Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.16.2 (tyrosine hydroxylase)
 14,760 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Catecholamines have previously been detected in numerous tissues and are thought to control a wide variety of physiological functions in bivalve molluscs. In the present study, alumina extraction and high-performance liquid chromatography reveal the presence of significant concentrations of 3,4-dihydroxyphenylalanine (DOPA), dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) in the hemolymph of the sea scallop, Placopecten magellanicus. The concentration of dopamine in the hemolymph averaged 223.8 ng/ml, (+/-48.4, SEM), equivalent to 10(-7) to 10(-6) M. Neither epinephrine nor norepinephrine was reliably detected in significant quantities. Previous studies have demonstrated physiological responses to dopamine with thresholds of 10(-9) to 10(-6) M, thus suggesting that this catecholamine may have an endocrine function. Furthermore, monitoring hemolymph concentrations of catechols might provide a sensitive measure of the physiological status of bivalves. For example, drugs known to affect catechol concentrations in other tissues also effect hemolymph levels. Administration of monoamine oxidase inhibitors such as pargyline, deprenyl, and clorgyline at 10(-4) M for 1 day of incubation followed by a 2-day wash resulted in decreased hemolymph concentrations of DOPAC and increased concentrations of its precursors, DOPA and dopamine. Incubation in 10(-4) M 3,5-dinitrocatechol, a catecholamine-O-methyl transferase blocker, for 1 day followed by a 2-day wash significantly increased the concentration of dopamine and DOPAC in the hemolymph. Scallops incubated in 10(-5) M alpha-methyl-p-tyrosine, a blocker of tyrosine hydroxylase, for 1 day followed by a 3-day wash in artificial seawater had significantly reduced concentrations of DOPA, dopamine, and DOPAC in the hemolymph. In addition to responding to pharmacological agents, dopamine levels also decreased significantly following thermal induction of spawning, thus suggesting that hemolymph concentrations of catechols might provide indices of reproductive activity and/or stress.
Gen Comp Endocrinol 2000 Apr
PMID:Catechol concentrations in the hemolymph of the scallop, Placopecten magellanicus. 1075 66

The effects of five neuropeptides (CGRP, SOM, SP, NPY, VIP), L-NAME (nitric oxide synthase inhibitor), and adrenaline on the contractile tone of the aortic anastomosis in the estuarine crocodile, Crocodylus porosus, were investigated. None of the neuropeptides, which had previously been found to be present in the aortic anastomosis, had any direct effect on the tension developed by ring preparations. L-NAME itself significantly increased the basal tone of the vascular ring preparations, suggesting a tonic release of nitric oxide in the preparation. Adrenaline produced concentration-dependent vasoconstrictions that were counteracted by profound reflex vasodilatations that were susceptible to blockade by L-NAME. Immunohistochemistry revealed the presence of nitric oxide synthase and tyrosine hydroxylase-containing (indicating the presence of a adrenergic innervation) nerve fibres in the adventitia and adventitio-medial border of the aortic anastomosis. These data demonstrate opposing actions of adrenaline and nitric oxide on the vascular smooth muscle in the anastomosis of the C. porosus. The morphology of the anastomosis, with the extremely thick muscular vessel wall, suggests a sphincter-like function for this vessel that could be controlled mainly by adrenergic and nitrergic mechanisms.
Gen Comp Endocrinol 2001 May
PMID:Nitric oxide, a potent vasodilator of the aortic anastomosis in the estuarine crocodile, Crocodylus porosus. 1131 25

The aim of this investigation was to assess whether in teleosts, as in mammals, nitric oxide (NO) is involved in the regulation of cellular activity in the adrenal homolog. Larval and juvenile stages of the rainbow trout, Oncorhynchus mykiss, were used, in which the adrenal homolog consists of chromaffin adrenergic and interrenal steroidogenic cells localized mainly in the head kidney where there are also ganglion cells and nerve fibres that innervate the gland. In 12-month-old juveniles, the immunohistochemical reaction for neuronal nitric oxide synthase (nNOS), which catalyzes the synthesis of NO, revealed the presence of this enzyme in some nerve fibres and ganglion cells and only rarely in chromaffin cells. The latter are identified by the immunohistochemical reaction for tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT). In larvae at 27 days postfertilization, numerous cells dispersed in the head kidney are nNOS positive, whereas the TH and PNMT positive cells are very rare. At hatching (31 days postfertilization), the positivity for nNOS in the cells of the head kidney disappears and reappears at 60 days posthatching in some nerve cells and fibres. These results suggest an involvement of NO in the regulation of adrenal function as in mammals and the nature of nNOS positive cells present in the head kidney of larvae of 27 days is discussed.
Gen Comp Endocrinol 2001 Oct
PMID:Immunohistochemical localization of nNOS in the head kidney of larval and juvenile rainbow trout, Oncorhynchus mykiss. 1170 68

