PubMed Health⌕ Search

Biomedical subjects

J Vriend

Publications and source records attributed to J Vriend.

At least 37 records · Page 2Linked to original sources
PubMed1986

Effects of afternoon injections of melatonin in hypothyroid male Syrian hamsters.

Male Syrian hamsters were kept under either 14 h light/10 h dark (lights on at 06.30 h) or 2 h light/22 h dark (lights on at 14.30 h) photoperiods. Groups of hamsters under each photoperiod were rendered hypothyroid by addition of 0.4% thiourea to the drinking water. These hamsters received, in addition, either a daily evening injection of saline or a daily injection of 25 micrograms melatonin in saline. Groups of intact controls and pinealectomized control hamsters were also maintained under the two photoperiodic conditions. After 10 weeks under the different conditions the hamsters were killed by decapitation, and serum samples assayed for thyroxin, thyroid-stimulating hormone (TSH), and prolactin (PRL). Pituitary extracts were assayed for TSH and PRL. Hypothyroidism in hamsters receiving thiourea was confirmed by radio-immunoassay data showing low serum thyroxin and greatly elevated serum TSH concentrations. Melatonin injections resulted in significant depression of serum TSH in thiourea-treated hamsters under short photoperiod compared to saline-injected controls. Both melatonin injections and short photoperiod resulted in a significant reduction of pituitary TSH in hamsters on thiourea compared to values obtained from similarly treated animals under the 14 h light/10 h dark photoperiod. Hypothalamic concentrations of thyrotropin-releasing hormone (TRH) were significantly elevated by melatonin injections and by short photoperiodic conditions, but not by thiourea administration. The short photoperiod resulted in testicular involution which was completely reversed by pinealectomy and partially reversed (to 53% of controls) by thiourea treatment. Involution of gonads was complete in thiourea-treated animals under short photoperiod, if they received melatonin injections.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Hypothyroidism of hypothalamic origin in pyridoxine-deficient rats.

Pyridoxine-deficient young rats (3 weeks old) had significantly reduced levels of pituitary TSH, serum thyroxine (T4) and tri-iodothyronine (T3) compared with pyridoxine-supplemented rats. The status of the pituitary-thyroid axis of normal, pyridoxine-supplemented and pyridoxine-deficient rats was evaluated by studying the binding parameters of [3H](3-methyl-histidine2)TRH in the pituitary of these rats. The effects of TRH and T4 injections on pituitary TSH and serum TSH, T4 and T3 of these two groups were also compared. The maximal binding of TRH receptors in the pituitary of pyridoxine-deficient rats was significantly higher than that of pyridoxine-supplemented control and normal rats, but there was no change in the binding affinity. Treatment with TRH stimulated TSH synthesis and release. It also increased serum T4 and T3 in both pyridoxine-supplemented and pyridoxine-deficient rats. Treatment with T4 decreased serum and pituitary TSH in both pyridoxine-supplemented and pyridoxine-deficient rats, compared with saline-treated rats. The increased pituitary TRH receptor content, response to TRH administration and the fact that regulation at the level of the pituitary is not affected in the pyridoxine-deficient rat indicates a hypothalamic origin for the hypothyroidism of the pyridoxine-deficient rat.

Animals↗
PubMed1985

Effects of pinealectomy and melatonin administration on thyroid follicles of blind Syrian hamsters.

Since previous studies have shown that an active pineal gland exerts an inhibitory effect on circulating levels of thyroxin in the Syrian hamster, a study was conducted to determine whether the histology and ultrastructure of the thyroid gland supported the conclusions drawn from the hormone data. The ultrastructure of thyroid glands of blinded male Syrian hamsters was compared to that of intact controls kept under a 14L/10D photoperiod, to that of blinded hamsters also pinealectomized, and to that of blinded hamsters receiving 80 micrograms/ml of melatonin in the drinking water. Serum thyroxin (T4) and serum thyrotropin (TSH) concentrations were determined by radioimmunoassay. After 10 weeks serum thyroxin concentrations were less than 50% of controls and concentrations were significantly reduced. EM examination revealed that blinded hamsters had an increased number of follicular cells with flattened epithelium and nondilated endoplasmic reticulum compared to intact controls. In blinded hamsters that were pinealectomized or treated with melatonin in the drinking water, the ultrastructure of the thyroid was not different from controls and serum thyroxin concentrations were restored to near normal. These ultrastructural data support the conclusion that the pineal gland is required to obtain inhibition of the pituitary-thyroid axis in blinded hamsters and that melatonin has a counter-inhibitory effect when administered via the drinking water.

