Time-dependent subpopulation induction in heterogeneous tumors

Time-dependent induction of clonal heterogeneity in the neoplastic micro-environment is analysed within the context of a competitive ecology. A model that describes a constant source for clonal emergence was analysed by Michelsonet al. (1987) as an extension of a model proposed by Jansson and Revesz (1974). The extended model has been termed the JRE Model. This paper extends these analyses to time-dependent emergence rates which may represent induction in the presence of a cytotoxic agent. If the analysis is constrained to the tumor micro-environment, and if the emergent subpopulation is drug resistant, then the model may describe the induction and emergence of drug resistant subclones in a growing neoplasm. Asymptotic closed form solutions are derived for a class of emergence rate functions which decay asymptotically to a constant mutation rate. This underlying mutation rate may represent spontaneous mutation to the resistant phenotype, and has been analysed stochastically (Coldmanet al., 1985). The asymptotic solutions to the time-dependent model approach the steady state solution for the JRE Model which represents the dynamics observed in the presence of a constant, spontaneous mutation rate. The clinical and biological implications of these results are discussed. Research support provided in part by Hungarian National Foundation for Scientific Research Grant No. 6032/6319 and ACS Grant IN45-Z and ACS PDT 243B.     

Characterization of acute and latent herpes simplex virus infection of dorsal root ganglia in rats.

The characteristics of HSV type-1 infection following subcutaneous inoculation in the dorsum of one hind paw of Sprague-Dawley rats were studied to determine whether infection in rats might more closely parallel the infection in man than is seen in other animals. The serologic and virologic characteristics of acute and latent ganglion infection conformed to those of human infection. Immunohistochemical studies suggested that sensory ganglion infection arose via centripetal axonal migration of virus as is hypothesized in man. In rat, small type B neuronal cell bodies appeared central to the maintenance of latent infection and reactivation observed during cocultivation of lumbar ganglia. Acute and latent lumbar sensory ganglion infection in rats after subcutaneous hind paw injection of HSV-1 appears to be another suitable model of this infection in man.     

Cis-analysis of a seed protein gene promoter: the conservative RY repeat CATGCATG within the legumin box is essential for tissue-specific expression of a legumin gene

A 2.4 kb fragment containing the 5'-flanking region and the 5'-noncoding sequence of the Vicia faba legumin gene LeB4 mediates high level seed-specific expression in transgenic tobacco plants. Deleted derivatives of this legumin upstream sequence were fused to the npt-II reporter gene to determine the tissue-specific activity of the chimeric constructs in stably transformed tobacco plants. The results indicate the presence of positive regulatory, enhancer-like cis elements within 566 bp of the upstream sequence. Most importantly, however, these elements are only fully functional in conjunction with the core motif CATGCATG of the legumin box around position -95, since destruction of the motif by a 6 bp deletion in an otherwise intact 2.4 kb upstream sequence drastically reduces expression in seeds. At the same time, low level expression in leaves is observed. The occurrence of similar CATGCATG consensus cis elements with alternating purine and pyrimidine base pairs in front of several other plant genes suggests a functional role of the motif in a wider range of plant promoters.     

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.     

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.     

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.     

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.