Therapeutic applications of viscous and injectable poly(ortho esters)

Poly(ortho esters) (POE) are hydrophobic and bioerodible polymers that have been investigated for pharmaceutical use since the early 1970s. Among the four described generations of POE, the third (POE III) and fourth (POE IV) are promising viscous and injectable materials which have been investigated in numerous biomedical applications. POE III has been extensively studied for ophthalmic drug delivery, it presents an excellent biocompatibility and is currently being investigated as a vehicle for sustained drug delivery to treat diseases of the posterior segment of the eye. POE IV is distinguishable by a highly reproducible and controlled synthesis, a higher hydrophobicity, and an excellent biocompatibility. It is currently under development for a variety of applications, such as ocular delivery, periodontal disease treatment and applications in veterinary medicine. This review will also focus on new perspectives for this promising family of polymers, such as guided tissue regeneration, treatment of osteoarthritis, as well as peptide and protein delivery.

Neonatal hypoglycaemia and withdrawal symptoms after exposure in utero to valproate

AIMS

To define, in a prospective study, the risk of hypoglycaemia-defined as blood glucose concentration < 1.8 mmol/l-in term infants exposed in utero to valproate and to describe the withdrawal symptoms.

METHODS

Twenty epileptic women were treated with valproate only during pregnancy and two were treated with valproate and carbamazepine. In the first trimester, the daily median dose of valproate was 1.0 g (range 0.3-4.2) and in the third trimester 1.2 g (range 0.3-4.8).

RESULTS

Thirteen of the 22 infants became hypoglycaemic. One infant had eight episodes of hypoglycaemia, one had three episodes, two had two episodes, and nine had one episode each. The lowest blood glucose concentration was 1.0 mmol/l. All episodes were asymptomatic. The maternal mean plasma concentration of total valproate during the third trimester correlated negatively with blood glucose concentration one hour after delivery (p < 0.0003) and with the development of hypoglycaemia (p < 0.0001). There was no evidence for hyperinsulinaemia as the cause of hypoglycaemia. Ten infants developed withdrawal symptoms, which correlated positively with the mean dose of valproate in the third trimester and the concentration of the free fraction of valproate in maternal plasma at delivery (p < 0.02).

CONCLUSIONS

Infants exposed to valproate in utero had a significantly elevated risk of hypoglycaemia, and withdrawal symptoms were often observed.

Blood glucose levels in a population of healthy, breast fed, term infants of appropriate size for gestational age

AIM

To determine blood glucose levels in a population of healthy, breast fed, term infants of appropriate size for gestational age.

METHODS

In a cross sectional study, the blood glucose concentration of 223 healthy, breast fed, term infants of appropriate size for gestational age was determined at different times (between one and 96 hours) after delivery. One sample of blood glucose was taken from each infant independent of the feeding time. The glucose concentration was correlated with sex, method of delivery, delivery with or without analgesia, smoking status of the mother, gestational age, umbilical cord pH, and Apgar score. Infants suspected of suffering from intrapartum hypoxia were excluded.

RESULTS

Blood glucose concentration one hour after delivery was not significantly lower than at any other time. Only two infants had low blood glucose concentrations one hour after delivery (1.4 and 1.9 mmol/l). There were no significant differences in blood glucose concentration between sexes, methods of delivery, infants delivered with or without analgesia, and infants born to smokers or non-smokers, and there was no further correlation between blood glucose concentration and gestational age, umbilical cord pH, or Apgar score.

DISCUSSION

Very few healthy, breast fed, term infants of appropriate size for gestational age have low blood glucose levels, and there is no indication for blood glucose monitoring in these infants.

Enantioselective separation of methadone and its main metabolite in human hair by liquid chromatography/ion spray-mass spectrometry

Optical isomers exhibit significant differences in their affinities for receptor sites, biotransformation and binding to serum and tissue proteins. Methadone has been used for the substitution of heroin addicts since 1964. The racemic form is used, i.e., a mixture of the biologically active R-form and the practically inactive S-form. To investigate methadone distribution, a chiral separation of the isomers was developed in human hair samples. The method involves decontamination of hair with water and acetone, pulverization in a ball mill, enzymatic hydrolysis in presence of deuterated internal standards, solid-phase extraction, and liquid chromatography/ion spray-mass spectrometry. Enantioselective separation of methadone and its main metabolite, EDDP, was obtained using an alpha1-acid glycoprotein column (100 by 4 mm ID). In all nine specimens obtained from subjects under racemic methadone treatment in a detoxification center, R- and S-enantiomers of methadone and EDDP were identified with the following concentrations: 2.58-10.22, 1.89-9.53, 0.42-1.73, and 0.40-2.10 ng/mg for R-methadone, S-methadone, R-EDDP, and S-EDDP, respectively. Results are suggestive of a predominance of the Renantiomer of methadone in human hair.

