Induction Of Adrenal Tyrosine Hydroxylase Research Articles

Nicotinic and muscarinic acetylcholine receptors are essential for the long-term response of tyrosine hydroxylase gene expression to chronic nicotine treatment in rat adrenal medulla

Nicotine induces tyrosine hydroxylase (TH) mRNA by interacting with nicotinic acetylcholine receptors (nAChRs) in cultured adrenal medullary cell systems; however, the mechanisms responsible for the induction of adrenal TH in response to systemically administered nicotine under in vivo conditions are more complex. In the present study, we tested whether nAChRs and muscarinic acetylcholine receptors (mAChRs) participate in the induction of adrenal TH observed after long-term treatment with nicotine. Chronic nicotine treatment (1.6 mg/kg, two daily injections spaced 12 h apart for 7 days) induced TH mRNA, TH protein and TH activity in rat adrenal medulla. This induction of TH gene expression was totally blocked when an antagonist of either nAChRs or mAChRs was administered prior to each nicotine injection. Repeated injections of the mAChR agonist bethanechol (5 mg/kg injected twice per day for 7 days) also produced increases in TH mRNA levels; however, TH protein levels and TH activity did not increase in response to bethanechol. In denervated adrenal glands chronic nicotine treatment did not lead to induction of either TH mRNA, TH protein or TH activity, whereas chronic bethanechol treatment led to induction of TH mRNA, but not TH protein or activity. These results suggest that agonist occupation of both nAChRs and mAChRs are essential for the complete response of TH gene expression to chronic nicotine treatment in rat adrenal medulla, but that stimulation of either cholinergic receptor by itself is not sufficient to elicit a full response. The results also suggest that both transcriptional and post-transcriptional mechanisms may potentially need to be regulated to induce TH protein in response to some stimuli.

Central Regulation of Adrenal Tyrosine Hydroxylase: Effect of Induction on Catecholamine Levels in the Adrenal Medulla and Plasma

The effect of induction of adrenal tyrosine hydroxylase (TH) by various centrally acting drugs on catecholamine levels in adrenal and plasma was investigated in rats. All the drugs tested, namely oxotremorine, Piribedil, B-HT 920, and HA-966, produced significant increases in adrenal dopamine content and plasma epinephrine level. Denervation of the adrenal abolished the increase in adrenal dopamine as it did the induction of tyrosine hydroxylase. The results suggest that the induced increase of adrenal TH activity, as mediated by certain drugs, results in an elevation of the plasma epinephrine level and that the adrenal dopamine content is a better indicator of the catecholamine-synthesizing capacity of the adrenal medulla than are the other catecholamines.

Central regulation of adrenal tyrosine hydroxylase: Interaction between dopamine and GABA systems

It has been previously demonstrated that nigrostriatal dopaminergic fibres participate in the neural regulation of the activity of adrenal tyrosine hydroxylase, specifically in its induction. To determine whether activation or inhibition of these fibres is responsible for this induction, the role of presynaptic dopamine receptors was investigated. Apomorphine (0.2 mg/kg), (+)3-PPP (10 mg/kg) and BHT 920 (1–3 mg/kg), drugs that are reported to bind to presynaptic dopamine receptors and thereby inhibit the release of that neurotransmitter, caused significant increases in the activity of the enzyme. As a central GABA (γ-aminobutyric acid) system is believed to exert inhibitory control over the release of dopamine, GABA agonists were also tested for their effects. Muscimol (3 mg/kg), γ-hydroxybutyrate (500 mg/kg) and HA-966 (150 mg/kg) produced significant induction of the adrenal enzyme; this induction was not blocked by dopamine postsynaptic receptor antagonists. After intraventricular administration (5 μg/rat) in normal animals, HA-966 produced significant induction of tyrosine hydroxylase. Its systemic administration did not induce the enzyme in animals with the adrenal denervated. When administered together at submaximal doses, HA-966 and BHT 920 produced an additive effect in the induction of adrenal tyrosine hydroxylase.

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.

