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Biomedical subjects

J Knopp

Publications and source records attributed to J Knopp.

At least 73 records · Page 4Linked to original sources
PubMed1980

Effect of propylthiouracil on 125I-L-triiodothyronine binding to the nuclei and on malic enzyme activity in rat liver cytosol.

The effect of propylthiouracil (PTU), triiodothyronine (T3) and thyroxine (T4) on malic enzyme activity of rat liver cytosol and on the binding of 125I-L-triiodothyronine to nuclear fraction was examined. Significant decrease of in vitro binding of 125I-T3 to the liver nuclei was found in rats fed PTU for 12 h, 24 h and 120 h. Hepatic malic enzyme activity was unchanged after 12 h, but markedly decreased after 24 h and 120 h of PTU treatment. In 120 h PTU fed animals the effect of T3 on malic enzyme activity was five times higher in comparison to an equimolar dose of T4. Finally, the effect of T4 on malic enzyme activity was observed which might result from the intrinsic activity T4 under the conditions of decreased T4 to T3 conversion due to PTU feeding. The obtained results show that there is a certain correlation between nuclear T3 binding and cytosol malic enzyme activity which is presumably induced directly through m-RNA synthesis stimulated by thyroid hormones.

Animals↗
PubMed1979

Inhibition of thyroid monoamineoxidase by thyroxine and some specific inhibitors.

Rat thyroid monoamine oxidase (MAO) was inhibited by the non-hydrazine derivatives paragyline and tranylcypromine to a higher degree than the hydrazine derivative iproniazide. MAO was also inhibited by monoiodotyrosine and thyroxine. These results indicate that MAO may be an important enzyme in the metabolism of biogenic amines, iodotyrosines and tyronines in the thyroid gland.

Animals↗
PubMed1979

The regional distribution of adenylate cyclase in individual nuclei of rat hypothalamus.

The regional distribution of adenylate cyclase (AC) activity in separated individual hypothalamic nuclei was studied. The highest activity was found in the paraventricular nucleus and the lowest activity in the median eminence. In several other hypothalamic nuclei, there was also found higher activity of AC than in the total hypothalamus. These data show that in the individual hypothalamic nuclei there exist considerable differences in the activity of adenylate cyclase that may indicate their different function in regulation of neuroendocrine phenomena.

Adenylyl Cyclases↗
PubMed1979

Monoamine oxidase and aspartate aminotransferase in cellular fractions of thyroid gland in rats after hypophysectomy and TSH stimulation.

UNLABELLED: Monoamine oxidase (MAO) and aspartate aminotransferase activities in cellular fractions of thyroid gland in rats after hypophysectomy and TSH treatment were investigated. MAO and aspartate aminotransferase activities in thyroid mitochondria were decreased after hypophysectomy and significantly increased after daily injection of TSH during five days to hypophysectomized rats. In microsomes after hypophysectomy a similar decrease of MAO activity was found but TSH was without effect on this activity. IN CONCLUSION: it is evident that MAO and aspartate aminotransferase in thyroid mitochondria the enzymes which could be a source for hydrogen peroxide to catalyze thyroid hormone synthesis are under the regulatory influence of TSH.

Animals↗
PubMed1978

The changes of in vitro 131I-iodine uptake in the thyroid gland of rats exposed to septal lesions and immobilization stress.

The in vitro uptake of 131I by the thyroid gland was investigated in rats after immobilization stress with special respect to animals lesioned in the septal area. Lesions in a septal area performed 10 days before decreased the iodide accumulation in the thyroid, while stress by immobilization increased it to the control basal value. Repeated immobilization in control rats did not produce any changes in the iodide uptake in vitro. ACTH injected in vivo stimulated the iodide 131I uptake in vitro by thyroid glands of hypophysectomized rats. It is concluded that immobilization stress in rats with septal lesions increases 131I-iodide uptake in vitro and that the increase was probably influenced by both catecholamines and glucocorticoids.

Animals↗
PubMed1978

Activity of adenylate cyclase and phospodiesterase in the pituitary and thyroid during postnatal period in rats.

Adenylate cyclase (AC) and phosphodiesterase (PD) activities in the pituitary and thyroid have been determined during postnatal period in rats. In both tissues the activity of both enzymes was found early after birth. In the pituitary gland AC activity increased significantly from the second to the seventh day, while it remained unchanged on the 16 th day and again increased on the 23rd day when the activity reached the value of adult rats. The activity of PD in the pituitary increased significantly from the second to 23rd postnatal day and in the adult rats the activity was similar as in two days old rats. In the thyroid gland AC activity remained unchanged during postnatal period of rats with the exception between the 16th and 23rd day when a small but significant difference was found. The activity of PD in thyroid was high on the first day after delivery and then decreased significantly on the seventh day. It increased again significantly on 23rd day when it was similar to the adult rats. However, between 23rd and 60th days the activity significantly dropped and significantly increased from 60th day to the adult age. These results suggest that in the rat the mechanism of adenylate cyclase system involved in the pituitary and thyroid functions could play a role in the regulation of the function of these tissues during postnatal development.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Effect of thiocyanate and other univalent anions on the binding of thyroxine to rat liver nuclei and homogenate.

The binding of thyroxine (125I-T4) in rat liver homogenate and isolated nuclei was investigated in vitro. In homogenate, the binding of T4 was modified by thiocyanate ion (SCN-) added to the incubation mixture as potassium thiocyanate. The displacing effect of SCN- increased with increasing concentrations of this compound, the lowest effective dose being that which significantly displaced T4 from liver homogenate (105 pmol per one ml medium). Moreover, SCN- significantly increased the displacing effect of unlabelled T4. In contrast, however, no effect of SCN- was found on the binding of T4 in the isolated liver nuclei. In sonicated nuclei no effect of SCN- on T4 binding was found, but specific binding of T4 under these circumstances was impaired. Finally, in a homogenate a displacing effect of other univalent anions (BF4-, ClO4- and MnO4-) was found resembling that of SCN-. It is suggested that, in the liver homogenate, SCN- displaces T4 from non-specific binding sites. This view is also supported by the fact that in liver nuclei, where specific binding sites prevail, no effect of SCN- was observed.

Animals↗
PubMed1977

Interaction of plasma membranes with influenza virus. VII. Effect on 3',5'-cyclic adenosine monophosphate phosphodiesterase activity.

In chick embryo cells (CEC) and plasma membranes (PM) isolated therefrom, three forms of 3',5'-cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) were demonstrated: (1) PDE activated only by Ca2+ (Ca-PDE); (2) PDE activated only by Mg2+ (Mg-PDE); and (3) PDE stimulated in the presence of 2 mM Mg2+ by low concentrations of Ca2+ (Ca-Mg-PDE). Purified influenza A virus, under suitable conditions, lowered the activities of these PDEs. The decrease was greater in samples incubated in the presence of adenosine triphosphate (ATP) than in those incubated in its absence.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1976

The effect of TRH on the anterior pituitary adenylate-cyclase activity of rat.

Synthetic thyrotropin releasing hormone was found to stimulate rat anterior pituitary adenylate cyclase activity. In the presence of guanosine triphosphate, no further stimulation was recorded; guanosine triphosphate alone also increased the adenylate cyclase activity. Prostaglandin E1 was found to stimulate a basal enzyme activity and this effect was significantly enhanced by guanosine triphosphate. It appears that guanosine triphosphate could be a modulator of adenylate cyclase activity in rat anterior pituitary in response to PGE1 but not to TRH.

Adenylyl Cyclases↗