Dynamics of tyrosine hydroxylase (TH) was studied in various brain regions and pituitary in relation to annual/seasonal and circadian variations in either sex of the catfish Heteropneustes fossilis. alpha-Methylparatyrosine inhibited TH activity significantly in a time-(in vivo study) and concentration-(in vitro study) dependent manner. The inhibition was higher in resting phase than preparatory phase and in females than males (time-course study). The apparent kinetic constant of inhibition (K(i)) varied both seasonally and regionally. The values were higher in resting phase and in the forebrain regions (telencephalon and hypothalamus) than medulla oblongata. No significant sex difference was noticed in the K(i) values in the same season. TH activity showed significant annual/seasonal variations with telencephalon and hypothalamus showing higher activity than medulla oblongata. The females showed significantly higher enzyme activity than males with a distinct activity peak in June (prespawning phase). Such an activity peak was apparently absent in males. TH activity showed significant circadian/diurnal variations, the highest activity was noticed at 12 h and the lowest at 24 h. The apparent Michaelis-Menten constant (K(m)) values (hypothalamic TH) for substrate (L-tyrosine) and cofactor (DMPH(4)) showed seasonal variations with the highest values in the resting phase, decreasing through preparatory and prespawning phases, to the lowest values in spawning phase. V(max) was the lowest in the resting phase and highest in the spawning phase. TH activity was low in the pituitary and could be detected in pooled samples from March (preparatory phase) to July (spawning phase). Activity showed significant variations, which could be correlated with the gonadosomatic index. The results show that TH activity could be positively correlated with the annual reproductive cycle. The enzyme activity could be also correlated with seasonal, sex, and regional variations in the apparent K(m) and V(max) values suggesting apparent differences in the affinity of the enzyme towards substrate and cofactor.
Gen Comp Endocrinol 2003 Jan
PMID:Brain tyrosine hydroxylase in the catfish Heteropneustes fossilis: annual and circadian variations, and sex and regional differences in enzyme activity and some kinetic properties. 1253 22

It is established that dopamine inhibits while GABA stimulates LH release in goldfish. In this study, we examine dopaminergic regulation of GABAergic activity in the hypothalamus of early recrudescent female goldfish (Carassius auratus). We utilize a unique technique that permits concomitant quantification and correlation of in vivo GAD65 and GAD67 mRNA with GABA synthesis rate in response to decreased dopamine levels. Catecholamine depletion was achieved by treatment with alpha-methyl-para-tyrosine methyl ester (alphaMPT; 240 microg/g body weight), an inhibitor of tyrosine hydroxylase. Endogenous GABA levels were increased by intraperitoneal administration of gamma-vinyl GABA (GVG; 300 microg/g body weight), an inhibitor of the GABA catabolic enzyme GABA transaminase. Dual treatment of GVG+alphaMPT increased serum LH levels 4-fold. However, LH mRNA levels in the pituitary remained stable, suggesting that treatments affected secretion and not synthesis. In the hypothalamus, GABA synthesis rates increased 30% in response to alphaMPT treatment. This was correlated (r=0.61; p<0.05) to increased levels of GAD67 mRNAs but not GAD65 (r=0.14; p>0.05). These observations suggest that catecholamines inhibit GABA synthesis in the goldfish hypothalamus through isoform specific regulation of GAD67.
Gen Comp Endocrinol 2005 Feb
PMID:Catecholamine depletion modulates serum LH levels, GAD67 mRNA, and GABA synthesis in the goldfish. 1563 45