Effect of vasopressin on the induction of adrenal tyrosine hydroxylase and phenylethanolamine N-methyltransferase

We have assessed the effect of arginine vasopressin (AVP) on adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) activities. Both enzymes show marked increases after systemic administration of AVP in the range of 66 and 100 μg/day. To determine whether the pituitary gland plays a role in these inductions, the effect of AVP (66 μg per day, given divided into 3 doses for 4 days) on the adrenal enzymes was studied in hypophysectomized rats. These animals showed induction of TH but not PNMT. This indicates that a pituitary factor(s) mediates the increase in PNMT caused by AVP. Adrenal TH activity was measured after the injection of AVP (1 or 2 μg per rat) into the lateral ventricle: there was a statistically significant increase in TH. TH was not induced in the denervated adrenal gland of rats administered AVP systemically. These findings suggest that AVP may act centrally to induce the enzyme. The continuous s.c. infusion of AVP by osmotic minipump at the rate of 1 μg/day for 6 days led to a striking increase in adrenal TH activity. However, PNMT did not increase significantly. It can be concluded that different mechanisms are involved in the induction of adrenal TH and PNMT caused by AVP. A neural mechanism is involved in TH induction, whereas PNMT induction requires release of a pituitary factor, presumably ACTH, but innervation of the adrenal is not needed for it. Moreover, the inductions of these two enzymes are differentially sensitive to the concentration of circulating AVP.

Functional cerebral activity of an analogue of serotonin formed in situ

Reduction of the serotonin content of the brain of rats (specifically in the medial raphe nucleus) by various means results in spontaneous increase of adrenal tyrosine hydroxylase activity. This neurally mediated induction is attenuated by appropriate administration of the serotonin precursor 5-hydroxytryptophan to the animals, along with carbidopa (Quik and Sourkes, J. Neurochem. 28, 137, 1977). In the present work adrenal tyrosine hydroxylase was induced by giving rats either the neurotoxin 5,7-dihydroxytryptamine (injected into the cerebral ventricles) or the monoamine depletor reserpine (given intraperitoneally). Other rats received alpha-methyltryptophan. This amino acid causes a marked decline of the serotonin content of the brain, but gives rise to relatively large amounts of alpha-methylserotonin in that organ (Roberge et al., Neuropharmacology 11, 197, 1972). Alpha-methyltryptophan had no effect on adrenal tyrosine hydroxylase activity but, when it was given with dihydroxytryptamine or reserpine, it prevented the induction of adrenal tyrosine hydroxylase that otherwise occurred. The results are discussed in relation to the effect of alpha-methyltryptophan on the content of indoles (tryptophan, serotonin, 5-hydroxyindoleacetic acid, alpha-methyltryptophan, alpha-methylserotonin) in the plasma and brain, as detected by HPLC. It is concluded that alpha-methylserotonin can functionally replace cerebral serotonin, at least in relation to the transneuronal regulation of adrenal tyrosine hydroxylase activity.

Effects of α-difluoromethylornithine on polyamine biosynthesis and tyrosine hydroxylase induction in the adrenal gland of the rat subjected to stress or apomorphine

Ornithine decarboxylase (ODC) and tyrosine hydroxylase (TH), the first enzymes in the polyamine and catecholamine biosynthetic pathways, respectively, are induced in the adrenal gland of the rat through the application of stressors or dopamine agonists. In the present work, following exposure of rats to cold, application of bodily restraint, or administration of apomorphine (APM), adrenal putrescine increased in proportion to the induction of ODC. Spermidine content increased by 60% after APM and about 30% after immobilization. Spermine was unaffected. To test whether the increases of ODC (and polyamines) are necessary to the slower and later induction of TH, induction of ODC in vivo was undertaken. α-Difluoromethylornithine (α-DFMO), an irreversible inhibitor of ODC, given orally or subcutaneously, almost completely abolished the induction of ODC by APM or immobilization, and inhibited the increase of putrescine in both cases, but did not affect spermidine after APM. Repeated administration of α-DFMO over several days did not affect the induction of adrenal TH. The results question whether increases of adrenal ODC activity and of putrescine are essential for the induction of TH in that gland.

