehydrated patients admitted to our ward with a history of acute diarrhoea. After a brief history and physical examination, an arterial blood-sample and electrocardiogram were obtained, and intravenous infusion was begun. Arterial blood-samples and electrocardiogram were repeated after each litre of replacement therapy and after rehydration was complete (as determined by clinical status and plasma sp. gr.). The compositions of the intravenous solutions used in 17
the different groups is shown in table
I.
TABLE I-COMPOSITION OF SOLUTIONS USED
(meq./l.)
The bicarbonate solution and acetate-2 were prepared at our laboratory. Acetate-1 (’ Isolyte E McGaw Laboratories, Milledgeville, Georgia) was supplied by the U. S. Agency for International Development.
The blood-samples were analysed for pH, carbon dioxide, electrolytes, hasmatocrit, and plasma sp. gr. The carbondioxide content was determined by Van Slyke manometric method. Sodium and potassium were determined on a Baird atomic flame photometer; calcium and magnesium on a Perkin-Elmer atomic absorption spectrophotometer, and pH on a Corning 12-B meter. RESULTS
Of the 17 patients, 9 received a solution containing acetate and 8 received a solution containing bi-