Effect of diabetic ketosis on jejunal glutaminase

The intestine is capable of shifting its major fuel source from glutamine in the fed animal to ketone bodies in the fasted animal. Glutaminase (EC 3.5.1.2), the entry enzyme of glutamine oxidation, was examined for its function as a determinant in the utilization of jejunal fuel during diabetes and fasting. Male Sprague-Dawley rats were made ketotic to varied degrees by either fasting or the induction of diabetes with graded doses of streptozotocin (SZ). Specific activity of glutaminase was decreased in the diabetic animals to 64% (p less than 0.05) of controls in the group receiving 110 mg/kg SZ and 82% of controls in the group receiving 65 mg/kg SZ and to 78% (p less than 0.05) of controls in the fasted animals. The activity of glutaminase in the small intestine was negatively correlated to the concentration of beta-hydroxybutyrate in the plasma (r = -0.97, p less than 0.025) and jejunum (r = -0.92, p less than 0.05) for the four groups of animals. Specific activity of glutaminase was decreased in all cell types isolated along the villus-crypt axis of the small intestine from diabetic and fasted rats compared with control rats. The quantity of glutaminase-protein was determined by a dot immunobinding assay using an antibody to purified glutaminase. The activity of glutaminase relative to immunoreactive glutaminase-protein was significantly decreased (p less than 0.05) to 53% of control values in the 110 mg/kg SZ group, 77% in the 65 mg/kg SZ group, and 70% in the fasted group. These data indicate that an inactivation of glutaminase-protein may play a role in the ability of the intestine to shift its fuel source from glutamine to ketone bodies during diabetes and fasting.     

Various proteinase inhibitors decrease prolactin and growth hormone release by anterior pituitary cells

Proteinase inhibitors were tested for their ability to inhibit prolactin (PRL) and growth hormone (GH) release by cultured anterior pituitary cells of the rat. Inhibitors of microbial origin (chymostatin, elastatinal, leupeptin) had either no or a moderate effect on hormone release while some tripeptide aldehydes, especially those with lysine at their C terminus, inhibited markedly PRL and to a lesser extent GH release. Boc-DPhe-Phe-lysinal was the most effective on lactotrophs inhibiting PRL release more than 50% at 10(-4) M. The site(s) of action of tripeptide aldehydes remain to be elucidated.     

Self-Renewal Capacity and Clonal Succession of Haemopoietic Stem Cells In Long-Term Bone Marrow Culture

Abstract. The CFU-s proliferative potential varied greatly during long-term cultivation. Most of the CFU-s in the cultures were represented by cells with low renewal capacity. Pre-CFU-s cells capable of producing multipotential colonies in methylcellulose, which contained CFU-s with a high proliferative potential, were identified in the culture. In cultivation of a mixture of cells of different karyotype their ratio changed rapidly from week to week. the findings were consistent with the hypothesis that haemopoietic stem cells are maintained in the culture by the products of a small number of clones which arise and decline in succession, and that pre-CFU-s, but not the CFU-s themselves, are clonogenic progenitors.     

Low-frequency respiratory mechanical impedance in the rat

A modified forced oscillatory technique was used to determine the respiratory mechanical impedances in anesthetized, paralyzed rats between 0.25 and 10 Hz. From the total respiratory (Zrs) and pulmonary impedance (ZL), measured with pseudorandom oscillations applied at the airway opening before and after thoracotomy, respectively, the chest wall impedance (ZW) was calculated as ZW = Zrs - ZL. The pulmonary (RL) and chest wall resistances were both markedly frequency dependent: between 0.25 and 2 Hz they contributed equally to the total resistance falling from 81.4 +/- 18.3 (SD) at 0.25 Hz to 27.1 +/- 1.7 kPa.l-1 X s at 2 Hz. The pulmonary compliance (CL) decreased mildly, from 2.78 +/- 0.44 at 0.25 Hz to 2.36 +/- 0.39 ml/kPa at 2 Hz, and then increased at higher frequencies, whereas the chest wall compliance declined monotonously from 4.19 +/- 0.88 at 0.25 Hz to 1.93 +/- 0.14 ml/kPa at 10 Hz. Although the frequency dependence of ZW can be interpreted on the basis of parallel inhomogeneities alone, the sharp fall in RL together with the relatively constant CL suggests that at low frequencies significant losses are imposed by the non-Newtonian resistive properties of the lung tissue.     

