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Biomedical subjects

A Rubio

Publications and source records attributed to A Rubio.

At least 145 records · Page 8Linked to original sources
PubMed1993

Thyroxine type II 5'-deiodinase activity in pineal and Harderian gland is enhanced by hypothyroidism but is independent of serum thyroxine concentrations during hyperthyroidism.

1. This paper studies the effect of thyroid status on 5'-D activity in pineal gland, Harderian gland, brown adipose tissue (BAT), pituitary gland, brain frontal cortex (BFC), and cerebellum. 2. Hypothyroidism clearly increased diurnal 5'-D activity in Harderian gland, BAT, pituitary gland, BFC, and cerebellum. In pineal gland, diurnal values of 5'-D activity were not affected by hypothyroidism. 3. Hypothyroidism in adult rats clearly enhanced nocturnal increase of 5'-D activity in pineal and Harderian gland. Congenital hypothyroidism also enhanced the nocturnal increase of 5'-D activity in pineal gland. 4. Hyperthyroidism inhibited 5'-D activity in pituitary gland, BFC, and cerebellum. A small inhibition, although significant, was found in BAT. 5. In pineal and Harderian gland, hyperthyroidism did not inhibit either the basal diurnal values of the enzyme or the nocturnal increase of its activity. 6. Results suggest that, in tissues where 5'D-activity is regulated by adrenergic mechanisms, mostly pineal gland and Harderian gland, the enzyme activity is independent of serum T4 concentrations during hyperthyroidism.

Adipose Tissue, Brown↗
PubMed1993

Adrenalectomy or superior cervical ganglionectomy modifies the nocturnal increase in rat pineal type II thyroxine 5'-deiodinase.

We studied the response of type II thyroxine 5'-deiodinase (5'-D) activity to superior cervical ganglionectomy (SCGX) or adrenalectomy (ADX) in the rat pineal gland and other tissues. The results show that no difference was found between controls and SCGX animals during the day, but at night, SCGX modified the day-night cycle of 5'-D activity in the pineal gland. In the same way, ADX did not modify the enzyme activity during the day in pineal gland, harderian gland, hypophysis, or brain frontal cortex (BFC). However, in brown adipose tissue (BAT), where thyroid hormone metabolism is extremely dependent on alpha 1-adrenergic stimulation by blood circulating catecholamines, 5'-D activity is significantly decreased. At the time point of maximal pineal 5'-D activity in controls (02:00 h), ADX animals did not exhibit the nocturnal increase of the enzyme activity that occurs with control rats. Moreover, at 04:00 h ADX did not show any effect on pineal 5'-D activity. These results seem to suggest that the presence of catecholamines in blood is necessary for the pineal 5'-D activity nocturnal increase, although it does not participate in regulating the basal enzyme activity during the day.

Adipose Tissue, Brown↗
PubMed1993

Thyroxine 5'-deiodinase type II activity in chick pineal and Harderian gland: nyctohemeral rhythmicity and its regulation by noradrenergic input.

Circadian rhythmicity of type II thyroxine 5'-deiodinase (5'-D) activity was studied in the pineal gland and Harderian glands of chicks. Only Harderian 5'-D activity showed a nyctohemeral rhythmicity with a maximal peak during the day time (1300), while no rhythm of enzyme activity was found in the pineal gland. Besides type II 5'-D activity, we found high basal levels of the type I isoenzyme in both glands; this activity was specifically suppressed by the addition of 6-n-propyl-thiouracil (PTU). However, day-night differences in Harderian 5'-D activity were maintained even after the addition of PTU. This activity was not affected for either continuous light exposure or darkness during the day. 5'-D activity seems to be regulated by the noradrenergic input, since the enzymatic activity was stimulated by a beta-adrenergic agonist, isoproterenol, and by the alpha-adrenergic agonist, phenylephrine, in both pineal and Harderian glands. Both drugs affected 5'-D activity in the Harderian gland by stimulating the enzyme activity over basal levels.

Animals↗
PubMed1993

Involvement of alpha- and beta-adrenergic receptors in the regulation of rat pineal N-acetyltransferase activity during development.

