Medical biology最新文献

Neuropeptide Y (NPY) is widely distributed in central and peripheral neurons. In sympathetic postganglionic neurons, NPY coexists with noradrenaline. NPY and its structural relative peptide YY (PYY) appear to exert three principally different effects at the sympathetic neuroeffector junction. Firstly, NPY has a direct postjunctional effect; this effect is manifested as a vasoconstriction when studied on the guinea pig iliac vein. Secondly, NPY has an indirect postjunctional effect in that it potentiates the response to various vasoconstrictors; this was studied on the rabbit femoral artery and vein, using noradrenaline and histamine, respectively, as vasoconstrictors. Thirdly, NPY acts prejunctionally in that it suppresses the release of noradrenaline from sympathetic nerve terminals; this was studied in the rat vas deferens. The aim of the investigation was to examine whether the three effects of NPY were mediated by the same type of receptor. For this purpose, we examined the effects of a series of NPY-related peptides, namely NPY, PYY, desamido-NPY, and five C-terminal fragments (NPY 19-36, NPY 24-36, PYY 13-36, PYY 24-36 and PYY 27-36). NPY and PYY were active in all three assay systems. The C-terminal amide appears to be crucial for maintaining the biological activity, since desamido-NPY was inactive in the three test systems. Interestingly, PYY 13-36 was almost as active as NPY and PYY in suppressing the electrically evoked contractions of the vas deferens; PYY 13-36 was inactive in the two other test systems. None of the shorter fragments had any biological activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of two opioid analgesics on performance and their interactions with diazepam were studied double-blind and cross over in ten healthy students. At two-week intervals the subjects received first a single oral dose of placebo, codeine (100 mg) or pentazocine (75 mg). Then, 1 h 30 min later they were all given diazepam (0.25 mg/kg) orally. Lastly, naloxone (0.4 mg) was injected intravenously at 4 h. In addition to this, the subjects on pentazocine received a second 75 mg dose at 3 h. Codeine and pentazocine alone failed to affect performance in objective tests (body sway, digit symbol substitution, flicker fusion, Maddox wing, nystagmus) recorded at 1 h 30 min. Visual analogue scales showed subjective drug effects: pentazocine made the volunteers talkative, contented, interested and energetic, whilst codeine rendered them mentally slow. 75 mg of pentazocine and 100 mg of codeine produced comparable plasma opiate activity (determined in morphine equivalents) according to radioreceptor bioassay with [3H]-dihydromorphine as a ligand. Impaired performance was clear at the tests done 1.5 and 2.5 h after diazepam. No major interactions were found between opiates and diazepam in objective tests with the exception that nystagmus was stronger after the combined treatment than after diazepam alone. Codeine reduced the absorption of diazepam. Subjectively codeine and pentazocine counteracted the effects of diazepam. The subjects overestimated their performance after opiate + diazepam when compared to diazepam alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Forty-four monoclonal antibodies (MAbs) prepared against heat-labile enterotoxins (LTs) from human (LTh) or porcine (LTp) E. coli isolates were characterised, especially with regard to their reactivity with epitopes shared with the heterologous LT and/or cholera toxin (CT), and their toxin neutralising activity. Of 24 MAbs against LTh (all directed against the B subunit portion) 12 cross-reacted with LTp and CT, 4 with LTp but not CT, and 1 with CT but not LTp; 7 MAbs reacted with LTh epitope(s) not shared by either LTp or CT. Among 20 MAbs against LTp (9 directed against the B subunits and 11 against the A subunit) 2 cross-reacted with LTh as well as CT, 13 with LTh but not CT, and 5 MAbs were specific for LTp. Irrespective of whether the anti-LT MAbs were directed against shared or unshared epitopes, or against the A or B subunits, they neutralised their homologous toxin in direct proportion to their toxin-binding titre. The results show how minute differences in enterotoxin primary structures e.g., the LTh and LTp B chains differ in only 4 of 103 amino acid residues, are associated with antigenic epitopes against which toxin-differentiating MAbs with neutralising activity can be produced. Such MAbs are promising tools for species-specific diagnostic detection of enterotoxins in clinical specimens.

