Barbara Nibbio

Catecholaminotropic effects of catecholamines in a teleost fish,Anguilla rostrata

SummaryInjections of physiological and supraphysiological doses of epinephrine (E) into cardiaccannulated eels cause a dose-related increase of plasma dopamine (DA) and norepineprine (NE) within 3 min. Likewise, both exogenous DA and NE increase the plasma titers of the respective other two catecholamines (CAs). The baseline titers of NE and E are closely correlated. Lack of a correlation of the baseline titers of NE and E with that of DA appears to be due to a faster disappearance rate of DA from the circulation. E is strongly hyperglycemic, and the weaker glycemic action of NE may be mediated via E release. The effects of E seem to depend on a spurt-like increase rather than its titer per se. The ability of the eel to cope with very fast, excessive increases of plasma CAs raises the question of the underlying mechanisms.

Endogenous codeine: Autocrine regulator of catecholamine release from chromaffin cells

In addition to the catecholamines (CAs) dopamine (DA), norepinephrine (NE) and epinephrine (E), perifused chromaffin cells of the eel secrete codeine and morphine. In controls, the release of NE and E is strongly correlated, while there is no correlation with DA. Low, physiological concentrations of codeine (500 pg/ml) reduce the release of NE and E, while 8-fold higher concentrations stimulate an instant, transitory release of all three CAs. Much higher concentration of codeine (100 ng/ml), corresponding to the therapeutically effective range in the human, again reduce the release of NE and E. Physiological and very high concentrations of morphine have no clear effect on CA release, while an intermediate concentration (38 ng/ml) increases the secretion of all three CAs. The opiate antagonist naloxone lowers the basal CA secretion and prevents the morphine-induced CA increase. During naloxone perifusion, a normally non-effective concentration (40 ng/ml) of codeine reduces the CA release. It appears that codeine is an autocrine regulator which suppresses CA release via naloxone-insensitive receptors, and stimulates CA release via opiate receptor(s). Co-released morphine may modulate the action of codeine.

Mitochondrial benzodiazepine receptors regulate oxygen homeostasis in the early mouse embryo.

The peripheral benzodiazepine receptor (Bzrp) has been implicated in the control of several processes, including mitochondrial biogenesis and embryo development. The present study examined the impact that specific Bzrp ligands have on oxygen homeostasis in the early mouse embryo. Day 9 embryos at the 16-18 somite pair stage were exposed to standard (21% oxygen) and suboptimal (5% oxygen) oxygen tensions in whole embryo culture. Analysis of gene expression used relative PCR to monitor changes in nuclear respiratory factor-1 (Nrf1), mitochondrial 16S ribosomal RNA (16S rRNA), and genes for several glycolytic enzymes. Ocular development was highly sensitive to periods of hypoxia through a mechanism blocked with the potent Bzrp ligand PK11195. Hypoxia led to a decline of Nrf1 and 16S rRNA levels also through a mechanism blocked with PK11195. Similar activity was observed for FGIN-1-27 whereas Ro5-4864 had contradictory effects. Morpholino-based gene knockdown of Nrf1 (anti-NRF1) produced a sequence-specific decrease in 16S rRNA insensitive to PK11195. These functional relationships suggest that Bzrp-dependent signals regulate the Nrf1 --> Tfam1 --> mtDNA --> 16S rRNA pathway in response to oxygen levels. The activity of PK11195 most likely has a pharmacodynamic basis with regards to specific embryonic precursor target cell populations, transducing a mitochondrial signal to an Nrf1 response analogous to retrograde regulation in yeast for mitochondria-to-nucleus signaling.

Catecholamines in adult lampreys: baseline levels and stress-induced changes, with a note on cardiac cannulation.

Abstract The circulating levels of dopamine, norepinephrine, and epinephrine (about 1300, 1300, and 3600 pg/ml, respectively) of the adult sea lamprey are very high when compared with the levels in teleosts and mammals, but similar to the levels found in the shark. Contrary to the situation in the shark, teleosts, and mammals, however, epinephrine has the highest plasma levels of the three catecholamines studied, and dopamine seems to be released mainly outside the brain. We find two types of responses: agitation causes a decrease of circulating dopamine, whereas decapitation causes an enormous increase of norepinephrine release. Details of a technique of heart cannulation for repeated blood sampling from individual lampreys are also given.

Impact of ethanol stress on components of the allantoic fluid of the chicken embryo.

Recent studies showed that the allantoic fluid of the chicken embryo is a depot for stress-released catecholamines and many free amino acids and related compounds, and that it is separated from plasma and the amniotic fluid by selective barriers. To gain further insights into the functions of the allantois and its barriers, we studied the impact of stress (intra-allantoic injection of 0.1 ml ethanol) on 39 free amino acids and related compounds of the allantoic fluid. Using an HPLC-fluorometric method, we found that the concentration of seven substances was significantly increased 20 min after injection of ethanol, and back to control levels within 40 minutes. Five of these compounds (asparagine, alanine, leucine, tyrosine, lysine) had previously been shown to occur in plasma at concentrations above those in the allantoic fluid. However, taurine and phosphoethanolamine increased in the allantoic fluid even though their concentrations in plasma tended to be lower than in allantoic fluid. These findings (1) reveal the existence of complex embryonic/extraembryonic autoregulations, and (2) raise the question of the regulatory mechanisms involved in the transfer of substances across the allantoic barrier(s).

