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D Gripois

Publications and source records attributed to D Gripois.

At least 37 records · Page 2Linked to original sources
PubMed1990

Adrenal tyrosine hydroxylase activation in the developing rat: influence of the thyroid status.

Adrenal tyrosine hydroxylase activation was elicited in developing control, hypo- and hyperthyroid rats by insulin-hypoglycaemia. Rats were deeply anaesthetized with chloroform at a low concentration, since intrinsic tyrosine hydroxylase activation was very low with this technique, as compared to Ketamine injection or chloroform at a high concentration. The study of time-course of tyrosine hydroxylase activation showed that the maximum value was observed 2 h after insulin administration. In control animals, tyrosine hydroxylase activation increased between 4 and 20 days, and then decreased. Hypothyroidism is associated with a decreased tyrosine hydroxylase activation between 4 and 50 days, as compared to controls and hyperthyroidism with an increased activation between 6 and 30 days. While tyrosine hydroxylase from saline-treated rats exhibits two different forms (with two apparent Km values for the cofactor), enzyme from insulin-treated animals was present in a single form with a Km corresponding to the low Km value of the saline-injected rats. At 6 and 14 days, hypothyroidism increases tyrosine hydroxylase Km values as compared to euthyroid animals.

Adrenal Glands↗
PubMed1989

Thyroxine-binding globulin and thyroxine-binding prealbumin in hypothyroid and hyperthyroid developing rats.

We present evidence based on equilibrium and non-equilibrium binding studies, as well as on immunological techniques, that of the two rat specific thyroid-hormone-binding proteins, i.e., thyroxine-binding globulin (TBG) and thyroxine-binding prealbumin (TBPA), TBG but not TBPA is regulated by the thyroid hormones (TH). Hypothyroidism, induced from the day of birth by daily treatment with propylthiouracil (PTU-rats), leads to dramatic and sustained increases of the TH-binding abilities of the sera measured at equilibrium, whereas hyperthyroidism, induced by treatment with thyroxine (T4-rats), leads to the decrease of these abilities. Polyacrylamide gel electrophoresis and isoelectrofocalisation of radioiodinated T4-labelled sera, together with immunoassay of TBPA, demonstrate that both effects are due to TBG, the levels of which rise in PTU-rats and decline in T4-rats, while TBPA levels do not respond to either depletion or excess of the thyroid hormones. TBG rather than TBPA appears as the key thyroid-hormone-binding protein of the rat, inasmuch as it alone expresses a regulatory function of the thyroid hormones at protein synthesis level.

Aging↗
PubMed1989

Effects of insulin on brain serotonin in the young rat: influence of thyroid status.

Thyroid status has been shown to modify the adrenal catecholaminergic response to insulin. The influence of thyroid status on the brain serotonergic response to insulin is the subject of the present report. Newborn rats were divided into three groups: euthyroid, hypothyroid (propylthiouracil given to the suckling mother), and hypothyroid-treated with triiodothyronine (T3) as replacement therapy. At 14 days of age, the animals in each group received either insulin (10 IU/kg SC) or saline. Levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in several brain regions. Hypothyroidism induced increases in hypothalamic 5-HT and 5-HIAA and in cortical 5-HIAA levels. The elevations in 5-HIAA levels were reversed by T3. Insulin treatment-induced increases in 5-HIAA levels in all brain regions of both the hypothyroid and the T3-replaced rats. Thyroid status thus influences the serotonergic response to insulin in the young rat, but contrary to what occurred in adrenals for catecholamines, hypothyroidism enhances the central serotonergic response to insulin.

Animals↗
PubMed1989

Influence of hypothyroidism on the ontogenic development of tyrosine hydroxylase induction in the adrenal glands of the rat.

The ontogenic development of the transsynaptic induction of adrenal tyrosine hydroxylase (TH), evoked by reserpine and nicotine was studied in control and hypothyroid young rats, aged 3-52 days. The enzymatic induction was measured as an increase in the enzyme activity, since this increase was shown to be impaired either by an inhibitor of RNA synthesis or by a ganglionic blocker. In the control animals, TH induction elicited by reserpine increases between 3 and 32 days of age. In the hypothyroid rats, the enzymatic induction is impaired up to 32 days; at 52 days the induction is similar in both groups of animals. When nicotine is used as a stimulating agent, hypothyroidism still impairs the enzymatic induction at 5 and 21 days, indicating that at least one of the mechanisms inhibited by hypothyroidism is localized in the adrenal chromaffin cells. The present results, taken together with previous findings dealing with adrenal epinephrine secretion, show that the thyroid hormones play a crucial role in the responses of the adrenal medulla to a stimulation in the developing rat, while they have no effect in the adult.