Animals↗
PubMed1985

Effects of melatonin and thyroxine replacement on thyrotropin, luteinizing hormone, and prolactin in male hypothyroid hamsters.

The effects of daily evening melatonin injections on plasma and pituitary levels of TSH, LH, and PRL in hypothyroid hamsters maintained under a 14-h light, 10-h dark photoperiod were investigated. Circulating levels of thyroid hormones were monitored, and testicular weights were recorded. Thiourea-induced increases in serum and pituitary TSH were significantly reduced by melatonin injections. Control hamsters, not receiving thiourea, responded to daily evening melatonin injections with a decrease in serum T4. Serum T3 levels were decreased by thiourea and increased by T4 replacement. The pituitary PRL content was significantly reduced below control values in hamsters receiving melatonin injections; the sensitivity to melatonin was inhibited by thiourea and restored by T4 replacement. T4 replacement injections were associated with a significant decrease in serum PRL and a significant increase in serum LH. Melatonin-induced testicular involution was attenuated by thiourea administration; this attenuation was reversed by T4 replacement. Similarly, a melatonin-induced decrease in serum LH was prevented by thiourea administration and restored by T4 replacement. The data suggest that melatonin injections increase the sensitivity of the pituitary to T4/T3 feedback inhibition of TSH. Furthermore, these data show that thyroid status may influence melatonin-induced changes in release of PRL and LH from the hamster pituitary. The data showing an interaction of thyroid hormones in the control of testicular size are interpreted as evidence that thyroid hormones play a major role in the mechanism regulating gonadal cycles in the hamster.

Animals↗
PubMed1985

Thyroid function in pyridoxine-deficient young rats.

In pyridoxine-deficient young rats hypothalamic serotonin was decreased with no changes in the dopamine and noradrenaline content. Serum thyroxine and tri-iodothyronine concentrations were much lower in the deficient rats as compared to pyridoxine-supplemented controls. No significant difference between deficient and control groups in the serum TSH concentration was detected. Highly significant decreases in the content of pituitary TSH and in the number of pituitary thyrotroph secretory granules were found. These results suggest that the hypothyroidism of pyridoxine-deficient young rats might be of hypothalamic origin.

Animals↗
PubMed1984

Coincidence of counter-antigonadal and counter-antithyroid action of melatonin administration via the drinking water in male golden hamsters.

Administration of melatonin via the drinking water prevented the gonadal involution and the thyroid hormone depletion normally observed in blinded hamsters. Ten weeks after blinding male hamsters had plasma thyroxin levels that were 57% of controls and testis weights that were 8% of controls. Administration of melatonin (80 microgram melatonin/ml drinking water) to blinded hamsters restored thyroxin levels to 86% of controls and testis weights to 93% of controls. Dose response data showed that as little as 1.25 microgram (approximately 10 microgram/hamster/day) produced a significant effect on testis weight, whereas the lowest dose required to produce a significant increase in thyroxin levels was 10 microgram/ml. The coincidence of counter-antigonadal and counter-antithyroid actions of melatonin suggests a single site of action.

Animals↗
PubMed1984

Effect of D, L-alpha-aminoadipate on the mediobasal hypothalamus and endocrine function in the rat.

