The effect of thyroid hormones on gluconeogenesis and forearm metabolism in man

The present study was designed to examine the effects of excess T3 on total body glucose production and forearm exchange of glucose, amino acids, and other metabolites. Five healthy male volunteers were studied after an overnight fast, before and 7 days after the administration of 150 micrograms/day T3. Glucose production (milligrams per kg/min) was measured using a primed continuous infusion of [3-3H]glucose and gluconeogenic index (micromoles per kg/min) was measured by following the conversion of infused [14C]alanine to [14C]glucose. Blood flow across the forearm was measured using capacitance plethysmography and forearm release of substrates was determined by the Fick principle. After T3 administration, there was a 3.7-fold rise in T3 from 150 +/- 15 to 530 +/- 12 ng/dl (P less than 0.001), with no change in insulin (12 +/- 1 microU/ml pre-T3 vs. 13 +/- 2 microU/ml post-T3) and glucagon (79 +/- 5 pre-T3 vs. 84 +/- 7 pg/ml post-T3). T3 administration resulted in an increase in plasma glucose (from 83 +/- 5 to 98 +/- 5 mg/dl; P less than 0.05), net glucose uptake by the forearm (from 250 +/- 90 to 712 +/- 60 nmol/100 ml forearm tissue X min; P less than 0.005) and glucose production (1.7 +/- 0.09 to 2.2 +/- 0.08 mg/kg X min; P less than 0.005), without a change in glucose clearance (2.1 +/- 0.02 vs. 2.0 +/- 0.02 ml/kg X min); the rate of conversion of [14C]alanine to [14C]glucose increased by 30% (0.56 +/- 0.03 to 0.74 +/- 0.03 mumol/ kg X min P less than 0.005). These values were associated with a 25% increase in blood lactate to 712 +/- 69 mumol/liter (P less than 0.05) and a 131% increase in lactate release across the forearm to 434 +/- 90 (P less than 0.005). Forearm release of alanine (96 +/- 29 nmol/100 ml forearm tissue X min) and glutamine (151 +/- 41 nmol/100 ml forearm tissue X min) increased by 90% (P less than 0.005 and P = 0.04, respectively), with no change in their concentrations. Forearm release of branched chain amino acids did not change, while those of their ketoacids, alpha-ketoisocaproate (KIC) and alpha-ketoisovalerate (KIV), doubled (to 64 +/- 9 mumol/liter for KIC and 39 +/- 6 mumol/liter for KIV; P less than 0.05). These were associated with a 45% increase in the branched chain amino acid levels and a 46% rise in both KIC and KIV levels to 41 +/- 9 and 28 +/- 7 mumol/liter, respectively (P less than 0.05). There was a concurrent significant (P less than 0.05) change in the arterial levels of phenylalanine (-32%), tyrosine (-29%), threonine (-20%), glycine (-20%), and serine (-15%), without any change in their efflux across the forearm. The data indicate that a pharmacologically induced rise in T3, to levels comparable to those seen in hyperthyroidism, results in enhanced glucose production, with an increase in glucose uptake by the forearm. The former can be partially accounted for by an increase in hepatic gluconeogenesis, glycogenolysis, or possibly increased renal glucose production...

Exercise in insulin-dependent diabetes mellitus: the effect of continuous insulin infusion using the subcutaneous, intravenous, and intraperitoneal sites

