Characterization of the cyclic AMP-independent actions of somatostatin in GH cells. II. An increase in potassium conductance initiates somatostatin-induced inhibition of prolactin secretion

The neuropeptide somatostatin inhibits prolactin release from GH4C1 pituitary cells via two mechanisms, inhibition of stimulated adenylate cyclase activity and an undefined cAMP-independent process. Somatostatin also hyperpolarizes GH4C1 cells and reduces their intracellular free Ca2+ concentration ([Ca2+]i) in a cAMP-independent manner. To determine whether these ionic changes were involved in the cAMP-independent mechanism by which somatostatin inhibited secretion, changes in cAMP levels were prevented from having any biological consequences by performing experiments in the presence of a maximal concentration of a cAMP analog. Under these conditions, inhibition of prolactin release by somatostatin required a transmembrane concentration gradient for K+ but not one for either Na+ or Cl-. However, elimination of the outward K+ gradient did not prevent somatostatin inhibition of vasoactive intestinal peptide-stimulated hormone release. Therefore, somatostatin's cAMP-mediated mechanism does not require a K+ gradient, whereas its cAMP-independent inhibition of secretion appears to result from a change in K+ conductance. Consistent with this conclusion, membrane hyperpolarization with gramicidin (1 microgram/ml) mimicked somatostatin inhibition of prolactin release. In addition, the K+ channel blocker tetrabutylammonium prevented the effects of somatostatin on the membrane potential, the [Ca2+]i and hormone secretion. Nonetheless, a K+ gradient was not sufficient for somatostatin action. Even in the presence of a normal K+ gradient, somatostatin was only able to inhibit prolactin release when the extracellular Ca2+ concentration was at least twice the [Ca2+]i. Furthermore, the calcium channel blocker, nifedipine (10 microM), which prevents the action of somatostatin to reduce the [Ca2+]i, specifically blocked inhibition of prolactin release via somatostatin's cAMP-independent mechanisms. Therefore, a decrease in Ca2+ influx through voltage-dependent Ca2+ channels produces both the fall in [Ca2+]i and inhibition of hormone secretion in response to somatostatin.     

Fibrinogen--proteolysis in acute myelogenous leukemia (AML)

Fibrinopeptides were measured as direct indices of thrombin, plasmin and elastase in plasma samples obtained from patients with AML. Peptide patterns observed were consistent with spontaneous or drug induced plasmin-specific fibrinogenolysis (AML FAB M 1/3), elastase mediated proteolysis (AML FAB M 3/4) or DIC (AML FAB 4/5). DIC was also observed in septic, agranulocytotic patients.     

Growth, dry matter partitioning, and diurnal activities of RuBP carboxylase in citrus seedlings maintained at two levels of CO2

The long-term response of citrus rootstock seedlings to CO₂ enrichment was examined in Carrizo estrange ( Poncirua trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] and Swingle citrumelo ( P. trifoliate x C. parodist Macf.]. Plaotlets 14 weeks old were transferred to outdoor controlled-environment chambers and maintained for 5 months from Feb. 14 to July 21. During this period, new growth (cm) of citrange and citrumelo shoots at 660 μl1⁻¹ was 94 and 69% greater, respectively, than at 330 μ1 1⁻¹. Total dry weight of both rootstock shoots had increased by over 100%. Growth of few species is affected this markedly by elevated CO₂ levels.
More carbon was partitioned to above-ground organs in CO₂-enriched citrus seedlings. Stem dry matter per unit length was also 32 and 44% greater in citrange and citrumelo, respectively. Total leaf area was increased by 124% in citrange and 85% in citrumelo due to greater leaf number and size. Variations in overall relative growth rate appeared to be related to the rapid, sequential, flush-type growth in citrus, in which an entire shoot segment with its associated leaves remains an active sink until fully expanded. RuBP carboxylase (EC 4.1.1.39) activity in leaves of recently-expanded flushes was higher in citrumelo plants grown at 660 vs 330 μ1 1⁻¹ CO₂ and changed diurnally for citrange (but not citrumelo) leaves at both CO₂ levels. The results are consistent with the hypothesis that positive long-term effects of CO² enrichment may be greater in species or during growth periods where sink capacity for carbon utilization is high.     

Contribution to the ecology ofMarsilea quadrifolia L.

Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia).     

One gene encodes two distinct Ia-associated invariant chains

Murine immune response region-encoded Ia antigens are associated not only with invariant (Ii) chain but also with several other polypeptides, most notably a 41K protein. The present report demonstrates a striking similarity between Ii and 41K. These polypeptides were found to be serologically cross-reactive, and they also display a similar peptide composition on partial enzymatic digestion. Both polypeptides are derived from distinct unglycosylated precursors, as demonstrated by tunicamycin treatment and cellfree translation. Hybrid selection of mRNA, as well as Northern blotting with an Ii cDNA, shows the presence of two mRNA coding for the Ii chain and the 41K protein. Rat fibroblasts transfected with a mouse genomic Ii clone synthesize both the murine Ii chain and the 41K protein. These observations demonstrate that a single Ii gene encodes two distinct but closely related proteins.     

