Insulin/C-peptide response to intravenous glucagon. A dose-response study in normal and non-insulin-dependent diabetic subjects.

The C-peptide and insulin secretory responses to increasing doses of iv glucagon (1, 2, 5, 10 micrograms/kg body weight and 1 mg (only diabetics] were investigated in six lean non-insulin-dependent diabetic patients and six normal subjects, matched for body weight and fasting blood glucose concentrations. A well defined relationship between glucagon dose and the C-peptide/insulin response was observed in both groups. The course of the dose-response curves was significantly different in diabetics. The maximal obtainable C-peptide response (E-max) was reduced to 53% of the response in normal subjects (P = 0.037), and the insulin response was reduced to 52% (P = 0.014). E-max was reached in diabetics with only 10 micrograms/kg of glucagon, whereas higher doses seem to be needed in the control group. However, the glucagon dose causing 50% of E-max (ED50) was not significantly higher. Thus, the widely accepted use of 1 mg of glucagon to test residual beta cell function secures a maximal response of both insulin and C-peptide in non-insulin-dependent diabetic subjects. In addition, our data support the theory that beta cell deficiency is a basic feature of non-insulin-dependent diabetes.

The bioavailability of thyroxine and 3,5,3'-triiodothyronine in normal subjects and in hyper- and hypothyroid patients.

A new method for the estimation of the bioavailability of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) is described based on gel separation followed by antibody extraction of labelled T4 and T3 from serum, and using the area under the curve of disappearance of the tracer (AUC) for the calculations. The peak serum concentrations of radioactive labelled T4 and T3 were reached approximately 90 min after oral administration of both tracers. The relative difference of duplicate estimations was below 10% (n = 3). The bioavailability of T4 in 6 euthyroid controls was in median 65% (range 64-75%), and it was significantly increased both in hyperthyroidism (88% (75-99%), n = 6, P less than 0.01) and hypothyroidism (84% (67-100%), n = 6, P less than 0.02). The bioavailability of T3 in 6 euthyroid controls was in median 78% (69-99%) and significantly greater than that of T4 (P less than 0.02). The bioavailability was unaffected by hyperthyroidism (79% (61-98%), n = 9) and hypothyroidism (77% (66-97%), n = 7). No significant difference between T4 and T3 bioavailabilities was found in hyper- or hypothyroidism. The clinical implication of the present study is that the bioavailability of T4 and T3 is almost identical and approximately 80% in patients with severe hypothyroidism.

The effects of phenytoin (diphenylhydantoin) on the extrathyroidal turnover of thyroxine, 3,5,3'-triiodothyronine, 3,3',5'-triiodothyronine, and 3',5'-diiodothyronine in man.

The extrathyroidal metabolism of T4, T3, rT3, and 3',5'-diiodothyronine (3',5'-T2) was studied before and after treatment with 350 mg phenytoin (DPH) daily for 14 days in six hypothyroid patients receiving constant L-T4 replacement. The total and free serum concentrations of the four iodothyronines were reduced by approximately 30% during DPH treatment, whereas the free fractions in serum were unaltered. Concomitantly, serum TSH increased 137% (P less than 0.02). The production rate (PR) of T4 decreased 16% (P less than 0.005), indicating decreased intestinal absorption (bioavailability) of oral L-T4 during DPH treatment. The fractional rate of 5'-deiodination of T4 to T3 increased from 27% to 31% (P less than 0.05), whereas the rate of 5-deiodination of T4 to rT3 decreased from 45% to 25% (P less than 0.05). The urinary excretion of free and conjugated T4 was 2.3% of the T4 PR and was unaffected by DPH. Thus, the amount of T4 metabolized through nondeiodinative pathways apart from urinary excretion increased from 25% to 44% (P less than 0.05). The apparent distribution volume (Vd) of T4 increased (P less than 0.05), whereas the pool size was unchanged. The PR of T3 did not change during DPH treatment, nor did the mean transit time or the cellular clearance. The rT3 PR was reduced by 54% (P less than 0.02) during DPH treatment. Concomitantly, the transit time increased 10-fold (P less than 0.05), whereas Vd and pool size increased 5-fold (P less than 0.01 and P less than 0.05, respectively). The turnover of 3',5'-T2, in contrast to that of the other iodothyronines, did not change significantly during DPH treatment. T3 formation from T4 was measured in liver microsomal fractions from rats treated for 8 days with DPH and was almost identical to that in untreated animals. The data demonstrate that DPH in therapeutic concentrations did not affect serum protein binding of the iodothyronines. DPH reduced the intestinal absorption of T4 and increased the nondeiodinative metabolism of T4. The resulting decrease in total and free serum T4 and T3 was associated with an increase in serum TSH, demonstrating reduced negative feedback on the pituitary. Our data do not support the assumption that DPH induces increased hepatic deiodinating enzyme activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of D,L-4-hydroxypropranolol on the thyroxine to 3,5,3'-triiodothyronine conversion in rat renal and liver microsomes.

