Release Of Total Radioactivity Research Articles

Interactions between the monocyte/macrophage and the vascular smooth muscle cell. Stimulation of mitogenesis by a soluble factor and of prostanoid synthesis by cell-cell contact.

The effect of soluble factors from the monocyte/macrophage (M phi) on cell proliferation and the functional effects of cell-cell contact on the arachidonic acid (AA) cascade were studied with vascular smooth muscle cells (SMCs). Peripheral blood M phi s were isolated by adherence or in a Percoll gradient, and alveolar M phi s were obtained by lavage. Conditioned medium (CM) was prepared by preincubating M phi s with medium alone or by separating SMC and M phi cocultures by a membrane insert. Cell proliferation (image analysis) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha, radioimmunoassay) were measured in SMCs. Labeled prostanoids and other eicosanoid metabolites were isolated by high-performance liquid chromatography from SMCs prelabeled with 14C-AA. M phi s did not synthesize 6-keto-PGF1 alpha. The CM enhanced proliferation but did not stimulate 6-keto-PGF1 alpha synthesis in SMCs. However, cell-cell contact in cocultures of SMCs with the same concentration of M phi s used to generate CM resulted in increased 6-keto-PGF1 alpha synthesis by SMCs. Since the stimulatory effect of cell contact was not blocked by butylated hydroxytoluene, it could not be attributed to an oxidative burst from M phi s. Functional studies showed that the stimulatory effect of cell contact was enhanced by exogenous free AA and by endogenous AA release through A23187. Release of total radioactivity from prelabeled SMCs was enhanced by cell contact, and this effect was blocked by indomethacin (IM). Cell contact did not increase the release of free AA from prelabeled SMCs, even in the presence of IM. Finally, cell contact only stimulated the formation of prostanoids (IM-sensitive eicosanoid metabolites) from prelabeled SMCs. Lipoxygenase and other products of AA were not formed through cell-cell contact. These data showed that M phi s express a soluble factor that enhances SMC proliferation without affecting prostanoid synthesis. Subsequent cell contact between SMCs and M phi s stimulates prostanoid synthesis, which may possibly serve as a local and focal homeostatic mechanism for the regulation of uncontrolled SMC proliferation in atherogenesis.

Inhibition of Microcystin-Induced Release of Cyclooxygenase Products from Rat Hepatocytes by Anti-Inflammatory Steroids

We showed previously that exposure to microcystin causes eicosanoid release. That study was extended further to test the effect of glucocorticoids on microcystin-induced release of [14C]arachidonic acid and its metabolites from rat hepatocytes previously treated with [14C]arachidonic acid. Release of total radioactivity was 4-fold greater from hepatocytes after 2-hr incubation with 1 microM microcystin than after incubation with control medium. Fluocinolone pretreatment decreased the microcystin-induced synthesis and release of prostacyclin by 24 +/- 2.6% (P less than 0.05) and thromboxane B2 by 39 +/- 3% (P less than 0.025). Treatment of hepatocyte cultures with either microcystin (1 microM) or steroids had no effect on cell viability or total cell protein. Total radioactivity released into the incubation medium was not affected by glucocorticoid alone. Under these conditions, the quantities of both prostaglandin F2 alpha and prostaglandin E2 released were not significantly different when control and microcystin-treated cultures were compared. The half-maximal inhibition (IC50) values obtained from the dose-response data for the inhibition of arachidonic acid release by steroids were comparable with normal cortisol levels in humans. Dose-response curves gave the following rank order of inhibitory potency: fluocinolone greater than dexamethasone greater than hydrocortisone. These results suggest that glucocorticoid therapy might be beneficial in microcystin toxicosis.

Dysregulation of arachidonic acid release and metabolism by atopic mononuclear cells

We studied the ability of monocytes to metabolize [3H]arachidonic acid (AA) provided exogenously by activated T cells, and the extent to which dexamethasone suppressed eicosanoid production by normal and atopic cells. [3H]AA metabolites were identified using a reverse-phase high pressure liquid chromatography system (HPLC). Unstimulated and PHA-stimulated T cells from normal and atopic subjects exhibited a similar uptake and time-dependent release of radiolabel, 90% of which was identified as free AA. The addition of autologous normal and atopic monocytes to these cultures enhanced the release of radiolabel, even in the absence of stimulation with mitogen. Atopic T cell/monocyte cultures released significantly (P = 0.046) more radiolabel than normal cells when stimulated with PHA. Furthermore, the monocytes from both normal and atopic subjects metabolized T cell derived [3H]AA into cyclo-oxygenase (CO) and lipoxygenase (LO) products. Under unstimulated conditions, atopic cells produced significantly (P = 0.04) less CO products than normal cells. In contrast, under PHA and calcium ionophore-stimulated conditions, the atopic cells produced significantly (P = 0.048) more prostaglandins than normal donor cells. Furthermore, although the total release of radioactivity was comparable in both groups, significantly less (P = 0.02) free AA remained in ionophore-stimulated culture supernatants from atopic cells. In order to study the regulation of AA release by normal and atopic T cells, dexamethasone (1 microM) was added to T cell cultures. Dexamethasone inhibited the release of [3H]AA from normal T cells to a significantly (P = 0.003) greater extent than it did to atopic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Chernobyl radionuclides in a Black Sea sediment trap.