Primeval cells: Possible energy-generating and cell-division mechanisms

Summary It is proposed that the first entity capable of adaptive Darwinian evolution consisted of a liposome vesicle formed of (1) abiotically produced phospholipidlike molecules; (2) a very few informational macromolecules; and (3) some abiogenic, lipid-soluble, organic molecule serving as a symporter for phosphate and protons and as a means of high-energy-bond generation. The genetic material had functions that led to the production of phospholipidlike materials (leading to growth and division of the primitive cells) and of the carrier needed for energy transduction. It is suggested that the most primitive exploitable energy source was the donation of 2H⁺+2e^– at the external face of the primitive cell. The electrons were transferred (by metal impurities) to internal sinks of organic material, thus creating, via a deficit, a protonmotive force that could drive both the active transport of phosphate and high-energy-bond formation.This model implies that proton translocation in a closed-membrane system preceded photochemical or electron transport mechanisms and that chemically transferable metabolic energy was needed at a much earlier stage in the development of life than has usually been assumed. It provides a plausible mechanism whereby cell division of the earliest protocells could have been a spontaneous process powered by the internal development of phospholipids. The stimulus for developing this evolutionary sequence was the realization that cellular life was essential if Darwinian survival of the fittest was to direct evolution toward adaptation to the external environment.     

Effect of endurance training and chronic isoproterenol treatment on skeletal muscle sensitivity to norepinephrine

The purpose of this study was to determine the influence of metabolic stresses, such as endurance training and chronic isoproterenol treatment, on skeletal muscle sensitivity to norepinephrine. Using an isolated perfused rat hindlimb preparation, dose-response curves for skeletal muscle oxygen consumption (VO2) and vascular resistance were obtained with control, endurance trained, and isoproterenol treated rats. No significant difference was found between control and experimental groups for non-stimulated VO2. In response to NE infusion, trained rats showed a significantly greater increase in VO2 compared to control rats while the response of the isoproterenol treated rats was of the same magnitude as the one for their respective control rats. At the highest dose of NE infused, the vasopressor response was significantly lower in trained rats compared to control rats. At none of the doses was there a significant difference in the vasopressor response between control and isoproterenol treated rats. These results suggest that repeated exposures to high levels of catecholamines, as produced during endurance training, leads to an increased sensitivity of skeletal muscle to the effect of norepinephrine.     

Performance ofin vitro propagatedAlnus glutinosa (L.) Gaertn. clones inoculated withFrankiae

Summary ThreeAlnus glutinosa (L.) Gaertn. clones, obtained byin vitro propagation techniques, were inoculated with four strains ofFrankia. The ability of these clones to nodulate and fix nitrogen was previously reported; this study deals with the performance of 12 different combinations of pairs of symbionts.Shoot fresh weight, shoot height and collar diameter were measured 60 and 82 days after inoculation. Shoot fresh weight seems to be more sensitive and reliable than the other parameters. Nitrogenase activity, measured by the acetylene reduction assay, was assayed 78 days after inoculation and was consistent with the biomass measurements.Better growth was observed when type N strains were used. Significant growth differences were observed between clones AG-2 and AG-8 on the one hand and clone AG-4 on the other. Thus, the use of genetically defined host plants and microsymbionts permitted the demonstration of significant performance variation even among cloned plants from the same provenance (AG-4 and AG-8).The duration of the experiment influenced the results with differences becoming less significant with time. This might be caused by an external limiting factor such as the pot size, competition for light,etc. But it could also be indicative of differences in nodulation speed among the treatments.     

Immunoreactive and biologically active somatostatin in human and sheep milk

The presence of immunoreactive and biologically active somatostatin in sheep and human milk has been demonstrated. Milk somatostatin exhibits similar chromatographic behavior to that of synthetic somatostatin-14 on both reversed-phase C18 and cation-exchange high-performance liquid chromatography columns. Milk, in contrast to plasma, contains only somatostatin-14-like material. Milk somatostatin was capable of inhibiting the basal and the prostaglandin-induced release of growth hormone from anterior pituitary cell cultures in a pattern similar to synthetic somatostatin-14. The concentrations of the peptide, as determined by radioimmunoassay, were found to be 113 pg/ml in human milk and 150 +/- 4.8 pg/ml (mean +/- range) in sheep milk. These values are severalfold higher than the corresponding concentration of the peptide in the plasma of these species. These findings are analogous to our previous observations concerning two other hypothalamic hormones, luliberin and thyroliberin [Baram, T., Koch, Y., Hazum, E. and Fridkin, M. (1977) Science (Wash. DC) 198, 300-302]. The high concentration of somatostatin and other neuropeptides in milk implies either an active concentrating mechanism in the mammary gland or an additional extrahypothalamic source for the synthesis and release of these peptides.