Adrenal response to iv administration of 1-24 ACTH (250 micrograms) was examined in normal volunteers under various conditions. The effect of basal cortisol levels was examined by performing the tests at 0800 h with and without pretreatment with dexamethasone. The effect of time of day was evaluated by performing the tests at 0800 h and at 1600 h, eliminating possible basal cortisol influence by pretreatment with dexamethasone. In the first set of tests, despite significantly different baseline levels, 30-min cortisol levels were not different (618 +/- 50 vs. 590 +/- 52 nmol/L). Afternoon cortisol levels in response to ACTH were found to be significantly higher than morning levels at 5 min (254 +/- 50 vs. 144 +/- 36 nmol/L, p less than 0.01) and at 15 min (541 +/- 61 vs. 433 +/- 52 nmol/L, p less than 0.02). This difference in response was no longer notable at 30 min (629 +/- 52 and 591 +/- 52 nmol/L). We tried also to determine the lowest ACTH dose which will elicit a maximal cortisol response. No difference was found in cortisol levels at 30 and 60 min in response to 250 and 5 micrograms 1-24 ACTH. Using 1 micrograms ACTH, the 30-min response did not differ from that to 250 micrograms (704 +/- 72 vs. 718 +/- 55 nmol/L, respectively). However, the 60-min response to 1 microgram was significantly lower (549 +/- 61 vs. 842 +/- 110 nmol/L, p less than 0.01). Using this low dose ACTH test (1 microgram, measuring 30-min cortisol level), we were able to develop a much more sensitive ACTH test, which enabled us to differentiate a subgroup of patients on long-term steroid treatment who responded normally to the regular 250 micrograms test, but had a reduced response to 1 microgram. The stability of 1-24 ACTH in saline solution, kept at 4 C, was checked. ACTH was found to be fully stable after 2 hs in a concentration of 5 micrograms/ml in glass tube and 0.5 micrograms/ml in plastic tube. It was also found to be fully stable, both immunologically and biologically, for 4 months, under these conditions. We conclude that the 30-min cortisol response to ACTH is constant, unrelated to basal cortisol level or time of day. It is therefore the best criterion for measuring adrenal response in the short ACTH test. The higher afternoon responses at 5 and 15 min suggest greater adrenal sensitivity in the afternoon, but further studies are needed to clarify this issue.(ABSTRACT TRUNCATED AT 400 WORDS)
The aggregation of Au nanoparticles in solution is induced and influenced by cationic and oligocationic species. This solution-state aggregation bears similarities to multilayer formation on surfaces but is more facile because of the nanoparticles' intrinsic instability in solution. Aggregation is followed by transmission electron microscopy (TEM) and the appearance of features at λ ) 600-900 nm in the absorbance spectrum. It is found that these features are a function of factors such as the aggregant size, charge, and concentration, and the method of mixing the components, and they can be related to aggregate morphology. It seems that there are two mechanisms that can act to cause aggregation. Multiply charged aggregants can bind nanoparticles together into dense aggregates, displaying a defined absorbance at ca. λ ) 700 nm, whereas singly charged aggregants cause a slower aggregation into string-like aggregates with a less defined absorbance. Whereas multiply charged aggregants can "cross-link" the layers in a multilayer structure on a surface, singly charged aggregants cannot.
Tailor-made auxiliaries for the control of nucleation and growth of molecular crystals may be classified into two broad categories: inhibitors and promoters. Tailor-made inhibitors of crystal growth can be used for a variety of purposes, which include morphological engineering and etching, reduction of crystal symmetry, assignment of absolute structure of chiral molecules and polar crystals, elucidation of the effect of solvent on crystal growth, and crystallization of a desired polymorph. As for crystal growth promoters, monolayers of amphiphilic molecules on water have been used to induce the growth of a variety of three-dimensional crystals at the monolayer-solution interface by means of structural match, molecular complementarity or electrostatic interaction. A particular focus is made on the induced nucleation of ice by mono- © 1995 International Union of Crystallography Printed in Great Britain -all fights reserved layers of water-insoluble aliphatic alcohols. The twodimensional crystalline structures of such monolayers have been studied by grazing incidence X-ray diffraction. It has become possible to monitor, by this method, the growth, dissolution and structure of self-aggregated crystalline monolayers, and indeed multilayers, affected by the interaction of solvent molecules in the aqueous subphase with the amphiphilic headgroups, and by the use of tailor-made amphiphilic additives.
Recent advances in the assembly of nanoparticle superstructures on electrodes are addressed here. Methods for the assembly and characterization of these arrays are summarized and their electronic, photoelectrochemical, and sensor applications are discussed. The Figure shows a one‐layer architecture of Au nanoparticles and tetracationic cyclophanes on an amine‐functionalized ITO support.
Electrically conducting "Nanoparticle nanotubes" (NPNTs), the combination of nanotube geometry with nanoparticle morphology, are prepared by the assembly of gold or silver nanoparticles on the pore walls of a silane-treated nanoporous aluminamembrane template. Self-sustained NPNTs can be obtained by dissolving the template. For more information, see the Communication by Rubinstein and co-workers on the following pages.
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