Influence of age and splanchnic nerve on glucagon-induced changes of adrenomedullary catecholamine content and blood glucose level in the avian group

Summary Glucagon (0.1 mg · 100 g body wt^-1) increased norepinephrine (NE) content in adult pigeon (31%) and parakeet (58%), decreased NE content in the adrenal medulla of newly-hatched pigeon (36%), parakeet (52%), and crow (44%) 0.5 h after treatment. Epinephrine (E) content decreased to 26% and 59% of control values, respectively, in newly-hatched pigeon and parakeet 0.5 h after treatment. Glucagon produced hyperglycemia irrespective of age and species. The results indicate that aging modulates glucagon-induced changes of catecholamine (CA) content. In the innervated (I) adrenal gland of pigeon, glucagon caused a 31% increase of NE content 0.5 h after injection, a 46% decrease of NE content 12 h after injection, and a 192% increase of NE 24 h after injection. In the I gland of pigeons, glucagon also caused a 61% decrease of E content 4 h after injection, and brought about a 100% increase of E 24 h after injection. Glucagon-induced changes of CA content differ significantly between the I and denervated (D) glands. The results indicate that the splanchnic nerve regulates release and/or resynthesis of CA induced by glucagon.Abbreviations ANOVA analysis of variance - CA catecholamine - D denervated - E epinephrine - I innervated - MS mean sum of squares - NE norepinephrine - PNMT phenylethanolamine-N-methyl transferase - SS sum of squares - SV source of variation - TH tyrosine hydroxylase     

Role of splanchnic nerve on steroid-hormone-induced alteration of adrenomedullary catecholamines in untreated and reserpinized pigeon

Summary The aim of the present investigation was to ascertain (1) the effect of steroid hormones (corticosterone, dexamethasone, deoxycorticosterone, progesterone, testosterone and oestrogen) on the neural regulation of adrenomedullary catecholamine (CA) content, and (2) the neural modulation of the effect of glucocorticoid hormones (corticosterone and dexamethasone) on reserpine-induced resynthesis of CA. The experiment was conducted on unilaterally splanchnic-denervated pigeons. The findings revealed that 7 consecutive days of steroid treatments (2.5 mg·kg b.w.^-1, i.m.) resulted in significant changes of CA content. Interestingly, the changes of epinephrine (E) content differed significantly between the innervated and denervated glands. This clearly indicates that the splanchnic nerve regulates steroid-induced alterations of E content in the pigeon. The results further revealed that the glucocorticoid hormones augmented reserpine-induced resynthesis of CA specifically in the innervated glands. This confirms that the splanchnic nerve is essential for the synergistic action of glucocorticoids and reserpine in accelerating resynthesis of CA.Abbreviations ANOVA analysis of variance - b.w. body weight - CA catecholamine - DBH dopamine--hydroxylase - df degrees of freedom - E epinephrine - i.m. intramuscular - i.p. intraperitoneal - mRNA messenger ribonucleic acid - NE norepinephrine - PNMT phenylethanolamine-N-methyl transferase - TH tyrosine hydroxylase     

Modulation of blood glucose by melatonin: a direct action on melatonin receptors in mouse hepatocytes.

