Circulating 3,3', 5'-triiodothyronine (reverse T3) in the human newborn

Serum concentrations of 3,3',5'-triiodothyronine (reverse T3 rT3), 3,3',5-triiodothyronine (T), and thyroxine (T4) were measured in cord blood and invenous blood samples obtained between 2 h and 30 days of postnatal life from healthy full-term newborn infants. The mean serum rT3 concentration of (mean plus or minus SE) 151 plus or minus 12 ng per 100 ml in 18 cord blood samples was significantly higher than the level (41 plus or minus 2 ng per 100 ml) in 27 normal adult sera; the corresponding mean serum T4 of 12.7 plus or minus 0.8 mug per 100 ml in cord blood also was significantly higher than that (8.6 plus or minus 1.9 mug per 100 ml) in 108 normal adults. By contrast, the mean serum T3 concentration in 15 cord blood samples, 24 plus or minus 3 mg per 100 ml, was significantly lower than the value of 126 plus or minus 3.2 ng per 100 ml measured in 108 normal adults. At 4 h of age the mean serum rT3 concentration (165 plus or minus 13 ng per 100 ml) in six newborns was 4ot significantly different from that in paired cord blood samples (194 plus or minus 25 ng per 100 ml); on the other hand, whenever, studied, the mean serum T3 and T4 levels were significantly higher at 4 h than at birth. The failure of serum rT3 concentrations to rise after delivery in response to the early neonatal thyrotropin (TSH) surge and at a time when serum T3 and T4 levels increase significantly prompted a study of the rT3 response to 10 IU of intramuscular TSH in three healthy adult subjects. Just as in the newborns, serum rT3 failed to rise appreciably in these subjects, even though serum T3 and T4 showed the expected increments. Serum rT3 concentrations in 1-4 day-old newborn infants did not differ significantly from values in the cord blood but were significantly lower in older neonates. The mean serum rT3 level in 5-7-day-old infants was higher than that in normal adults, but in 9-11 day and 20-30-day-old infants, mean rT3 values were statistically similar to the adult value. The mean serum T3 concentrations in neonates between 1-30 days old were either higher than or comparable to the values of normal adults. The mean serum T4 concentrations in neonates between birth and 30 days of age were significantly higher than the mean adult level. The mean serum rT3 to T4 ratios (rT3/T4) were elevated in 1-4-day-old neonates; the values in older neonates were similar to those in adults. These results suggest that (a) factors other than TSH are important modulators of serum rT3 in man; (b) high serum rT3 concentration in the newborn becomes comparable to that in the normal adult by 9-11 days of neonatal life.

The diagnosis of Hashimoto's thyroiditis

Computer methods were used to estimate the usefulness of several clinical signs and laboratory tests in the diagnosis of chronic lymphocytic (Hashimoto's) thyroiditis. Information was drawn from the records of 217 patients with this disease seen at two hospitals in Southern California. The parameters studied included the physical characteristics of the thyroid gland; the appearance of the radioisotope thyroid scan; the response to a perchlorate discharge test; the serum antithyroglobulin antibody titer; the serum TSH concentration measured by radioimmunoassay; the thyroid radioiodine uptake response to exogenous TSH stimulation; and the serum PBI-T4I difference. Of the above, the PBI-T4I difference was deleted, being of limited value. The TSH stimulation test and serum TSH measurement were considered as alternative ways to evaluate thyroid reserve. Therefore, five diagnostic markers remained, all useful but not definitive. Computer and rule-of-thumb methods (two or more of the five markers positive) were tested for successful diagnosis of 145 patients with Hashimoto's thyroiditis proven by pathological examination of biopsied tissue; 23 of these were patients not used in the original pool of data. As a rule of thumb, it was found that Hashimoto's thyroiditis is the likely diagnosis if two or more out of the five useful markers are in its favor. For best results, four and preferably all of the five criteria should be tested. If this is done, the expected diagnostic accuracy for patients with Hashimoto's disease is by the rule-of-thumb method 67% correct, 21% indecisive, and 12% false negative; by computer methods it is 88% correct, 4% indecisive, and 8% false negative. By each method the number of false positive diagnoses was equivalent to 25% of the total number of patients with this disease. The false positive results nearly all occurred in patients with goiter associated with a defect in thyroid hormone synthesis.

Arginine vasotocin in the rabbit subcommissural organ

Subcommissural organs of young and mature rabbits were analyzed for their content of arginine vasotocin by radioimmunoassay. Younger animals had significantly greater quantities of this peptide. There was no detectable arginine vasopressin or oxytocin in subcommissural organ extracts. It is concluded that the subcommissural organ represents, in addition to the pineal and the fetal neurohypophysis, another significant source of arginine vasotocin in the mammalian central nervous system.