Using the glutamate analog, D,L-alpha-aminoadipic acid (D,L-alpha AA), experiments were conducted to examine the nature, extent, and specificity of its toxicity in the mediobasal hypothalamus and to determine its effect on endocrine homeostasis. Neonatal rats received daily injections of D,L-alpha AA (4 g/kg BW) on postnatal days 5-10 and were killed at various post-treatment intervals. Sex-matched littermates were given equimolar amounts of NaCl and served as controls. Treated rats killed 18 days post injection weighed slightly less than controls and had reduced testicular, ovarian, and uterine weights, but the differences were not statistically significant. In D,L-alpha AA treated rats serum and pituitary levels of TSH and PRL were comparable to control values. Pituitary content of LH (male's and female's) and FSH (female's), however, was lower (P less than 0.05) in D,L-alpha AA treated rats than in controls, but serum levels were not significantly different. Distinct cytopathologic changes were evident in the arcuate nucleus and median eminence of D,L-alpha AA-treated rats killed at 2 and 6 h post injection only. By 12 h evidence of acute damage had largely disappeared. Both glial and ependymal cells underwent edematous swelling and necrosis, but neurons were largely unaffected. Evidence of reactive changes, such as gliosis, infiltration of microglia, and removal of debris, however, were not very conspicious. A random sample of mediobasal hypothalami of rats killed 18 days post injection failed to show any detectable lesion or residual effects of earlier pathology. Age at the time of exposure to the gliotoxin was found to be an important variable affecting both extent and duration of injury. The most deleterious effects were observed when the gliotoxin was administered in the form of a single injection on postnatal day 5 only. The results suggest that normal neuronal activity and endocrine homeostasis, specifically gonadotropin, may be irreversibly altered as a consequence of transient disruption of the glial compartment.

2-Aminoadipic Acid↗
PubMed1984

Multi-exponential water proton spin-lattice relaxation in biological tissues and its implications for quantitative NMR imaging.

This in vitro study was undertaken to examine whether water proton spin-lattice relaxation in biological tissues is adequately described by a single time constant T1, to define under what circumstances a multi-exponential approach is indicated, and to study the implications of multi- exponentiality for quantitative NMR imaging. Water proton relaxation curves were measured with the 180-tau-90 method at 60 MHz. Uni- and bi-exponential curves were fitted to the empirical curves using chi 2 as a criterion for the goodness of fit. An F-test was applied to test the validity of each exponential term as it was added to the fitting function. Taking into account experimental accuracy, the uni-exponential model appeared to be an adequate description of the relaxation data for necrotic tissue. Eyelens and fat showed distinct bi- exponentiality , while liver, spleen, salivary gland, tumour, and muscle presented intermediate cases. The bi-exponential analysis generally yields a minor component with a fast relaxation time, T11 less than 20 ms, and a slow relaxation major component with T12 greater than 300 ms. A simplified bi-exponential model is proposed for implementation in quantitative NMR imaging. The results seem to be consistent with current views about water proton spin-lattice relaxation in biological tissues.

Adenocarcinoma↗
PubMed1984

Influence of the pineal gland and circadian rhythms in circulating levels of thyroid hormones of male hamsters.

Thyroxin (T4) and triiodothyronine (T3) were measured by radioimmunoassay in serum of hamsters sacrificed at 4-hr intervals throughout the daily light-dark cycle (14L/10D). Both T4 and T3 concentrations increased significantly during the L period of the daily cycle and decreased during the D period of the cycle; A.M. versus P.M. differences in free thyroxin indices (FTI) were also studied using the T4 and T3 uptake assays of Nuclear Medical Laboratories (Dallas, Texas). The free thyroxin index was significantly greater in serum samples of hamsters sacrificed at 7 P.M. than at 7 A.M. (lights on at 6:30 A.M.). Serum taken at 7 P.M. had less unsaturated binding sites than serum taken at 7 A.M. No significant A.M. versus P.M. differences in free thyroxin index were found in blind hamsters, although blind hamsters had significantly lower T4 and FTI than controls. Placing melatonin in the drinking water at a dose of 80 micrograms/ml did not significantly influence hormone levels. The greatest difference in hormone concentrations between control and blinded hamsters was found in P.M. samples. Blind hamsters had FTIs that were 48% of P.M. controls. Pinealectomy prevented the effects of blinding on T4 levels and FTIs.