In vivo biogenic amine efflux in medial prefrontal cortex with imipramine, fluoxetine, and fluvoxamine

In vivo brain microdialysis was used to determine the effects of the standard tricyclic antidepressant imipramine and the two selective serotonin reuptake inhibitors (SSRIs) antidepressants, fluoxetine and fluvoxamine, on extracellular levels of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in rat medial prefrontal cortex. When given intraperitoneally (IP), imipramine increased NE in the microdialysis perfusate, and elevated DA and 5-HT to a lesser extent. Similar dose-dependent increases in DA and 5-HT were detected after IP fluoxetine, although NE was less affected. In contrast, IP fluvoxamine produced no change in basal NE nor DA, although a large increase in 5-HT occurred at an intermediate dose. When administered directly into cortex, all three antidepressants increased 5-HT by the same amount in a dose-dependent fashion. Intracortical imipramine and fluoxetine increased NE, and fluoxetine and fluvoxamine both increased DA, with fluoxetine doing so at a lower concentration. These data suggest that the SSRIs are not entirely selective for serotonin in vivo.

Does learned helplessness induction by haloperidol involve serotonin mediation?

Learned helplessness (LH) is a behavioral depression following inescapable stress. Helpless behavior was induced in naive rats by the dopamine D2 receptor blocker haloperidol (HDL) in a dose-dependent manner, with the greatest effects seen at 20 mg/kg (IP). Rats were tested 24 h after injection. Haloperidol (IP) increased release of serotonin (5-HT) in medial prefrontal cortex (MPC) as measured by in vivo microdialysis. Perfusion of HDL through the probe in MPC caused increased cortical 5-HT release, as did perfusion of both dopamine and the dopamine agonist apomorphine. Our previous work found that increased 5-HT release in MPC correlates with the development of LH. The present work suggests that increased DA release in MPC, known to occur with both inescapable stress and with HDL, may play a necessary but not sufficient role in the development of LH. Also, this suggests that increased DA activity in MPC leads to increased 5-HT release in MPC and to subsequent behavioral depression.

Cyclic adenosine 3',5'-monophosphate and glucose stimulate thyroxine 5'-deiodinase type II in cultured mouse neuroblastoma cells

Nutrient modulation increases mouse neuroblastoma (NB) T4-5'-deiodinase II (T4-5'-D II) activity. Carbohydrates are more potent than either amino acids or glycerol as nutrient sources. Glucose rapidly (2 to 4 hours) enhances NB enzyme activity and the response is dependent on new protein synthesis. The present study was performed to further characterize this glucose effect and explore its relationship to the cyclic adenosine monophosphate (cAMP) system in these cells. NB T4-5'-D II activity reached a maximum level (sixfold) in response to glucose (10 mmol/L) at 16 hours and thereafter remained constant up to 22 hours before reverting back to basal level between 24 and 30 hours. This pattern of response allowed the performance of detailed studies on maximum glucose activated NB T4-5'-D II under transient equilibrium conditions during the 16- to 22-hour period. Addition of dibutyryl cAMP (dbcAMP) (1 mmol/L) at this stage significantly increased enzyme activity (twofold at 2 hours and fourfold at 4 and 6 hours) compared with glucose alone. There was an additive response to dbcAMP under these maximum glucose-activated conditions. Nonactivated NB T4-5'-D II showed a twofold response to dbcAMP (1 mmol/L) at 4 hours in a glucose-free medium. Under these conditions, glucose (10 mmol/L) also increased enzyme activity twofold. Combined studies with dbcAMP and glucose increased enzyme activity fourfold at 4 hours. Subsequent studies were performed with forskolin (10 mumol/L) and cholera toxin (1 nmol/L), modulators of endogenous cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular Cloning and Characterization of c-erb-A mRNA Species in Mouse Neuroblastoma Cells