Effect of Eimeria falciformis infection on the development of toxoplasmosis in mice

White mice previously infected with 10(2), 10(3) or 10(4) Eimeria falciformis oocysts on days 0, 5, 10 or 30 were inoculated per os with 10(1), 10(2), 10(3) or 10(4) Toxoplasma oocysts. While the results obtained for mice with higher Toxoplasma inocula were consistent, animals with 10(1) and 10(2) oocysts previous inoculation with Eimeria showed important differences related with those infected only with Toxoplasma. For example, survival time was higher in animals infected with both parasites, especially if inoculated with Eimeria 30 days before Toxoplasma infection. Furthermore the number of T. gondii cysts found in the animals previously infected with Eimeria was lower compared with mice inoculated with Toxoplasma only. Body weight of mice infected with Toxoplasma previous infection with Eimeria was almost normal in relation to those infected only with Toxoplasma, indicating a probable pathological effect due to the parasite, more evident in "non immunized" mice.     

Two adjacent epitopes on a synthetic dodecapeptide induce lactate dehydrogenase B-specific helper and suppressor T cells

The outcome of an immune response to the enzyme lactate dehydrogenase B (LDH-B) is determined by the interplay between two types of regulatory T lymphocytes, T helper (Th) and T suppressor (Ts) cells. Most mouse strains are capable of generating Th but not Ts cells, and are therefore high responders to LDH-B in terms of both antibody production and antigen-specific T-cell proliferation. However, in strains expressing the b or k allele at the E beta locus of the major histocompatibility complex (Mhc), Ts cells are induced that partly or totally abrogate the proliferative response of Th cells to LDH-B. As a result, these strains are phenotypically medium (E beta b expressors) or low (E beta k expressors) responders. Because the suppression in the LDH-B system is antigen-specific (i.e. it only affects LDH-B-specific Th cells), it is conceivable that the Th and Ts cells use the antigen itself to communicate with each other. To investigate this possibility, we set out to determine which epitopes of the LDH-B molecule are recognized by Th and Ts cells. On the basis of previous studies, a loop structure extending from residue 211 to residue 224 of pig LDH-B appeared to be preferentially recognized by most Th-type (class II Mhc-restricted, proliferating) clones. By using a synthetic peptide, we demonstrate here that both Th and Ts cells are induced by the 211-222 stretch of LDH-B sequence. The use of two further dodecapeptides, each with a single amino-acid substitution in comparison with the pig 211-222 sequence, has revealed that Th and Ts cells have different fine specificities. Thus the loop appears to have two closely linked, if not overlapping, epitopes, one recognized by Th and the other by Ts cells. This finding is consistent with two possible mechanisms of suppression, namely bridging of Th and Ts cells by antigen and subsequent transmission of a suppressive signal, and competition for antigen between Th and Ts cells.     

Sex-dependent effects of non-H-2 loci on lethal GVH reaction induced across an H-2 barrier

