Showing papers by "Erasmus University Rotterdam published in 1976"

Evidence for inhibin-like activity in bovine follicular fluid.

Abstract: THE negative feedback action of testicular steroids on circulating levels of luteinising hormone (LH) is well known. It is less clear how the testis influences follicle-stimulating hormone (FSH). The existence of ‘inhibin’, a water-soluble testicular product that inhibits the secretion of FSH, was first postulated in 1932 (ref. 1); recently, inhibin activity has been detected in rete testis fluid2, testicular tissue3, spermatozoa4 and seminal plasma5. Immunisation of rabbits with the inhibin fraction of bull seminal plasma has produced an antiserum which raised plasma FSH levels when injected into male and female rats6. It has been suggested7 that, in the male, inhibin may be produced by the Sertoli cells of the testis. If this is the case, one wonders if inhibin could also be produced by granulosa cells of the ovary. We have, therefore, looked for the presence of a specific FSH-suppressing agent in ovarian follicular fluid by comparing the effects of fluid and peripheral plasma on the levels of FSH and LH in newly castrated male rats.

Fatty acid activation: specificity, localization, and function.

Abstract: Publisher Summary This chapter discusses fatty acid activation Most cells can metabolize fatty acids The most important pathways are β-oxidation to acetyl-CoA; esterification with glycerol phosphate, glycerol derivatives, sphingosine, glycol, and long-chain alcohols; chain elongation; desaturation; and α and ω oxidation Fatty acid molecules are completely ionized at physiological pH values The carboxylate ion is chemically unreactive toward nucleophilic substitution Esters, thioesters, and acid anhydrides, in which both the carboxylate resonance and the negative charge on the carboxyl group disappear, are more reactive Both microsomal and mitochondrial long-chain fatty acid activation is stimulated by the presence of high concentrations of several salts Both activities are also strongly stimulated by the addition of the particle-free supernatant from several rat tissues Purified mammalian acyl-CoA synthetases are very specific in their nucleotide requirement

On Invariants, Canonical Forms and Moduli for Linear, Constant, Finite Dimensional, Dynamical Systems

Abstract: A linear, constant, finite dimensional dynamical system is thought of as being represented by a triple of matrices (F,G,H), where F is an n × n matrix, G an n × m matrix, and H an p × n matrix; i.e. there are m inputs, p outputs and the state space dimension is n. The dynamical system itself is $$ \mathop {\text{x}}\limits^. = {\text{Fx}}\;{\text{ + }}\;{\text{Gu,}}\;{\text{y}}\;{\text{ = }}\;{\text{Hx}} $$ (1.1) or, if one prefers discrete time systems $$ {{\text{x}}_{{\text{t}} + 1}} = {\text{F}}{{\text{x}}_{\text{t}}}\;{\text{ + }}\;{\text{G}}{{\text{u}}_{\text{t}}}{\text{,}}\;{{\text{y}}_{\text{t}}}\;{\text{ = }}\;{\text{H}}{{\text{x}}_{\text{t}}} $$ (1.2) A change of coordinates in state space changes the triple of matrices (F,G,H) into the triple (SFS-1, SG, HS-1). Let DS denote the space of all triples (F,G,H); i.e. DS is affine space of dimension np + n2 + nm.

Resolution problems in echocardiology: a source of interpretation errors.

Abstract: Resolution is the ability of the echocardiographic system to distinguish closely lying structures. This is usually defined in two directions: laterally (lateral resolution) and in depth (axial resolution). With use of short ultrasonic pulses, axial resolution is not a major problem. By far the more important problem is the limited lateral resolution that results from the finite beam width of current ultrasonic devices. This results in the display of echoes that originate from off-axis structures. How these off-axis or “spurious echoes” affect the display is a function of the way the echographic information is handled. In conventional M-mode tracings, spurious echoes are displayed at a site where there is no directly corresponding anatomic structure, whereas with two-dimensional imaging, these echoes may result in important distortions of structures. The underlying principles are illustrated by a clinical experiment wherein the ball of a Starr-Edwards mitral valve prosthesis serves as a target of known shape and dimensions. These data are used to elucidate some of the problems and potential errors encountered in the interpretation of clinical M-mode recordings of the aorta, mitral valve and the left ventricular endocardium as well as their cross-sectional analysis. They also explain the present limitations of quantification of left ventricular performance from crosssectional images.

