The role of polyamines in animal cell physiology

The ubiquitous distribution of polyamines in nature suggests that they fulfil some fundamental role(s) in living organisms. In animal cells, polyamine content closely parallels changes in the rate of cell proliferation so that the highest content is always observed in rapidly growing cells. The activity of ornithine decarboxylase (which is the first enzyme in the polyamine biosynthetic pathway) has been found to increase significantly in many systems shortly after exposure to hormones. Also, addition of polyamines greatly stimulates cell-free macromolecular synthesis. Observations such as these have suggested that polyamine accumulation stimulates cell growth and is important in the regulation of macromolecular biosynthesis. However, it is also possible to interpret such data as evidence that polyamine accumulation is the result, not the cause, of increased cell growth. This review supports the latter concept and re-examines the significance of the early induction of ornithine decarboxylase activity and of the stimulatory effects of exogenous polyamine on macromolecular synthesis. It is proposed that the polyamines are important only in maintaining cell growth that has already been stimulated by other factors and that their biosynthesis is to a large extent determined by the accumulation of RNA in the cell.     

Effects of EEG of the osmotic opening of the blood-brain barrier in rats

EEG activity was recorded in rats submitted to osmotic opening of the BBB by intracarotid mannitol infusion.This procedure produced an immediate short-lasting depression of the EEG and a tardive paroxysmal EEG activity. Both these phenomena were more relevant on the ipsilateral hemisphere. In some instances a tonico-clonic seizure was recorded.Pre-treatment with diazepam abolished the occurrence of the tardive EEG and behavioral modifications.In accord with previous findings, focal seizure activity is likely to be responsible for the metabolic abnormalities associated with osmotic opening of the BBB. This preparation therefore produces in the brain unphysiological states in respect to local metabolism and electrical function.     

Influence of exogenous NO donator and variations in the Ca<Superscript>2+</Superscript> content on transport activity related to tonoplast proton pumps in ontogenesis and under hyperosmotic stress

The changes in transport activity of tonoplast proton pumps under the influence of exogenous NO donator and modulation of Ca²⁺ concentration jointly and separately were investigated at different stages of ontogenesis and under hyperosmotic stress. The results suggest that both exogenous NO donator and Ca²⁺ ions can influence the activity of transport processes related to tonoplast and this influence is especially evident in the period of growth and accumulation of metabolites. Under hyperosmotic stress, H⁺-pyrophosphatase plays a more important role than H⁺-ATPase: the activity of the former increases 2.3-fold compared to the control osmotic conditions, whereas the activity of H⁺-ATPase is practically unchanged. H⁺-pyrophosphatase was more responsive to the presence of exogenous NO donator and to variations in Ca²⁺ concentration. The effects of exogenous NO donator on tonoplast proton pumps depended on the concentration of Ca²⁺, which apparently can mediate NO action.     

A physical domain of herpes simplex virus ICP8 is expressed and active in Escherichia coli.

In this report, we describe a series of procedures to assay the function of fusion genes in Escherichia coli and the specific application to the carboxy-terminal third of the herpes simplex virus type 1 (HSV-1) DNA-binding protein ICP8. E. coli cells containing the cloned HSV-1 BamHI G fragment with the HSV-1 BamHI-G-V site, map unit 0.388, nearest the tet promoter in pBR322 synthesized an active product containing a portion of ICP8. The new product induced phenotypic alterations in recipient hosts that were measurable and stable yet limited to the stability of the plasmid. The corresponding cloned DNA from the characterized HSV-1 DNA-binding protein mutant tsHA1 exhibited a predictable temperature-sensitive phenotype. Screening procedures based on the loss of induction of the parental plasmid-induced phenotype in E. coli cells allowed us to select additional mutations. One of these, which conferred a phenotype different from that of tsHA1, was transferred to the viral genome by marker transfer techniques. We suggest that any mutant could be isolated in any sequence, provided that the wild-type coding sequences induce alterations in E. coli cells. The observed alterations should have relevance in determining the mode of action of the protein in its normal environment.     