Abstract The mouse neuroblastoma cell line is an excellent model in which to study thyroid hormone action and metabolism, particularly in neural tissue. We therefore undertook the molecular cloning and characterization in these cells of putative thyroid hormone receptors related to c-erb-A. Since rat brain tissue contains multiple cell types, and because of possible subtle differences between species (mouse and rat), we therefore screened a new cDNA library constructed from mouse neuroblastoma cell mRNA with synthetic oligonucleotide probes based on the published nucleotide sequence of the c-erb-A gene in whole rat brain. Despite the fact that this rat brain cDNA sequence is now recognized to represent a c-erb-A alpha 1 form, the cDNA clones that we isolated were all members of the newly-recognized c-erb-A alpha 2 form. This identification was made on the basis of nucleotide sequence divergence downstream of the nucleotide corresponding to amino-acid residue 370 in the predicted coding region. The two longest mouse neuroblastoma cDNA clones, clone 29 (1796 bp) and clone 32 (1410 bp), were 93% to 94% homologous with the c-erb-A alpha 2 and c-erb-A alpha 1 forms in their DNA binding and thyroid hormone binding domains (up to amino-acid residue 370 in the latter). Both clones 29 and 32 were incomplete in that they terminated at their 3'ends at an internal Eco R1 site. Fortunately this 120 bp (40 derived amino-acid) truncation was downstream of the reported thyroid hormone binding domain. The 5'untranslated end of clone 29 (446 bp) was of interest because a region of its nucleotide sequence (279 bp) revealed a high degree of homology (87%) with rat brain c-erb-A alpha 1. This highly conserved region in clone 29 appeared to be important in the regulation of translation because only clone 32, in which this region was truncated, efficiently translated protein in a cell-free system. The protein product of clone 32 did not bind thyroid hormone. Northern blot analysis of mouse neuroblastoma mRNA with site-specific synthetic oligonucleotides revealed that the c-erb-A alpha 2 species was dominant (major band of 2.4 kb), with a lesser amount of the c-erb-A alpha1 species (major band of 1.8 kb).

IN CONCLUSION

1) We report the molecular cloning of c-erb-A variants in a specific neural tissue cell type, namely mouse neuroblastoma cells; 2) The cells contained predominantly the c-erb-A alpha 2 subtype; 3) This c-erb-A alpha 2 form was unique up to bp 167 at its 5'untranslated end, and was then followed, up to the ATG initiation codon, by a highly conserved region common to all c-erb-A a species; 4) The 5'untranslated region appeared to play a role in the translational efficiency of this mRNA; 5) The protein product of the c-erb-A alpha 2 mRNA in these cells did not appear to bind thyroid hormone. In view of this finding, the physiological role of the c-erb-A alpha 2 protein remained speculative and may involve a represser function at the thyroid hormone responsive element.

Carbohydrate feeding increases total body and specific tissue 3,5,3'-triiodothyronine neogenesis in the rat

The glucose-fed rat, in contrast to the chow-fed animal, has a higher serum total T3 concentration and an increase in the hepatic content of T4 5'-deiodinase (type I) activity. The mechanism and significance of these glucose-induced changes in T3 metabolism are elucidated in this study. To focus on extrathyroidal thyroid hormone metabolism the kinetic parameters were determined in thyroidectomized T4-replaced rats (1.25 micrograms T4/100 g BW.day). Kinetics of T4 and T3 were studied separately by infusing labeled hormone to equilibrium. Glucose feeding for 72 h (G) significantly increased both the total and free serum T3 concentrations compared to the respective means in the chow-fed control group (P). The glucose-induced changes in serum T3 reflect the approximate doubling of T3 production to 14.7 +/- 0.6 ng/h.100 g in G rats compared to 7.6 +/- 0.7 ng/h.100 g in P rats. The higher T3 production rate in the G group is due to a significant increase in the fractional total body T4 to T3 conversion (0.33 +/- 0.02) compared to that in the P group (0.19 +/- 0.02). The tissue (liver, kidney, brain, and brown adipose tissue) concentration of T4 (nanograms per g wet wt) was significantly increased in the G group. The increase ranged from 54% in liver to 80% in kidney, brain, and brown adipose tissue. The tissue concentration of T3 (nanograms per g wet wt) was even more dramatically increased by glucose feeding than was T4. The glucose-induced increment in organ T3 ranged from 2.5-fold (kidney, muscle, and brain) to 5-fold (liver and white adipose tissue) to 12-fold (brown adipose tissue). These data indicate that the increase in serum total and free T3 concentrations associated with glucose feeding reflects augmented total body T3 production from T4. The effect of the enhanced T3 neogenesis was generalized, as the T3 content was increased in each organ studied. Thus, glucose feeding has unique effects on T3 metabolism.

