Modulation of cyclic AMP accumulation in GH3 cells by a phorbol ester and thyroliberin.

4 beta phorbol-12, 13-dibutyrate (PDBu) stimulated cyclic AMP accumulation in GH3 pituitary tumour cells in the presence of isobutylmethylxanthine. This effect persisted after preincubation of cells with cholera or pertussis toxins. In contrast, vasoactive intestinal polypeptide (VIP)-stimulated cyclic AMP accumulation was inhibited by PDBu in a dose dependent fashion (IC50 = 5.

Studies on the involvement of calcium and calmodulin in the action of growth-hormone-releasing factor.

A possible role for Ca2+ and calmodulin in the action of growth-hormone-releasing factor (GHRF) was investigated. Low extracellular Ca2+ (less than 100 microM), methoxyverapamil, flunarizine, cinnarizine, and Co2+ decreased both basal and GHRF-stimulated growth-hormone secretion, but did not totally inhibit GHRF-stimulated secretion. A calmodulin antagonist, W7, abolished GHRF-stimulated GH secretion, with no effect on basal secretion.

Discriminative effect of gamma-glutamyl transpeptidase inhibitors on metabolism of leukotriene C4 in peritoneal cells.

Leukotrienes are naturally-occurring metabolites of arachidonic acid that are formed via the 5-lipoxygenase pathway in several tissues. Rat peritoneal cells (RPC) can produce leukotrienes C4, D4 and E4 (LTC4, LTD4 and LTE4) in response to stimulation with the calcium ionophore A23187 (1,2). The mechanism of enzymatic conversion of LTC4 to LTD4 is presumed to be via the action of gamma-glutamyl transpeptidase (gamma-GTPase, Figure 1) and has been demonstrated with purified enzymes from rat and porcine kidneys (3-6).

The relationship between pertussis-toxin-induced ADP-ribosylation of a plasma-membrane protein and reversal of muscarinic inhibition of prolactin secretion in GH3 cells.

Pertussis toxin (PT) caused the ADP-ribosylation of a Mr-41 000 protein in GH3-cell plasma-membrane preparations. This effect, and muscarinic inhibition of prolactin release, were reversed at similar rates by pretreatment of intact cells with PT. These results suggest that the Mr-41 000 protein is modified in intact GH3 cells, and that this protein (a component of the putative Ni unit of adenylate cyclase) is involved in the expression of muscarinic inhibition.

Pharmacological and biochemical evidence for metabolism of peptide leukotrienes by guinea-pig airway smooth muscle in vitro.

It has been demonstrated that leukotriene (LT)C4 is metabolized to LTD4 via the action of the enzyme gamma-glutamyl transpeptidase. LTD4 is, in turn, converted by the enzyme aminopeptidase to LTE4. In the present study, the pharmacological effects of the aminopeptidase inhibitor, L-cysteine and the gamma-glutamyl transpeptidase inhibitor, L-serine borate, on peptide LT concentration-response curves were evaluated in isolated guinea-pig trachea.

A radioimmunoassay for the histamine H2-antagonist, tiotidine.

A specific and sensitive radioimmunoassay (RIA) for the histamine H2-antagonist, tiotidine, has been developed. The assay is based upon competition of tiotidine with [3H]-tiotidine for antibody (Ab) obtained from immunized rabbits. The immunogen used was a glutaraldehyde coupled conjugate of the tiotidine derivative (ICI 147,655) and bovine serum albumin (BSA).

Pertussis toxin blocks the inhibitory effect of muscarinic cholinergic agonists on cyclic AMP accumulation and prolactin secretion in GH3 anterior-pituitary tumour cells.

The inhibition of prolactin secretion and cyclic AMP accumulation in GH3 cells by muscarinic agonists was blocked by preincubation of the cells with pertussis toxin (islet-activating protein). There was a lag of approx. 80 min in the onset of the effect on secretion.

Muscarinic acetylcholine receptor activation causes inhibition of cyclic AMP accumulation, prolactin and growth hormone secretion in GH3 rat anterior pituitary tumour cells.

Acetylcholine, oxotremorine and carbachol, compounds that exhibit muscarinic agonist activity, maximally inhibited basal prolactin secretion from GH3 cells by approx. 50% and intracellular cyclic AMP levels by approx. 20%.

A radiochemical assay for detection of leukotriene B4 production from isolated cells.

A radiochemical procedure for quantitating the effect of inhibitors of leukotriene B4 (LTB4) biosynthesis is described. Rat peritoneal cells were labeled with 3H-arachidonic acid and stimulated with the calcium ionophore A23187. 3H-LTB4 was isolated by processing on C18-Sep Pak cartridges followed by reverse-phase high pressure liquid chromatography (HPLC).

Determination of SRS-A release from guinea-pig lungs by a radioimmunoassay.

A sensitive radioimmunoassay for leukotrienes (LTs) has been developed. Rabbits were immunized with a conjugate of LTD4 and bovine serum albumin, prepared by using 1,5-difluoro-2,4-dinitrobenzene as the coupling agent. The assay can detect 0.