Cyclic nucleotide-dependent phosphorylation of intestinal epithelium proteins.

Abstract: THE function of cyclic AMP as an important regulator of ion and fluid transport in the small intestine -has been well documented1. The non-dividing (maturating crypt cells and the differentiated villous cells are the main sources of cyclic AMP-mediated secretion of water and electrolytes during experimental cholera in rats and guinea pigs2,3. It has been proposed that cyclic AMP, analogous to its possible mode of action in kidney4 and toad bladder5 epithelial cells, controls ion movements across the apical membrane of the intestinal epithelial cell (enterocyte) by changing the state of phosphorylation of some protein(s) in the intestinal brush border6. Studies have shown, however, that adenylate cyclase2,7, the high affinity form of particulate cyclic AMP phosphodiesterase (unpublished observation) and receptor bound cyclic AMP (ref. 8) are localised predominantly in the basal–lateral membranes of the villous cell. In contrast, the luminal membrane is enriched in components of the cyclic GMP system, such as guanylate cyclase9,10, cyclic GMP phosphodiesterase (unpublished observation) and receptor-bound cyclic GMP (ref. 8). The polarisation of both systems in the enterocyte would be more consistent with a model in which cyclic GMP, rather than cyclic AMP, is involved in the regulation of ion transport across the brush border, whereas cyclic AMP action might be confined to the contraluminal membrane. To test this hypothesis further, we have studied the subcellular distribution of specific substrate proteins for cyclic nucleotide-dependent protein kinases in isolated villous cells from rat small intestine.

The effect of calcium ions on testosterone production in Leydig cells from rat testis.

Abstract: Leydig-cell suspensions, prepared from rat testes, were incubated with different amounts of Ca2+ with and without added luteinizing hormone. The basal testosterone production in the absence of luteinizing hormone was unaffected by the Ca2+ concentration in the incubation medium. The luteinizing hormone-stimulated testosterone production, however, was progressively decreased in the absence of Ca2+ to one-third of that with 2.50 mM-Ca2+. This decrease in luteinizing hormone-stimulated testosterone production was independent of the different concentrations of luteinizing hormone (0-10mug/ml) used and could be restored by the addition of Ca2+ to the incubation medium. The restoration of the stimulation was achieved within 30 min after the addition of Ca2+ to the medium. Activation of cyclic AMP-dependent protein kinase by luteinizing hormone was not decreased by omission of Ca2+ from the incubation medium, suggesting that Ca2+ may be involved in steroidogenesis at a stage beyond the luteinizing hormone receptor-adenylate cyclase-protein kinase system.

Moduli and canonical forms for linear dynamical systems II : the topological case

Abstract: In this paper we study real linear dynamical systems\(\dot x = Fx + Gu,y = Hx,x \in R^n \) = state space,u ∈R m = input space,y ∈R p = output space, under the equivalence relation induced by base change in state space; or in other words we study triples of matrices with real coefficients (F, G, H) of sizesn × n, n × m, p × n respectively, under the action(F, G, H.) →(TFT−1,TG, HT−1) ofGL n (R), the group of invertible realn × n matrices. One of the central questions studied is: “do there exist continuous canonical forms for this equivalence relation?”. After various trivial obstructions to the existence of such forms have been removed the answer is very roughly: no ifm ≥ 2, p ≥ 2, yes ifm = 1, orp = 1. For a precise statement cf. theorem 1.7.

Correlation of protein kinase activation and testosterone production after stimulation of Leydig cells with luteinizing hormone.