Animals↗
PubMed1983

Proton spin-lattice relaxation studies of tissue response to radiotherapy in mice.

Proton spin-lattice relaxation times were measured with pulsed NMR spectroscopy at 60 MHz for a range of tissues from healthy and tumour-bearing mice. T1 appeared to be significantly longer in the tumour than in any other tissue. Clearly distinct values of T1 were found for the vital and necrotic parts of the tumour. Non-involved tissues of tumour-bearing mice, viz. spleen, muscle, and salivary gland tissue, showed an increase in T1 relative to normal values. Irradiation of healthy mice with 6 MeV x-rays to a total-body dose of 15 Gy induced a shortening of T1 in the spleen. Similar experiments on tumour-bearing mice showed a decrease of T1 in the tumour, the spleen, the kidneys, and the liver. Attempts were made to interpret the results in terms of tissue hydration.

Adenocarcinoma↗
PubMed1983

Evidence for pineal gland modulation of the neuroendocrine-thyroid axis.

Experiments with rats and hamsters have provided evidence for an inhibitory action of the pineal gland on the neuroendocrine-thyroid axis. While maintenance of these animals in short photoperiod results in reduced levels of circulating thyroxin (T4), pinealectomy restores the levels to normal. Recent studies suggest that an active pineal gland produces a substance which inhibits thyrotrophin-releasing hormone release from the hypothalamus. Several investigators have concluded that endogenous melatonin, produced in the pineal gland, could account for the inhibitory action of the pineal gland on blood T4 levels. Although melatonin administration has been reported to inhibit blood T4 levels in both rats and hamsters, under certain experimental conditions melatonin administration can be demonstrated to have a counter-antithyrotrophic effect resulting in increased blood levels of T4 and thyrotrophin. Assay of blood levels of melatonin of rats and hamsters under various experimental conditions will be necessary to distinguish physiological from pharmacological effects of melatonin. Lesion studies as well as studies with melatonin implants in the brain, suggest that the site of action is in the anterior hypothalamus. The effects of melatonin on the neuroendocrine-thyroid axis are similar to its effects on the neuroendocrine-gonadal axis, leading to the hypothesis of a common site of action for the thyroid and gonadal effects of melatonin. Although many pineal 'factors' have been postulated to account for the action of this gland, an action of melatonin on the serotonergic system of the brain stem could account for the data.

Animals↗
PubMed1983

Influence of the pineal gland on hypothalamic content of TRH in the Syrian hamster.

Blinding adult female hamsters by bilateral orbital enucleation caused an increase in thyrotropin-releasing hormone (TRH) content of the medial basal hypothalamus and also led to an increase in TRH content in the remainder of the hypothalamus (dorsal hypothalamus). Although pinealectomy by itself had no significant effect on the neuroendocrine-thyroid axis, this surgical procedure prevented the inhibition of serum thyroxin observed in blinded hamsters. Pinealectomy also prevented the increase in TRH content of medial basal and dorsal hypothalamus observed in blinded hamsters. The results are consistent with the view that the pineal gland has a CNS site of action and provide evidence that the anti-thyroid influence of the pineal gland can be explained by pineal inhibition of TRH release.

Animals↗
PubMed1983

Counterantigonadotropic effect of melatonin administered via the drinking water.