In the present in vitro study, interactions of both cAMP-protein kinase A (PKA) and protein kinase C (PKC) systems were investigated in the estradiol-17beta (E2) regulation of forebrain (hypothalamus and telencephalon) tyrosine hydroxylase (TH) activity in the female catfish Heteropneustes fossilis in vitellogenic phase. E2 produced biphasic effects on TH activity: low concentrations (10(-12)-10(-5) M) stimulated, and high concentrations (10(-3)-10(-4) M) inhibited enzyme activity (Tukey's test, P<0.05). Co-incubations of the enzyme preparations with cAMP (1.0 mM), IBMX (1.5 mM) or theophylline (1.5 mM) and a low concentration of E2 (10(-9) M) increased TH activity significantly. However, the co-incubations with a high concentration of E2 (10(-3) M) decreased it significantly. Pre-incubations of the enzyme preparations with cAMP (0.1 mM), followed by different concentrations of E2 (10(-12), 10(-9), 10(-4), and 10(-3) M) produced concentration-dependent biphasic effects. The pre-incubations with a low concentration of E2 (10(-9) M), followed by different concentrations of cAMP (0.05-1.0 mM) produced a significant concentration-dependent stimulation of TH activity and that with a high concentration of E2 (10(-3) M) produced a significant decrease in TH activity. Co-incubations of high and low E2, with or without cAMP, and PKA inhibitor (H-89) decreased TH activity significantly. The incubations with H-89 abolished the stimulatory effect of low E2 or low E2+cAMP and intensified the inhibitory effect of high E2 or high E2+cAMP combination. Co-incubations with PKC inhibitor (calphostin C) did not influence the stimulatory effect of low E2 but lowered the stimulatory effect of low E2+cAMP treatment. Kinetic studies showed that the stimulatory effect of a low E2 concentration was due to a decrease in apparent Km and an increase in apparent Vmax for both cofactor and substrate, and the inhibitory effect of a high E2 concentration was due to reverse changes in the kinetics. The stimulatory effect of cAMP alone or in combination with low E2 was related to decreased Km and increased Vmax for the cofactor. The inhibitory effect of PKA and PKC blockers, alone or in combination with E2 and/or cAMP was due to increased Km and decreased Vmax of the enzyme for the cofactor. The present data suggest that E2 modulates the short-term activation of brain TH activity differentially and may involve mainly the cAMP-PKA system.
Gen Comp Endocrinol 2005 Apr
PMID:Estrogen regulation of in vitro brain tyrosine hydroxylase activity in the catfish Heteropneustes fossilis: interactions with cAMP-protein kinase A and protein kinase C systems in enzyme activation. 1574 12

Previously, we reported that hypothalamic explants isolated from male leopard frogs (Rana pipiens) implanted with 17beta-estradiol (E2), but not 5alpha-dihydrotestosterone (DHT), released significantly higher levels of gonadotropin-releasing hormone (GnRH) in response to a veratridine challenge. In this study, we measured changes in GnRH soma size, circulating luteinizing hormone (LH), and gonadosomatic index (GSI) in response to these two steroid hormones to further assess the impact of these hormones on the hypothalamic-pituitary-gonadal axis. Sexually mature male R. pipiens were implanted with silastic capsules containing cholesterol (Ch; control), E2, or DHT for 20 days. GnRH immunocytochemistry (ICC) revealed that both E2 and DHT significantly enlarged GnRH soma size without affecting the total number of GnRH neurons in the forebrain. The effects of E2 and DHT were specific, since neither hormone altered the soma size of tyrosine hydroxylase neurons in the dorsomedial posterior tuberculum. Circulating LH levels were significantly reduced in animals treated with both steroid hormones, with E2 exerting the most potent inhibitory effect. A significant inverse correlation was observed between the GSI and GnRH soma size in Ch controls, suggesting animals with larger GnRH neurons tended to have smaller gonads. Overall, our results showed that both steroid hormones induced the accumulation of GnRH and ultimately the swelling of the GnRH soma. Further, larger GnRH neurons were associated with smaller gonads and lower circulating levels of LH, suggesting a link between enlarged GnRH neurons and an overall decrease in the reproductive activity of R. pipiens.
Gen Comp Endocrinol 2005 Apr
PMID:Steroid-induced changes in the morphology of GnRH neurons in the male leopard frog, Rana pipiens: correlation with plasma gonadotropin and gonadal size. 1574 16

