Comparison of isoproterenol and dibutyryl adenosine cyclic 3',5'-monophosphate stimulation of thyroxine 5'-deiodinase activity in cultured pineal glands from euthyroid and hypothyroid rats

Pineal function: impact of microarray analysis

Microarray analysis has provided a new understanding of pineal function by identifying genes that are highly expressed in this tissue relative to other tissues and also by identifying over 600 genes that are expressed on a 24-h schedule. This effort has highlighted surprising similarity to the retina and has provided reason to explore new avenues of study including intracellular signaling, signal transduction, transcriptional cascades, thyroid/retinoic acid hormone signaling, metal biology, RNA splicing, and the role the pineal gland plays in the immune/inflammation response. The new foundation that microarray analysis has provided will broadly support future research on pineal function.

Night/day changes in pineal expression of >600 genes: central role of adrenergic/cAMP signaling

The pineal gland plays an essential role in vertebrate chronobiology by converting time into a hormonal signal, melatonin, which is always elevated at night. Here we have analyzed the rodent pineal transcriptome using Affymetrix GeneChip(R) technology to obtain a more complete description of pineal cell biology. The effort revealed that 604 genes (1,268 probe sets) with Entrez Gene identifiers are differentially expressed greater than 2-fold between midnight and mid-day (false discovery rate <0.20). Expression is greater at night in approximately 70%. These findings were supported by the results of radiochemical in situ hybridization histology and quantitative real time-PCR studies. We also found that the regulatory mechanism controlling the night/day changes in the expression of most genes involves norepinephrine-cyclic AMP signaling. Comparison of the pineal gene expression profile with that in other tissues identified 334 genes (496 probe sets) that are expressed greater than 8-fold higher in the pineal gland relative to other tissues. Of these genes, 17% are expressed at similar levels in the retina, consistent with a common evolutionary origin of these tissues. Functional categorization of the highly expressed and/or night/day differentially expressed genes identified clusters that are markers of specialized functions, including the immune/inflammation response, melatonin synthesis, photodetection, thyroid hormone signaling, and diverse aspects of cellular signaling and cell biology. These studies produce a paradigm shift in our understanding of the 24-h dynamics of the pineal gland from one focused on melatonin synthesis to one including many cellular processes.

Pretranslational regulation of rhythmic type II iodothyronine deiodinase expression by beta-adrenergic mechanism in the rat pineal gland

It has been demonstrated that type II iodothyronine deiodinase is present in rat pineal gland, and the deiodinase activity markedly increases during the hours of darkness, primarily through beta-adrenergic mechanism. We have studied the relationship between pineal type II iodothyronine deiodinase messenger RNA (mRNA) and the deiodinase activity to elucidate the mechanisms involved in the nocturnal rise in pineal deiodinase activity. Northern analysis has demonstrated that type II iodothyronine deiodinase mRNA is expressed in rat pineal gland, and the mRNA markedly increases during the hours of darkness. The nocturnal increase in pineal type II iodothyronine deiodinase activity is preceded by the increase in its mRNA. Daytime isoproterenol administration resulted in a rapid increase in pineal type II iodothyronine deiodinase mRNA followed by the increase in deiodinase activity. Propranolol treatment, bilateral superior cervical ganglionectomy, or constant light exposure significantly suppressed the nocturnal rise in type II iodothyronine deiodinase mRNA as well as the deiodinase activity. Moreover, isoproterenol or (Bu)2AMP stimulated type II iodothyronine deiodinase mRNA and the deiodinase activity in cultured rat pineal glands. These results suggest that the rhythmic change in pineal type II iodothyronine deiodinase activity is regulated at least in part at the pretranslational level by a beta-adrenergic mechanism transmitted through superior cervical ganglia.

Northern analysis of type II iodothyronine deiodinase mRNA in rat Harderian gland

It has been known that type II iodothyronine deiodinase activity is present in rat Harderian gland and the activity is significantly increased by isoproterenol administration. We have performed Northern analyses to study whether the transcript for type II iodothyronine deiodinase is expressed in rat Harderian gland and whether the isoproterenol stimulation of type II iodothyronine deiodinase activity in rat Harderian gland is due to the change in its mRNA level. Northern analyses have demonstrated that type II iodothyronine deiodinase mRNA, approximately 7.5 kb in size, is expressed in rat Harderian gland, and the mRNA levels as well as the deiodinase activities are greater in hypothyroid rats than those in euthyroid rats. Type II iodothyronine deiodinase mRNA levels and the deiodinase activities in Harderian gland were increased by isoproterenol administration, and the increase in the mRNA levels preceded that in the deiodinase activities. These results indicate that 7.5 kb transcript for type II iodothyronine deiodinase is expressed in rat Harderian gland and beta-adrenergic stimulation of type II iodothyronine deiodinase activity is due at least in part to the increase in its mRNA level.

