E. B. Marliss

The diabetic syndrome of the ‘BB’ Wistar rat: Possible relevance to Type 1 (insulin-dependent) diabetes in man

SummaryThe diabetes which occurs spontaneously in the ‘BB’ Wistar rat has many affinities with human Type 1 (insulin-dependent) diabetes. It occurs in a non-obese, standard, laboratory rat derived from a non-inbred Wistar line. Both sexes are affected, with onset corresponding approximately to the time of sexual maturation. Both genetic and immune factors are involved in the aetiology, but their precise nature remains to be defined. Evolution of the overt clinical syndrome occurs over a period of hours to a few days. An intense insulitis is found, accompanied by selective destruction of B cells. Although insulitis may precede diabetes by many weeks, within 7–21 days after glycosuria the B cells are completely destroyed and have disappeared and the islets are few, small and with little residual inflammation. If untreated, marked wasting of body tissues, including fat and muscle protein, dehydration, and ketosis supervene. Careful study of littermates reveals glucose intolerance in 10%–25%, accompanied always by insulitis and these rats may subsequently develop insulin-dependent diabetes. Marked lymphopenia, mainly of thymus-derived (T) lymphocytes, both precedes and is sustained during glucose intolerance and overt diabetes. This lymphopenia appears to be associated reliably with insulitis, and may be a simple marker of susceptibility thereto. Abnormalities of nerves, testicles, and a tendency towards increased frequency of lymphomas have been found. Further research in this animal could lead to insights into aetiology, pathophysiology and complications potentially applicable to man.

The spontaneously diabetic Wistar rat (the “BB” rat)

SummaryA longitudinal study of 51 weanlings from 5 litters of “BB” Wistar rats was undertaken to characterize the time course of the spontaneous diabetic syndrome. Nine rats developed overt diabetes. An abnormal glucose tolerance preceded the onset of the syndrome in 6 of these 9 rats. No other “clinical” or metabolic variable measured was predictive of the development of this syndrome. In these rats, the onset was remarkably abrupt, followed by rapid clinical deterioration with marked hyperglycaemia, glycosuria, ketonaemia and hypoinsulinaemia attained within 2 to 8 days. Pronounced insulitis was present in the early stages of the syndrome, resulting in complete B-cell destruction at the time of sacrifice at 7 to 40 days. Among the 42 littermates, 9 revealed sequential abnormalities in oral glucose tolerance tests performed at weekly intervals (to age 90–120 d) though remaining aglycosuric and maintaining normal fasting plasma glucose levels. In 7 of these rats, a milder form of the same islet inflammatory lesion seen in the overtly diabetic animals was present. Thus the new features identified are: 1) a time course of evolution from normoglycaemia to overt diabetes telescoped into a period of days, and 2) a “chemical” stage or form with an insulitis similar to that found in the early stages of overt diabetes.

The effects of prolonged fasting on plasma triglyceride kinetics in man

Studies were undertaken to examine triglyceride turnover in obese humans on isocaloric balanced diets and during prolonged (3-5 wk) fasting. The data were related to plasma concentrations of insulin (IRI), glucagon (IRG), and free fatty acids (FFA) and to blood ketone concentrations. The triglyceride turnover rates were also related to the plasma triglyceride concentration. This relationship was the same in the obese on isocaloric balanced diets as that we have previously observed in lean humans on similar diets. The relationship between triglyceride turnover and concentration changed during prolonged fasting in a way that suggested that triglyceride removal was impaired. This viewpoint is consistent with the known effects of fasting on adipose tissue lipoprotein lipase activity. In another group of fasted obese, refed with a hypocaloric diet, the relationship returned toward normal. In addition to the impaired triglyceride removal, prolonged fasting resulted in a decrease in triglyceride production. This decrease occurred despite an increase in plasma FFA. After 3-5 wk of fasting the IRI was about 50% of the initial value, while the IRG was the same as the initial value. While triglyceride production fell during fasting, the blood ketone concentration rose. Others have seen similar changes in ketones and triglycerides in livers perfused with medium in which the ratio of insulin to glucagon fell. The rate of triglyceride production was not related to body weight. However, regardless of nutritional state, it was positively related to the basal plasma insulin levels. These data indicate that, in man as in animal preparations, insulin may regulate hepatic triglyceride production.