Adrenal Glands↗
PubMed1989

Tyrosine content, influx and accumulation rate, and catecholamine biosynthesis measured in vivo, in the central nervous system and in peripheral organs of the young rat. Influence of neonatal hypo- and hyperthyroidism.

The influence of neonatal hypo- and hyperthyroidism on different aspects of tyrosine metabolism in the hypothalamus, striatum, brainstem, adrenal glands, heart and brown adipose tissue (BAT) were studied in 14-day old rats. The synthesis rate of catecholamines (CA) was also determined in vivo after the injection of labelled tyrosine. Hypothyroidism increases tyrosinaemia and endogenous tyrosine concentration in the hypothalamus and BAT. Hyperthyroidism decreases tyrosinaemia and endogenous tyrosine levels in the striatum, adrenals and heart. The accumulation rate of tyrosine determined 30 min after an intravenous injection of the labelled amino acid has been determined in the organs, together with the influx of the amino acid, determined within 20s. Hypothyroidism increases tyrosine accumulation rate in all the organs studied, and tyrosine clearance is decreased in the striatum and brainstem; together with an increased tyrosinaemia, this leads to a normal influx. The influx of tyrosine is increased in the hypothalamus. Hyperthyroidism decreases tyrosine accumulation rate in all the organs except the adrenals. These results indicate that the thyroid status of the young rat can influence tyrosine uptake mechanisms, without modifying an organ's tyrosine content. The fact that hypothyroidism increases tyrosine influx in the hypothalamus without modifying it in the brainstem and striatum reflects an heterogeneous reactivity to the lack of thyroid hormones in different brain structures. Neonatal hypothyroidism decreases the CA synthesis rate in the striatum, the heart and the interscapular brown adipose tissue, while synthesis was enhanced in the brainstem and the adrenals. It is likely that these variations in CA synthesis are due to thyroid hormone modulation of tyrosine hydroxylase activity, the enzyme which catalyses the rate limiting step in CA biosynthesis.

Adipose Tissue, Brown↗
PubMed1988

Developmental pattern of dopamine beta-hydroxylase induction in the adrenals of the rat. Influence of neonatal hypothyroidism.

The extent of dopamine beta-hydroxylase induction elicited by reserpine was measured in young rats rendered hypothyroid from birth and in controls. Hypothyroidism impairs adrenal dopamine beta-hydroxylase induction in the young rat up to 50 days of age and also in the adult. In contrast, hypothyroidism has practically no effect on brainstem dopamine beta-hydroxylase induction.

Adrenal Glands↗
PubMed1987

Adrenal dopamine content of the developing rat. Influence of the thyroid status and insulin-hypoglycaemia.

Neonatal hypothyroidism accelerates the postnatal evolution of the adrenal dopamine (DA) content and concentration in the young rat. In 14-day-old control animals, insulin-hypoglycaemia leads to a transient increase in adrenal dopamine content up to 159% above the value in saline-injected animals. This increase is already at its maximum 1 h after insulin administration and lasts 7 h. In the hypothyroid animals, the DA increase evoked by hypoglycaemia is impaired in magnitude (74%) and duration (4 h).

Adrenal Glands↗
PubMed1986

Adrenal medullary responses to insulin-induced hypoglycaemia in the young rat. Influence of thyroid hormones.

The adrenal medulla of normal, hypothyroid and hyperthyroid young rats was stimulated by insulin-induced hypoglycaemia. In normal rats, insulin-induced adrenal epinephrine secretion increases during the first 10 days of post-natal life. Hypothyroidism retards the development of adrenal response; hyperthyroidism facilitates the development of this response. At 14 days, when insulin-induced adrenal epinephrine depletion is the same for all groups, the recovery of adrenal catecholamines stores after depletion is linear and takes less than 48 h. Recovery rate is slightly slower for hyperthyroid rats than for either hypothyroid or control rats at 14 days. Following epinephrine depletion, adrenal tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) activities are increased for a few days in the control rats, corresponding to a transsynaptic induction. Hypothyroidism impairs TH induction and completely suppresses DBH induction; hyperthyroidism impairs TH induction, but has no effect on DBH induction. These data show that the various processes related to CA synthesis, in the adrenal medulla of the developing rat, are controlled in different ways by the thyroid hormones.

Adrenal Medulla↗
PubMed1986

Adrenal phenylethanolamine-N-methyltransferase activity in the young rat: influence of thyroid hormones and insulin-induced hypoglycemia.

