The effect of bombesin on basal, alpha-methyl-p-tyrosine, haloperidol, morphine, bremazocine and stress-induced prolactin secretion

Intravenously administered bombesin lowered basal PRL levels in conscious male rats and prevented the morphine, bremazocine and stress-induced PRL secretion. The same dose of bombesin had no effect on PRL levels in alpha-methyl-p-tyrosine pretreated rats and did not affect haloperidol-stimulated PRL release. These results show that bombesin given intravenously acts as an inhibitor of PRL secretion and suggests that it does not act on the lactotrope itself but rather by an increase of the inhibitory dopaminergic tone.     

Mice with Spontaneous Mammary Tumors Develop Type-Specific Neutralizing and Cytotoxic Antibodies Against the Mouse Mammary Tumor Virus Envelope Protein gp52

Sera from C3H mammary tumor-bearing mice contain cytotoxic antibodies for mouse mammary tumor virus (MMTV)-producing cells, based on (51)Cr release in a complement-dependent serum cytotoxicity assay. The cytotoxic antibodies could be absorbed by purified C3H MMTV gp52 and C3H MMTV-infected cat cells (C3H [MMTV] CrFK) containing cell surface MMTV gp52. However, purified MMTV p27 and uninfected CrFK cat cells were negative. Absorption of the sera with GR (MMTV) CrFK cells also removed all of the cytotoxicity, whereas absorption with RIII (MMTV) CrFK cells was negative, even though all three infected cat cells contained equivalent amounts of gp52. The same C3H cytotoxic sera also neutralized the focus-forming capacity of a C3H MMTV pseudotype of Kirsten sarcoma virus containing MMTV gp52. In contrast, sera from mammary tumor-bearing GR and RIII mice did not neutralize the pseudotype. Furthermore, neutralization could be achieved only by anti-gp52 but not by anti-gp36, -p27, -p14, or -p10 C3H MMTV sera. The gp52's of C3H, GR, and RIII MMTV could also be distinguished by using a type-specific competition radioimmunoassay employing (125)I-gp52 of C3H MMTV and a hyperimmune rabbit anti-C3H MMTV serum. To demonstrate these differences directly, we studied the primary structure of gp52 on the surface of the C3H, GR, and RIII (MMTV) CrFK cells. Two-dimensional tryptic peptide maps of the cell surface lactoper-oxidase-catalyzed iodinated gp52's revealed a greater number of peptides common to the gp52's of C3H and GR MMTVs than to RIII MMTV gp52. These results demonstrate that gp52 is a major target antigen for both cytotoxic and neutralizing antibodies, that the cell surface and virion-associated gp52's of C3H, GR, and RIII MMTV contain both group- and type-specific determinants, and that C3H and GR MMTV gp52's are antigenically more related to each other than to RIII MMTV gp52. Furthermore, C3H mammary tumor-bearing mice develop type-specific antibodies capable of recognizing unique gp52 determinants and, therefore, are able to distinguish the gp52 of C3H MMTV from the gp52's of GR and RIII MMTV.     

Modulation of the phase heterogeneity of aminoglycerophospholipid mixtures by sphingomyelin and monovalent cations: maintenance of the lamellar arrangement in the biological membranes

The phase behaviour of mixed molecular species of phosphatidylethanolamine, phosphatidylserine and sphingomyelin of biological origin were examined in aqueous co-dispersions using synchrotron X-ray diffraction. The co-dispersions of phospholipids studied were aimed to model the mixing of lipids populating the cytoplasmic and outer leaflets in the resting or scrambled activated cell membrane. Mixtures enriched with phosphatidylethanolamine and phosphatidylserine were characterized by a phase separation of non-lamellar phases (cubic and inverted hexagonal) with a lamellar gel phase comprising the most saturated molecular species. Inclusion of sphingomyelin in the mixture resulted in a suppression of the hexagonal-II phase in favour of lamellar phases at temperatures where a proportion of the phospholipid was fluid. The effect was also dependent on the total amount of sphingomyelin in ternary mixtures, and the lamellar phase dominated in mixtures containing more than 30 mol%, irrespective of the relative proportions of phosphatidylserine/sphingomyelin. A transition from gel to liquid-crystal phase was detected by wide-angle scattering during heating scans of ternary mixtures enriched in sphingomyelin and was shown by thermal cycling experiments to be coupled with a hexagonal-II phase to lamellar transition. In such samples there was evidence of a coexistence of non-lamellar phases with a lamellar gel phase. A transition of the gel phase to the fluid state on heating from 35 to 41 °C was evidenced by a progressive increase in the lamellar d-spacing. The presence of calcium enhanced the phase separation of a lamellar gel phase from a hexagonal-II phase in mixtures enriched in phosphatidylserine. This effect was counteracted by charge screening with 150 mM NaCl. The effect of sphingomyelin on stabilizing the lamellar phase is discussed in the context of an altered composition in the cytoplasmic/outer leaflets of the plasma membrane resulting from scrambling of the phospholipid distribution. The results suggest that a lamellar structure can be retained by the inward translocation of sphingomyelin in biological membranes. The presence of monovalent cations serves also to stabilize the bilayer in activated cells where a translocation of aminoglycerophospholipids and an influx of calcium occur simultaneously.Abbreviations PC phosphatidylcholine - PE phosphatidylethanolamine - PS phosphatidylserine - SAXS small-angle X-ray scattering - SM sphingomyelin - WAXS wide-angle X-ray scattering - XRD X-ray diffraction     

Properties of Bovine Oligodendroglia Isolated by a New Procedure Using Physiologic Conditions

A new class of procedures, previously shown to permit the isolation of pure oligodendroglia from whole rat cerebrum, has been applied with equal or greater success for the bulk isolation of this cell type from bovine white matter. Thus, the generality of this approach has been demonstrated. The bovine preparations have a purity of greater than 90% intact, phase-bright oligodendroglia and are obtained in a yield of 8 x 10(6) cells per gram of white matter. Within 1 day it is possible to obtain a preparation containing 60 mg of protein from a single cell type. These cells show a higher degree of ultrastructural preservation of all cytoplasmic constituents than previously obtained. The values for protein (33 pg/cell), DNA (5.4 pg/cell), and lipid (5-6 pg/cell) are very similar to those obtained with an earlier procedure. The cell lipids are rich in galactolipid, which comprises 20% of the total. The activity of the "myelin-specific" enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37), is 4.7 mumol/min/mg protein, similar to that obtained previously for isolated oligodendroglia and about 25-40% of that found in myelin. The activity of 5'-nucleotidase (EC 3.1.3.5) in the cells is about 10% of that in myelin or white matter.