We have studied the influence of DBA/2 non-H-2 antigens on the lethal graft-versus-host reaction (GVHR) developed across an H-2 barrier. (DBA/2 x B10.D2)F₁ x B10.D2 (H-2 ^d) backcross (BC) mice were typed for their allelic constitution at nine genetically independent chromosome markers and used as individual cell donors simultaneously for two to three (DBA/2 X B10.D2)F₁ recipients incompatible for DBA/2 non-H-2 antigens alone and two to three (DBA/2 x B10.BR)F₁ recipients incompatible for DBA/2 non-H-2 antigens and H-2^k. The results showed that, when compared with that developed in a control group incompatible for H-2 ^kalone [B10.D2(B10.D2xB10.BR)F₁], the GVHR mortality seen in the presence of an additional incompatibility for DBA/2 non-H-2 antigens [(DBA/2 X B10.BR)F₁recipients] is significantly delayed but only in female mice. An analysis of individual BC donors indicated that this protective effect of DBA/2 non-H-2 antigens correlates with incompatibility for gene(s) linked to the Pgm-1 chromosome marker. In contrast, incompatibility for gene(s) linked to Mod-1 and Es-3 markers accelerates GVHR mortality, but only in male mice. Finally, the results obtained with (DBA/2 x B10.D2)F₁ and (DBA/2 x B10.BR)F₁ recipients were compared; they showed that the intensity of the GVHR developed by cells from individual BC donors against a given set of DBA/2 non-H-2 antigens correlates well with that developed by the same BC donor against the same set of non-H-2 antigens plus H-2^k. We conclude that certain non-H-2 genes (and antigens) can modulate the intensity of the GVHR developed across an H-2 barrier. The number of such genes is probably great; their effects are strong and complex, and can be sex-dependent.     

Influence of the neonatal (clomiphene) inhibition of estradiol imprinting on gonadal development and gonadal and thyroid hormone production later in life

Treatment of newborn rats with clomiphene citrate during the first 5 days of life gave rise to a marked decrease in body mass and to a still greater decrease in gonadal mass. A decrease was also observed in the testicular diameter of the males. The females showed a 43% increase in their estradiol levels over the control and an increase in the sensitivity to gonadotropins. Thyroxine level, which was also determined in view of the known gonadotropin-thyrotropin overlap, showed no change 6 weeks after pretreatment with clomiphene, while the thyroid gland responded to gonadotropin in the same manner as to thyrotropin.     

Adenosine Triphosphatase Activity at the External Surface of Chicken Brain Synaptosomes

An ATP-hydrolysing activity on the external surface of intact synaptosomes from chicken forebrain has been investigated. The observed ATPase activity was not due to leakage of the intracellular ATPase activities, of artefacts resulting from breakage of the nerve endings during the incubation and isolation periods, or to possible contamination by other subcellular particles. Disruption of the synaptosomes resulted in an approximately 2.5-fold increase of the basal, Mg2+-dependent ATPase activity, suggesting that the plasma membrane was acting as permeability barrier to the substrate. ATP hydrolysis was maximal (0.8 mumol Pi/min/mg protein) at pH 8.2 in a medium containing either Mg2+ or Ca2+ ions. Ouabain (0.2 mM) and oligomycin (2 micrograms/mg protein) had no appreciable effect on this ATPase activity. Kinetic studies of the enzyme revealed an apparent Km value of ATP of approximately 4 x 10(-5) M. These data are consistent with the view that the observed ATP hydrolysis was being catalysed by an ectoenzyme, i.e., an enzyme in the plasma membrane of the nerve endings with its active site facing the external medium. The rapid hydrolysis of the released ATP is a suspected function for this ecto-ATPase.     

Thyroid Hormones and Derivatives Inhibit Flunitrazepam Binding

Thyroid hormones and their derivatives were found to inhibit [3H]flunitrazepam binding stereospecifically and in a monophasic manner. Among the compounds tested, D-thyroxine was the most potent inhibitor (IC50 = 0.5 microM). The naturally occurring L-thyroxine was about 40-fold less potent (IC50 = 20 microM). The structure-activity relationships seem to imply that the thyronine base has the principal role in the inhibition of benzodiazepine receptor binding. The type of inhibition was examined with the most potent inhibitor, D-thyroxine, by Scatchard analysis. The apparent dissociation constant (KD) of the [3H]flunitrazepam binding increased and the receptor density (Bmax) decreased as a function of D-thyroxine concentration; this is characteristic of mixed-type inhibition.