Melatonin receptors were studied in isolated mouse hepatocytes using the 2[(125)I]iodomelatonin binding assay. The binding of 2[(125)I]iodomelatonin to hepatocytes isolated from the mouse using collagenase was stable, saturable, reversible and of high affinity. The equilibrium dissociation constant (K(d)) obtained from saturation studies was 10.0 +/- 0.4 pmol/l (n = 16), which was comparable to the K(d) obtained from kinetics studies (6.9 +/- 1.2 pmol/l, n = 3), and the maximum number of binding sites (B(max)) was 2.9 +/- 0.4 fmol/mg protein (n = 16). The relative order of potency of indoles in competing for 2[(125)I]iodomelatonin binding was 2-iodomelatonin > 2-phenylmelatonin > 6-chloromelatonin > melatonin > 6-hydroxymelatonin > N-acetylserotonin, indicating that the binding was mediated by the ML(1) receptor subtype. The linear Rosenthal plots, the close proximity of the Hill coefficient to unity and the monophasic competition curves suggest that a single class of 2[(125)I]iodomelatonin binding sites is present in the mouse hepatocytes. Guanosine 5'-O-(3-thiotriphosphate) dose-dependently inhibited 2[(125)I]iodomelatonin by lowering the affinity of binding, while no inhibitory effects of adenosine nucleotides were observed, suggesting that the binding sites are G-protein linked. Western immunoblotting was used to identify the melatonin receptor subtype in mouse hepatocytes using anti-Mel(1a) and anti-Mel(1b). Hepatocyte membrane extract reacted with anti-Mel(1b) but not anti-Mel(1a) giving a peptide-blockable band of 36 kD, supporting the hypothesis that the melatonin receptors in mouse hepatocytes are of the Mel(1b) subtype. Melatonin injection and a high plasma glucose level affected 2[(125)I]iodomelatonin binding in the whole mouse liver homogenates. Plasma glucose was elevated by mid-light intraperitoneal injection of melatonin (4 and 40 mg/kg body weight) in a dose-dependent manner with maximum elevation achieved 1 h after injection. 2[(125)I]Iodomelatonin binding at this time showed increased K(d) with no changes in B(max). When the plasma glucose returned to normal within 2 h, the binding remained lowered with increased K(d) but no changes in B(max). Elevation of plasma glucose by 2-deoxyglucose injection (500 mg/kg), on the other hand, decreased the binding by decreasing the B(max) without affecting the K(d). Suppression of plasma glucose by insulin injection (3 IU/kg) did not change the binding. Thus, melatonin may act directly on the liver to elevate the plasma glucose level, and changes in plasma glucose level itself may in turn affect hepatic melatonin binding.     

Influence of a single neonatal melatonin treatment on the basal and thyrotropin or melatonin modified blood thyroxine level of adult rats

Neonatal melatonin treatment caused a significant increase in thyroxine (T4) level at one month of age. Preexposure to melatonin in neonatal age and reexposure after one month accounted for a still greater increase in T4 production. Rats neonatally exposed to melatonin did not respond to TSH at one month of age.     

Influence of oral glucose load upon blood glucose level in relation to the time of day

Blood glucose levels were estimated at different times of day in fasted rats and after 30, 60,90 and 120 min, since oral glucose load. Circadian variations in basal glucose levels and in the levels after glucose load were observed with the highest values noted between 11 a.m. and 7 p.m., and the lowest ones about midnight. These variations were most prominent when the measurements were performed 60 min after glucose load. Circadian variation in glucose tolerance was also revealed with the best tolerance at about midnight while the worst one was noted at noon and in the afternoon.     

The blood glucose content in newborn rats depending on level and pattern of spontaneous motor activity