Intra-uterine treatment of a hypothyroid fetus

A woman in her 24th week of gestation was referred for treatment of hypothyroidism, after she underwent radioablation of the thyroid during the 13th week of gestation. Because of the high risk of hypothyroidism in the fetus, prenatal administration of intramuscular T-4 to the fetus was begun at 32 weeks. The last dose of T-4 was given 2 weeks before delivery; cord blood levels of T-4 and T-3 were undetectable and the TSH concentration was markedly elevated. The case illustrates several important physiological concepts regarding thyroid hormone and TSH metabolism in the fetal-placental unit, including the minimal placental permeability to iodothyronines and TSH, independent function (including feedback control) of the fetal hypothalamic-pituitary-thyroid axis, and the TSH response at parturition. In addition we suggest that administration of T-4 to the hypothyroid fetus in utero is an acceptable modality of treatment and may help to minimize irreversible mental retardation in known high risk infants. However, further studies are necessary to assess the effectiveness and safety of this approach.

The circulating vasopressinase of pregnancy: species comparison with radioimmunoassay

A vasopressin substrate radioimmunoassay (RIA) system is described for the measurement of the vasopressinase elaborated during pregnancy. Results show that vasopressinase activity increases in the sera of pregnant women throughout gestation. At term, under the in vitro conditions described, pregnancy serum degrades vasopressin (Pitressin) at a rate of 53 mU. per milliliter of serum per minute. Serum obtained from paired umbilical cord samples had an activity of 9.2 muU per milliliter per minute; amniotic fluid obtained at delivery had an activity of 16.6 muU per milliliter per minute. Pregnancy serum obtained from sheep, rabbits, and rats, ovine umbilical cord serum, and ovine amniotic fluid had no detectable vasopressinase activity. Normal human male serum, nonpregnant female serum, and serum from women taking contraceptive agents also exhibited no activity.

Radioimmunoassayable avt and avp in adult mammalian brain tissue: comparison of normal and brattleboro rats

Arginine vasopressin (AVP) and vasotocin (AVT) were measured by radioimmunoassay in extracts of cerebral cortex, cerebellum, brain stem, pineal, hypothalamus, and neurohypophysis from normal Long-Evans rats. AVP was present in expected concentrations in pituitary and hypothalamus and there was no evidence of its accumulation elsewhere. AVT was not detectable in these tissues (within the limits imposed on our assay by the presence of excessive amounts of AVP) but was easily detectable in pineal tissue with a concentration of 22.4 plus or minus 6.6 muU/gland. Extracts of neurohypophysis and pineal glands from homozygous Brattleboro rats (rats with hereditary hypothalamic diabetes insipidus) revealed the total absence of AVP and AVT. We conclude that the Brattleboro rat is incapabel of synthesizing biologically active neurohypophyseal peptides which contain arginine in position 8.

Spontaneous and amino acid-stimulated glucagon secretion in the immediate postnatal period. Relation to glucose and insulin

The extent and significance of spontaneous glucagon secretion in the immediate postnatal period were investigated in groups of normal infants studied cross-sectionally and longitudinally. Arginine-and alanine-stimulated glucagon secretion was also studied. Plasma glucagon concentrations were correlated with prevailing glucose and insulin concentrations. The characteristic fall in blood glucose, reaching a nadir within hours of birth, was associated with a significant increase in glucagon concentration. Despite persistence of relative glucopenia, glucagon did not change appreciably between 2 and 24 h of life. A further significant elevation in glucagon concentration occurred from day 1 to day 3 of life associated with a return of glucose to euglycemic levels. In contrast to the sluggishness of pancreatic glucagon release, glucagon-like immunoreactivity rose markedly to mean levels of approximately 2,000 pg/ml after introduction of formula feeding. No significant changes in insulin levels were observed in these studies. Arginine infusion via an umbilical vein catheter into six infants within 6 h of birth elicited a brisk, almost threefold increment in glucagon concentration (from 339+/-85 to 940+/-254 pg/ml) in blood obtained from, or close to, the portal circulation. Bolus injection of alanine (1 mmol/kg) into a peripheral vein to six infants resulted in significant increments in glucagon (mean maximal, 128 pg/ml) as well as glucose and insulin. The observations suggest that spontaneous glucagon secretion may be an important factor in neonatal glucose homeostasis. Secretion seems more brisk in response to amino acid stimulation than to a falling glucose concentration.

Alanine stimulation of the pancreatic alpha- and beta-cell in the neonatal lamb

Alanine infusion in the newborn sheep produced a significant increase in plasma immunoreactive insulin concentrations without a change in plasma glucose or glucagon levels. In contrast, a brisk response of glucagon and glucose were seen in adult sheep after similar infusions. These data suggest that in newborn lambs pancreatic β-cell responsiveness matures earlier than the α-cell response.