Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay

In the standard model of particle physics, the weak interaction is described by vector and axial-vector couplings only. Nonzero scalar or tensor interactions would imply an additional contribution to the differential decay rate of the neutron, the Fierz interference term. We derive a limit on this hypothetical term from a measurement using spin-polarized neutrons. This method is statistically less sensitive than the determination from the spectral shape but features much cleaner systematics. We obtain a limit of b=0.017(21) at 68.27% C.L., improving the previous best limit from neutron decay by a factor of four.

Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam

We present a precision measurement of the axial-vector coupling constant g_{A} in the decay of polarized free neutrons. For the first time, a pulsed cold neutron beam was used for this purpose. By this method, leading sources of systematic uncertainty are suppressed. From the electron spectra we obtain λ=g_{A}/g_{V}=-1.27641(45)_{stat}(33)_{sys}, which confirms recent measurements with improved precision. This corresponds to a value of the parity violating beta asymmetry parameter of A_{0}=-0.11985(17)_{stat}(12)_{sys}. We discuss implications on the Cabibbo-Kobayashi-Maskawa matrix element V_{ud} and derive a limit on left-handed tensor interaction.

Effects of imidazoline derivative RX871024 on insulin, glucagon, and somatostatin secretion from isolated perfused rat pancreas

The effects of the imidazoline compound RX871024 on arginine-induced insulin, glucagon, and somatostatin secretion in the isolated perfused rat pancreas have been investigated. Arginine induced biphasic insulin, glucagon, and somatostatin release when infused for 20 min at 20 mM concentration and 3.3 mM glucose in the medium. RX871024, at 10 microM, did not influence basal hormone secretion but enhanced arginine-stimulated insulin and somatostatin release. In contrast, glucagon secretion was markedly inhibited by 10 microM imidazoline. RX871024 (1 microM) did not significantly affect arginine-induced insulin and somatostatin secretion but had an inhibitory effect on the second phase of glucagon release. In conclusion, RX871024 exerts a complex effect on the endocrine pancreas challenged by arginine, comprising stimulation of insulin and somatostatin release and inhibition of glucagon release. These effects on hormone release probably constitute the main mechanism of the antidiabetogenic action of the imidazolines.

Secretory, biosynthetic and cationic responses to 2-(N-PHENYL-INDOYL)IMIDAZOLE in rat pancreatic islets

The secretory, biosynthetic and cationic effects of a novel insulinotropic agent with an imidazoline structure, 2-(N-phenyl-indoyl)imidazole hydrochloride (RX 871024) was investigated in rat pancreatic islets. In the 1.0-10-microM range, this agent augmented, in a concentration-related manner, the release of insulin from islets incubated at intermediate concentrations of d-glucose (4.0-7.0 mm), this enhancing action fading out at both lower a nd higher d-glucose levels. When the concentration of RX 871024 was raised to 1.0 mm, severe inhibition of glucose-stimulated insulin output was observed. The imidazole derivative (10 microM) failed to enhance glucose-stimulated biosynthetic activity in islets exposed to l-[4-3H]phenylalanine; a modest inhibition of the islet peptide tritiation was even recorded at 4.0 mm d-glucose. The positive insulinotropic action of RX 871024 (10 microM) coincided with a decrease in 45Ca net uptake, unchanged outflow of 86Rb and stimulation of 45Ca efflux from prelabelled islets, the latter effect being only partially suppressed in the absence of extracellular Ca2+. These findings suggest a multifactorial mode of action of RX 871024 in islet cells, with emphasis on both an apparent stimulation of Ca2+ influx and, independently of this effect, an intracellular redistribution of the divalent cation. The imidazole compound is proposed, therefore, to display suitable attributes to bypass site-specific defects of d-glucose metabolism in the B-cell of non-insulin-dependent diabetic patients.

Effect of trapidil derivative AR 12456 on intracellular cholesterol homeostasis in human hepatoma cell line Hep G2

The effect of trapidil derivative AR12456 on intracellular cholesterol metabolism was investigated in human hepatoma cell line HepG2. AR12456 enhanced the uptake and degradation of(125)I-LDL in a dose-dependent manner. The drug inhibited cholesterol synthesis and esterification without affecting cellular cholesterol content and bile acid synthesis; cholesterol efflux was slightly increased. These results show that the inhibition of cholesterol synthesis together with the enhanced expression of LDL receptors may partially explain the hypocholesterolemic activity of compound AR12456.