Hypotension and adrenal tyrosine hydroxylase in spontaneously hypertensive rats

1. 1. Hypotension caused by administration of reserpine evokes a compensatory reflex increase in sympathetic nerve activity leading to an induction of tyrosine hydroxylase (TH). 2. 2. Different antihypertensive drugs produced different effects on TH activity in the adrenal glands of spontaneously hypertensive rats (SHR), at doses which caused an equivalent reduction in systolic blood pressure. 3. 3. Reserpine and phenoxybenzamine caused an increase in TH activity in the adrenal gland whereas guanethidine, bretylium, clondine and intraventricular injection of 6-hydroxydopamine failed to alter adrenal TH activity. 4. 4. There is no correlation between the induction of adrenal TH and a fall in systolic blood pressure. 5. 5. Every blood pressure reduction does not always lead to an increase in preganglionic nerve activity. 6. 6. Clonidine and 6-hydroxydopamine cause lowering of blood pressure by a reduction of sympathetic outflow as evidenced by a decrease in plasma dopamine β-hydroxylase activity.

Trans-synaptic induction of adrenal tyrosine hydroxylase following amphetamine treatment in the rat

Daily injections of d-amphetamine sulfate (5 mg/kg), given in combination with the hepatic microsomal inhibitor iprindole, increased the tyrosine hydroxylase activity in rat adrenals by 41% after 4 days. Choline acetyl-transferase activity also increased significantly. Neither change was observed in animals whose adrenals had been denervated (by transection of the splanchic nerve), thus indicating that the increases were mediated by the central nervous system and by trans-synaptic mechanisms. The chronic administration of methamphetamine increases tyrosine hydroxylase activity in the adrenal glands of the chicken (MANDELL and MORGAN, 1970) and the rat (BUENING and GIBB, 1974). BREESE, COOPER and MUELLER (1974) hove noted similar increases in adrenal tyrosine hydroxylase activity in animals receiving 5 mg/kg of d-amphetamine twice daily for 3 days. The mechanisms by which amphet-amines modify adrenal tyrosine hydroxylase activity could involve direct actions on chromaffin cells (e.g., to release catecholamine molecules, thereby activating feedback mechanisms coupled to the enzyme), or central actions (to activate the flow of impulses along the preganglionic cholinergic nerves innervating the adrenal, thereby increasing enzyme activity via trans-synaptic mechanisms (COSTA, GUIDOTTI and HANBAUER, 1974). To explore the latter possibility, the extent to which treatment with d-amphetamine changes tyrosine hydroxylase activity in adrenals previously subjected to surgical denervation was determined.

Choline potentiates the trans-synaptic induction of adrenal tyrosine hydroxylase by reserpine probably by enhancing the release of acetylcholine

Choline or reserpine causes a trans-synaptic induction of adrenal tyrosine hydroxylase activity. To examine further the relationship between impulse flow, mediated by reserpine, and the effects of choline, we injected rats with both agents concurrently. Their simultaneous administration elevated tyrosine hydroxylase activity to a level higher than the increase caused by either agent alone. These observations suggest that reserpine acts by increasing the rate of impulse flow, while choline acts by increasing the amount of ACh released per impulse.

Catecholamine depletion as a factor in the induction of adrenal tyrosine hydroxylase

1. 1. The activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines, was measured in homogenates of rat adrenal gland following various drugs to determine whether depletion of catecholamines may also be a factor in induction of TH. 2. 2. In contrast to reserpine, treatment of rats with guanethidine for 1 day or 4 days failed to elevate adrenal TH activity, suggesting that hypotension (and the subsequent increase in nerve activity) is not sufficient stimulus for induction of adrenal TH. 3. 3. Reserpine depletes the adrenal catecholamine, whereas guanethidine does not do so. It seems that depletion of catecholamine by reserpine may also be a factor which can lead to an increase in adrenal activity. 4. 4. Support for the suggestion is derived from the observation that interference with reserpine-induced depletion of catecholamine by pargyline, reduced the increase in adrenal TH activity by reserpine. 5. 5. Phentolamine which does not deplete catecholamine failed to cause induction of TH. 6. 6. It is concluded that depletion of catecholamines may also be a factor regulating adrenergic TH activity.