The regulation by alpha- and beta-adrenergic receptor agonists of rat pineal N-acetyltransferase (NAT) activity during development was studied. We found that isoproterenol, a beta-adrenergic agonist, exhibited a weak stimulatory effect on pineal NAT activity during the first 3 weeks of age. Indeed, the drug did not mimic the effect of darkness on pineal NAT activity until the fourth week of age. The results might be explained by the existence of other mechanisms, in addition to those that involve beta-adrenergic receptors, which regulate pineal NAT activity during early postnatal development. In line with this, we determined that phenylephrine, an alpha 1-adrenergic agonist, stimulated NAT activity during both the day and at night in 2-week-old rats, while exhibiting no effect in adult rats. Methoxamine, an alpha 1-adrenergic agonist more selective than phenylephrine, also activated NAT activity in young, but not in adult, rats. Moreover, prazosin, a selective alpha 1-adrenergic receptor blocker, prevented pineal NAT activation by norepinephrine or darkness at night in 2-week-old rats, but not in adult animals. The results suggest that alpha 1-adrenergic receptors may be more important than beta-adrenergic receptors in regulating rat pineal NAT activity during development.

Animals↗
PubMed1992

Melatonin potentiates cyclic AMP production stimulated by vasoactive intestinal peptide in human lymphocytes.

The present paper demonstrates the effect of melatonin on cyclic AMP production in human lymphocytes from peripheral blood. Melatonin by itself did not influence cyclic AMP accumulation in these cells at any dose studied; however, the drug potentiated the effect of vasoactive intestinal peptide (VIP) on the cyclic nucleotide production. In the presence of physiological concentrations of VIP (either 1, 10 or 100 pM), melatonin potentiated cyclic AMP production. However, at high doses of VIP (either 1, 10 or 100 nM), melatonin exhibited no such effect. The results suggest that human lymphocytes are a target for melatonin and that it may participate, jointly with VIP, in the regulation of immune function.

Cyclic AMP↗
PubMed1992

Synergistic action of melatonin and vasoactive intestinal peptide in stimulating cyclic AMP production in human lymphocytes.

In the present study we investigated the synergistic effect of melatonin and vasoactive intestinal peptide (VIP) on cyclic AMP production in human blood lymphocytes. As shown by our group previously, VIP alone behaved as a potent activator of cyclic AMP production in human lymphocytes. On the other hand, melatonin alone did not affect the intracellular levels of cyclic nucleotide at any time or dose studied. However, when cells were incubated with melatonin plus VIP, melatonin potentiated the effect of the peptide. This effect can be observed in the presence of physiological doses of both melatonin (10-100 pM) and VIP (1-100 pM). The effect is specific for VIP because with other peptides belonging to the secretin-VIP family the effect was not observed. Results suggest that melatonin, in conjunction with VIP, may directly participate in the regulation of immune function in the human.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Adrenergic regulation of type II 5'-deiodinase circadian rhythm in rat harderian gland.

This paper reports on the regulation of the nyctohemeral profile of type II thyroxine 5'-deiodinase (T45'D) activity in the rat harderian gland. Harderian gland T45'D activity exhibits a nighttime increase with maximal values late in the dark period (0200-0400 h) and basal values during the daytime. The nocturnal rise of the deiodinating activity was prevented by either exposure of animals to light at night, injecting the animals with both alpha- and beta-adrenergic receptor blockers, or bilateral superior cervical ganglionectomy (SCGx). However, adrenalectomy did not affet the enzyme activity in the harderian gland. In brown adipose tissue (BAT), where thyroid hormone metabolism is extremely dependent on alpha 1-adrenergic stimulation by blood-circulating catecholamines, adrenalectomy significantly decreased T45'D activity. Deiodinating activities in brain frontal cortex (BFC) and pituitary gland were unaffected by adrenalectomy. Unlike in the harderian gland, SCGx did not modify the T45'D activity in either BAT, BFC, or the pituitary gland. The results suggest that elevated plasma catecholamines are not required for harderian gland T45'D activation and that the nyctohemeral profile of the enzyme activity in the harderian gland is dependent on the noradrenergic input from the superior cervical ganglia.

Adrenalectomy↗
PubMed1992

Prediction of diltiazem plasma concentration curves from limited measurements using compliance data.

