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Biomedical subjects

A G Vagenakis

Publications and source records attributed to A G Vagenakis.

At least 19 recordsLinked to original sources
PubMed1992

Varicella pneumonia in adults. A review of pulmonary manifestations, risk factors and treatment.

Pneumonia is a rare but serious and occasionally fatal complication of varicella. Two cases of varicella pneumonia were successfully treated with acyclovir in our department. We reviewed the pulmonary manifestations of varicella, the risk factors and the effect of acyclovir on varicella pneumonia on immunocompetent adults. Early, aggressive therapy with acyclovir seems to abort the catastrophic consequences of varicella pneumonia, while oral acyclovir chemoprophylaxis is probably beneficial in high-risk populations with chickenpox.

Acyclovir↗
PubMed1992

Development of thyrotropin circadian rhythm in infancy.

Normal children and adults show a similar pattern of diurnal variation of TSH secretion with lower values at 1100 h and higher around 2300 h. The purpose of this study was to investigate the age of appearance of TSH circadian rhythm. In 57 fullterm infants 0-6 months old and in 37 premature infants 1-4 weeks old TSH was measured at 1030, 1100, 1130 h and 2230, 2300, and 2330 h. No diurnal rhythm was detected in both premature and fullterm infants less than 4 weeks of life. After the first month of life a significant difference between AM and PM values was observed in fullterm infants. In infants 1-2 months old mean +/- SEM AM and PM values were 2.8 +/- 0.2 and 3.5 +/- 0.4 mU/L, respectively (P less than 0.025), in infants 3-4 months old 3.0 +/- 0.6 and 4.1 +/- 0.8 (P less than 0.01) and in infants 5-6 months old 1.8 +/- 0.2 and 2.6 +/- 0.3 (P less than 0.0005). These data clearly indicate that the development of TSH circadian rhythm starts after the first month of life.

Circadian Rhythm↗
PubMed1992

Abnormal overnight dexamethasone suppression test in subjects receiving rifampicin therapy.

We have studied the effects of rifampicin on the overnight 1-mg dexamethasone suppression test usually employed to exclude suspected Cushing's syndrome. Previous observations indicate that in humans, rifampicin profoundly attenuates the biological effects of hydrocortisol and prednisolone, probably by increasing the metabolism of these drugs in the liver. The study was carried out in 16 normal volunteers. All subjects had a normal overnight 1-mg dexamethasone suppression test (468 +/- 86 vs. 32 +/- 21 nmol/L; mean +/- SD). In 8 subjects treated with rifampicin (600 mg) for 10 days, the inhibitory effect of dexamethasone on serum cortisol was completely prevented (575 +/- 114 vs. 434 +/- 82). In the remaining 8 rifampicin-treated subjects, the inhibitory effect of 1, 2, or 3 mg dexamethasone on serum cortisol was not observed. When 4 mg dexamethasone were administered, the serum cortisol level was 193 nmol/L, above the expected normal suppression value. The plasma dexamethasone concentration was very low after rifampicin treatment (range, 1.2-4.8 nmol/L). We conclude that when patients are treated with rifampicin, the standard overnight dexamethasone suppression test not only has no diagnostic value, but can be very misleading.

Adult↗
PubMed1989

Endocrine aspects of menopause.

Oocyte depletion and ovarian aging results in profound alterations at the biological level. The reduction in numbers of follicles leads to reduction of circulating inhibin and increased serum FSH, characteristic marker of ovarian failure. The remaining follicles are overstimulated and premature ovulation may ensue. This, leads to luteal deficiency and reduction in progesterone production and relative hyperestrogenemia. The above changes characterize the premenopausal period. In a second phase, anovulatory cycles interchange with premature and occasionally normal ovulatory cycles. This phase is characterized by increased FSH and LH and decreased progesterone/estradiol ratio resulting in irregular bleeding, endometrial hyperplasia, polyps, fibromas, mammary dystrophies, disturbance of mood, appetite and thermoregulation. Lastly, the sensitivity of ovarian follicles to FSH and LH is lost with a decline of E2 below 20 pg/ml produced almost exclusively from peripheral conversion from circulating androgens. The beneficial effects of E2 are lost resulting in atrophy of the sensitive tissues, decreased calcium absorption, increased bone resorption, accelerated bone loss and osteoporosis, rise in serum triglycerides, increased VLDL and LDL lipoproteins, increased LDL/HDL cholesterol, a profile which favors atherosclerosis.

