Pyridostigmine enhances even if it does not normalize the growth hormone responses to growth hormone-releasing hormone in patients with Cushing's disease.

Subjects with Cushing's disease have diminished growth hormone (GH) response to growth hormone-releasing hormone (GHRH). The aim of our study was to investigate the underlying mechanism of this diminished GH response in these patients using pyridostigmine (PD), an acetylcholinesterase inhibitor, which is reported to increase GH secretion by reducing somatostatin tone. Eight subjects with untreated Cushing's disease (caused by a pituitary adenoma) and 6 control subjects received GHRH 100 micrograms in 1 ml of saline, as intravenous bolus injection 60 min after (1) placebo (2 tablets, p.o.) or (2) PD (120 mg, p.o.). After GHRH plus placebo, the GH peak (mean +/- SEM) was significantly lower in subjects with Cushing's disease (2.4 +/- 0.5 micrograms/l) compared to control subjects (25.1 +/- 1.8 micrograms/l, p less than 0.05). After GHRH plus PD, the GH peak was significantly enhanced both in subjects with Cushing's disease (7.1 +/- 2.3 micrograms/l, p less than 0.05) and in control subjects (42.3 +/- 4.3 micrograms/l, p less than 0.05). In patients with Cushing's disease, the GH response to GHRH plus PD was lower with respect to the GH response to GHRH alone in normal subjects. We conclude that hypercortisolism may cause a decrease in central cholinergic tone which is in turn hypothesized to be responsible of an enhanced somatostatin release from the hypothalamus. However, other metabolic or central nervous system alterations may act synergistically with hypercortisolism in causing GH inhibition in patients with Cushing's disease.     

Induction of DNA bending by bifunctional intercalating agents of the 7H-pyridocarbazole family

The structures and binding energetics of selected complexes formed between the deoxynucleotides d(CpGpGpCpG).d(CpGpCpCpG), d(CpGpApTpCpG)2, d(GpCpGpCpCpG).d(CpGpGpCpGpC), and d(CpGpCpCpCpG)2 with the DNA bifunctional intercalating agent ditercalinium and three of its rigid linking chain derivatives have been investigated theoretically by means of a molecular mechanics approach that takes into account nucleic acid flexibility, ligand flexibility and solvent dielectric effects (R. Lavery, in: Unusual DNA structures, eds S. Harvey and R. Wells (Pergamon, New York, 1988) p. 189; R. Lavery, in: DNA bending and curvature, eds W.K. Olson et al. (Adenine Press, New York, 1988) p. 191). The piperidinium chains of the bis-intercalating ligands are always located in the major groove of DNA. For the energy-minimized complexes the ligand proceeds to bind following preferentially the 5'-pyrimidine-purine-3' alternating sequence, thus dictating the number of internal exclusion sites. The complexes with three exclusion sites will present (i) a bending of the structure towards the major groove, and (ii) a non-ideal distribution of unwinding angles; complexes with less than three exclusion sites will remain essentially linear. The absence of a bend does not preclude other types of local deformations of the base-pairs such as inclination, buckle and tip. The proposed structures of the d(CpGpApTpCpG)2 complexes are in agreement with NMR structural results. The possible relevance of these findings to a previously proposed mode of interaction for ditercalinium-like DNA ligands is discussed.     

In Situ Analysis of Na,K-ATPase α1- and α3-Isoform mRNAs in Aging Rat Hippocampus