Abstract: The effect of different doses of luteinizing hormone on activation of protein kinases, cyclic AMP and testosterone production was studied in purified rat testis Leydig-cell preparations in the presence of 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor). In addition, the nature of the protein kinases present in these cells and other tissues was investigated. The following results were obtained. 1. With all the amounts of luteinizing hormone used (0.1-1000 ng/ml), both activation of protein kinase and stimulation of testosterone production were demonstrated. With the lowest amount of luteinizing hormone (0.1 ng/ml), an 8.4+/-0.9% (S.E.M.,n=6) stimulation of protein kinase activation occurred, increasing to 100% with 1000 ng/ml, compared with 3.2+/-1.0%(S.E.M.,n=7) and 100% stimulation of testosterone production with 0.1 and 100 ng/ml respectively. 2. With amounts of luteinizing hormone up to 1 ng/ml (which gave half-maximal stimulation of testosterone production) no detectable increases in net cyclic AMP production were obtained. With higher amounts of luteinizing hormone, cyclic AMP production increased, but maximal production was not reached with 1000 ng/ml. 3. Two isoenzymic forms of protein kinase were present in Leydig cells and seminiferous tubules; type I was eluted with 0.075 M-and type II with 0.22-0.25 m-NaCl from DEAE-cellulose columns. 4. The protein kinase activity was not affected by the presence of erythrocytes in the Leydig-cell preparation, but varied depending on the type of histone used as substrate (histone F2b greater than mixed greater than histone F1).

Postnatal undernutrition: an alternative method.

Abstract: Rat pups were undernourished from birth by placing them for 12 hr/day with a normal lactating mother and 12 hr/day with a nipple-ligated mother each day for 25 days. The method resulted in a marked delay in the body growth of the undernourished pups, especially during the first 2 weeks of life. Observations of the behavior of the mothers towards the underfed pups were made at different times of the day and compared to the behavior of the mothers suckling well-fed pups. The results show that (1) nipple-ligated mothers are able to provide adequate maternal care for undernourished pups, and (2) both ligated and nonligated mothers caring for underfed pups spend more time with those pups than mothers caring for well-fed pups.

The relation between cell proliferation, differentiation and ultrastructural development in rat intestinal epithelium.

Abstract: The ultrastructural development of the principal cells in rat small intestine was studied by morphometric analyses in relation to the exact cell position along crypt and villus. From the bottom to the tip of the crypt, a gradual increase occurred in absolute size of the total cell, the cytoplasm, the terminal web and of nearly all cell organelles. Also, the relative size of the cytoplasm, mitochondria, microvilli and endoplasmic reticulum increased during crypt cell differentiation. No sudden changes in ultrastructure were observed in the so-called “critical decision zone”, normally located halfway up the crypt where the proliferative activity ceases. At the crypt-villous junction a 1.4–3 fold increase in cell size, cytoplasm, terminal web and of most organelles was noted. Expansion of the proliferative cell compartment over the total length of the crypt as occurs during recovery after a low X-irradiation dose (72 h after 400 R) does not affect the normal development of cellular ultrastructure. These findings are discussed in relation to biochemical and cell kinetic data.

Radiation myelopathy of the thoracic spinal cord

Abstract: The authors reviewed and recalculated the dose, number of fractions, and overall treatment time of 19 patients who developed radiation myelopathy of the thoracic spinal cord after radiation therapy for carcinoma of the lung. The 19 patients represented the "usable" yield of 4 different hospitals over a 10-year period; from the files of these institutions over the same time period, the data of 24 patients who received essentially the same treatment but did not developed radiation myelopathy were analyzed. There were no significant differences between the total dosages employed, the number of fractions, or the dose per fraction. There was, however, a difference in the overall treatment time, in the sense that the treatment of those patients who later developed radiation myelopathy was longer than that of the nonmyelopathy cases. In contrast to expectation, the blood pressure of the patients who later developed radiatiation myelopathy was lower than that of the nonmyelopathy cases.