The Chernobyl nuclear power station accident released large quantities of vaporized radionuclides, and, to a lesser extent, mechanically released small (less than 1-10 micron) aerosol particles. The total release of radioactivity is estimated to be out of the order of 1-2 x 10(18) Bq (3-5 x 10(7) Ci) not allowing for releases of the xenon and krypton gases. The 137Cs releases of 3.8 x 10(16) Bq from Chernobyl can be compared to 1.3 x 10(18) Bq 137Cs released due to atmospheric nuclear weapons testing. Chernobyl-derived radionuclides can be used as transient tracers to study physical and biogeochemical processes. Initial measurements of fallout Chernobyl radionuclides from a time-series sediment trap at 1,071 m during June-September 1986 in the southern Black Sea are presented. The specific activities of 137Cs, 144Ce and 106Ru in the trap samples (0.5-2, 4-12 and 6-13 Bq g-1) are independent of the particle flux while their relative activities reflect their rates of scavenging in the order Ce greater than Ru greater than Cs.

External Ca-independent release of norepinephrine by sympathomimetics and its role in negative feedback modulation.

The release of [3H]norepinephrine from isolated mouse vas deferens has been measured. 1-Phenylephrine and 1-norepinephrine significantly enhanced the spontaneous release of radioactivity. As shown by a combination of HPLC and scintillation spectrometry, the release of total radioactivity in response to 1-phenylephrine or 1-norepinephrine consisted mainly of [3H]norepinephrine. Evidence has been obtained that the release of endogenous norepinephrine by exogenous norepinephrine and 1-phenylephrine is independent of the external Ca2+ concentration. The released endogenous norepinephrine in turn inhibits the release of norepinephrine in response to electrical field stimulation. In the presence of yohimbine, the enhancement of spontaneous release due to 1-phenylephrine (or to 1-norepinephrine) was not affected, whereas there was a significant superimposed release of [3H]norepinephrine in response to field stimulation, indicating that the inhibition of stimulation-induced norepinephrine release is an alpha 2-adrenoceptor-mediated process. An important consequence of these findings is to question previous interpretations that the effects of administration of 1-norepinephrine or 1-phenylephrine are due exclusively to their direct effects on the effector cells. The Ca-independent release of endogenous norepinephrine might partly initiate their pharmacological responses. It is concluded that this Ca-independent release is of functional importance, since norepinephrine may accumulate in a concentration sufficient to modulate the release of norepinephrine from varicosities in response to electrical stimulation.

Effects of adrenergic drugs on pressor responses to hypothalamic stimulation.

The posterior area of the hypothalamus of anaesthetized cats was superfused with artificial cerebrospinal fluid through a push-pull cannula. Electrical stimulation with the non-insulated tip of the cannula elicited a rise of the mean arterial blood pressure. Superfusion of the hypothalamic posterior area with tolazoline or piperoxan caused a dose-dependent inhibition of the pressor responses to electrical stimulation. Labelling of the posterior area with 3H-noradrenaline 2 h before the beginning of the superfusion showed that the inhibitory effect of tolazoline on the pressor responses was accompanied by an increased release of total radioactivity and an enhanced per cent release of 3H-noradrenaline, while that of its metabolites was reduced. Superfusion of the nucleus of the solitary tract with clonidine evoked a dose-dependent inhibition of the pressor responses to electrical stimulation of the ipsilateral hypothalamic posterior area. It is concluded that 1. Alpha-adrenoreceptors are present in the posterior hypothalamus and are involved in the blood pressure rise elicited by its electrical stimulation. 2. A feedback mechanism is present in the hypothalamus which regulates the release of noradrenaline and which is mediated by alpha-adrenoreceptors; inhibition of the regulation of the release of noradrenaline by alpha-adrenoreceptors blocking agents leads to an enhanced release of the neuro-transmitter. 3. Activation of the inhibitory pathways of the nucleus of the solitary tract by clonidine diminishes the pressor response to electrical stimulation of the hypothalamic posterior area. 4. Two adrenergic systems localized in different areas of the central nervous system oppose each other in their regulatory effects on arterial blood pressure.