哺乳动物松果腺:其生物合成能力和生理意义

哺乳动物松果腺是视觉系统的一个退化器官。主要的明-暗周期与松果腺褪黑素生成的昼夜波动同步。明-暗周期的信息通过中枢和外周交感神经的一系列复杂神经元从眼传递到松果腺。在松果腺内,神经信号以褪黑素合成和释放在夜间升高为标志的内分泌信号表现出来。褪黑素是一种高活力的激素,它在调制光照周期对各种哺乳动物的季节性生殖中起着重要作用。褪黑素除影响生殖外,在机体内作用广泛。     

Characterization of transferrin receptors on plasma membranes of lactating rat mammary tissue

Little is known about the transport of iron into the mammary secretory cell and the process of milk iron secretion. The concentration of iron in milk is remarkably unaffected by maternal iron status, suggesting that the uptake of iron into the mammary gland is regulated. It is known that iron enters other cells via transferrin receptor-mediated endocytosis. This study was designed to isolate and characterize the mammary gland transferrin receptor in lactating rat mammary tissue using immunochemical techniques. The existence of functional mammary gland transferrin receptors in lactating rodents was demonstrated using radiolabel-binding techniques. Isolation of mammary transferrin receptors by affinity chromatography was confirmed using immunoelectrophoresis and slot blot analysis. The intact transferrin receptor was found to have a molecular weight of 176 kd as determined by Western blotting followed by scanning densitometry. Reduction of the receptor with beta-mercaptoethanol gave a molecular weight of 98 kd. An additional immunoreactive band of 135 kd was observed. The presence of transferrin receptors in normal lactating rat mammary tissue is likely to explain iron transport into mammary tissue for both cellular metabolism and milk iron secretion.     

A PLIOCENE SPECIES OF VULPES FROM YUSHE,SHANXI

<正> The Yushe County in Shanxi Province is one of the most famous "dragon bone" localities in China. Teilhard de Chardin's monographs on the fossil mammals from Yushe made it well known internationally as well. However, the work so far done there is far from completion, especially when compared with the recent achievements in stratigraphic work on late Cenozoic     

Hybrid DNA tracts may start at different sites during meiotic recombination in gene b2 of Ascobolus

The initiation of hybrid DNA in the b2 spore colour gene was investigated by the analysis of non-Mendelian segregation asci in the progeny of crosses involving several allelic b2 mutations. These analyses showed that, instead of the unique initiation region of hybrid DNA in b2, assumed previously by Paquette and Rossignol (1978), there are multiple sites for hybrid DNA starting. They produce major and minor fractions of hybrid DNA. The major fraction starts upstream of the left end of the gene, propagates rightwards and can cover its entire length. The minor fractions do not span the left b2 end. One of them is detected within the left half of the gene, the others within its right half.     

Characterization of an anion-permeable channel from sugar beet vacuoles: effect of inhibitors

The vacuole occupies 25-95% of the plant cell volume and plays an essential role in maintaining cytoplasmic homeostasis of nutrients and ions. Recent patch-clamp studies identified ion channels and electrogenic pumps as pathways for the movement of ions and metabolites across the vacuolar membrane (tonoplast). At high cytoplasmic Ca²⁺ (>10^-6 M) and negative potentials (inside the vacuole) non-selective channels of the `slow-vacuolar (SV)-type' were activated resulting in anion release or cation influx. In the present study these vacuolar channels were characterized pharmacologically by ion channel inhibitors. The cation-transport inhibitors Ba<sup>2+</sup>, TEA<sup>+</sup> and amiloride caused only partial and reversible block of the `SV-type'channels, whereas anion-transport inhibitors strongly affected the vacuolar channels. Pyridoxalphosphate and the dimethylaminecarboxylate derivates anthracene-9-carboxylic acid and C 144 reversibly blocked the channels up to 70% and Zncl₂ up to 95%. DIDS and SITS inhibited this channel irreversibly up to 95%. The block developed under a variety of experimental conditions using solutions containing combinations of permanent cations and anions. The DIDS binding site is located on the cytoplasmic surface of the tonoplast, as intravacuolar DIDS did not block the channels. DIDS concentrations in the micromolar range, efficient in blocking 70—80% of the `SV-type' channels did not significantly affect ATP-induced or pyrophosphate-induced proton-pumps. Stilbene derivatives may therefore be useful tools for studies on the substrate binding site on this vacuolar channel and for channel isolation.     

Principal/agent theory and decision making in health care

Principal/agent theory, an economics concept that defines an agency relationship as "a contract under which one or more persons engage another person (the agent) to perform some service on their behalf which involves delegating some decision-making authority to the agent," is held to be applicable to the patient/physician relationship, in contrast to the view that this is a fiduciary relationship, not a contractual one. The distinction between fiduciary and contractual relationships is illuminated in the process of evaluating objections to the application of the principal/agent theory to the patient/physician relationship. The ability of the principal/agent theory to reveal important features of advance directives, understood as public documents rather than as confidential instructions from patient to physician, is also examined.     

An extract from Prospects and Risks of Gene Technology: The Report of the Enquete Commission to the Bundestag of the Federal Republic of Germany

We are pleased to publish an English translation of the crucial section on germ line gene therapy from the Report of the German Enquete Commission. This section of the Report raises basic ethical questions concerning embryo research, as well as more specific questions relating to germ line gene therapy. This form of gene therapy involves genetic modification of the germ cells. Such a modification would be passed on to any descendents of the person whose genes had been altered. The Report had previously dealt with somatic gene therapy, which does not affect the germ line and hence is not passed on to descendents.     

Activity of alkaline phosphatase in uterine flushings of dairy cows affected with ovarian cysts or endometritis

Both uterine horns of 14 dairy cows with ovarian follicular cysts, and four animals affected with purulent endometritis were flushed via catheter using 30 ml phosphate buffered saline, following evisceration at a local abattori. Activity in the flushing media of alkaline phosphatase (ALP) and aspartate aminotransferase (GOT) were examined. Ovaries were prepared for light microscopy. Amount and morphological integrity of luteinized tissue found on the ovaries were reflected by correspondent levels in ALP activity, which was higher in the media taken from the ipsilateral to the luteal tissue situated uterine horns (651 +/- 228 vs 244 +/- 62 u/l, n = 3). Only cows having relatively large amounts of luteal tissue on the cystic ovaries (as in luteinized follicular cysts) exhibited very high ALP activity in uterine flushings (2693 +/- 1348 u/l, n = 2). Results suggest the existence of local relationships between luteal tissue in the ovary and the ipsilateral uterine horn in cows with ovarian follicular cysts.