Simultaneous extraction of beta-endorphin and leu- and met-enkephalins from human and rat plasma

A simple, rapid and reliable procedure is described to simultaneously concentrate and purify beta-endorphin, leu- and met-enkephalins from small volumes of human and rat plasma before radioimmunoassay is performed. It uses C18 Sep-Pak reverse phase cartridges. The effectiveness of different protease inhibitors in preventing degradation of opiates by plasma and different solvent systems for eluting opiates is also evaluated.     

On the application of a constitutive equation for whole human blood

In consideration of the pulsatile blood flow in a conduit, the constitutive equation for the whole human blood of F. J. Walburn and D. J. Schneck (Biorheology, Vol. 13, 1976, pp. 201-210) is utilized. Governing equations are solved numerically yielding the velocity and the shear stress distributions. These results are discussed and compared with the Newtonian fluid, Casson's fluid, and Bingham fluid applications.     

Perceptual constraints on optimal foraging: The effects of variation among foragers

Summary We present a simple model of habitat selection in which individuals differ in their ability to discriminate between resource sites' profitabilities. The model investigates the effects of violating the ideal assumption of the well-known ideal free distribution (IFD). We show that (1) variability in perceptual limits within a population can significantly change the distribution of foraging animals even though the mean perceptual limit is the same, (2) the direction of this change depends on the proportion of the population that choose randomly between resource sites and (3) better perceivers are more likely to be found at individually more profitable sites, which, because of undermatching with respect to the IFD, are also the absolutely more profitable sites. We note that variability in perceptual limits almost always led to an undermatching of organisms to resources, thereby extending previous workers' results implying that the incorporation of any form of perceptual limits leads to undermatching with respect to the IFD.     

DNA Polymerase II of Escherichia Coli in the Bypass of Abasic Sites in Vivo

The function of DNA polymerase II of Escherichia coli is an old question. Any phenotypic character that Pol II may confer upon the cell has escaped detection since the polymerase was discovered 24 yr ago. Although it has been shown that Pol II enables DNA synthesis to proceed past abasic sites in vitro, no role is known for it in the bypass of those lesions in vivo. From a study of phage S13 single-stranded DNA, we now report SOS conditions under which Pol II is needed for DNA synthesis to proceed past abasic sites with 100% efficiency in vivo. Overproduction of the GroES(+)L(+) heat shock proteins, which are members of a ubiquitous family of molecular chaperones, eliminated this requirement for Pol II, which may explain why the role of Pol II in SOS repair had eluded discovery. Mutagenesis accompanied SOS bypass of abasic sites when the original occupant had been cytosine but not when it had been thymine; the quantitative difference is shown to imply that adenine was inserted opposite the abasic sites at least 99.7% of the time, which is an especially strict application of the A-rule. Most, but not all, spontaneous mutations from Rif(s) to Rif(r), whether in a recA(+) or a recA(Prt(c)) cell, require Pol II; while this suggests that cryptic abasic lesions are a likely source of spontaneous mutations, it also shows that such lesions cannot be the exclusive source.     

Hypertrophic osteoarthropathy in cystic fibrosis.

Seven adult patients with cystic fibrosis who had radiological evidence of hypertrophic osteoarthropathy were reviewed. In five of the patients symptoms were particularly pronounced at times of acute infective exacerbations; appropriate treatment of the infective episodes resulted in reduction or resolution of the bone pain and joint effusions. Despite this symptomatic relief periosteal changes persisted radiologically and their chronic nature was indicated by changes in the midshafts of long bones. Four of the seven patients had transient gynaecomastia or mastalgia related to infective exacerbations. It is hypothesised that a neuroendocrine mechanism--namely, release of vasoactive intestinal polypeptide--might account for the osteoarthropathy.