The in vitro effect of D,L-4-hydroxypropranolol, a major pharmacological active metabolite of the beta adrenoceptor blocking drug D,L-propranolol, on the thyroxine (T4) to 3,5,3'-triiodothyronine (T3) conversion has been studied using rat renal and liver microsomal fractions. The results showed, that primarily the metabolite, but also the parent drug inhibits the T3-production in a dose dependent manner. The potency, expressed as the 50% inhibition of the T3-production, was reached using 65 +/- 12 (SD) microM D,L-4-OH-propranolol and 1000 +/- 22 (SD) microM D,L-propranolol, respectively in both tissues. The efficacy of 4-OH-propranolol corresponded to a maximal inhibition of 86 +/- 7% while it for D,L-propranolol corresponded to 58 +/- 6% (P less than 0.001). The beta adrenoceptor agonist isoprenaline itself did not effect the T4 to T3 conversion but considerably opposed the inhibitory effect of D,L-4-OH-propranolol but not of D,L-propranolol. The D-isomer form of propranolol, which is without beta receptor blocking activity inhibited the T3-production in the same degree as D,L-propranolol. Evaluation of the enzyme kinetic data suggested that 4-OH-propranolol caused a competitive inhibition of both T4 and DTT. It is concluded, that the metabolite D,L-4-OH-propranolol is a much more potent and efficacious inhibitor of the T4-5'-deiodination than D,L-propranolol.

The extrathyroidal conversion of 3,5,3'-triiodothyronine to 3,5-diiodothyronine in patients with liver cirrhosis.

Simultaneous kinetic studies of 3,5-diiodothyronine (3,5-T2) and T3 were performed in 8 patients with biopsy proven cirrhosis and in 15 healthy subjects using the single injection, noncompartmental approach. The following T3 kinetic data were obtained in patients with cirrhosis and normal subjects (mean +/- SD): serum T3 (nmol/liter) 1.27 +/- 0.30 vs. 1.79 +/- 0.28 (P less than 0.001); MCR [liters X day-1 X (70 kg)-1] 22.9 +/- 5.3 vs. 26.7 +/- 4.4 (P less than 0.10); production rate [nmol X day-1 X (70 kg)-1] 29.0 +/- 9.6 vs. 47.7 +/- 9.0 (P less than 0.001). In patients with cirrhosis serum 3,5-T2 levels were reduced to 58 +/- 38% of those found in normal subjects (P less than 0.02). The MCR was unaffected, 125 +/- 85%, whereas the production rate was reduced to 57 +/- 26% (P less than 0.005). The conversion rate from T3 to 3,5-T2 was unaltered, 96 +/- 34% of that found in normals. It is concluded that reduced serum levels of 3,5-T2 in cirrhosis are due to a diminished amount of substrate, T3, and not to decreased 3'-deiodination of T3 or to an increase clearance of 3,5-T2.

Simultaneous turnover studies of thyroxine, 3,5,3' and 3,3',5'-triiodothyronine, 3,5-, 3,3'-, and 3',5'- diiodothyronine, and 3'-monoiodothyronine in chronic renal failure.