This analysis illustrates the importance of compliance in understanding intrapatient variation in plasma drug concentrations during 2 weeks of repeated (4 times daily) administration. Plasma concentration data are presented from 4 illustrative patients enrolled in a dose-ranging randomised clinical trial comparing diltiazem with placebo for the prevention of painful vaso-occlusive crises in sickle cell disease. Nonlinear regression was used to fit a 1-compartment model (using 1 elimination constant for the first dose and another for subsequent doses) to the observed diltiazem concentration curves for individual patients, taking into account the time of administration of each dose. Actual dosage intervals were obtained from an electronic device (the Medication Event Monitoring System). The parameters estimated from fitting the actual compliance curves were then used to predict the curves obtained if compliance had been as prescribed (perfect compliance curves). Comparison of the actual and perfect compliance curves shows that within-patient variation in plasma diltiazem concentrations over time can only be understood when the timing of drug administration is included in the analysis. We conclude that dynamic compliance data are important in those situations where close monitoring of treatment is required and may be important in population pharmacokinetic modelling when limited data are available from each patient.

Anemia, Sickle Cell↗
PubMed1991

Stimulation of adenosine A2 receptors induces catalepsy.

The central administration of the adenosine A2 agonist CGS 21680 induced catalepsy in the rat. This effect was counteracted by the previous systemic administration of the adenosine antagonist theophylline or the D2 agonist BHT-920. These results are in agreement with the view that adenosine A2 receptors regulate central dopamine D2 transmission and underline the potential antipsychotic activity of A2 agonists.

Adenosine↗
PubMed1991

In vivo activation of pineal N-acetyltransferase but not type II thyroxine 5'-deiodinase by phenylephrine in young rats.

The regulation by alpha- and beta-adrenergic agonists of pineal N-acetyltransferase (NAT) and type II thyroxine 5'-deiodinase (5'-D) in rats at either 2 or 6 weeks of age was studied. The pattern of stimulation was different because NAT activity could be clearly activated by an alpha-adrenergic agonist, phenylephrine, only in 2-week-old rats. However, isoproterenol, a beta-adrenergic agonist, was able to stimulate NAT activity in rats at both 2 and 6 weeks of life. On the other hand, phenylephrine was always ineffective in stimulating 5'-D activity, while isoproterenol clearly activated it at both ages. These results strongly suggest a role for alpha-adrenergic receptors, in addition to beta-adrenergic receptors, in regulating rat pineal NAT activity during development.

Adrenergic alpha-Agonists↗
PubMed1991

Nyctohemeral rhythmicity of type II thyroxine 5'-deiodinase activity in the pineal gland but not in the Harderian gland of the Swiss mouse.

Type II thyroxine 5'-deiodinase (5'-D) activity in both pineal and Harderian glands of the Swiss mouse was studied. Pineal 5'-D activity exhibited a nyctohemeral profile with a maximal peak value at 05.00 h, which coincides with that for pineal melatonin production. However, no rhythm of 5'-D activity in the Harderian gland could be found. In pineal gland, light at night inhibited the nocturnal increase in 5'-D activity, while isoproterenol, a beta-adrenergic agonist, could not stimulate the enzyme. In the Harderian gland, neither darkness, nor light or night, or isoproterenol were capable of modifying basal values of 5'-D activity.

Animals↗
PubMed1991

Beta- and alpha-adrenergic receptors are involved in regulating type II thyroxine 5'-deiodinase activity in the rat Harderian gland.

The role of alpha- and beta-adrenergic receptors in regulation of rat Harderian gland type II thyroxine 5'-deiodinase (5'-D) activity was investigated. Our results show that isoproterenol, a beta-adrenergic agonist, and phenylephrine, an alpha-adrenergic agonist, elicited increases in Harderian gland 5'-D activity. The activation was dependent on the time and the dose of the drug. Other adrenergic agonists, i.e., norepinephrine, methoxamine or terbutaline, also clearly increased the enzyme activity. Moreover, administration of propranolol, a beta-adrenergic blocker, or prazosin, an alpha-adrenergic blocker, completely prevented the activation of the enzyme induced by norepinephrine. Results show a clear regulation by adrenergic mechanisms of 5'-D activity in the rat Harderian gland, where alpha- and beta-adrenergic receptors appear to be involved.

Animals↗