Islet cell surface and lymphocyte antibodies often precede the spontaneous diabetes in the BB rat

SummaryThe diabetic syndrome of the BB rat shows many homologies with that of human insulin-dependent diabetes and evidence that the onset of the disease is associated with the presence of autoantibodies, including islet cell surface antibodies. In this study, sera were sampled serially from weaning to 157 days of age from 26 BB rats in two low-incidence litters, and 22 rats of three high-incidence litters. Clinical and metabolic variables were monitored concurrently with blood lymphocyte counts. Islet morphology was correlated at sacrifice. In the high-incidence litters, eight rats developed insulin-dependent diabetes, five impaired glucose tolerance, and the remaining nine all showed insulitis. In the low-incidence litters, only one animal showed impaired glucose tolerance and another insulitis. In the high-incidence litters 16 rats (73%) had islet cell surface antibodies compared with 4 out of 26 (15%) low-incidence controls (p<0.002). Antibodies reactive with Wistar rat spleen lymphocytes were present in all high-incidence rats compared with 19% (5 out of 26) among the control litters (p<0.002). Time courses of islet cell surface and lymphocyte antibody appearance and their peak values varied, but already at weaning the levels of both antibodies were increased among the high-incidence litter rats (p< 0.001). Islet cell surface and/or lymphocyte antibodies were therefore present in the majority of animals at an age where neither morphological nor metabolic evidence of the diabetic syndrome were yet detected. All rats that showed any form of the syndrome were lymphopenic. These findings suggest that BB rats have an abnormal immune response which predisposes to later development of insulin-dependent diabetes, often preceded by the presence of islet cell surface and/or lymphocyte antibodies.

Turnover and recycling of glucose in man during prolonged fasting

The effect of prolonged (3-5 wk) fasting on tracer-determined glucose turnover and of recycling radioactive glucose has been examined. We followed the specific activity of plasma glucose after the simultaneous administration of 1-14C-glucose and 3-3H-glucose. The rate of glucose turnover decreased during prolonged fasting. Recycling of radioactive glucose was estimated by two different techniques: (1) the appearance of 14C in positions 2 to 6 glucose was measured; (2) the difference in the slopes of specific activity decline for 1-14C-glucose and for 3-3H-glucose was calculated. The two methods of estimating the radioactive recycling gave results similar to each other. The amount of glucose recycled did not change during prolonged fasting. However, in view of the decline in glucose production during fasting, the proportion of glucose production which was represented by recycling increased. Based on weight and urinary nitrogen loss an estimate of the glucose production from amino acids and glycerol was obtained. The difference between the rate of glucose production from the contribution of amino acids and glycerol and that estimated by radioisotopic techniques was much larger than the measured rate of recycling. This finding suggests that either a large exchange of 12C with 14C occurred in some glycolytic intermediates or that a hitherto unknown source of carbon for glucose production appeared during prolonged fasting.

Insulin, glucagon, and amino acids during glycemic control by the artificial pancreas in diabetic man.

The artificial endocrine pancreas (AEP) can normalize glycemia at rest and with meals. To determine whether insulin, glucagon, and amino acid profiles are also normalized, nine diabetics on subcutaneous insulin (S/C) and AEP control were compared to ten normal controls (NC). Glycemia was monitored continuously over 10 hr during which meals were consumed. Insulin infusion rate, and the levels of immunoreactive insulin (IRI) (in NC), free insulin (in S/C and AEP), C-peptide, glucagon, and amino acids are reported. Glycemia in AEP started at somewhat higher levels than in NC, but with breakfast and thereafter, it was identical. In S/C, hyperglycemia prevailed throughout, with no systematic change in free IRI. In AEP, both basal and peak free insulin levels, measured in four patients, were significantly higher than in NC. C-peptide values were significantly lower in diabetics and did not change with meals. Basal glucagon values were not different in the three groups and changes with meals were of small magnitude. Branched chain amino acids were higher in S/C and did not increase as in NC. In AEP, levels were lower than NC after the first two meals. Similarly, lysine and threonine were lower in AEP than in NC at the same times. Alanine, though similar at the onset, was lower 2 hr postbreakfast and higher 2 hrs postsupper in AEP and S/C compared to NC. These studies demonstrate that glycemic control with AEP is accompanied by hyperinsulinemia, which could account for the amino acid responses and the small alterations in immunoreactive glucagon (IRG) patterns. Further refinement is needed to obtain full normalization of metabolic profiles.

The metabolic response to glycemic control by the artificial pancreas in diabetic man.