The postnatal evolution of adrenal phenylethanolamine-N-methyltransferase (PNMT) activity is slightly accelerated by hypothyroidism and slowed by hyperthyroidism. In 14-day-old rats a single stimulation of the adrenals by insulin-induced hypoglycemia does not lead to any change in enzymatic activity. If the stimulation is repeated for 4 days, it leads to a net increase in adrenal PNMT activity in the control rats, while no increase occurs in hypo- or hyperthyroid animals.

Adrenal Glands↗
PubMed1985

[Influence of neonatal hypothyroidism on the response of the adrenal medulla of young rats to a physiological stimulation].

The adrenal medulla of control and hypothyroid young rats was stimulated through insulin hypoglycaemia. In the control animals, the intensity of the depletion of the adrenal epinephrine, which occurs in response to hypoglycaemia, increases up to 10 days of age. Neonatal hypothyroidism results in a retarded evolution. Following epinephrine depletion, the activities of adrenal tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) are transitorily increased in the 14 day-old controls; these increases are the consequence of transsynaptic inductions. Hypothyroidism decreases TH induction and completely suppresses that of DBH.

Adrenal Medulla↗
PubMed1983

Adrenal epinephrine depletion after insulin-induced hypoglycaemia in young hypothyroid rats.

We studied the influence of the thyroid hormones on the development of the ability of the adrenal glands to release epinephrine after stimulation by insulin-induced hypoglycaemia in the young rat. In animals rendered hypothyroid from birth, this development is delayed as compared to control rats. Administration of thyroxin to these animals restores the ability of the adrenals to deplete epinephrine. These results may indicate an influence of the thyroid hormones on the development of the functional innervation of the adrenal medulla in the young rat.

Adrenal Glands↗
PubMed1983

Evolution of plasma dopamine-beta-hydroxylase in hypo- and hyperthyroid young rats.

The influence of neonatal hyper- and hypothyroidism on plasma dopamine-beta-hydroxylase (DBH) activity was studied in young rats from 5 to 30 days of extrauterine life. In the newborn rat, plasma DBH activity was four times higher than in the adult. In the control animals, the enzymatic activity increased for 15 days after birth and then decreased. In the hyperthyroid rats the first part of this evolution (i.e. the neonatal increase) is accelerated, while in hypothyroidism the following decrease is retarded. The significance of these changes is discussed in relation to the functional development of the sympathetic nervous system.

Animals↗
PubMed1982

Uptake and turnover rate of norepinephrine in interscapular brown adipose tissue of the young rat. Influence of hypothyroidism.

Norepinephrine uptake and turnover rate were measured in the interscapular brown adipose tissue of normal and hypothyroid young rats. At the age of 15 days, hypothyroidism lowers the uptake of norepinephrine. This fact could partially explain why the norepinephrine content of the tissue has previously been found reduced in these animals when compared to controls. In the same animals, the turnover rate of norepinephrine is reduced by 80%. This indicates a decrease of the sympathetic tonus in the tissue.

Adipose Tissue, Brown↗
PubMed1980

Influence of hypo- and hyperthyroidism on noradrenaline metabolism in brown adipose tissue of the developing rat.

We studied the noradrenaline content, and monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) activities in brown adipose tissue (BAT) of normal, hypothyroid, and hyperthyroid developing rat. In the newborn, thyroid hormones are necessary for the increase in noradrenaline content which occurs between 0 and 5 days. Hypothyroidism increases both MAO and COMT activities. Hyperthyroidism decreases MAO activity but not noradrenaline content or COMT activity. In the full-term fetus, hypothyroidism decreases noradrenaline content as in the newborn, and also decreases MAO and COMT activities. It is suggested that thyroid hormones could modulate BAT nonshivering thermogenesis by regulating the level of noradrenaline, the direct mediator of heat production.

Adipose Tissue, Brown↗
PubMed1980

Tyrosine hydroxylase activity and catecholamine content in the adrenals of young hypo- and hyperthyroid rats.

The weight, the tyrosine hydroxylase (TH) activity and the catecholamine (noradrenaline and adrenaline) content of young rat adrenals have been measured from birth to 20 days after birth in relation to hypo- and hyperthyroidism. Hypothyroidism impairs the adrenal growth, while hyperthyroidism has no effect on the adrenal weight. Hypothyroidism is associated with an enhancement of TH activity and catecholamine content. In hyperthyroid rats, the increase in TH activity and catecholamine content is slower than in controls. In adult animals, TH activity and catecholamine content are less affected by thyroid function.

Adrenal Glands↗