Aged↗
PubMed1988

Pituitary-thyroid interaction: effects of thyroid hormone, non thyroidal illness and various agents on TSH secretion.

Recent developments in thyroid hormone metabolism have helped to understand the complex events which characterize the regulation of TSH secretion. Plasma T3 concentration as well as intrapituitary T3 generation from T4, exert a profound effect on TSH synthesis and release. Pituitary Type II deiodinase differs from Type I deiodinase found in other tissue such as liver and kidney, and in fact different conditions such as hypothyroidism and hyperthyroidism affect these enzymes in opposite direction. Thyroid hormones exert other effects on the pituitary such as increased synthesis of substance P, increased synthesis of GH, and decreased TRH receptors, TRH also modifies its own receptors in the pituitary and exerts modulatory effects on TSH molecule. Patients with non thyroidal illness may display TSH molecules with decreased biological activity. Various agents used in every day praxis may alter TSH and thyroid secretion. The physician must be aware of changes in order to avoid diagnostic pitfalls.

Animals↗
PubMed1979

Iodide-induced hypothyroidism: a potential hazard during perinatal life.

The administration of iodide to pregnant and nursing rats induces hypothyroidism in the term fetus and neonatal rat through age 10 days as indicated by an increase in the serum concentration of thyroid-stimulating hormone and a decrease in the serum of thyroxine and triiodothyronine. Thyroid function returned to normal from age 18 through 60 days in spite of continued iodide administration, strongly suggesting that resistance to the inhibitory effect of iodide on thyroid hormone synthesis is developed at approximately 18 days of age. This perinatal rat model can be used to study the mechanisms responsible for iodide-induced hypothyroidism and goiter in human newborns whose mothers received iodide-containing medications during pregnancy.

Animals↗
PubMed1979

The thyroid.

Explore the source record for details and available documents.

Adult↗
PubMed1979

The role of sulfhydryl groups on the impaired hepatic 3',3,5-triiodothyronine generation from thyroxine in the hypothyroid, starved, fetal, and neonatal rodent.

