Effects of b-adrenoceptor-blockade on stress-induced adrenocorticotrophin release in humans

We investigated the mechanisms of stress-induced alterations in adrenocorticotrophin (ACTH) release. Tandem parachutists received either a placebo or the β-adrenoceptor antagonist propranolol prior to a first time parachute jump. Blood samples were drawn 4 h before, immediately after, and 1 h after the jump. Cortisol and catecholamine concentrations displayed a significant stress-induced increase in both groups. The ACTH plasma concentrations significantly increased in the placebo and the propranolol group, with significantly more pronounced changes in the propranolol-treated subjects compared to the placebo group. These data demonstrated a stress-induced increase of ACTH plasma concentrations in humans that was enhanced by β-blockade. Accepted: 15 December 1997     

Stabilization and gas chromatographic analysis of the four stereoisomers of 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) in rat blood

A method for the stabilization and gas chromatographic analysis of the four stereoisomers of C(+/-)P(+/-)-1,2,2-trimethylpropyl methylphosphonofluoridate (C(+/-)P(+/-)-soman) in rat blood samples is described. Satisfactory stabilization of all four stereoisomers is obtained by (i) acidification of the blood sample to pH 4.2 at 0 degrees C, to stabilize the C(+/-)P(+) isomers, (ii) addition of aluminum ions (2.5 mM) for complexation of fluoride ions, which prevents regeneration of C(+/-)P(-)-soman by free fluoride ions from soman-inhibited aliesterase, and (iii) addition of 2,2-dimethylpropyl methylphosphonofluoridate in order to occupy covalent binding sites for C(+/-)P(-)-soman. The stereoisomers of soman and internal standard are extracted from the blood-stabilizing buffer mixture with a Sep-Pak C18 cartridge and are subsequently eluted with ethyl acetate with overall extraction recoveries of 52 +/- 8%. The four soman stereoisomers are resolved and analyzed on a wide-bore capillary Chirasil Val column, synthesized, and coated in house, which also resolves the internal standard C(+/-)P(+/-)-1,2,2-[U-2H]trimethylpropyl methylphosphonofluoridate from C(+/-)P(+/-)-soman. Alternatively, the gas chromatographic analysis can be performed on a wide-bore capillary Chirasil Val column, identical with the commercially available Chirasil Val column, when combined in series with a Carbowax 20M column. This system resolves the four stereoisomers of soman and the internal standard C(-)P(+)-1,2,2-trimethylpropyl [U-2H]methylphosphonofluoridate. Using an alkali flame ionization detector, the detection limit of our procedure is ca. 250 pg soman isomer/blood sample.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.