Regulation of thyroid hormone metabolism in rat liver fractions

The nature of the conversion of thyroxine (T₄) to triiodothyronine (T₃) and reverse triiodothyronine (rT₃) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T₃ and 2.5-fold rise of rT₃ levels determined by specific radioimmunoassays was observed over 6 h after the addition of T₄. An enzymic process is suggested that converts T₄ to T₃ and rT₃. For T₃ the optimal pH is 6 and for rT₃, 9.5. The converting activity for both T₃ and rT₃ is temperature dependent and can be suppressed by heat, H₂O₂, merthiolate and by 5-propyl-2-thiouracil. rT₃ and to a lesser degree iodide, were able to inhibit the production of T₃ in a dose related fashion. Therefore the pH dependendy, rT₃ and iodide may regulate the availability of T₃ or rT₃ depending on the metabolic requirements of thyroid hormones.     

The biological properties of bovine parathyroid hormone (1–41), a fragment generated from the native hormone by human leukocytes

Native bovine parathyroid hormone (bPTH) was found to be readily cleaved with human leukocyte elastase to yield the fragments bPTH(1–41) and bPTH(42–84). These were then isolated by reverse-phase HPLC and characterised by gas-phase sequencing and amino acid analysis. The biological activities of these fragments were assessed in an adenylate cyclase bioassay using the rat osteosarcoma cell line UMR106. bPTH(1–41) was found to have approximately twice the molar potency of the native hormone from which it was derived, bPTH(42–84) had no biological activity and did not modulate the adenylate cyclase response to these cells to the native hormone. The possible physiological significance of these observations is discussed.     

Amino Acid Sequences of Neuropeptides in the Sinus Gland of the Land Crab Cardisoma carnifex: A Novel Neuropeptide Proteolysis Site

The sinus gland is a major neurosecretory structure in Crustacea. Five peptides, labeled C, D, E, F, and I, isolated from the sinus gland of the land crab have been hypothesized to arise from the incomplete proteolysis at two internal sites on a single biosynthetic intermediate peptide "H", based on amino acid composition additivities and pulse-chase radiolabeling studies. The presence of only a single major precursor for the sinus gland peptides implies that peptide H may be synthesized on a common precursor with crustacean hyperglycemic hormone forms, "J" and "L," and a peptide, "K," similar to peptides with molt inhibiting activity. Here I report amino acid sequences of these peptides. The amino terminal sequence of the parent peptide, H, (and the homologous fragments) proved refractory to Edman degradation. Data from amino acid analysis and carboxypeptidase digestion of the naturally occurring fragments and of fragments produced by endopeptidase digestion were used together with Edman degradation to obtain the sequences. Amino acid analysis of fragments of the naturally occurring "overlap" peptides (those produced by internal cleavage at one site on H) was used to obtain the sequences across the cleavage sites. The amino acid sequence of the land crab peptide H is Arg-Ser-Ala-Asp-Gly-Phe-Gly-Arg-Met-Glu-Ser-Leu-Leu-Thr-Ser-Leu-Arg-Gly- Ser-Ala-Glu- Ser-Pro-Ala-Ala-Leu-Gly-Glu-Ala-Ser-Ala-Ala-His-Pro-Leu-Glu. In vivo cleavage at one site involves excision of arginine from the sequence Leu-Arg-Gly, whereas cleavage at the other site involves excision of serine from the sequence Glu-Ser-Leu. Proteolysis at the latter sequence has not been previously reported in intact secretory granules. The aspartate at position 4 is possibly covalently modified.     

下丘脑外侧区注射TRH对大鼠胃酸分泌的影响

本文采用连续收集胃腔灌流法,观察下丘脑外侧区(LHA)注射促甲状腺激素释放激素(TRH)对大鼠胃酸分泌的影响,并分析TRH在LHA促进胃酸分泌的作用机制。结果表明:(1)LHA注射TRH(1μg)明显地刺激胃酸分泌;(2)预先向LHA注射酚妥拉明(10μg)、美多心安(5μg)及胃泌素抗体1μl(1:640)并不影响TRH的泌酸作用,如预先向LHA注射阿托品(5μg)则可消除TRH的泌酸效应;(3)垂体摘除及肾上腺切除均不影响TRH的泌酸作用;(4)隔下迷走神经切断后,LHA注入TRH的泌酸效应仍然出现,但持续时间显著缩短;腹腔交感神经节摘除后,TRH仍能促进胃酸分泌,但分泌量少而平稳。以上结果提示:LHA是TRH中枢泌酸效应的有关结构之一,其中枢机制是通过胆碱能M受体中介的,腹腔交感神经节和膈下迷走神经是TRH泌酸效应的传出途径。前者引起的泌酸反应出现较早且引起泌酸高峰,但持续时间短;后者则引起低平的持续分泌。     

Endocytosis of α1-acid glycoprotein variants and of neoglycoproteins containing mannose derivatives by a mouse hybridoma cell line (2C11–12). Comparison with mouse peritoneal macrophages

Macrophages from various origins are known to express membrane lectins that mediate the endocytosis of mannose-bearing glycoconjugates. Most macrophage tumor cell-lines lack such receptors. In this paper we show by flow cytometry analysis that a newly generated macrophage hybridoma (2C_11–12), which displays several macrophage characteristics, also expresses mannose membrane lectins, resulting in the internalization of fluoresceinylated neoglycoproteins into acidic compartments.Thioglycolate elicited mouse peritoneal macrophages and the 2C_11–12 hybridomas were compared by flow cytometry with regard to the binding and endocytosis of ₁-acid glycoprotein (AGP) variants separated by affinity chromatography on immobilized concanavalin A. AGP C eluted specifically with methyl -mannopyranoside, which contains two bi-antennary oligosaccharides, was endocytosed as mannosylated serum albumin (Man-BSA). In both types of macrophages, the fluoresceinylated ligands were internalized in acidic compartments as demonstrated by the fluorescence intensity increase upon monensin post-incubation. However the behaviour of the internalized ligands was found to be quite different. AGP C and Man-BSA were rapidly degraded by thioglycolate elicited peritoneal macrophages and excreted in the medium as small peptide fragments; conversely they remained a longer time in the 2C_11–12 hybridoma.     