The role of nonprotein sulfhydryl groups (NPSH) in the decreased in vitro hepatic 3',3,5-triiodothyronine (T(3)) generation from thyroxine (T(4)) in the starved, hypothyroid, fetal and 1- to 4-d-old neonatal rat and dwarf mouse was assessed. NPSH were measured in fresh 25% liver homogenates prepared in 0.1 M PO(4)/10 mM EDTA buffer. As compared with values in adult male rats, NPSH concentration was decreased in the 2-d-starved (1.1+/-0.04 (mean+/-SE) vs. 2.2+/-0.15 mmol/250 g wet liver weight, P < 0.001), fetal (1.0+/-0.04 vs. 3.2+/-0.08, P < 0.001), 1-d-old neonatal (1.1+/-0.03 vs. 2.1+/-0.04, P < 0.001), and hypothyroid (thyroidectomized 60 d) (1.4+/-0.06 vs. 2.2+/-0.15 P < 0.001) rat. NPSH were also decreased in the hypothyroid, hypopituitary dwarf mouse as compared with values in their normal litter mates (1.3+/-0.03 vs. 2.0+/-0.2, P < 0.01). Chronic administration of T(3) (0.5 mug/100 g body wt per d) markedly increased hepatic T(3) generation from T(4) in the thyroidectomized rat and in the dwarf mouse to values similar to those observed in the normal rodent without affecting NPSH concentration. In contrast, T(3) administration to the starved rat did not alter either hepatic T(3) generation from T(4) or NPSH. Reduced glutathione concentration was also markedly decreased in the starved rat (fed; 1.05+/-0.075 mmol/250 g wet tissue vs. starved 0.38+/-0.02, P < 0.001). Dithiothreitol (DTT), a thiol reducing agent, increased hepatic T(3) generation from T(4) in the normal adult male rat by 45+/-5% in six experiments. When compared to DTT-stimulated control homogenates, the addition of DTT completely restored hepatic T(3) generation in starved rats, partially restored T(3) generation in 1- and 4-d-old neonates, but had little or no effect in the fetal and hypothyroid rat and dwarf mouse. Liver homogenates stored for 6 mo at -20 degrees C lost their capacity to generate T(3) from T(4). NPSH concentrations in the frozen homogenates decreased progressively with increasing storage and were absent by 6 mo. 5'-Deiodinase activity correlated with NPSH concentration in the stored homogenates (r = 0.95, P < 0.005). Addition of DTT partially restored hepatic T(3) generation in the frozen homogenate. It is concluded that NPSH are important for the action of the liver 5'-deiodinase. The decreased hepatic T(3) generation in the starved rat is associated with decreased NPSH but not with a decrease in the absolute quantity of 5'-deiodinase because provision of sulfhydryl groups restored hepatic T(3) generation to normal. In contrast, the decreased hepatic T(3) generation in the adult hypothyroid rodent and in the fetal rat is probably due to a decrease in the enzyme concentration per se. In the 1- and 4-d neonatal rat, the decrease in hepatic T(3) generation is secondary to a decrease in NPSH and the deiodinating enzyme.

Aging↗
PubMed1979

Thyrotropin-releasing hormone is not required for thyrotropin secretion in the perinatal rat.

To determine the role of thyrotropin-releasing hormone (TRH) in the regulation of thyroid-stimulating hormone (TSH) secretion in the perinatal period, a physiological approach of neutralizing circulating TRH in the fetal and early neonatal rat was employed. TRH-antiserum (TRH-AS) raised in rabbits and administered daily to low iodine-propylthiouracil (LID-PTU)-fed pregnant rats from days 12 to 19 of gestation markedly impaired the rise in serum TSH to LID-PTU when compared with normal rabbit serum-treated controls. In contrast, fetal serum TSH was unaffected by TRH-AS. The binding capacity of TRH-AS in the fetal serum (111 ng/ml) far exceeded circulating TRH in the fetus. Similarly, acute TRH-AS administration to the pregnant rat fed LID-PTU markedly decreased the serum TSH concentration in the mother, but not in the fetus, 60 min after TRH-AS administration. Chronic TRH-AS administration to neonatal rats whose nursing mothers were fed LID-PTU was in-effective in decreasing the elevated serum TSH in the neonate through day 8 of life, whereas a slight but significant decrease in serum TSH was observed on day 10. Chronic daily TRH-AS administration to neonatal rats through day 10 of life had no effect on the later development of the hypothalamic-pituitary-thyroid axis. These findings suggest that TRH does not participate in TSH regulation during the perinatal life in the rat and that thyroid hormones are probably the main regulators of TSH secretion during this period. Placental TRH is not important in regulating TSH secretion in the fetal rat. Furthermore, TRH "deprivation" during neonatal life does not prevent normal later development of the hypothalamic-pituitary-thyroid axis.

Animals↗
PubMed1979

Dietary-induced alterations in thyroid hormone metabolism during overnutrition.