Thyrotropin-releasing hormone stimulates inositol phosphate production in normal anterior pituitary cells and GH3 tumour cells in the presence of lithium.

Phosphatidylinositol (Ptd Ins) breakdown in response to thyrotropin-releasing hormone (TRH) was measured after preincubation of both normal rat anterior pituitary cells and GH3 tumour cells with [3H]inositol by the determination of [3H]inositol phosphate accumulation in the presence of lithium (which inhibits myo-inositol phosphatase). The method employed, which was originally developed for use with tissue slices, was adapted for isolated cells in monolayer culture. In GH3 cells, TRH stimulated the breakdown of phosphoinositide in a manner similar to that reported previously using alternative methods.

Development of a sensitive method for measurement of leukotriene production by isolated cells.

Washed rat peritoneal cells (RPC) rapidly and efficiently incorporated exogenous [3H]-arachidonic acid (AA). Exposure of labeled RPC to the calcium ionophore A23187 induced production of [3H]-leukotriene C4, D4 and E4 (LTC4, LTD4 and LTE4) and [3H]-prostaglandins (PGs). The radiolabeled lipoxygenase metabolites were isolated by a combination of organic extraction, silicic acid chromatography and reverse-phase high pressure liquid chromatography (RP-HPLC).

Antenatal pregnancy complications and fetal growth retardation.

This study reports the associations between antenatal complications, subnormal urinary oestriol excretion and perinatal death in 500 pregnancies when the baby weighed less than the 10th centile for gestational age at birth, compared with those in a series of 500 pregnancies when the baby was of a normal weight for gestation. The overall incidence of antenatal complications was not higher in those pregnancies in which the fetus was growth retarded, although early onset pre-eclampsia, threatened abortion, diabetes mellitus and accidental haemorrhage were commoner (P less than 0.05).

Mortality and morbidity of fetal growth retardation.

This study reports the fetal outcome in 500 pregnancies when the baby weighed less than the 10th centile for gestational age at birth, compared with that in a series of 500 pregnancies where there was a normal weight for gestation. Fetal growth retardation (0-9th centile) had a significant positive association with perinatal mortality (5.2% versus 1.

Plasmid (pKM101)-mediated Weigle reactivation in Escherichia coli K12 and Salmonella typhimurium LT2: genetic dependence, kinetics of induction, and effect of chloramphenicol.

In Escherichia coli K12 the reactivation of UV-irradiated phage in UV-irradiated cells (Weigle reactivation) is inhibited if the protein synthesis inhibitor chloramphenicol is present during the post-irradiation incubation. In contrast, in E. coli K12 or Salmonella typhimurium LT2 containing the plasmid pKM101 the kinetics of the W-reactivation response were not affected by chloramphenicol.

Inhibition of acyltransferase in lymphocytes by concanavalin A.

The effects of concanavalin A and succinylated concanavalin A on the transformation of mouse splenic lymphocytes, and on early biochemical events in the transformation, were compared. 1. The transformation of lymphocytes is biphasic with respect to concanavalin A concentration with optimal activation at about 1 microgram/ml.

Immunological specificity of natural opsonins and their role in the cross-reactivity between Staphylococcus aureus Mardi and Escherichia coli 101.

The immunochemical specificity of the observed cross-reactivity between Escherichia coli strain 101 and Staphylococcus aureus strain Mardi was examined. The cross-reactivity was shown to be dependent upon mucopeptide antibodies which are present in normal and immune sera. Although both organisms contained surface antigens with immunodominant glucuronic acid residues, in vitro phagocytosis studies indicated that antibodies directed against these antigens were not significantly involved in the opsonization process.

Mutagenesis and repair deficiencies of Escherichia coli umuC mutants are suppressed by the plasmid pKM101.

The presence of the drug resistance plasmid pKM101 restored the ability of Escherichia coli umuC mutant strains to be mutated by methyl methanesulfonate. Inducible (Weigle) reactivation of ultraviolet-irradiated bacteriophage lambda was not observed in uvrA6 umuC mutant strains lacking pKM101 but was observed if the plasmid was present in the strains. In a uvrA+ umuC36 strain pKM101 increased the efficiency of the Weigle reactivation process.

Nonribosomal nature of novel, stable ribonucleic acid species accumulated by blue-green bacteria.

The facultatively chemoheterotrophic blue-green bacterium Aphanocapsa 6714 accumulates two novel, stable ribonucleic acid species when deprived of sources of carbon and energy. At least one of these species is nonribosomal.

Precursor of 5S ribosomal ribonucleic acid in the blue-green alga Anacystis nidulans.

The maturation of 5S ribosomal ribonucleic acid (rRNA) in the obligately photoautotrophic unicellular blue-green alga Anacystis nidulans has been studied by using polyacrylamide gel electrophoresis and T1 ribonuclease oligonucleotide analysis. A. nidulans mature 5S rRNA (m5) is of approximately the same molecular weight as the 5S rRNA of Escherichia coli, and is derived by cleavage of a precursor (p5) containing a few (three to six) additional nucleotides.