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M Pavlovic-Hournac

Publications and source records attributed to M Pavlovic-Hournac.

35 records · Page 2Linked to original sources
PubMed1979

Hormonal regulation of thyroidal protein phosphokinase activities. II. Differential sensitivity of type I and type II cAMP-dependent enzymes to the treatment of rats with thyroxine.

Two cAMP-dependent protein kinase activities can be separated from rat thyroid cytosol. Their elution properties during the gel chromatography, as well as their sedimentation coefficients after sucrose-gradient ultracentrifugation and their capacity to dissociate in the presence of histones, suggest they are like the Type I and Type II protein kinases described in many other tissues. The sensitivity of the two types of kinases to thyroxine treatment is different. The activity of Type I is not changed during the first 5 days of treatment. Thereafter, it decreased by about 50% and is maintained at that level for up to one month. The activity of the Type II enzyme decreased rapidly by about 30-40% already on the second day of treatment, and after 10 days it reached 50% of the initial level. This differential reactivity of the two types of enzymes to the thyroxine treatment leads to profound modifications in their relative activities between the second and the fifth day of treatment. The significance of these results and the possible role of the two types of kinases in the control of different steps of iodine metabolism have been discussed.

Animals↗
PubMed1978

Hormonal regulation of cAMP-independent protein phosphokinase activities: thyroxine and cortisol control of enzymes from rat liver cytosol.

Thyroxine control of cAMP-independent histone and casein phosphokinase activities was studied in thyroidectomized rats treated with thyroxine. All activities were evaluated in the presence of a thermostable inhibitor of cAMP-dependent enzymes. Cytosol enzymes can be resolved by sucrose gradient ultracentrifugation into three peaks of histone kinase activity (3.2S, 5S and 7.2S) and two peaks of casein kinases (3.6S and 7.1S). Neither thyroidectomy nor subsequent treatment of operated animals with thyroxine modifies the total histone kinase activity estimated, either in total cytosol or after its fractionation by the sucrose gradient ultracentrifugation. The activity ratios of different peaks were, however, changed. Casein kinase activity was significantly decreased after thyroidectomy (about 50%). Subsequent treatment with thyroxine restored this activity to its initial value. Sucrose gradient ultracentrifugation analysis showed that thyroxine action on the casein kinase activity is very specific. Only molecules that sediment in the 9S region were significantly stimulated by the hormone. Cortisol action on the casein kinase activity was studied in adrenalectomized animals treated with hormone for 24 h. Cortisol decreases the total casein kinase activity by about 30%. Sucrose gradient ultracentrifugation analysis showed that the population of molecules sedimenting at about 9S was the most sensitive to cortisol. The above data show that both thyroxine and cortisol control, in a selective way, the activities of cAMP-independent protein kinases. The same kinase molecules can be under double control by two different hormones that have opposite effects.

Adrenal Glands↗
PubMed1977

Discontinuity of thyroid gland response to hormonal stimulation: effect of TSH and cAMP on iodide organification.

The action of TSH on the process of iodide organification was studied in rat thyroid glands under different experimental in vitro incubation conditions. The effects on glands of both short and prolonged exposure to TSH were evaluated using two different procedures: continuous and pulse labelling of thyroids with radioactive iodide. It was demonstrated that during prolonged contact with thyroid cells, TSH stimulates iodide organification periodically. This periodic effect is cyclic and is composed of a stimulatory and an inhibitory phase. Each cycle lasts 30-45 min, and several cycles follow one another in a regular manner. Furthermore, it has been shown that the periodic effect of THS is due to an intrinsic property of the thyroid cell to respond in a cyclic manner to hormonal stimulation. TSH stimulated the accumulation of organic iodide only when introduced at a precise phase of the cycle. The same type of discontinuous thyroid cell response was obtained when TSH was replaced by its intracellular mediator, cAMP. This indicates that the initiation of the cyclic response to hormonal stimulation is localized at the steps after that of cAMP formation. It seems, therefore, that this cyclic response of thyroid glands is not related to the recently observed phenomenon of desensitization. This phenomenon, characterized by the development of resistance in many target organs and cells toward their respective hormonal stimulators, is due to modifications in steps preceding those of cAMP formation. The discontinuity of thyroid gland response to both TSH and cAMP described in this work seems to be a new phenomenon, whose physiological significance and possible molecular mechanisms are discussed.

Animals↗
PubMedDate not supplied

Modification of protein kinase pattern in human placentae during gestation.

The cAMP-dependent and cAMP-independent histone kinases have been studied in the two subcellular compartments (cytosol and particulate fraction) from placentae of different gestational age. The total protein kinase activity, as well as its distribution between the two compartments, changes during the period of gestation. The total activity is significantly increased in full-term placentae. The increase is much greater for the cAMP-dependent (400 per cent), than for the cAMP-independent (270 per cent) protein kinases. It is much higher (400 per cent) in the cytosol than in the particulate fraction (170 per cent); consequently, the particulate fraction of term placentae shows a relatively lower proportion of protein kinase activity (26 per cent of the total activity) than the corresponding fraction of young placentae (37 per cent). DEAE-cellulose chromatography revealed the presence of two cAMP-dependent protein kinase peaks which correspond to Type I and Type II isoenzymes described in many mammalian tissues (Corbin, Keely and Park, 1975). The Type II isoenzyme is predominant in both first- and third-trimester placentae. The increase in protein kinase activity in term placentae is due to the selective activation of the Type II kinase only. The activity of the Type I isoenzyme remained unchanged throughout the period of gestation. The third peak eluted from the DEAE-cellulose column corresponds to a cAMP-independent sucrose-gradient ultracentrifugation into two distinct peaks similar to those already observed in several rat tissues (Toru-Delbauffe, Ohayon and Pavlovic-Hournac, 1983). The protein kinase patterns of both young and term placentae remain stable during the incubation of the tissues 'in vitro' for three hours.

Cyclic AMP↗