The present study evaluates the sequential extra-thyroidal monodeiodination of thyroid hormones through tri-, di-, and monoiodothyronines in chronic renal failure (CRF) in man. Simultaneous turnover studies of T4, T3, rT3, 3,5-diiodothyronine (3,5-T2), 3,3'-T2, 3',5'-T2, 3'5'-T2, and 3'-monoiodothyronine (3--T1) were conducted in six patients with CRF (creatinine clearance, 9-18 ml/min) using the single-injection, noncompartmental approach. Serum levels of T4, T3, and 3,5-T2 were reduced to two thirds of control levels (P less than 0.05), whereas serum rT3 and 3,3'-T2 levels were reduced to a minor degree. Serum 3'-5'-T1 was doubled (p less than 0.05). The MCRs of T4, rT3, and 3',5'-T2 were enhanced to 168%, 127%, and 187% of normal (P less than 0.05), respectively, whereas those of T3, 3,5-T2, 3,3'-T2, and 3'-T1 were unaffected. The mean production rates (PRs) of the iodothyronines in CRF were as follows (CRF vs. control values, expressed as nanomoles per day/70 kg): T4, 119 vs. 125; T3, 26 vs. 44 (P less than 0.01); rT3, 49 vs, 48; 3,5-T2, 3.5 vs. 7.2 (P less than 0.001); 3,3'-T2, 25 vs. 35 (P less than 0.01); 3',5'-T2, 25 vs. 14 (P less than 0.01); and 3'-T1, 39 vs. 30. Previous studies have demonstrated reduced phenolic ring (5'-) deiodination of T4 in CRF, which is supported by the present finding of unaltered PR of T4 and reduced PR of T3. In contrast the 5'-deiodination of T3 leading to the formation of 3,5-T2 was found unaffected by CRF, since the conversion rate (CR) of T3 to 3,5-T2 (PR 3,5-T2/PR T3) was unaltered (16% vs. 15% in controls). The tyrosylic ring (5-) deiodination of T4 to rT3 was unaffected in patients with CRF, the CR being 42% vs. 40% in controls, in contrast to an enhanced CR of rT3 to 3',5'-T2 (53% vs. 29%, P less than 0.01), which also is a 5-deiodination step. In conclusion, our data show that CRF profoundly changes the kinetics of all iodothyronines studied. Furthermore, our data are compatible with the existence of more than one 5'-deiodinase as well as more than one 5-deiodinase in man.

Vitamin D metabolism in insulin-dependent diabetes mellitus.

A significant loss of bone has been observed in diabetes mellitus. The pathogenesis is unknown, but an impairment of vitamin D metabolism might be involved. Consequently, we have studied vitamin D metabolism in five groups of insulin-dependent diabetic patients. Significantly reduced levels of serum 25(OH)D were seen only in patients with diabetic nephropathy. The serum levels of 1,25 (OH)2D were reduced only in diabetic ketoacidosis but normalized during recovery. It is concluded that vitamin D metabolism is largely normal in adult insulin-dependent diabetes, and it seems unlikely that a disturbance of the vitamin D metabolism can explain the bone loss in the ordinarily controlled diabetics.

Simultaneous measurement of 3,5-diiodothyronine and 3,5,3'-triiodothyronine turnover kinetics in euthyroid hyperthyroid, and hypothyroid subjects.

Simultaneous kinetic studies of 3,5-diiodothyronine (3,5-T2) and T3 were performed in 15 healthy controls (8 men and 7 women), 7 hyperthyroid patients (2 men and 5 women), and 6 hypothyroid women using the single injection, noncompartmental approach. The serum concentrations (picomoles per liter), MCRs (liters . day-1 . (70 kg)-1), and production rates (PRs; nmol . day-1 . (70 kg)-1) of 3,5-T2 in healthy men and women were (mean +/- SD): 100 +/- 23 vs. 80 +/- 23 (P = NS), 59 +/- 31 vs. 123 +/- 58 (P less than 0.025), and 5.6 +/- 1.9 vs. 9.1 +/- 2.6 (P less than 0.02). The conversion rate (CR) of T3 to 3,5-T2 was 12.0 +/- 3.8% in men compared to 18.5 +/- 3.7% in women (P less than 0.01). Serum 3,5-T2 levels in five mildly hyperthyroid women were elevated to 123 +/- 33 pmol/liter (P less than 0.05), whereas the MCR and PR were unchanged. However, two hyperthyroid men with more pronounced elevation of serum T3 had enhanced PRs (26.9 and 23.9 nmol . day-1 . (70 kg)-1). The CR in hyperthyroid women was significantly reduced to 5.6 +/- 2.9% (P less than 0.001). The serum levels, MCR, and PR of 3,5-T2 in hypothyroid women were: 58 +/- 25 pmol/liter (P = NS), 71 +/- 52 liters . day-1 . (70 kg)-1 (P = NS), and 3.4 +/- 2.4 nmol . day-1 . (70 kg)-1 (P less than 0.005). The CR was enhanced to 34.8 +/- 15.7% (P less than 0.05). Our data demonstrate that in euthyroid subjects, approximately 15% of T3 is deiodinated to 3,5-T2, and this 5'-deiodination of T3 is influenced by thyroid function.