Expression and nocturnal increase of type II iodothyronine deiodinase mRNA in rat pineal gland

It has been demonstrated that thyroxine deiodinating activity is present in rat pineal gland, and its activity increases significantly during the night time. We have studied whether mRNA for type II iodothyronine deiodinase is expressed in rat pineal gland and whether the nocturnal rise of pineal T4 deiodinating activity is due to the change in type II iodothyronine deiodinase mRNA level. Reverse transcription-polymerase chain reaction amplification and Northern blot analyses have demonstrated that type II iodothyronine deiodinase mRNA is expressed in rat pineal gland and its mRNA level increases markedly at midnight. These results suggest that the nocturnal rise in pineal T4 deiodinating activity is due to the change in type II iodothyronine deiodinase mRNA level.

2D-PAGE analysis: adrenergically regulated pineal protein AIP 37/6 is a phosphorylated isoform of cytosolic malate dehydrogenase

The adrenergic transmitter norepinephrine (NE) dramatically increases the prominence of only two out of the hundreds of [35S]methionine-labeled pineal proteins resolved by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). One of these regulated proteins is AIP 37/6 (37 kDa, pI approximately 6). The labeling of this protein is increased approximately 100-fold by NE. In the study presented here the identity of AIP 37/6 was investigated. The results of microsequencing, immunochemical analysis of 2D-PAGE blots and size exclusion chromatography indicate that AIP 37/6 is an isoform of cytosolic malate dehydrogenase (cMDH; approximately 36.3 kDa; pI approximately 6.5). Associated studies indicate that this isoform is phosphorylated whereas the bulk of cMDH is not. Cotranslational phosphorylation of cMDH is discussed.

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.

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.

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.

Adenosine effects on the rat pineal gland in vitro: cyclic adenosine monophosphate levels, N-acetyltransferase, and thyroxine type II 5'-deiodinase activities and melatonin production

The presence of adenosine and its receptors in the pineal gland suggests that they could have a regulatory influence on pineal physiology. Rat pineal glands cultured in the presence of the adenosine analog 5'-N-ethylcarboxamido adenosine (NECA) promoted a significant increase in pineal adenosine 3'5'-monophosphate (cAMP) content, similar to that caused by the beta-adrenergic receptor agonist isoproterenol (ISO). A potentiation of the cAMP response occurred when the glands were simultaneously stimulated with both NECA and ISO. Whereas high cAMP levels induced by ISO were associated with an increased N-acetyltransferase (NAT) activity and rise in the melatonin production and release, the NECA-induced rise in cAMP concentration failed to promote an increase in the activity of either NAT or another pineal enzyme thyroxine 5'-deiodinase type II; likewise, pineal melatonin levels did not rise.

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.

Type II thyroxine 5'-deiodinase activity in the rat brown adipose tissue, pineal gland, Harderian gland, and cerebral cortex: effect of acute cold exposure and lack of relationship to pineal melatonin synthesis

The effect of acute cold exposure for 6 hours on nocturnal type II thyroxine 5'-deiodinase (5'-D) activity was studied in brown adipose tissue (BAT), Harderian gland, cerebral cortex, and pineal gland of the rat. Moreover, the effect of iopanoic acid (IOP), a potent inhibitor of 5'-D activity, on both pineal N-acetyltransferase (NAT) activity and melatonin content in rats maintained in a cold environment was also examined. Results show that acute cold exposure significantly increases 5'-D activity in BAT but not in either the pineal gland, Harderian gland, or cerebral cortex. In all tissues, the injection of IOP reduced dramatically 5'-D activity, while exposure of the animals to light at night reduced 5'-D activity in pineal gland but not in either the Harderian gland or BAT while light exposure at night increased cerebrocortical 5'-D activity. Cold exposure did not change either pineal NAT activity or the melatonin content of the gland. Finally, when pineal 5'-D activity was inhibited by IOP treatment, neither nocturnal pineal NAT activity nor melatonin content was affected.