The metabolic response to exercise in insulin-dependent diabetic (IDD) man was assessed during continuous insulin infusion using the subcutaneous (CSII), intravenous (CIVII), and intraperitoneal (CIPII) routes. During the basal period, plasma glucose levels were higher with CIPII (153 +/- 17 mg/dl) than with CSII (117 +/- 13 mg/dl) or CIVII (118 +/- 17 mg/dl). Basal free insulin concentrations were similar for CSII (12.3 +/- 10 microU/ml) and CIVII (12.4 +/- 1.4 MicroU/ml) but lower in CIPII (8.5 +/- 1.0 microU/ml, P less than 0.05). Exercise on a stationary bicycle at 75 W for 60 min produced a decline of plasma glucose in each protocol that was significantly only during CIVII (55 +/- 11 mg/dl, P less than 0.01). Insulin levels remained unchanged throughout the study period in all protocols. In normals, insulin values decreased during exercise and remained below basal levels through the recovery period (P less than 0.05), while plasma glucose remained unchanged. Plasma glucagon and epinephrine levels were similar in all protocols and remained unchanged with exercise, while plasma norepinephrine tended to be higher than normal in all diabetic subjects. Significant differences between normal and diabetic subjects (P less than 0.05) were observed for blood ketone bodies, while blood lactate, glycerol, and plasma FFA were similar. Normalization of intermediary metabolites occurred only with CIVII. Continuous insulin infusion provides near-normal glycemic and metabolic control before, during and following exercise in IDD man. However, to produce normal blood concentrations of intermediary metabolites during exercise, the insulin infusion rate may be excessive in terms of its hypoglycemic effect. CSII appears to be a safe, accessible, and adequate method for treating diabetic man during exercise.

Leupeptin inhibits adrenocorticotropic hormone-induced protein breakdown in the conscious dog

To elucidate the role of proteinase inhibitors in the regulation of protein breakdown in vivo, we measured the effect of leupeptin on the rate of appearance of leucine in the plasma compartment in overnight-fasted conscious dogs. Two groups of dogs were studied. The control group (I) received saline infusion, and the experimental group (II) was rendered hypercatabolic with daily administration of adrenocorticotropic hormone (ACTH) (500 U/d) for 4 d.ACTH treatment increased plasma cortisol from 2+/-0.4 to 17+/-2 mug/dl (P < 0.005). It raised plasma leucine levels (mumol/liter) from 123+/-6 in I to 206+/-5 in II (P < 0.01) and its rate of appearance into the plasma compartment (micromoles per kilogram per minute) from 3.1+/-0.1 in I to 4.6+/-0.3 in II (P < 0.01). Whole blood alanine concentration (micromoles per liter) increased by 50% (from 387+/-31 to 577+/-53, P < 0.01) and whole blood glutamine concentration (micromoles per liter) increased from 653+/-51 to 917+/-93 (P < 0.01). Leupeptin infusion in the ACTH-treated group significantly decreased both the concentration of plasma leucine and its rate of appearance. Blood glutamine declined by 30% (P < 0.05) after leupeptin, but no effect on blood alanine was observed. Leupeptin had no effect on the saline control group. These data indicate that leupeptin decreases the accelerated rate of protein breakdown induced by cortisol excess. The fact that it did not affect protein degradation in controls may indicate that control of protein breakdown in the postabsorptive state may differ from that during accelerated turnover. Thus, the antibiotic proteinase enzyme inhibitors may be potentially useful in treating conditions of inappropriate protein breakdown.