Reverse T3 and modulators of the calcium messenger system rapidly decrease T4-5'-deiodinase II activity in cultured mouse neuroblastoma cells

Neural T3 neogenesis is modulated by the enzyme T4-5'-deiodinase type II (T4-5'-DII). Hypothyroidism increases the activity of rat pituitary and cerebral cortex enzyme activity. Mouse neuroblastoma cells (NB41A3) incubated in thyroid hormone deficient medium also show a significant increase in T4-5'-DII activity. This response is rapidly (less than 30 minutes) reversed by reverse T3 (rT3) suggesting a mechanism independent of nuclear T3 receptor binding or new protein synthesis. This report details a series of studies performed to elucidate the nature of this rT3 effect. Confluent neuroblastoma cell culture preparations maintained in hypothyroid medium showed a 2-3 fold increase in T4-5'-DII activity compared to preparations in standard medium (p less than 0.001). RT3 (1-50 nM), the calcium ionophore A23187 (0.3-1.5 microM) and the phorbol ester TPA (0.1-1.0 microM) reversed the effect of thyroid hormone deficient medium on enzyme activity (p less than 0.001). Each agent showed a similar time course with maximal effect occurring between 15-30 minutes post medium supplementation. The suppressive effect of A23187 (1.5 microM) and TPA (0.5 microM) on enzyme activity was not additive. In addition, the combination o of rT3 (50 nM) and A23187 (1.5 nM) did not decrease enzyme activity compared to each agent alone. In contrast, the combined addition of rT3 (50 nM) and TPA (0.5 microM) did have an additive effect on neuroblastoma T4-5'-DII activity. A similar pattern of response was found, when the effects of these agents were analyzed on T4-5'-DII activity in neuroblastoma cells incubated in N-FSC.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain lipoprotein lipase is responsive to nutritional and hormonal modulation

Functional lipoprotein lipase activity was recently described in rat brain. The present study was performed to further characterize the biologic significance of brain lipoprotein lipase (heparin releasable component) and elucidate regulatory factors. Comparative studies were performed on tissue (brain, adipose, and heart) heparin releasable lipoprotein lipase in the fasted and diabetic (streptozotocin 100 mg/kg BW IP) rat. Both fasting (96 hours) and diabetes (ten days) significantly decreased brain (cortical) (P less than .05) and adipose (epididymal fat pad) (P less than .001) lipoprotein lipase activity. In contrast, heart muscle enzyme activity was significantly increased (P less than .001) in response to fasting and diabetes. Refeeding (Purina chow 96 hours) and insulin replacement (96 hours) reversed these changes in tissue lipoprotein lipase consequent to fasting and diabetes, respectively. There was a positive correlation between the changes in serum insulin concentration and adipose lipoprotein lipase, but there was no correlation between this parameter and brain or heart lipoprotein lipase. In addition, although T3 therapy normalized the low T3 state associated with both fasting and diabetes, it had no effect on the enzyme activity in the studied tissues. However, subsequent studies demonstrated that hypothyroidism (2 weeks post thyroidectomy) significantly decreased brain lipoprotein lipase activity (P less than .001) and increased both the adipose (P less than .025) and heart (P less than .025) enzyme activity. T3 replacement (0.8 micrograms/100 BW/d for 1 week) reversed the effects of hypothyroidism. However, the relationship between brain enzyme activity and serum T3 was nonlinear as hyperthyroidism tended to reduce brain LPL activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose and insulin reverse the effects of fasting on 3,5,3'-triiodothyronine neogenesis in primary cultures of rat hepatocytes