Earlier we have shown that administration to newborn rats of the pentose phosphate cycle inhibitor hydroquinone leads to a change in intensity and pattern of spontaneous periodic motor activity (SPMA) characteristic of early stages of development. The most typical was the disappearance of the rest period from the near-minute “activity-rest” cycle and the appearance of uninterrupted motor activity. In several cases, especially after 10 days of development, there was noted an enhancement in the SMPA pattern of the motor activity complexes following in the decasecond rhythm. In this study, on the 3–10-day old rats maintained under conditions of free behavior there was studied the blood glucose content in the animals at various periods of the activity-rest cycle. Apart from the SPMA phase, its composition (pattern) characterizing the maturity level and functional state of spinal motor centers was taken into account. In the 3, 7 and 10-day old rats at the rest period, the glucose concentration was established to differ depending on the motor activity pattern. In the case of the decasecond periodicity, it amounts to 5.7 ± 0.2, 6.3 ± 0.3, and 7.5 ± 0.3 mmol/l, while at the minute one—6.1 ± 0.4, 7.8 ± 0.3, and 7.8 ± 0.1 mmol/l. At the moment of bursts of motor excitation, the glucose concentration falls to 5.2 ± 0.1, 6.1 ± 0.4, and 7.1 ± 0.3 mmol/l at the decasecond and to 5.4 ± 0.5, 6.7 ± 0.2, and 7.6 ± 0.3 mmol/l at the near-minute rhythm (for the 3-, 7-, and 10-day old animals, respectively). The results obtained on the 5-day rat pups differ qualitatively from those observed in other age groups. Thus, the glucose concentration at the rest period amounts to 6.8 ± 0.2 at the decasecond and to 6.7 ± 0.4 mmol/l at the nearminute periodicity. At the period of motor excitation accompanied by the presence of the decasecond activity rhythm, the glucose concentration falls to the level of 6.0 ± 0.2 mmol/l by differing statistically significantly from the observed one in the rest state. In the case of the appearance of the minute rhythm, the glucose concentration amounts to 5.8 ± 0.3 mmol/l. The obtained data indicate that reproduction of the minute and decasecond rhythms recorded in composition of SPMA is accompanied by a change in the blood serum glucose level. The degree of a decrease of its concentration correlates with a certain activity rhythm: at the decasecond one the fall is 9, 13, 3, and 7%, whereas at the minute rhythm—11, 13, 14, and 2% (for the 3-, 5-, 7- and 10-day old rats, respectively). It is to be noted that a certain effect on the activity pattern is produced by the degree of satiety of the rat pups, the gastric emptying being accompanied by an increase in expression of the decasecond rhythm and of brief jerks. Besides, there occur the significant seasonal oscillations of the blood serum glucose concentration in the newborn rat pups—at the summer period it is statistically significantly higher than at the winter—spring period.     

Attenuating effect of melatonin on pyridoxal-stimulated release of adrenomedullary catecholamines in the rat

AimsTo investigate the ability of melatonin (MEL) to suppress adrenomedullary catecholamine (CAT) release in the rat, with pyridoxal (PL) being used as an adrenomedullary stimulus and liver and gastrocnemius muscle glycogenolysis acting as indices of CAT release.Main methodsMEL (1–4 mg/kg, i.p.) and PL (300 mg/kg, i.p.) were administered separately or together to male Sprague–Dawley rats (275–300 g), and blood samples for the assay of plasma glucose and CATs were periodically collected for up to 3 h after PL. Immediately thereafter, the liver and gastrocnemius muscle were surgically removed and used for the assay of glycogen. The role of adrenoceptors in PL-induced glycogenolysis was examined by parallel experiments in which idazoxan (IDX, 1 mg/kg), propranolol (PRO, 2 mg/kg) or metoprolol (MET, 2 mg/kg) were administered alongside MEL. In addition, MEL (4 mg/kg) was co-administered with taurine (TAU, 2.4 mmol/kg), a known adrenomedullary membrane stabilizer.Key findingsMEL attenuated the release of adrenomedullary CATs and accompanying liver and gastrocnemius muscle glycogenolysis due to PL in a dose-dependent manner. A co-treatment with MEL and an adrenoceptor blocker had a greater attenuating effect on PL-induced glycogenolysis and hyperglycemia than MEL but without impinging on the CAT levels seen with MEL alone. Evidence of maximal inhibitory action by MEL on PL-induced plasma CAT elevation was suggested by the about equal levels of plasma CATs after treatments with MEL and with MEL plus TAU.SignificanceThe present study demonstrates the modulatory effect of MEL of exogenous origin on adrenomedullary CAT secretion when present in supraphysiological concentrations.     

Modulation by beta-adrenoceptors and angiotensin II receptors of splanchnic nerve evoked catecholamine release from the adrenal medulla.