Plasma melatonin levels in Syrian hamsters were augmented by the addition of melatonin to the drinking water. Preliminary experiments in pinealectomized hamsters indicated that doses in the range of 2-5 micrograms/ml in the drinking water would produce variable levels of plasma melatonin, approximately in the physiological range (10-100 pg/ml). Two protocols were used, one to demonstrate the antigonadotropic effect of melatonin and the other to elicit the counter-antigonadotropic effect. In the antigonadotropic protocol, 100-g intact male hamsters were housed under a 14-h light, 10-h dark cycle for 10 weeks. Contrary to our hypothesis, there was no effect of melatonin in the drinking water on testis mass (dose range, 0.059-50 micrograms/ml). The counterantigonadotropic protocol involved the use of 100-g male hamsters that were blinded and housed under conditions similar to those of the first protocol. They received melatonin in concentrations ranging from 1.8-320 micrograms/ml. At 10 weeks, the blinded hamsters receiving no melatonin had the expected drop in testis mass to 0.56 g. In the range from 2.4-10 micrograms/ml melatonin, there was a highly variable response, but generally, higher doses resulted in higher testis mass. In the range of 20-320 micrograms/ml, the blind hamsters had mostly normal appearing large testes (mean, 3.3 g). The following conclusions were reached. 1) We produced the well known counterantigonadotropic effect of melatonin by administration via the drinking water ad libitum. 2) We could not produce the antigonadotropic effect by similar means.

Animals↗
PubMed1982

Effects of melatonin on thyroid physiology of female hamsters.

The effects of melatonin administration on thyroid physiology of female hamsters was investigated. A protocol of 25 micrograms given daily as subcutaneous injections late in the light period was found to inhibit blood levels of thyroxin (T4), triiodothyronine (T3) and thyrotropin (TSH). The free T4 index (FT4I) and the free T3 index (FT3I) were also significantly inhibited by melatonin injections. Decreasing the photoperiod under which the hamsters were kept, from 14 h light/10 h dark (14L/10D) to 10L/14D also resulted in decreased blood levels of these hormones. A protocol of melatonin injections using 2.5 mg daily, on the other hand, did not significantly inhibit blood levels of thyroid hormones or TSH; injection of this dose every afternoon into hamsters in long photoperiod significantly augmented the blood levels of T4. Continuously available melatonin in the form of subcutaneous implants of 1 mg melatonin in beeswax did not inhibit blood levels of thyroid hormones; furthermore, such implants prevented the inhibitory effects of injections of 25 micrograms melatonin. The results are consistent with the hypothesis that melatonin interferes with neurotransmitters which influence the synthesis or release of hypothalamic thyrotropin-releasing hormone.

Animals↗
PubMed1981

The half-life of melatonin elimination from rat plasma.

Tritiated or unlabeled melatonin was infused intra-arterially into unanesthetized male Sprague-Dawley rats. Blood samples were collected from the jugular vein over the next two hours and the melatonin concentrations determined in the plasma by liquid scintillation counting or by RIA. Data from the tritiated melatonin experiments gave a half-life of 23 min, and data from the RIA experiments gave a half-life of 17 min.

Animals↗
PubMed1980

Evidence for a thyrotropin-releasing hormone inhibitor in the pineal gland.

Extracts of bovine pineal glands were filtered through Sephadex G-25 and tested for their effect on TRH-induced TSH release in cell cultures of dispersed rat pituitary glands. Highly significant anti-TRH activity was found in material which was retarded on G-25. This material was purified sequentially on Sephadex G-10, Sephadex LH-20, and high pressure reverse phase liquid chromatography columns. The ability of partially purified material to inhibit TRH-induced TSH release by dispersed pituitary cells and to displace [3H]TRH from pituitary tumor cell membranes was interpreted as evidence for a TRH inhibitory factor (TRH-IF) in bovine pineal glands. Evidence for binding to TRH receptors included parallel competition displacement curves with synthetic TRH and data showing that excess TRH could overcome both the inhibition of TRH-induced TSH release and the inhibition of [3H]TRH binding by TRH-IF. Copurification of anti-TRH bioactivity (as tested in dispersed pituitary cell cultures) and anti-TRH-binding activity (as tested in membrane preparations) suggests that the inhibitory activity in pineal extracts results from the binding of a TRH antagonist to receptors. Reports by others of PRL release-inhibiting activity in pineal extracts were confirmed. PRL release-inhibiting activity copurified with TRH-IF.

Animals↗