Dopamine (DA) plays a key inhibitory role in pubertal development of the European eel, but how DAergic neuronal activity is regulated is not known in this species. In order to investigate the regulation of DA inhibition at the molecular level, we developed a quantitative real-time RT-PCR (qrtRT-PCR) assay, using the Light Cycler system, for the expression of eel tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. Two different reference genes were compared: the previously cloned eel cytochrome b, and eel acidic ribosomal phosphoprotein P0, the latter of which we cloned and partly sequenced. To further validate the assay, different methods of total RNA extraction were tested and compared. When applied to cDNA extracted from dissected brains of juvenile eels, the expression of TH was highest in the olfactory bulb, followed by the telencephalon including preoptic area, and the di-/mesencephalic areas excluding the optic lobes. TH expression in the optic lobes and in the medulla oblongata was low, whereas no expression could be detected in corpus cerebellum. This distribution pattern is in agreement with earlier studies on TH in the eel using immunohistochemistry, RT-PCR, and Northern blotting. The developed qrtRT-PCR assay provides a new tool for understanding the mechanisms regulating central DA inhibition of puberty in juvenile eels.
Gen Comp Endocrinol 2005 May 15
PMID:A quantitative real-time RT-PCR assay for European eel tyrosine hydroxylase. 1586 57

Little is known about the neural control of female responses to male courtship. Female European starlings in breeding condition with high concentrations of estrogen select mates based on variation in song and approach nest boxes broadcasting male song. In contrast, outside of the breeding season (when estrogen is low) females do not display the same response to male song. The catecholamines dopamine and norepinephrine regulate behaviors important for mate choice such as arousal, attention, sexual motivation, and goal-directed approach responses, suggesting a role for catecholamines in female responses to male song. In the present study, treating females with a dopamine agonist inhibited, whereas an antagonist stimulated female interest in nest boxes broadcasting male song. In a second study immunocytochemistry was used to examine the distribution of the phosphorylated (i.e., active) form of tyrosine hydroxylase (pTH), the rate-limiting enzyme for catecholamine synthesis. Exposure to male song in breeding condition females reduced pTH density in brain regions involved in social behavior (lateral septum, ventromedial nucleus of the hypothalamus) and a region involved in visual processing (nucleus of Edinger-Westphal) but not song control regions. Opposite patterns of pTH labeling densities were observed in the same regions in response to song in non-breeding condition females. pTH in the ventral tegmental area was also affected by song and female endocrine condition. Overall, the present data support an inhibitory role for dopamine in female responses to courtship and suggest that endocrine state and catecholamines interact to regulate this behavior.
Gen Comp Endocrinol
PMID:Evidence that female endocrine state influences catecholamine responses to male courtship song in European starlings. 1760 57

Dopamine (DA) has a pivotal role in avian prolactin (PRL) secretion, acting centrally through D(1) DA receptors to stimulate PRL secretion by operating through vasoactive intestinal peptide (VIP). DA also inhibits PRL secretion by activating D(2) DA receptors at the pituitary level. This study was designed to investigate the distribution of DA neurons in the native Thai chicken, utilizing tyrosine hydroxylase (TH) as a marker for dopaminergic neurons. The differential expression of hypothalamic TH immunoreactive (TH-ir) neurons was also compared across the reproductive cycle. The results revealed that TH-ir neurons and fibers were found throughout the brain of the laying hen and were predominantly located within the diencephalon and mesencephalon. The observed distribution pattern of TH immunoreactivity was consistent with that reported previously in several avian species. However, changes in the number of TH-ir neurons in the nucleus intramedialis (nI) were observed across the reproductive cycle and correlated directly with variations in PRL levels. The population of TH-ir neurons in the nI increased significantly during the egg incubation period, where circulating PRL levels were the greatest. This study indicates, for the first time, that an association exists between DA neurons and the regulation of the reproductive system in the native Thai chicken. There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species and it is suggested that the differential expression of DA neurons in the nI might play a role in the control of VIP secretion and subsequent PRL release in such birds.
Gen Comp Endocrinol 2008 Oct
PMID:The dopaminergic system in the brain of the native Thai chicken, Gallus domesticus: localization and differential expression across the reproductive cycle. 1876 40


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