THE ADRENERGIC SYSTEM AND SYMPATHOMIMETIC AMINES

Adrenergic receptor behaviors of mesenchymal stem cells obtained from different tissue sources and the effect of the receptor blockade on differentiation

In this study, it was aimed to analyze behavioral changes of adrenergic receptors (ARs) in first three passages and osteogenic/adipogenic differentiation of mesenchymal stem cells (MSCs) derived from placenta fetal membrane (FM) and bone marrow (BM). It was also aimed to evaluate effects of receptor blockade on differentiation. We obtained first three passages of MSCs from placenta and BM samples. For cell identification, the cells were analyzed by flow cytometry using CD34, CD45 and CD3, CD105 antibodies in each passage. The effects of propranolol and phenoxybenzamine at incremental doses were analyzed by MTT. In addition, cell cultures were separately maintained with the blockers or without after second passage. After each passage and differentiation, α1A, α1B, α2A, α2B, β1, β2, β3 AR-mRNA expressions analyzed by RT-qPCR technique. BMP6 and PPARG mRNA expressions only after differentiation and passage 3 were analyzed. A microscopic examination was also performed. Our results showed that AR expression behaviors were different in MSCs obtained from different tissue sources. In particular, α_1A-AR and α_2A-AR were expressed with considerably high coefficients in differentiation under blocker effect in BM-derived MSCs. No such coefficients were observed in any group of placental MSCs. In addition, it was found that the blockers stimulated adipogenesis in BM-derived MSCs during osteogenic differentiation. MSCs exhibit protein expressions that vary according to source of tissue and differentiation. Given that MSCs from different sources are used for repair and modulation, our study makes implications of this variable expression intriguing in the clinical practice.

The inhibitory action of noradrenaline and other monoamines on spinal neurones

1. L-Noradrenaline (NA), 5-hydroxytryptamine (5-HT) and acetylcholine (ACh) were administered micro-electrophoretically to feline lumbar neurones while recording their spike potentials extracellularly.2. There was no evidence to suggest that NA acts as an excitatory transmitter in the spinal cord.3. NA had potent inhibitory effects on some interneurones as revealed by a depression of spontaneous and synaptic firing and on the firing to a local application of an excitant amino acid. The effects on Renshaw cells and motoneurones were less marked.4. The depressant actions of 5-HT were less marked than those of NA. ACh and carbamylcholine had depressant effects on some NA-sensitive interneurones but were invariably far less potent and on other NA-sensitive cells were completely inactive.5. NA had no detectable effect on the normal spike amplitude but when the action potentials were reduced by excessive depolarization then both NA and synaptic inhibition increased the spike amplitude; this effect could be due to a hyperpolarization of the cell membrane.6. There was a correlation between the distribution of NA-sensitive cells and the relative densities of NA-containing terminals in various layers of the grey matter.7. It was postulated that NA acts as an inhibitory transmitter released from the terminals of descending pathways in the spinal cord. Other possible mechanisms were discussed but lacked experimental support.

Modification of the cerebrovascular response to noradrenaline by bile duct ligation

The effects of intracarotid infusions of noradrenaline on the cerebral vasculature were studied in seven baboons with bile duct ligation. Infusion of 8 mug and 16 mug/min of noradrenaline resulted in a significant decrease in cerebral blood flow in the jaundiced animals. In normal baboons, these doses produced cerebrovascular dilatation. These results indicate that there is an increased cerebrovascular sensitivity to noradrenaline in the obstructive jaundice which follows bile duct ligation. It is postulated that noradrenaline smooth muscle uptake mechanisms are disturbed allowing a greater concentration of the amine at the receptor sites.

Effects of jaundiced plasma on vascular sensitivity to noradrenalin

Alterations in renal perfusion have been shown in a variety of liver diseases. We have examined the possibility that the syndrome is due to a renal vascular hypersensitivity to noradrenalin (NA). Isolated perfused kidneys and segments of rabbit femoral artery were used. Potentiation of the pressor effects of injected NA occurred in all (five artery and five kidney) preparations when jaundiced baboon plasma was perfused. These changes were significant (P less than 0.05) in nine out of the ten experiments. Controls to which normal baboon plasma was administered showed no such change. No correlation was found between the degree of NA potentiation and the plasma concentrations of bilirubin (total and conjugated), serum glutamic oxaloacetic transaminase, blood urea nitrogen, serum glutamic pyruvic transaminase, alkaline phosphatase, Na+ ions or K+ ions in the jaundiced plasma. Plasma renin levels were not significantly changed. When arteris were perfused with Krebtentiation of NA was found. Perfusion of sodium taurocholate or sodium deoxycholate (400 mug/ml) yielded no potentiation. Thus, the altered renal perfusion associated with jaundice may be attributed to a potentiated pressor response to NA which may be caused by an increased level of cholesterol carried on the beta-lipoprotein.

Effects of amphetamine derivatives on brain dopamine and noradrenaline

1. Intracisternally administered metaraminol, alpha-methyl-octopamine, alpha-methyl-m-tyramine, and alpha-methyl tyramine were found to lower brain noradrenaline without having an effect on brain dopamine.2. Amphetamine, mephentermine, and norephedrine had no effect on brain catecholamines after intracisternal injection.3. There was no reduction in brain dopamine content after intracisternal injection of alpha-methyl-m-tyramine, yet the resulting brain concentration of alpha-methyl-m-tyramine was several times higher than after intraperitoneal injection of alpha-methyl-m-tyrosine, which decreased brain dopamine.4. The decreased synthesis of labelled catecholamines from (14)C-tyrosine after alpha-methyl-m-tyrosine suggested that this compound inhibits tyrosine hydroxylase in addition to its action of displacing brain amines.