In the present study, we have evaluated the effect of both facilitatory beta 2-adrenoceptor and angiotensin II receptor on the release of adrenal catecholamines induced by electrical stimulation of the splanchnic nerve in anaesthetized and vagotomized dog. In these experiments, individual or combined treatments with the beta 2-adrenoceptor antagonist ICI 118551 (0.3 mg/kg i.v.), the converting enzyme inhibitor captopril (2 mg/kg i.v.), or the angiotensin II receptor antagonist saralasin (2 micrograms.kg-1.min-1 i.v.) were found to significantly decrease the release of adrenal catecholamines during splanchnic nerve stimulation (5-V pulses of 2 ms duration for 3 min at 1 Hz) whatever the order of administration of the drugs. On the other hand, the infusion of angiotensin II (20 ng.kg-1.min-1) was shown to potentiate the release of adrenal catecholamines in response to electrical stimulation, and this effect was totally blocked by treatment with saralasin (4 micrograms.kg-1.min-1 i.v.). This facilitating angiotensin mechanism differed from beta-adrenoceptor facilitating mechanism, since following beta-blockade with ICI 118551, angiotensin II infusion still significantly potentiated the release of catecholamines during splanchnic nerve stimulation. These observations thus suggest that both facilitating beta 2-adrenoceptors and angiotensin II receptors can independently modulate the release of adrenal catecholamines.     

Benzodiazepine inhibition of the stimulation-evoked catecholamine release from bovine adrenomedullary cells in culture

Effect of benzodiazepines on evoked catecholamine (CA) release from a primary culture of bovine adrenal medullary cells was investigated. Midazolam at high doses (> 10 μ M) inhibited CA release evoked by acetylcholine (ACh), excess K⁺ and veratridine but not by A23187 or caffeine in Ca²⁺ -free media. Other benzodiazepines, diazepam, clonazepam, nitrazepam and R05-4864, as well as 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195) and ethyl-β-carboline-3-carboxylate (βCCE) also inhibited ACh-evoked CA release but only at high concentrations. The inhibitory effect of midazolam on ACh-evoked CA release was not affected by R015-1788, a central-type benzodiazepine receptor antagonist which itself had no effect on basal and ACh-evoked CA release. Facilitatory action of Bay K 8644 on CA release evoked by 20 mM K⁺ was reduced by midazolam, PK11195 and R05-4864. Further, ACh-evoked ⁴⁵Ca uptake was markedly reduced by midazolam and R05-4864 in association with the inhibition of CA release. These results suggest that benzodiazepines at high doses, inhibit the evoked CA release from adrenal chromaffin cells possibly through the blockade of Ca²⁺ influx. Possible involvement of receptor subtypes of benzodiazepines in regulating CA secretion is discussed.     

Influence of muscular exercise on blood catecholamine levels in rats]

Lactacidemia, catecholaminemia and blood pressure have been measured in normal rats submitted to a swimming exercise. They are overloaded (6% body weight). Lactacidemia is increased after 15 minutes swimming. Adrenalinemia and noradrenalinemia are also statisticaly increased. Blood pressure falls during the exercice period. Hypotension is prevented by beta adrenergic blockade.     

Influence of 1,3-butanediol on blood glucose concentration and pancreatic insulin content of streptozotocin-diabetic rats.

Male rats were made diabetic by intravenous administration of 75 mg/kg of streptozotocin and were fed, via a pair-feeding regimen, high-fat diets +/- 1,3-butanediol (BD) at 13.5 and 27% of the dietary calories for 30 days and 31 days, respectively. 1,3-Butanediol was added to the diets primarily as a replacement for fat. Food consumption and rat weight were recorded daily. Whole blood glucose concentrations were determined weekly. At sacrifice, liver, pancreas and epididymal fat pads were excised and blood samples were collected. Liver was analyzed for protein and lipid; pancreas was weighed and analyzed for insulin; fat pads were weighed and discarded; and blood was analyzed for glucose and lipid. The 13.5% BD diet increased the beta-hydroxybutyrate, acetoacetate and cholesterol concentrations, decreased the glucose concentration in blood, and increased the insulin content of the pancreas. The BD diets did not affect the concentrations of phospholipid, triglyceride, cholesterol and fatty acid in the liver; fatty acid concentrations in the blood; or the epididymal fat pad weight. The results suggest that BD produced a slight amelioration of the diabetic condition, which may have resulted from an increased capacity of the pancreas to synthesize insulin. In addition, the data provide further evidence suggesting that in the rat BD is oxidized to the ketone bodies, beta-hydroxybutyrate and acetoacetate.