The extrathyroidal effect of D,L-propranolol on 3,3',5'-triiodothyronine, 3',5'-diiodothyronine, 3,3'-diiodothyronine, and 3'-monoiodothyronine kinetics.

The effect of D,L-propranolol (80 mg daily) on the peripheral monodeiodination of rT3, 3',5'-diiodothyronine (3',5'-T2), 3,3'-diiodothyronine (3,3'-T2), and 3'-monoiodothyronine (3'-T1) was studied in seven out-patients with severe pretreatment hypothyroidism. The patients were maintained euthyroid on a constant L-T4 replacement therapy. A bolus injection technique was used; MCR, production rate (PR), and conversion rate were determined using a noncompartmental kinetic model. During D,L-propranolol, serum rT3 and 3',5'-T2 increased (P less than 0.02), and 3,3'-T2 seemed to decrease. The MCRs of rT3, 3',5'-T2, and 3,3'-T2 (P less than 0.02) decreased during drug treatment. The MCR and PR of 3'-T1 were reduced, albeit not significantly (P less than 0.10). The PR of 3,3'-T2 was reduced (P less than 0.02), whereas the PRs of rT3 and 3',5'-T2 were unaltered. The conversion rate of rT3 to 3',5'-T2 was unaltered. No changes were seen in the apparent distribution volumes of the iodothyronines studied. The results are compatible with the assumption that D,L-propranolol, or a metabolite thereof, inhibits the 5'-deiodination of all of the iodothyronines.

Isolation of radioactive iodothyronines for kinetic studies: a comparison of two methods.

A method based on the principle of gel separation followed by antibody extraction (GSAE) has been developed for isolation of radioactive thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3'5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2) and 3'monoiodothyronine (3'-T1) in serum. This method was used for the estimation of the metabolic clearance rate (MCR( of the iodothyronines using the single injection, non-compartmental approach, and was compared to the conventional trichloroacetic acid precipitation/ethanol extraction (TCA-E) technique. The GSAE method excluded the co-determination of radioactive iodine ad iodoproteins, whereas the co-determination of radiolabelled daughter iodothyronines was found negligible. The relative difference of duplicate estimation of MCR was approximately 10%. Using the TCA-E method for isolation of tracer, the MCR of T4, T3 and rT3 was underestimated to a minor degree (20%), whereas the MCRs of 3,3'-T2, 3'5'-T2 and 3'-T1 were 20-40% of the estimated by the GSAE method. In conclusion the GSAE method was found suitable for kinetic studies of iodothyronines, whereas the TCA-E method cannot be used for turnover studies of 3,3'-T2, 3'5'-T2 or 3'T1.

Kinetic studies of thyroxine, 3,5,3'-triiodothyronine, 3,3,5'-triiodothyronine, 3',5'-diiodothyronine, 3,3'-diiodothyronine, and 3'-monoiodothyronine in patients with liver cirrhosis.