The incorporation and esterification by cultured human fibroblasts of vesicle- or low density lipoprotein-derived free [3H]cholesterol was examined. The rate of the cellular uptake of free [3H]cholesterol from lipid vesicles was similar in both LDL-receptor positive lung fibroblasts and in LDL-receptor negative fibroblasts. When human LDL was used as the carrier of free [3H]cholesterol, however, the LDL-receptor positive lung fibroblasts incorporated significantly more [3H]cholesterol than did the LDL-receptor negative cells. The exchangeable free [3H]cholesterol was available for intracellular esterification. The formation of [3H]cholesteryl esters was markedly inhibited by lysosomotropic drugs, either indicating a partly lysosomal esterification reaction, or implying that free [3H]cholesterol moves through the lysosomal compartment on its way to intracellular esterification sites. Either way, the lysosomes appear to have a metabolic role in the metabolism of exchangeable free [3H]cholesterol.

Evidence suggests that exogenous GnRH and agonist analogues have short-term stimulatory effects on rat Leydig cell function - when administered intratesticularly. Since rat Leydig cells possess GnRH receptors and their endogenous ligand has not yet been identified the physiological importance of the observations for testis function is unknown. To address this issue we have determined the consequences of blockade of testis GnRH receptors on Leydig cell function under both normogonadotrophic and hypogonadotrophic stimulation of the testis in vivo. A GnRH antagonist (ANT) was used to achieve receptor blockade but during continuous systemic infusion ANT occupied pituitary GnRH receptors and markedly reduced serum LH, FSH, testosterone, and intratesticular testosterone in adult and 30 d old immature male rats. These results were similar to those obtained by administration of a GnRH antiserum which did not bind to testis GnRH receptors. Thus, blockade of testis GnRH receptors during hypogonadotrophism did not produce additional inhibition of steroidogenesis by Leydig cells. However, direct continuous infusion of ANT into one testis produced greater than 90% occupancy of GnRH receptors while reducing GnRH receptors by only 50% in the contralateral testis. Unilateral intratesticular infusion did not reduce serum LH, FSH, Prolactin or testosterone levels despite 75% occupancy of pituitary GnRH receptors. Thus, both ANT infused and saline infused testes were exposed to the same gonadotrophic stimulants but in the former GnRH-R were essentially non-existent. Compared to the control testis, the ANT infused testis showed a 20-30% reduction in LH, FSH, lactogen receptors and 30-40% fall in testosterone content. Identical results were obtained in adult and 30 d-old male rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Data from several experimental approaches strongly suggest that Sertoli cells exert a paracrine control of the two main testicular functions, androgen secretion and spermatogenesis. Further evidence supporting this role of Sertoli cells was obtained by coculture of Sertoli cells with other testicular cells. Coculture of pig or rat Sertoli cells with pig Leydig cells produces an increase in the hCG receptor number and an increase in the steroidogenic activity of Leydig cells. Pretreatment with FSH further increases the values of these two parameters. These biochemical changes were associated with ultrastructural changes in Leydig cells. The effects of Sertoli cells on Leydig cells depend upon the ratio of the two cells and on the substrate in which the cells are cultured. Moreover, Leydig cells produce an increase in the FSH receptor number and in the FSH stimulation of plasminogen activator production by Sertoli cells. Coculture of rat or pig Sertoli cells with rat germ cells, induces an increase in the RNA and DNA biosynthetic activities of germ cells. Most of the stimulatory effects seemed to be mediated by diffusible factors, secreted by Sertoli cells, but full expression of the stimulatory action was observed when germ cells were in contact with other cells. In this coculture system, a fraction of rat germ cells containing mainly mature forms of spermatocytes inhibited rat Sertoli cell RNA and DNA synthesis, but had no effect on pig Sertoli cells. On the contrary, a fraction of rat germ cells richer in spermatogonias and preleptotene spermatocytes, stimulated rat Sertoli cell DNA synthesis but was without effect on pig Sertoli cells. These results clearly show that the stimulatory effects of Sertoli cells on Leydig and on germ cells which are not species specific are mediated mainly by diffusible factors, the secretion of which is regulates by FSH.