The cellular mechanisms by which carbohydrate refeeding reverses the effect of fasting on T3 metabolism were studied in primary cultures of hepatocytes (24 h) harvested from 48-h fasted rats. Net T3 neogenesis (T3 generated from T4) in the fasted hepatocyte preparations (9.2 +/- 0.9 pmol/min X 100 mg protein) was significantly less (P less than 0.001) than that in hepatocyte cultures derived from 72-h glucose-fed rats (41 +/- 0.8 pmol/min X 100 mg protein). Preincubation (18 h) with either glucose (2.5-10 mM) or insulin (10-500 nM) significantly increased the fasted hepatocyte T3 levels to 28 +/- 0.6 and 22 +/- 1.3 pmol/min X 100 mg protein, respectively. Furthermore, incubation with both of these agents demonstrated a greater effect on hepatic T3 neogenesis than with either alone. Fasted hepatocyte T3 neogenesis was enhanced by enrichment with dithiothreitol (5 mM), but the T3 generation remained significantly less than that in cells exposed to glucose or insulin. Studies with glucose analogs demonstrated that preincubation with 2-deoxyglucose (5 mM) significantly increased (P less than 0.001) hepatocyte T3 neogenesis, but 3-O-methylglucose (5 mM) had no effect. In contrast, the insulin-mimetic compounds Concanavalin-A or spermine did not stimulate T3 neogenesis in the fasted hepatocyte cultures. Thus, rat hepatocytes sustained in primary culture for 24 h retain the T3 metabolic characteristics of the intact animal. Glucose and insulin reverse the effect of fasting on hepatocyte T3 neogenesis. The additive response to glucose and insulin suggests that T3 neogenesis is modulated through different mechanisms. The replication of the glucose effect by 2-deoxyglucose and the inability of dithiothreitol to reverse the effect of fasting on hepatocyte T4 5'-deiodinase activity suggest that neither intermediates in the glycolytic pathway nor thiol cofactors mediate the glucose effect. Thus, the restoration of liver T3 metabolism consequent to carbohydrate refeeding of the fasted rat may be mediated by the glucose and insulin responses.

Modulation of adipose lipoprotein lipase by thyroid hormone and diabetes. The significance of the low T3 state

The present study was performed to assess the potential relationship between the low T3 syndrome and hypothyroidism. Comparative studies were performed on the relative effects of diabetes and insulin on heparin-releasable adipose lipoprotein lipase (LPL) in the intact and hypothyroid rat. Hypothyroidism for 10 days (Tx) significantly increased adipose LPL activity (5.8 +/- 0.2 mu eq/g/h) compared with the activity (3.6 +/- 0.4 mu eq/g/h) in the normal group. Diabetes for 72 h (streptozocin, STZ, 10 mg/100 g body wt, i.p.) significantly reduced (P less than 0.005) adipose LPL activity in the Tx model. However, despite the suppressant effect of diabetes (43 +/- 11%), the enzyme activity remained equivalent to the normal group. Insulin stimulated adipose LPL in the Tx-diabetic group. The enzyme demonstrated a synergistic response to insulin and hypothyroidism. Subsequent studies were performed in the intact diabetic rat, a low T3 state. Adipose LPL activity was reduced to a similar degree by diabetes (79 +/- 2%) irrespective of the serum T3 concentration. Furthermore, the magnitude of the adipose LPL stimulation by insulin was not modulated by the endogenous serum T3. However, co-treatment of the diabetic group with T3 and insulin blunted the adipose LPL response to insulin. These various modulations in adipose LPL activity were associated with significant but opposite changes in serum triglyceride levels in both the hypothyroid and intact rat. These studies demonstrate that hypothyroidism counteracts the suppressant effect of diabetes on heparin-releasable rat adipose LPL activity and magnifies the enzyme response to insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin inhibits rat hepatic T4-5'-deiodinase. The effect is independent of the associated hypoinsulinemia

