Do cyclic nucleotides promote the trans-synaptic induction of tyrosine hydroxylase?

A novel mechanism prevents the development of hypertension during chronic cold stress

1 Chronic cold exposure of rats (7 days in a cold room at 4 degrees C) attenuated the sympathetic nerve stimulation (NS)-induced overflow of noradrenaline (NE) (measured by high-performance liquid chromatography, coupled to electrochemical detection) appearing in the perfusate/superfusate of the perfused mesenteric arterial bed as well as the increase in the perfusion pressure. 2 The same type of cold exposure resulted in an increase in tyrosine hydroxylase (TH) gene expression measured in the superior cervical ganglion and NE content measured in the mesenteric artery obtained from cold-exposed rats. 3 Addition of sodium nitroprusside, a nitric oxide (NO) donor, to the buffer perfusing the mesenteric arterial bed obtained from rats maintained at room temperature also resulted in an attenuation of the NS-induced overflow of NE and increase in perfusion pressure. 4 N(c)-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, placed in the drinking water prevented the attenuation of the pre- and post-junctional responses to NS of the mesenteric arterial bed obtained from cold-exposed rats. 5 L-NAME treatment also increased the cold-induced elevation of blood pressure seen in whole animals. 6 The present results are consistent with the idea that cold exposure leads to a concomitant increase in sympathetic nerve activity and production of NO. We hypothesize that the increase in production and release of NO results in a decrease in the biologically active form of NE despite increased synthesis and release of the catecholamine. 7 It is concluded that the above-mentioned interactions serve as a protective mechanism offsetting the increased release and action of NE from sympathetic nerves and thus preventing the development of hypertension.

Vasoactive intestinal peptide induces both tyrosine hydroxylase activity and tetrahydrobiopterin biosynthesis in PC12 cells

Vasoactive intestinal peptide plays an important role in the trans-synaptic activation of tyrosine hydroxylase in sympathoadrenal tissues in response to physiological stress. Since tyrosine hydroxylase is thought to be subsaturated with its cofactor, tetrahydrobiopterin, we tested the hypothesis that up-regulation of tyrosine hydroxylase gene expression following vasoactive intestinal peptide treatment is accompanied by a concomitant elevation of intracellular tetrahydrobiopterin biosynthesis. We also investigated the second messenger systems involved in vasoactive intestinal peptide's effects on tetrahydrobiopterin metabolism. Our results demonstrate that treatment of PC12 cells for 24 h with vasoactive intestinal peptide induced intracellular tetrahydrobiopterin levels 3.5-fold. This increase was due to increased expression of the gene encoding GTP cyclohydrolase, the initial and rate-limiting enzyme in tetrahydrobiopterin biosynthesis, which was blocked by the transcriptional inhibitor, actinomycin D. Activation of tyrosine hydroxylase and GTP cyclohydrolase by vasoactive intestinal peptide was mediated by cyclic-AMP. Furthermore, stimulation of cyclic-AMP-mediated responses or protein kinase C activity induced the maximal in vitro activities of both tyrosine hydroxylase and GTP cyclohydrolase; the responses were additive when both treatments were combined. Induction of sphingolipid metabolism had no effect on the activation of tyrosine hydroxylase, while it induced GTP cyclohydrolase in a protein kinase C-independent manner. Our results support the hypothesis that intracellular tetrahydrobiopterin levels are tightly linked to tyrosine hydroxylation and that tetrahydrobiopterin bioavailability modulates catecholamine synthesis.

A dual role for the cAMP-dependent protein kinase in tyrosine hydroxylase gene expression

Tyrosine hydroxylase (TH) catalyzes the conversion of L-tyrosine to 3,4-dihydroxy-L-phenylalanine, the first and rate-limiting step in catecholamine biosynthesis. The cAMP-dependent protein kinase (PKA) phosphorylates and activates the TH enzyme and is thought to mediate transcriptional induction of the TH gene. To better understand the functional role of PKA in TH gene regulation, we studied TH gene expression at the transcriptional, translational, and post-translational levels in several PKA-deficient cell lines derived from rat PC12 pheochromocytoma cells. Strikingly, all PKA-deficient cell lines analyzed in this study showed substantial deficits in basal TH expression as measured by TH enzymatic activity, level of TH immunoreactivity, TH protein level, and steady-state mRNA level. Interestingly, the steady-state level of mRNA correlated well with levels of TH activity, immunoreactivity, and protein. In addition, PKA-deficient cell lines lacked transcriptional induction of the TH gene following treatment with dibutyryl cAMP. Cotransfection of PKA-deficient cells with an expression plasmid for the catalytic subunit of PKA fully reversed transcriptional defect, as indicated by robust transcriptional induction of a reporter construct containing 2400 bp of TH upstream sequence in all PC12 cells tested. These data indicate that the PKA system regulates both the basal and the cAMP-inducible expression of the TH gene primarily at the transcriptional level in PC12 cells.