The results of our recent studies on purified rat Leydig cells indicate that there are no major qualitative differences in the stimulating effects of LH and LHRH agonists on steroidogenesis via mechanisms that are dependent on calcium. This was demonstrated by using inhibitors of calmodulin and the lipoxygenase pathways of arachidonic acid metabolism. Using the fluorescent indicator quin-2, it was shown that LH and LHRH agonist increase intracellular calcium levels; LH was more potent than LHRH agonist (max increase in concentrations obtained were 500 nM and 60 nM respectively). This difference was probably the result of a direct effect of cyclic AMP (whose production is stimulated by LH but not by LHRH) because cyclic AMP analogues were as potent as LH in increasing calcium levels. These studies indicate a major role for calcium in the control of steroidogenesis in testis Leydig cells.

Rat testicular interstitial fluid (IF) contains a polypeptide factor(s) which when added to Percoll-purified rat Leydig cells in vitro, enhances both basal and hCG-stimulated production of testosterone in a dose-dependent manner. To assess the possible physiological significance of this factor(s), its levels in testicular IF from individual rats were assessed following the suppression of intratesticular levels of testosterone by either (a) treatment with anti-LH, (b) induction of unilateral cryptorchidism, or (c) treatment with ethane-1,2-dimethane sulphonate (EDS). These treatments suppressed testosterone levels in IF by 80 to 99% and in each instance levels of the IF-factor were increased. This increase occurred as early as 5h after anti-LH treatment, but restoration of normal intratesticular levels of testosterone at 20-40 h after anti-LH treatment by testosterone injection failed to normalize levels of the IF-factor. In contrast, injection of LH into normal rats raised IF testosterone to supranormal levels and this was associated with a reduction in levels of the IF-factor, and similar effects of hCG were observed in rats pretreated with anti-LH. Therefore, whilst these studies suggest that the IF-factor(s) may be of physiological importance, its local regulation does not appear to involve a straightforward negative feedback control by testosterone.

Most blood cells derived from the bone-marrow are known to possess only a limited number of heavily sialylated glycoproteins. We have recently isolated a major sialoglycoprotein on leukocytes and found that this glycoprotein, termed leukosialin, is ubiquitously present on various human leukocytes, granulocytes, monocytes/macrophages and T- and B-lymphocytes. Our studies showed that leukosialin is significantly glycosylated by O-linked oligosaccharides (90 chains/molecule). The structures of those O-linked oligosaccharides are characteristic to each cell lineage and maturation stage. The polypeptide portion of these molecules are, however, apparently the same, with a molecular size of 52 KDa. So it will be interesting to explore the possibility that leukosialin expresses different functions by having different O-glycosylation in a variety of hematopoietic cells.

Glucocorticosteroids are highly effective in treating various acute and chronic diseases, but their long-term use is often accompanied by side effects, such as osteoporosis of skeleton and bones and atrophy of the skin. Clinically, many of these side effects involve changes in connective tissue. Glucocorticoid effects on connective tissue metabolism are, however, sometimes beneficial for instance, in the treatment of keloids or autoimmune connective tissue diseases. Recent advances in the biochemical technology have provided tools to examine the molecular mechanisms by which glucocorticoids affect connective tissue. These studies have shown distinct alterations in the extracellular matrix as a result of glucocorticoid treatment. This knowledge is useful for the further development of glucocorticosteroids with desirable action spectrum and with minimal side effects.