Somatostatin decreases the serum 3,5,3'-triiodothyronine (T3) concentration in athyreotic subjects treated with L-thyroxine (T4). The present study was performed to determine the effect of somatostatin on T4-5'-deiodinase activity in rat tissue homogenate preparations. This enzyme is an important regulator of T3 production. Continuous somatostatin infusion at high dose (4 micrograms/kg per min subcutaneously) and low dose (0.8 micrograms/kg per min subcutaneously) for 48-72 h significantly increased (P less than 0.001) the mean aorta plasma somatostatin-like immunoreactivity concentration to 786 +/- 65 and 448 +/- 58 pg/ml, respectively compared with the normal mean of 69 +/- 17 pg/ml in the carbohydrate-fed rat (20% glucose in water ad lib.). The mean hepatic T4-5'-deiodinase activity at both 48 h (100 +/- 5 pmol/min per 100 mg protein) and 72 h (90 +/- 7 pmol/min per 100 mg protein) was significantly reduced in the high-dose group (P less than 0.005), compared with the mean enzyme activity in the glucose-fed control group (138 +/- 6 pmol/min per 100 mg protein). There was a negative correlation (r = -0.9, P less than 0.01) between the alterations in the peripheral plasma somatostatin-like immunoreactivity concentration and hepatic T4-5'-deiodinase activity. High-dose somatostatin did not consistently lower the serum T3 concentration in the glucose-fed rat. Somatostatin had no effect on pituitary T4-5'-deiodinase activity in the glucose-fed rat. High-dose somatostatin also significantly inhibited (P less than 0.01) the glucose-refeeding reactivation of hepatic T4-5'-deiodinase in the 72-h-fasted rat. The mean enzyme activity after 96 h was 96 +/- 8 pmol/min per 100 mg protein compared with 127 +/- 4 pmol/min per 100 mg protein in the refed control group. Somatostatin had a similar inhibitory effect on serum T3. There was a positive correlation (r = 0.5, P less than 0.01) between the somatostatin-induced alterations in serum T3 and hepatic T4-5'-deiodinase during refeeding. A significant positive correlation (r = 07, P less than 0.005) was noted between the somatostatin effect on hepatic T4-5'-deiodinase activity and the induced hypoinsulinemia in the fed group. In addition, a significant negative correlation (r = -0.9, P less than 0.001) was noted between the suppressed enzyme activity and the serum glucose/insulin ratio in the refed group. However, although low-dose somatostatin also induced the same degree of hypoinsulinemia (P less than 0.05) in the fed and refed groups it had no effect on hepatic T4-5'-deiodinase activity. Furthermore, despite the induction of hyperinsulinemia during refeeding, the high dose somatostatin inhibitory effect on enzyme activity persisted. Thus, somatostatin inhibited hepatic T4-5'-deiodinase activity in the carbohydrate-fed rat and prevented the carbohydrate-refeeding normalization of enzyme activity in the 72-h-fasted rat. The effect of somatostatin on enzyme activity was independent of the associated hypoinsulinemia. In the carbohydrate-fed animal the somatostatin effect was selective, as the hormone had no effect on pituitary T4-5'-deiodinase activity. These data suggest that somatostatin could play a role in the peripheral metabolism of thyroid hormones.

Glucagon does not modulate the alterations in T3 metabolism consequent to dietary manipulation and diabetes

Low serum T3 levels and hyperglucagonemia are characteristic features of a number of catabolic states such as fasting and uncontrolled diabetes. The present study was performed to elucidate the relationship between this hyperglucagonemia and T3 metabolism. Serum glucagon and T3 and hepatic T4-5'-deiodinase activity (T4 leads to T3) were examined in groups of rats (T4-treated) fed (chow versus carbohydrate), fasted, or diabetic (streptozotocin 100 mg/kg i.p.) for 48-72 h. In the carbohydrate-fed (20% glucose in H2O ad libitum) group the mean serum T3 concentration and mean hepatic T4-5'-deiodinase activity were significantly higher (P less than 0.01) and the mean serum glucagon level significantly lower (P less than 0.05) than the respective means in the chow-fed control group. The mean serum T3 concentration was significantly less (P less than 0.05) in both the fasted (72 h) and diabetic (72 h) groups compared with the control mean, whereas the mean serum glucagon values were similar to the chow-fed group. The mean hepatic T4-5'-deiodinase activity was low in the diabetic group (P less than 0.05) but similar in the fasted group compared with the chow-fed control. A significant inverse correlation (r = -0.9; P less than 0.001) was noted between these alterations in serum T3, hepatic T4-5'-deiodinase activity, and serum glucagon, suggesting that glucagon could be a modulator of T3 metabolism. Hyperglucagonemia was induced in the glucose-fed group with a continuous glucagon infusion for 48 h (0.15 micrograms/kg/min s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)