Role of insulin in the regulation of leucine kinetics in the conscious dog

To study the effect of insulin on leucine kinetics, three groups of conscious dogs were studied after an overnight fast (16-18 h). One, saline-infused group (n = 5), served as control. The other two groups were infused with somatostatin and constant replacement amount of glucagon; one group (n = 6) received no insulin replacement, to produce acute insulin deficiency, and the other (n = 6) was constantly replaced with 600 muU/kg per min insulin, to produce twice basal hyperinsulinemia. Hepatic and extrahepatic splanchnic (gut) balance of leucine and alpha-ketoisocaproate (KIC) were calculated using the arteriovenous difference technique. l,4,5,[(3)H]Leucine was used to measure the rates (micromoles per kilogram per minute) of appearance (Ra) and disappearance (Rd), and clearance (Cl) of plasma leucine (milliliters per kilogram per minute). Saline infusion for 7 h resulted in isotopic steady state, where Ra and Rd were equal (3.2+/-0.2 mumol/kg per min). Acute insulin withdrawal of 4-h duration caused the plasma leucine to increase by 40% (P < 0.005). This change was caused by a decrease in the outflow of leucine (Cl) from the plasma, since Ra did not change. The net hepatic release of the amino acid (0.24+/-0.03 mumol/kg per min) did not change significantly; the arterio-deep femoral venous differences of leucine (-10+/-1 mumol/liter) and KIC (-12+/-2 mumol/liter) did not change significantly indicating net release of the amino and ketoacids across the hindlimb. Selective twice basal hyperinsulinemia resulted in a 36% drop in plasma leucine (from control levels of 128+/-8 to 82+/-7 mumol/liter, P < 0.005) within 4 h. This was accompanied by a 15% reduction in Ra and a 56% rise in clearance (P < 0.001, both). Net hepatic leucine production and net release of leucine and KIC across the hindlimb fell markedly. These studies indicate that physiologic changes in circulating insulin levels result in a differential dose-dependent effect on total body leucine metabolism in the intact animal. Acute insulin withdrawal exerts no effect on leucine rate of appearance, while at twice basal levels, insulin inhibited leucine rate of appearance and stimulated its rate of disappearance.

Disposal of alpha-ketoisocaproate: roles of liver, gut, and kidneys

The alpha-keto analogues of the branched-chain amino acids, and particularly that of leucine, alpha-ketoisocaproate (KIC), have been found to reduce urea synthesis and as a result have been proposed for the treatment of uremia and portal systemic encephalopathy. Because little is known about the fate of these keto acids in the intact animal, we examined the disposal of a KIC load in five conscious overnight-fasted dogs with catheters previously implanted in an artery, and in the portal, hepatic, and renal veins. During the absorptive period (54 +/- 9 min; range, 20-75 min), 62 +/- 5% of the administered load (6,358 +/- 662 mumol) of the keto acid was absorbed as KIC and 23 +/- 3% was transaminated across the gut and entered as leucine. The hepatic uptake of KIC was equivalent to 35 +/- 5% (2.316 +/- 419 mumol) of the administered load, and of that, one-third was transaminated to leucine and two-thirds were converted to ketone bodies. The splanchnic output of KIC amounted to 1,732 +/- 256 mumol of 27 +/- 2% of the administered load, half of which was transaminated across the kidneys to leucine. As a result, the amount of KIC reaching the extrahepatic extrarenal tissues as KIC carbon amounted to 15% of the load administered. We conclude that the majority of an intragastrically administered KIC load reaches the (extrarenal) peripheral tissues in the form of leucine or ketone bodies. The study also underscores the importance of the "gut," the kidneys, and the liver in metabolism of the absorbed KIC load.

Absorption and disposition of a glucose load in the conscious dog

The quantitative disposition of an intragastrically administered glucose load was studied in eight conscious 18-h fasted dogs using isotopic and arteriovenous (A-V) techniques. During the control period, the gut utilized 25% of the basal net hepatic glucose output (2.8 +/- 0.2 mg.kg-1.min-1). After glucose ingestion, 80% of the load was absorbed as glucose, 11% was converted across the gut to lactate and alanine, and 4% was oxidized to CO2. Two percent of the load remained in the gut 4 h after glucose administration and 3% was unaccounted for. During the absorptive period, net hepatic glucose balance (NHGB) varied considerably (mean range = output of 1.8 to uptake of 9.1 mg.kg-1.min-1), while endogenous hepatic glucose production (Ra hp) showed a consistent 80% suppression. The total net hepatic glucose uptake during the absorptive period (150 +/- 10 min) accounted for the disposal of 24 +/- 10% of the ingested load, and the amount of glucose escaping the splanchnic bed was 40 +/- 3%. Overall NHGB correlated positively with basal arterial glucose and insulin levels and negatively with basal arterial glycerol and FFA and with peak absorptive arterial glucose and insulin levels. These data suggest that the hepatic response to an ingested glucose load depends in part on the degree of metabolic fast of the animal at the time of glucose ingestion; the latter may be a major determinant of the roles played by the tissues in glucose disposal.