Regulation of adrenal tyrosine hydroxylase activity: Neuronal versus local control studied with apomorphine

Administration of apomorphine to rats leads to a temporary decrease in adrenal catecholamines and a long-term increase in adrenal tyrosine hydroxylase activity. The kinetic characteristics of tyrosine hydroxylase of the apomorphine-treated and control rats were determined. A significant increase in V max was observed in the treated group as compared to controls; however, there was no change in the K m for the cofactor DMPH 4 or tyrosine between the two groups in undialyzed or dialyzed preparations, indicating that the increase in tyrosine hydroxylase activity was probably due to an increase in enzyme protein. The temporary decrease in adrenal catecholamines was found to be due to increased secretion after apomorphine treatment, even though the concentration of injected apomorphine appeared to be sufficient to inhibit adrenal tyrosine hydroxylase. This was further substantiated by the fact that the decrease in adrenal catecholamines was prevented by adrenal denervation. The delayed increase in tyrosine hydroxylase activity after apomorphine treatment was observed in hypophysectomized rats; however, it was abolished after splanchnic nerve transection. A relationship was sought between the decrease in adrenal catecholamines and increase in adrenal tyrosine hydroxylase activity. When apomorphine and L-3,4-dihydroxyphenylalanine ( L-DOPA) were administered simultaneously, there was no short-term decrease in adrenal catecholamine content but the increased tyrosine hydroxylase activity was still observed. Also, the administration of α-methyl- p-tyrosine to rats decreased the concentration of adrenal catecholamines and yet did not affect adrenal tyrosine hydroxylase activity. The results suggest that increased nerve activity, and not adrenal catecholamine concentrations, regulates the induction of adrenal tyrosine hydroxylase. Furthermore, regulation would be by way of some central mechanism involving dopamine-sensitive receptors.

Biosynthesis of Tyrosine Hydroxylase in Rat Adrenal Medulla after Exposure to Cold

Exposure of rats to cold increases the content of tyrosine hydroxylase [EC 1.14.16.2; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating)] in adrenal medulla, causing a long-lasting enhancement of the enzymatic activity. We have used an antibody specific to tyrosine hydroxylase to study the molecular mechanisms involved in the trans-synaptic induction of adrenal tyrosine hydroxylase. The rate of [(3)H]-leucine incorporation into adrenal tyrosine hydroxylase was measured by specific immunoprecipitation at various times after exposure to cold (4 hr). This enhanced rate of incorporation was evident between 11 and 30 hr after the beginning of exposure to cold, but not at 7 and 50 hr. The increase of (3)H incorporation preceded the maximal enhancement of adrenal tyrosine hydroxylase activity, which occurred about 30 hr after stimulation. Neither the activity of tyrosine hydroxylase nor the rate of (3)H incorporation into tyrosine hydroxylase in cervical sympathetic ganglia was changed by 4 hr of exposure to cold. The rate of degradation of tyrosine hydroxylase was estimated at 26 and 50 hr after the beginning of cold stress, as determined by the technique of double-isotope labeling. The data indicate that the tyrosine hydroxylase degradation rate was not reduced by exposure to cold. Thus, the induction of adrenal tyrosine hydroxylase appears to be due to an increased rate of its synthesis.

Potentiation of drug-initiated adrenal tyrosine hydroxylase induction by diazepam.

The increase in in vitro adrenal tyrosine hydroxylase (TH) activity caused by drugs which produce an increase in preganglionic nerve activity as a result of actions outside the central nervous system was increased by the administration of diazepam. However, other central nervous system depressants such as pentobarbital, phenobarbital and diphenylhydantion were not found to share this property. Adrenal enzyme induction provoked by isoproterenol and 6-hydroxydopamine was increased by diazepam administration, whereas that produced by reserpine or insulin was not altered. The enhanced adrenal TH activity produced by diazepam pretreatment and isoproterenol administration could not be attributed to an increase in intensity or to an altered body temperature. Administration of 5-hydroxytryptophan can antagonize the induction of adrenal TH produced by isoproterenol, however, it did not block the TH induction produced by concurrent administration of diazepam and isoproterenol. The effect of diazepam on adrenal TH induction may be the result of its ability to interfere with central nervous system amine containing nerve functions which modulate preganglionic nerve activity, but the particular neurotransmitter system involved has not been determined.

Induction of adrenal tyrosine hydroxylase in organ culture

Tyrosine hydroxylase activity in cultured rat adrenal glands is increased during incubation in vitro in a medium containing a high concentration of potassium. The increase is abolished by inhibiting protein synthesis or by blocking catecholamine release. Depolarization and release of catecholamines caused by high concentrations of potassium results in tyrosine hydroxylase induction.