Turnover studies of T4, T3, rT3, 3',5'-diiodothyronine (3',5'-T2), 3,3'-diiodothyronine (3,3'-T2), and 3'-monoiodothyronine (3'-T1) were performed in 10 patients with alcoholic cirrhosis of the liver and 9 euthyroid, healthy controls using the single injection, noncompartmental approach. The kinetics of all 6 iodothyronines were studied in the same individuals. A newly developed, simple and reproducible gel separation technique, followed by antibody extraction, was used for the quantitation of tracer in serum. Serum T4, T3, and 3,3'-T2 levels were reduced in patients with liver cirrhosis, whereas serum rT3 and 3',5'-T2 levels were increased, Serum 3'-T1 levels were unaltered. A general tendency toward reduced MCRs was observed. The following median MCRs (liters per day per 70 kg BW) were found (cirrhotics vs. controls): T4, 1.13 vs. 1.19 (P = NS); T3, 16 vs. 20 (P less than 0.05); rT3, 81 vs. 147 (P less than 0.01); 3',5'-T2, 131 vs. 279 (P less than 0.01); 3,3'-T2, 533 vs. 1116 (P less than 0.01); and 3'-T1, 375 vs. 539 (P less than 0.05). The production rates (nanomoles per day per 70 kg BW) of T4, rT3, and 3,'5'-T2 were not significantly altered in patients with cirrhosis (cirrhotics vs. controls): 100 vs. 117, 47.5 vs. 52.0, and 14.5 vs. 13.9, respectively. In contrast, the following pronounced reductions in production rates of T3, 3,3'-T2, and 3'-T1 were found: 19.1 vs. 38.8 (P less than 0.01), 13.2 vs. 36.8 (P less than 0.01), and 15.7 vs. 28.6 (P less than 0.05), respectively. Assuming that thyroidal secretion contributes little rT3 and 3',5'-T2, the conversion rates from T4 to rT3 and further to 3',5'-T2 were calculated and found to be unaffected in patients with liver cirrhosis (48% vs. 34% in controls and 34% vs. 26% in controls, respectively). No tendency toward major changes in the activity of the nondeiodinative metabolic pathways was observed. In conclusion, our data show that liver cirrhosis profoundly changes the kinetics of all iodothyronines studied. Further, the 5-deiodination of T4 and rT3 is unaffected in patients with liver cirrhosis. In contrast, a general inhibition of the 5'-deiodinations seems to exist in patients with liver cirrhosis. Thus, our data are compatible with the existence of a common 5-deiodinase and a common 5'-deiodinase for the sequential deiodination of the iodothyronines in man.

Serum 3'-monoiodothyronine levels in normal subjects and in patients with thyroid and non-thyroid disease.

Serum 3'monoiodothyronine (3'-T1) levels were estimated by means of a specific radioimmunoassay (RIA) preceded by an ethanol extraction. The recovery of 3'T1 was in mean (+/-SEM) 110 +/- 9%, and the lower detection limit was 23 pmol/l. Serum levels of 3'T1 in 34 euthyroid healthy subjects were (median (range)) 55 pmol/l (less than 23 - 168 pmol/l), in 13 hyperthyroid patients 133 pmol/l (70 - 265 pmol/l) (P less than 0.01) and in 13 hypothyroid patients less than 23 pmol/l (less than 23 - 68 pmol/l) (P less than 0.01). In 11 patients with chronic renal failure serum 3'-T1 levels were highly increased 285 pmol/l (115 - 1538 pmol/l) (P less than 0.01) and correlated inversely to creatinine clearance (R = -0.68, P less than 0.05). In patients with liver cirrhosis serum 3'-T1 levels were unaffected, whereas in 19 patients with endogenous depression studied before and after recovery from the depression serum levels decreased from 70 pmol/l (less than 23 - 248 pmol/l) to 30 pmol/l (less than 23 - 95 pmol/l) (P less than 0.01). Administration of propranolol 40 mg b.i.d. for 2 weeks did not affect serum 3'-T1 levels. The study shows that 3'-T1 is present in serum from euthyroid man and varies with thyroid function. Further, it is suggested that 3'-T1 in contrast to other iodothyronines primarily is eliminated by the kidneys.

Serum levels of T4, T3, reverse T3, 3,3'-diiodothyronine and 3',5'-diiodothyronine in obesity, before and after jejuno-ileal bypass.

Serum T4, 3,5,3'triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3, rT3), 3,3'-diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2) and thyrotrophin (TSH) levels were studied in nineteen obese patients before and 6, 12, and 18, months after a jejuno-ileal bypass. Before surgery, the obese patients had increased serum T3 levels compared with a group of lean, matched controls (median: 1.94 nmol/l v. 1.44 nmol/l, P less than 0.01). Serum T3 decreased to normal (1.64 nmol/l) 18 months after surgery. A slight decrease was also observed in serum 3,3'-T2 levels, whereas progressive reductions in serum concentrations of rT3 and 3',5'T2 occurred. Eighteen months postoperatively the serum levels of rT3 and 3',5'-T2 had decreased from 0.676 nmol/l to 0.430 nmol/l (P less than 0.02) and 55.2 pmol/l to 40.0 pmol/l (P less than 0.01), respectively, and the values at 18 months were also reduced compared with the control group [0.722 nmol rT3/1 (P less than 0.01), 51.4 pmol 3',5'-T2/1 (P less than 0.01)]. concomitant with the decrease in serum level of the iodothyronines, serum TSH concentrations increased from 0 Micro U/ml to 0.9 microu/ml (P less than 0.01).