Diet-induced alterations in thyroid hormone concentrations have been found in studies of long-term (7 mo) overfeeding in man (the Vermont Study). In these studies of weight gain in normal weight volunteers, increased calories were required to maintain weight after gain over and above that predicted from their increased size. This was associated with increased concentrations of triiodothyronine (T3). No change in the caloric requirement to maintain weight or concentrations of T3 was found after long-term (3 mo) fat overfeeding. In studies of short-term overfeeding (3 wk) the serum concentrations of T3 and its metabolic clearance were increased, resulting in a marked increase in the production rate of T3 irrespective of the composition of the diet overfed (carbohydrate 29.6 +/- 2.1 to 54.0 +/- 3.3, fat 28.2 +/- 3.7 to 49.1 +/- 3.4, and protein 31.2 +/- 2.1 to 53.2 +/- 3.7 microgram/d per 70 kg). Thyroxine production was unaltered by overfeeding (93.7 +/- 6.5 vs. 89.2 +/- 4.9 microgram/d per 70 kg). It is still speculative whether these dietary-induced alterations in thyroid hormone metabolism are responsible for the simultaneously increased expenditure of energy in these subjects and therefore might represent an important physiological adaptation in times of caloric affluence. During the weight-maintenance phases of the long-term overfeeding studies, concentrations of T3 were increased when carbohydrate was isocalorically substituted for fat in the diet. In short-term studies the peripheral concentrations of T3 and reverse T3 found during fasting were mimicked in direction, if not in degree, with equal or hypocaloric diets restricted in carbohydrate were fed. It is apparent from these studies that the caloric content as well as the composition of the diet, specifically, the carbohydrate content, can be important factors in regulating the peripheral metabolism of thyroid hormones.

Adult↗
PubMed1979

Seasonal variation and the influence of body temperature on plasma concentrations and binding of thyroxine and triiodothyronine in the woodchuck.

Woodchuck plasma was collected during four seasons of the year and assayed for total and dialyzable (free) T4 and T3 and for rT3. Plasma concentrations of total and free T4 and T3 were higher in the spring (T4, 5.4 +/- 0.6 microgram/dl; free T4, 3.0 +/- 0.4 ng/dl; T3, 202 +/- 22 ng/dl; free T3, 0.51 +/- 0.04 ng/dl) and lower in the prehibernatory fattening period in summer (T4, 2.3 +/- 1.0 microgram/dl; free T4, 1.2 +/- 0.5 ng/dl; T3, 45 +/- 27 ng/dl; free T3, 0.16 +/- 0.10 ng/dl) and fall (T4, 3.2 +/- 1.0 microgram/dl; free T4, 1.3 +/- 0.2 ng/dl; T3, 130 +/- 12 ng/dl; free T3, 0.25 +/- 0.02 ng/dl). In spite of the extremely high concentrations of T3 in the winter (437 +/- 32 ng/dl), free T3 concentrations (0.034 +/- 0.003 ng/dl), when measured at the appropriate temperature for hibernation, were significantly lower than those found at other seasons of the year. Plasma binding of T3 was lower during the summer and increased again to approximately double the spring value during the winter. rT3 was at or below the sensitivity of the method (6 ng/dl) at all seasons. It is suggested that the wide seasonal variations in thyroid hormone concentrations and altered plasma protein binding may represent important adaptations influencing the metabolic rate and the process of hibernation in the woodchuck.

Animals↗
PubMed1979

Aspergillus flavus as a cause of thyroiditis in an immunosuppressed host.

Disseminated aspergillosis is a major complication in immunosuprressed patients. Infiltration of the thyroid with Aspergillus organisms occurs in approximately 20% of autopsies in patients dying with disseminated disease. The present report describes Aspergillus thyroiditis, Hashimoto's thyroiditis, and possible hypothyroidism in a patient with disseminated aspergillosis.

Aspergillosis↗
PubMed1979

Ophthalmopathy after neck irradiation therapy for Hodgkin's disease.

Ophthalmopathy associated with autoimmune thyroid disease (Graves' ophthalmopathy) may occur years after irradiation of the neck for nonthyroid malignant disease. Two patients developed this complication 2 and 18 years after irradiation treatment of Hodgkin's disease: one with hypothyroidism associated with Hashimoto's thyroiditis and the other with hyperthyroidism. Careful long-term observation of thyroid function following neck irradiation is recommended in view of this unusual complication and the frequent occurrence of hypothyroidism.

Adult↗