Pituitary adenylate cyclase activating polypeptide provokes cultured rat chromaffin cells to secrete adrenaline

Pituitary adenylate cyclase activating polypeptide (PACAP) provoked the rat chromaffin cells to secrete adrenaline. Within 20 min, the amount of adrenaline secreted by PACAP (10(-8) M) was as much as that caused by acetylcholine (10(-4) M). PACAP, but not acetylcholine, induced a long-term (over 120 min) increase in secretion of adrenaline. PACAP also activated adenylate cyclase and elevated cytosolic Ca2+ concentration. Furthermore, we found immunoreactive PACAP and PACAP binding sites in the rat adrenal medulla. These results suggest that PACAP has an important role in stimulating secretion of adrenaline in the adrenal medulla.

Preganglionic nerve stimulation increases mRNA levels for tyrosine hydroxylase in the rat superior cervical ganglion

Increased synaptic stimulation of sympathetic neurons in vivo causes a delayed increase in the activity and the amount of tyrosine hydroxylase (TH). To determine whether these changes result from an increase in the messenger RNA for TH, the rat preganglionic cervical sympathetic trunk was electrically stimulated unilaterally for 90 min, and 48 h later RNA was extracted from stimulated and contralateral control superior cervical ganglia. Northern blots probed with a cDNA for TH demonstrated that nerve stimulation produced about a 2.5-fold increase in the amount of TH mRNA in the ganglion. These results indicate that synaptic stimulation leads to an increase in TH mRNA, either by increasing the rate of transcription of the TH gene or by increasing the stability of its mRNA.

Adenylate cyclase activity of adrenal chromaffin vesicles

Biochemical studies have provided conflicting interpretation as to the presence of adenylate cyclase in or on the chromaffin vesicle of the adrenal medulla. Various histochemical procedures were employed and a slight amount of reaction product was detected. It is suggested that a small amount of adenylate cyclase is associated with the chromaffin vesicle.

The alpha-bungarotoxin site and its relation to the cholinergic and nerve growth factor mediated increases in tyrosine hydroxylase activity in cultures of sympathetic ganglia and chromaffin cells

alpha-Bungarotoxin has been proposed to interact with a membrane site in neuronal tissue which has the characteristics of a nicotinic acetylcholine receptor and also a trophic receptor. A nerve cell function which is affected by both nicotinic stimulation and nerve growth factor is the induction of tyrosine hydroxylase. For this reason, alpha-bungarotoxin was tested on the carbachol-induced increase and nerve growth factor-mediated increase in tyrosine hydroxylase activity in two preparations of neuronal origin, organ cultures of rat superior cervical ganglia and cultured bovine adrenal medullary cells. The results demonstrate that the alpha-bungarotoxin site is not involved in tyrosine hydroxylase induction.

Alterations in norepinephrine, serotonin, c-AMP, and transsynaptic induction of tyrosine hydroxylase after spinal cord transection in the rat

Tyrosine hydroxylase (TH) activity and the concentrations of norepinephrine (NE), serotonin (5-HT), and cyclic adenosine 3',5'-monophosphate (c-AMP) were measured in the heart, adrenals, and brain stem of paraplegic rats. Following spinal cord transection NE concentration in the heart dropped to 30% within 24 hours and that of 5-HT decreased to 60% of control. Tyrosine hydroxylase activity in the adrenals reached a peak at five days and was still twice that of sham-operated controls thirty days later. Five days following transection the TH activity and c-AMP levels in the brain stem were elevated while NE concentration remained low. At seven days, however, NE and 5-HT levels were higher than in controls while TH activity and c-AMP concentration dropped to control levels. The increase in TH activity in the brain stem may be due to curtailed end-product feedback inhibition and to reduced receptor activation. The sustained induction of the adrenal TH is probably a consequence of a continual stimulation of splanchnic nerves.

Effects of synaptic and antidromic stimulation on tyrosine hydroxylase activity in the rat superior cervical ganglion

1. The effects of orthodromic and antidromic stimulation of the rat superior cervical ganglion on the specific activity of the enzyme tyrosine hydroxylase have been studied. 2. Orthodromic stimulation of the ganglion via the sympathetic trunk produced an increase in the activity of tyrosine hydroxylase when measured 3 days later while causing no change in the protein content of the ganglion. This increase in the specific activity of tyrosine hydroxylase was blocked by administration of the nicotinic antagonist, hexamethonium. 3. Antidromic stimulation of the superior cervical ganglion by stimulating the internal carotid nerve, the external carotid nerve or both nerves simultaneously produced no change in the specific activity of tyrosine hydroxylase. 4. Parallel increases in tyrosine hydroxylase activity and protein content per ganglion were seen when the internal carotid nerve was stimulated but similar changes were seen in "sham-stimulated" animals. These "non-specific" changes were apparently produced by the trauma involved in the extensive dissection necessary to position electrodes on this nerve trunk. 5. We conclude that an increase frequency of firing in post-ganglionic neurones is not a sufficient stimulus to elevate the specific activity of tyrosine hydroxylase. Rather some other aspect of nicotinic receptor stimulation seems to be required.