REGULATION OF SUBSTANCES IN ALLANTOIC AND AMNIOTIC FLUID OF THE CHICKEN EMBRYO

Traditionally, the avian allantois has been considered a respiratory organ and a dumping ground for metabolic wastes. We tested the hypothesis that the allantoic fluid is also a depot for free amino acids and related compounds. To gain further insight in the specific role of the allantoic fluid, we included plasma and the amniotic fluid in this study. The work was carried out in 13- and 14-day-old chicken embryos. Using an HPLC-fluorometric technique, 40 of the 41 amino acids and related compounds investigated were detected. The amniotic fluid contained 32 compounds, while plasma and allantoic fluid contained 38 and 39 compounds, respectively. The glucose concentration was determined with a hexokinase technique. It was highest in plasma and lowest in the amniotic fluid. We identified three barriers that hyper- and hyporegulate a number of compounds: (1) a blood/allantois barrier, (2) a blood/amnion barrier, and (3) an allantois/amnion barrier. Compared with plasma and allantoic fluid, the amniotic fluid is a mostly hyporegulated environment.

Catecholamines in head and body blood of eels and rats

1. When compared with other vertebrates, the circulating titers of norepinephrine and epinephrine of the yellow eel are very low. 2. The ratio of the catecholamine titers in the eel differs from that reported for other vertebrates. 3. Following decapitation, the titers of the catecholamines are higher in head blood than in body blood of both unanesthetized and anesthetized eels. In decapitated rats, only the dopamine titer is higher in head blood. 4. As in the lamprey, agitation stress causes a drop of circulating catecholamines. However, other forms of stress cause the expected increase. 5. It appears that many data on catecholamines in both brain and circulation of vertebrates in general have been influenced by stress effects.

The avian allantois: A depot for stress-released catecholamines

Plasma and amniotic and allantoic fluid of 10- and 14-day-old chicken embryos contain free dopamine (DA), norepinephrine (NE), and epinephrine (E). Compared with postnatal chickens, concentrations of DA and E in the plasma are very high, and they are even higher in the allantoic fluid. In contrast, the allantoic concentration of NE is below the plasma level. In the amniotic fluid, the concentrations of all three catecholamines (CAs) are below the plasma levels. High concentrations of DA and E in the allantoic fluid after opening of the egg shell decline during the following 24 hr, which indicates that they are due to stress. Asphyxia, handling, disturbance of allantoic fluid, and cooling are also perceived as stress and are followed by immediate accumulation of CAs in the allantoic fluid. DA and E respond to stress in like manner, while NE often responds with an opposite trend. It appears that the avian allantois, in addition to its role in respiration and urea disposal, also serves the instant CA removal from the circulation. Both the amniotic and the allantoic membranes of the chicken should be ideal models for the study of CA transport mechanisms.

Circulatory catecholamines in the eel: origins and functions

While the three catecholamines (CAs) dopamine (DA), norepinephrine (NE) and epinephrine (E), are wide-spread in tissues of the American eel (Anguilla rostrata), the bulk of these CAs in the systemic blood originates from chromaffin cells in the wall of the posterior cardinal veins. In addition, the brain and unidentified structures in the opisthonephric kidney also release appreciable quantities of CAs. The functional realms attributed to systematically circulating CAs in teleosts comprise cardiovascular, respiratory, osmoregulatory, metabolic and endocrinotropic actions. In the eel, cardiovascular and respiratory effects are well established. However, we were unable to prove a physiological role of the CAs in osmoregulation. On the other hand, the eel is the only species among five vertebrates of greatly varying phylogenetic position (the others: hagfish, lamprey, rat, human) in which physiological doses of E were hyperglycemic. As in lamprey and rat, DA and NE are released in the eel by physiological doses of E. In addition, DA and NE also release the respective other two CAs. The physiological significance of the catecholaminotropic (CA-tropic) interactions remains to be established; however, the CA-tropic effect of E does not require the presence of the brain or ‘preganglionic’ nerve cells. In the eel, mild stress causes an immediate ‘unorthodox’ drop of plasma CAs, while stronger stress is followed by the expected increase of plasma CAs.

Effects of exogenous somatostatin and antisomatostatin on serum parameters of the American eel

1. Bolus injections of a wide range of concns. of somatostatin and of antisomatostatin, in cardiac-cannulated eels had no specific effects on serum osmolality, sodium, potassium and chloride. 2. A presumably physiological dose of somatostatin had a pronounced and sustained hyperglycemic effect beginning 160 min after the injection, which was absent at higher doses. However, an extremely high dose caused an early, temporary hyperglycemia. 3. Antisomatostatin also caused a hyperglycemia, which appeared after 20 min and lasted less than 24 hr. 4. It appears that, in the freshwater eel, somatostatin affects both hyper- and hypoglycemic mechanisms and that these effects depend on its concn and/or site of action.