Antagonism by theophylline of respiratory inhibition induced by adenosine

The effects on respiration of an analogue of adenosine, L-2-N6-(phenylisopropyl)adenosine (PIA), and of the methylxanthine, theophylline, were determined in 19 vagotomized glomectomized cats whose end-tidal PCO2 was kept constant by means of a servo-controlled ventilator. Integrated phrenic nerve activity was used to represent respiratory output. Our results show that PIA, whether given systemically or into the third cerebral ventricle, depressed respiration. Systemically administered theophylline stimulated respiration. Theophylline given intravenously, or into the third ventricle not only reversed the depressive effects of previously administered PIA but caused further increases of respiration above the control level. Prior systemic administration of theophylline blocked both respiratory and hypotensive effects of subsequently administered PIA. Effects of either agent on medullary extracellular fluid pH did not explain the results. We conclude that the adenosine analogue PIA, acts to inhibit neurons in the brain that are involved in the control of respiration and that its effects are blocked by theophylline. We suggest that adenosine acts as a tonic modulator of respiration and that theophylline stimulates breathing by competitive antagonism of adenosine at neuronal receptor sites.     

Effect of bromocriptine on prostacyclin release and cyclic nucleotides on rat aortic and uterine tissues

The effect of bromocriptine mesylate on cyclic nucleotides and PGI₂ release by rat aortic and uterine tissues was investigated. Treatment of rats with bromocriptine (10 mg kg⁻¹ I.P. daily for 14 days) increased PGI₂ release by the thoracic aorta from 0.67 ± 0.02 to 1.4 ± 0.03 ng/mg wet tissue (P < 0.001; n = 6). This increase was antagonized by treatment with sulpiride (15 mg kg⁻¹). Incubation of the arterial tissue with bromocriptive (50 ug ml⁻) in vitro also stimulated PGI₂ release. Mepacrine (160 μg ml⁻) significantly decreased both basal and stimulated PGI₂ release. Incubation of myometrial tissue from pregnant rats with bromocriptine (50 μg ml⁻¹) in vitro significantly decreased PGI₂ release from 1.25 ± 0.07 to 0.60 ± 0.08 ng/mg wet tissue (P < 0.05, n = 6).It also elevated uterine cAMP from 40 ± 2 to 64 ± 3 pmoles/100 mg wet tissue. Both effects were antagonized by sulpiride. Bromocriptine did not affect uterine cGMP or the cyclic nucleotides in the aorta. It is concluded that the increase in aortic PGI₂ was mediated via activation of dopamine D-2 receptors that stimulate phospholipase A₂ enzyme. The decrease in myometrial PGI₂ release may be related to the increase in uterine cAMP resulting from activation of dopamine D-1 receptors. Previous studies suggested a role for PGI₂ in implantation in the rat. The results suggest that the inhibitory effèct on uterine PGI₂ may underlie the reported inhibition of bromocriptine on implantation. On broad basis, the decrease in uterine PGI₂ together with the reported luteolytic effect of bromocriptine point to a potential role for the compound in postcoital contraception.     

Circumsporozoite protein of Plasmodium berghei: gene cloning and identification of the immunodominant epitopes.

The gene encoding the circumsporozoite (CS) protein of the rodent malaria parasite Plasmodium berghei was cloned and characterized. A cDNA library made from P. berghei sporozoite RNA was screened with a monoclonal antibody for expression of CS protein epitopes. The resulting cDNA clone was used to isolate the CS protein gene from a lambda library containing parasite blood-stage DNA. The CS protein gene contains a central region encoding two types of tandemly repeated amino acid units, flanked by nonrepeated regions encoding amino- and carboxy-terminal signal and anchorlike sequences, respectively. One of the central repeated amino acid unit types contains the immunodominant epitopes.