Decrease in muscarinic cholinergic response of the rat heart following treatment with 6-hydroxydopa

Pretreatment with 6-hydroxydopa (6-OHDOPA) at birth produced a decrease in the number of [3H]quinuclidinyl benzilate ([3H]QNB) binding sites in adult rat heart homogenates. The treatment caused hyposensitivity to acetylcholine (ACh) but did not alter the maximal negative inotropic action of ACh in isolated atria of the rat. These results suggest that 6-OHDOPA affects the negative inotropic response to ACh by modifying the receptor number or through an effect on a step between receptor activation and biological response.

Regulation of rat adrenal dopamine beta-hydroxylase. II. Receptor interaction in the regulation of enzyme synthesis and degradation

Rat adrenal gland dopamine beta-hydroxylase is under neuronal regulation from the splanchnic nerve and hormonal control via adrenal cortical glucocorticoids. The regulatory systems act in different ways; neuronal stimuli induce dopamine beta-hydroxylase synthesis while hormonal stimulation inhibits enzyme degradation. Despite these mechanistic differences, both systems require a normally innervated cholinergic receptor to exert their effect. The enzyme response to either neural stimulation or ACTH administration is blocked by splanchnic denervation. Glucocorticoid stimulation of dopamine beta-hydroxylase, however, can occur after adrenal denervation, suggesting that ACTH acts on a receptor which requires splanchnic innervation, but glucocorticoids act distal to the receptor. Similar results were obtained when the effect of these manipulations were studied on phenylethanolamine N-methyltransferase, another enzyme in the catecholamine biosynthetic pathway. A model attempting to unify these and earlier findings is presented, in which the splanchnic nerve is involved in regulating both adrenal cortical glucocorticoidogenesis (by allowing ACTH to act on glucocorticoid synthesis) and adrenal medullary catecholamine biosynthesis (by induction of enzyme synthesis.).

Possible role for cyclic nucleotides and phosphorylated membrane proteins in postsynaptic actions of neurotransmitters

The postsynaptic actions of some neurotransmitters may be mediated through cyclic nucleotides and cyclic nucleotide-dependent phosphorylation of specific membrane proteins in postsynaptic cells. In addition to providing a molecular basis for the actions of several neurotransmitters and of certain drugs affecting behaviour, the model suggests a mechanism by which neurotransmitter signals may be converted into electrophysiological responses in postsynaptic cells.

Ornithine decarboxylase activity: control by cyclic nucleotides

Both exposure to cold and administration of aminophylline result in rapid increases in cyclic adenosine monophosphate (cyclic AMP) in the adrenal medulla and adrenal cortex. These increases are followed by dramatic increases in ornithine decarboxylase activity is due to new enzyme systhesis. The data suggest that the decarboxylase activity is regulated by an increase in cyclic AMP.

Neuronal control of neurotransmitters biosynthesis during development

Studies on neuronal control mechanisms of neurotransmitters biosynthesis during the development of peripheral and central autonomic synapses are reviewed. Particular emphasis is placed on investigations of developing peripheral sympathetic ganglia and brain in chick embryo and chick. Studies on the development of autonomic neurons and synapses under different pharmacological conditions are reported. Principally the effect of a) the administration of drugs and precursors such as L-dopa, 3H-dopa, 6-OH dopa; b) the prenatal administration of reserpine; c) the blockade of cholinergic receptors; d) the nerve growth factor (NGF) is analyzed. Results of developmental studies on chick ciliary ganglia are summarized. The review particulary underlines the importance of combining the use of sensitive microchemical methods to pharmacological tools in exploring the development of regulatory mechanisms at the cellular level.

Further evidence for a cAMP dependent regulation of tyrosine-3-monoxygenase induction in adrenal medulla: effect of denervation

Unilateral adrenal denervation caused a gradual decrease of adenylate cyclase activity in rat adrenal medulla. The extent of the increase in adrenal medullary 3',5'-cyclic adenosine monophosphate (cAMP) content elicited by injections of carbamylcholine declined gradually folling adrenal denervation. Three or nine days after denervation carbamylcholine caused rise of cAMP and a delayed increase of tyrosine-3-mono-oxygenase (TH) activity of similar magnitude in intact and denervated adrenal medullae. However, after an interval of 15 days or longer following denervation the increase in TH activity elicited by carbamylcholine was greatly reduced. These results support previous proposals that cAMP is involved as a second messenger in the trans-synaptic induction of TH.

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.