Abstract To determine the effect of glycemic control by the artificial pancreas on the other metabolic consequences of diabetes, five renebese male insulin-dependent diabetic subjects were studied first on s.c. insulin and then during artificial pancreas (AEP) control. Glycemia was continuously monitored, and the circulating concentrations of factate, pyruvate, alanine, free fatty acids (FFA), beta hydroxybutyrate, and triglycerides were measured during breakfast, lunch, snack, and supper. The metabolic profiles were compared to normal control subjects. Glycemic excursion with meals during AEP control was normalized (min, 76 ± 8 mg/dl; max, 157 ± 20 mg/dl), compared to administration of s.c. insulin (min, 173 ± 52; max, 279 ± 49 mg/dl). Postabsorptive concentrations of lactate and pyruvate were elevated for diabetic subjects on s.c. insulin treatment and during AEP control. However, the postmeal peaks of lactate and pyruvate observed in the normal control individuals were restored during AEP control. Although alanine concentrations were similar for all groups at the start of the experiment, the postprandial increase that occurred with breakfast for the normal subjects was delayed until lunch for both diabetic groups. The elevated FFA concentrations with s.c. insulin were entirely normalized during AEP control, whereas beta hydroxybutyrate concentrations were incompletely corrected. These studies demonstrate that a short period of glycemic control during meals restores toward normal other metabolic intermediates influeneed by insulin. For further refinement in metabolic control, a more prolonged period of normoglycemia may be required.

Blood Glucose Control and Insulin Clearance in Unrestrained Diabetic Dogs Portally Infused with a Portable Insulin Delivery System

SummaryLong term glucose control in pancreatectomised dogs has been obtained with portal insulin therapy. When compared to a previous similar study using peripheral infusions, 20% less exogenous insulin was required and peripheral fasting insulin levels were 30% lower. Animals (n = 5) were unrestrained, conscious and carried a programmable insulin pump for 163–224 days. In the post-absorptive state blood glucose was normal (87±5 mg/dl) as was plasma insulin (10±1 mU/l) with porcine insulin infused at a basal rate of 0.36±0.01 mU/kg/min. Following ingestion of a standard mixed meal the infusion rate was increased to 2.47±0.09 mU/kg/ min for 7 1/2 h resulting in post-prandial normalisation of blood glucose. Peripheral plasma insulin levels were twice normal during the post-prandial infusion, but only half those previously reported with peripheral infusions. Insulin clearance rates were 37 ml/kg/min in the basal state and rose significantly post-prandially. In the absence of extra meal-time insulin the clearance rate was unaffected by the resulting post-prandial hyperglycaemia and similar to values observed with insulin infused peripherally at 0.45±0.03 mU/kg/min. No significant increase in the post-prandial rate of insulin clearance relative to the fasting rate was observed with peripherally administered insulin. It was thus concluded that portal insulin replacement in pancreatectomised dogs could normalise both blood glucose and insulin in the fasting state, but post-prandial peripheral insulin levels remained elevated.

Renal excretion of uric acid during prolonged fasting

Serum and urine uric acid were evaluated during prolonged therapeutic fasting in 15 obese patients. With increasing ketonemia the serum uric acid rose from a control value of 5.9 +/- 0.4 to 12.5 +/- 1.0 mg/100 ml at 7 days and then decreased progressively to 7.7 +/- 1.3 mg/100 ml by 28 days despite sustained ketonemia. The uric acid clearance were 5.5 +/- 0.9, 1.8 +/- 0.2, and 4.4 +/- 1.5 ml/min at days 0, 7, and 25 of fasting. At the same times the creatinine clearances were 114 +/- 11, 80 +/- 6, and 64 +/- 6.3 ml/min. There was no evidence of a renal tubular abnormality as assessed by glycosuria, bicarbonaturia, or increased phosphaturia. Urate binding to plasma proteins remained unchanged. Acute studies of the renal handling of uric acid revealed a uricosuric response to the administration of sodium lactate or sodium bicarbonate by intravenous infusion and low-dose acetylsalicylic acid orally. This renal tubular response departs significantly from that observed during the overnight fasted state and could not be accounted for by extracellular fluid volume expansion or the induced acid-base changes.

Blood glucose regulation using closed- and open-loop insulin delivery systems. II. Peripheral primed square wave infusions.

SummaryGlucose was infused into anaesthetized dogs before and after pancreatectomy. In the diabetics blood glucose was regulated first by closed-loop and then by open-loop insulin delivery schemes. Insulin requirements for the latter were determined by resolving the former into a sequence of 3 different infusion rates: during the baseline and recovery periods, basal insulin was delivered at 0.37±0.02 mU/kg/min, while during the 60 min glucose infusion (10 mg/kg/min) there was an 8 min infusion at 4.96±0.37 mU/kg/min and a 52 min component at 1.85±0.08 mU/kg/min. With the open-loop method under these highly standardized conditions glycaemia was similar to normal controls but IRI levels were significantly higher, 13.5 vs 8.0 μU/ml (p<0.05) in the baseline and recovery periods and 74 vs 25 μU/ml (p<0.05) during the glucose infusion. It was concluded that: constant normogly-caemia can be maintained in the basal state by a constant rate of peripheral insulin delivery but at rates resulting in peripheral hyperinsulinaemia; the glycaemic response to glucose infusion can be normalized by a two component waveform of insulin delivery; and the closed-loop method can serve as a useful guide in determining insulin requirements.