Binding and internalization of gold-conjugated somatostatin and growth hormone-releasing hormone in cultured rat somatotropes

Summary The synthetic peptides somatostatin (SRIF) and growth hormone-releasing hormone (GRH) were coupled directly to colloidal gold of different particle sizes. Both conjugates were biologically active in displacing the corresponding radiolabeled hormones from high affinity binding sites in pituitary membranes. Release of growth hormone (GH) from cultured anterior pituitary cells was modulated by both conjugates alone or in combination. Ultrastructural studies were performed with cells incubated at 4° C (2 h) and 37° C (2 min-2 h) with one of the labeled peptides or their combination. Somatotropes were identified by immunostaining with anti-rGH followed by protein A-ferritin, thus obtaining a triple labeling. Both hormone conjugates were internalized in different vesicles in the beginning but accumulated during longer incubation times in the same compartment. The secretory vesicles and the nucleus were not labeled by any hormone conjugate. In contrast to SRIF-gold, the uptake of GRH-gold conjugate decreased with longer incubation times. This effect could be neutralized by simulatenous incubation of the somatotropes with both regulating hormones. Hence, whereas the binding and internalization of SRIF by somatotropes do not seem to be influenced by GRH, the corresponding processes for GRH are stimulated by the presence of SRIF.     

Induction of hormone receptor formation in the unicellular tetrahymena

Studies based on treatment with antibodies to thyrotropic hormone, luteotropic hormone, growth hormone or adrenocorticotropic hormone have shown that although the unicellular Tetrahymena does not possesssui generis receptors to all polypeptide hormones, such binding structures may arise, or become established in the membrane of the unicellular Tetrahymena in the presence of exogenous hormone. The Tetrahymena subjected to hormonal imprinting still contained an increased amount of hormone after six generation changes, which suggested that either hormone production had been induced by treatment, or the internalized hormone had not been degraded intracellularly. Thus the role of hormonal imprinting in receptor formation has also been substantiated by the immunocytochemical approach used in the present study.     

Humoral factors released during trauma ofAplysia body wall

1. Preliminary, general chemical characteristics of substances in artificial sea water (ASW) washed through stimulated body wall (SBW) and in hemolymph taken from noxiously stimulated animals (SHL) were consistent with those of classical neurotransmitters, amino acids, and small- to medium-sized peptides. 2. 5-Hydroxytryptamine (5HT) and acetylcholine (ACh), unlike SBW and SHL, caused relaxation when perfused into isolated body wall. FMRFamide produced a biphasic response--brief contraction followed by prolonged relaxation. 3. Small cardioactive peptide (SCPB) caused body wall contractions similar to those produced by SBW and SHL, except that SCPB contractions displayed more desensitization and were completely blocked by 30 mM CoCl2. SCPB and SBW contractions were synergistic. 4. Dopamine caused persistent body wall contractions similar to those of SBW and SHL. Dopamine contractions were reduced but not blocked by 30 mM CoCl2. Unlike SBW activity, dopamine activity was reduced by alkalinization. 5. Glutamate and taurine produced strong but usually short-lasting body wall contractions. Adenosine, octopamine, arginine vasotocin, and cholecystokinin (CCK-8) caused weak or variable contractions. Met-enkephalin and somatostatin caused no obvious body wall responses. 6. When superfused over the fully sheathed abdominal ganglion, FMRFamide, met-enkephalin, glutamate, aspartate, and taurine reduced the magnitude of the gill-withdrawal reflex elicited by siphon nerve stimulation. 7. Taken together with earlier results, these data suggest a preliminary framework for trauma signal pathways. It is proposed that stress hormones (perhaps including FMRFamide, SCPs, 5HT, and dopamine) are released into hemolymph from neuroendocrine cells. Effective amounts of active intracellular solutes such as amino acids may also be released by extensive cellular rupture. Various humoral signals produce slow effects that contribute to hemostasis, balling up, increased cardiac output, and reflex suppression.     

Farnesylacetone, a sesquiterpenic hormone of Crustacea, inhibits electron transport in isolated rat liver mitochondria

Farnesylacetone (C18 H30 0) is a male hormone extracted from the androgenic gland of crab, Carcinus maenas. Appropriate enzymatic assays, as well as spectrophotometric studies, indicate that micromolar concentrations of farnesylacetone interact with the electron transport pathway of rat liver mitochondria. By the use of artificial electron donors and electron acceptors, it is shown that farnesylacetone immediately inhibits the electron transfer within complex I (NADH ubiquinone reductase activity) and complex II (succinate ubiquinone reductase activity). It is proposed that farneylacetone could interact with these two complexes of the respiratory chain at the level of the iron-sulfur centers implicated in the dehydrogenase activities. These observations are compared with the results obtained with terpenic molecules which interact with mitochondrial respiration.