Abstract: Age-related changes in the expression of Na,K-ATPase α1- and α3-isoform mRNAs were analyzed by in situ hybridization in the Fischer-344 rat hippocampus. Quantification of signal density with cRNA probes in rat hippocampus at 3 months of age showed (a) α1 content is 1.5 times higher in granule than in pyramidal cell layers, whereas α3 content shows the opposite ratio and (b) α3 label is found in large clusters related to mossy cells and basket cells and in medium clusters corresponding to interneurons within the dendritic fields of CA1–3. In the 24-month-old rats as compared with the young animals, the α1 signal is increased more than sevenfold in the dendritic fields and is not significantly changed in perikaryal layers. The α3 signal is reduced about threefold ( p < 0.0001, ANOVA, n = 6) in perikaryal layers, is almost completely absent over the interneurons, basket cells, and mossy cells, and is not significantly changed in dendritic fields. These data indicate age-related, cell- and isoform-specific alterations in pretranslational regulation of Na,K-ATPase α isoforms. The striking changes in the dendritic fields, mossy cells, and GABAergic basket cells and interneurons may constitute early and sensitive markers for age-related alterations in hippocampal function, before cell loss.     

Ubiquity of Cysteine- and Metalloproteinase Activities in a Wide Range of Trypanosomatids

We have analysed the proteinase profiles of 11 species from 7 different genera of trypanosomatids by in situ detection of enzyme activities on SDS-PAGE gels containing co-polymerized gelatin as substrate, and the use of specific proteinase inhibitors. Our survey indicates that while cysteine- and metalloproteinases are distributed ubiquitously among trypanosomatids, there are marked differences between the enzyme profiles from the monogenetic (Crithidia, Herpetomonas, Leptomonas) and digenetic (Trypanosoma, Endotrypanum, Phytomonas, Leishmania) species. The detected metalloproteinase activities, ranging in size from 50–100 kDa, partitioned into the detergent-phase after Triton X-114 extraction, while most of cysteine proteinases, of three distinct molecular mass ranges (30–50 kDa, 80–100 kDa and 116–205 kDa), partitioned into the aqueous phase. Thus, within this group of organisms, the metalloproteinase activities seem to be predominantly membrane-associated proteins. We also show that the plant parasites of the genus Phytomonas exhibit a distinctive cysteine proteinase profile that might be exploited further as a criterion for taxonomy of the genus.     

Conservation genetics: beyond the maintenance of marker diversity

One of the major problems faced by conservation biologists is the allocation of scarce resources to an overwhelmingly large number of species in need of preservation efforts. Both demographic and genetic information have been brought to bear on this problem; however, the role of information obtained from genetic markers has largely been limited to the characterization of gene frequencies and patterns of diversity. While the genetic consequences of rarity may be a contributing factor to endangerment, it is widely recognized that demographic factors often may be more important. Because patterns of genetic marker variation are influenced by the same demographic factors of interest to the conservation biologist, it is possible to extract useful demographic information from genetic marker data. Such an approach may be productive for determining plant mating systems, inbreeding depression, effective population size, and metapopulation structure. In many cases, however, data consisting only of marker frequencies are inadequate for these purposes. Development of genealogical based analytical methods coupled with studies of DNA sequence variation within and among populations is likely to yield the most information on demographic processes from genetic marker data. Indeed, in some cases it may be the only means of obtaining information on the long-term demographic properties that may be most useful for determining the future prospects of a species of interest.     

A method for studying histochemical reactions in intact human dentine with a polarizing incident light microscope

Localization and distribution of non-specific esterases has been studied in intact human dentine, by reflected light microscopy. The method of specimen preparation described here permits the visualization of optical sections in depth within the specimen at high optical resolution. Non-specific esterase was found deposited as discrete bands across the tubules. or as droplets, or as a diffuse microsomal variety in the dentinal tubules and in the interglobular spaces. It was possible to distinguish the droplet variety from the microsomal variety, of esterase within the same tubule, by means of a novel optical method using antiflex and differential interference contrast systems of reflected light microscopy. It was found that the coefficient of reflection of dentine diminished gradually from the enamel to the pre-dentine and was inversely related to the scattering of light in dentine. This scattering plays an important role in the formation of the image with reflected light microscopy. The reflected light microscope offers an economically attractive alternative or a supplementary mode of microscopy to the confocal scanning microscopes for studying intact dentine at varying depths.