Properties of renin substrate in rabbit plasma with a note on its assay

1. Rabbit plasma enzymes that degrade angiotensin I are inhibited completely by the combination of 2,3-dimercaptopropan-1-ol (10mm), EDTA (10mm) and chlorhexidine gluconate (0.005%, w/v). These compounds do not modify the reaction of renin with renin substrate and are termed the selective inhibitors. 2. The renin substrate concentration of plasma can be measured as angiotensin I content by incubating plasma plus the selective inhibitors with renin for a time sufficient to allow complete utilization of renin substrate. 3. This reaction obeys first-order kinetics to substrate concentrations of at least 1000ng. of angiotensin I content/ml. In general, the renin substrate concentrations of normal rabbit plasmas are less than 1000ng. of angiotensin I content/ml. Thus the time required for the complete release of angiotensin I from normal plasma is inversely related to renin activity and is independent of renin substrate concentration. 4. A method for the assay of renin substrate, taking these reaction kinetics into account, is presented.     

Microdifferentiation in a Natural Population of DROSOPHILA MELANOGASTER to Alcohol in the Environment

Strains of D. melanogaster derived from a vineyard population were more resistant to alcohol in the environment than strains from a population derived from an area removed from the vineyard. Within the vineyard population those strains most closely associated with alcohol in the environment in the cellar were more resistant than those collected outside the cellar. There was evidence of gene flow between the inside and outside cellar components of this population, but microdifferentiation had occurred within the cellar in spite of this. The adaptation appears to be independent of the ADH system and involves both additive and dominance genetic effects. D. simulans, a species not found in the cellar and susceptible to the presence of alcohol, showed no differentiation between vineyard and removed populations.     

Glutamine Synthetase/Glutamine: alpha-Ketoglutarate Aminotransferase in Chloroplasts from the Marine Alga Caulerpa simpliciuscula

The enzymic capacities for ammonia assimilation into amino acids have been investigated in chloroplasts from the siphonous green alga Caulerpa simpliciuscula (Turner) C. Ag. The results show that these chloroplasts differ from those of higher plants in having present simultaneously the enzymic capacities to permit assimilation of ammonia by two pathways. Glutamine synthetase (EC 6.3.1.2) activity at levels up to 4 μmoles per mg chlorophyll per hour were found in soluble extracts of the chloroplasts. Glutamine(amide):α-ketoglutarate aminotransferase (oxidoreductase ferredoxin) (EC 1.4.7.1) activity at levels up to 1.4 μmoles per mg chlorophyll per hour was detected by incubation of photosynthetically active chloroplasts either in light or with reduced ferredoxin. Together these enzymes provide the capacity for the conventional pathway of ammonium assimilation in chloroplasts via glutamine. A similar level of a glutamate dehydrogenase with an unusually low K_m for ammonia which has been described previously in these chloroplasts provides the second potential pathway.     

Episodic and TRH induced growth hormone release in primary hypothyroidism of man and rat.

In 27 hypothyroid subjects studied over 20 to 120 minutes, the concentration of serum growth hormone (GH) was variable with the amplitude and frequency of the secretory patterns similar to those reported by others for normal individuals. Serum GH, after the administration of thyrotropin releasing hormone (TRH) did not differ from values observed as spontaneous surges, in contrast to a consistent increase in thyrotropin and prolactin. Episodic secretion of GH persisted in thyroidectomized rats and did not differ significantly from that present in intact controls. It is concluded that episodic GH secretion is not abolished in primary hypothyroidism and that TRH is not a constant GH secretagogue in human subjects with hypothyroidism.     

Demonstration of Ia antigens on mouse intestinal epithelial cells by immunoferritin labeling

Several kinds of epithelial cells that express H-2 antigens were studied by immunoferritin labeling with an antiserum reacting only with antigens of theI region of theH-2 complex. Spleen lymphocytes were used to test the labeling system and the effect of the epithelial cell dissociation procedure on Ia antigens. Immunoglobulin-positive B10.BR lymphocytes were labeled with an anti-la^k serum (A.TH anti-A.TL serum absorbed with BALB/c and B10.D2 cells), while congenic B10.D2 lymphocytes were unlabeled. The distribution of labeled Ia antigens on living B10.BR lymphocytes was patchy, while on cells fixed in periodate-lysine-paraformaldehyde before labeling, the distribution of label was continuous. Fixation evidently immobilized Ia antigens in the lymphocyte membrane. Trypsin and collagenase, as used in the epithelial cell dissociation procedure, had no discernible effect on the Ia antigens of lymphocytes. The epithelial cells studied included the columnar absorptive cells of the small intestine, uterine lining epithelium, tracheal brush cells, and pancreatic exocrine and duct cells. These cells were fixed before dissociation from their respective tissues. Ia antigens were detected only on the columnar absorptive cells of the small intestine. These cells labeled equally well with an antiserum reacting only with theK -end of theH-2 complex. In both cases, congenic control intestinal cells were unlabeled. Thus, intestinal epithelial cells appear to express theIa, K, and presumablyD regions of theH-2 complex, while the other epithelial cell types express only the K and D antigens. On fixed intestinal epithelial cells, Ia and H-2K antigens were continuously distributed on the lateral and basal cell membranes including the zonula adherens, but the antigens were absent from the apical microvillous membrane and the zonula occludens.     

Notoedres muris infestation in a naked-tailed rat Melomys cervinipes

Large numbers of Notoedres muris were present in thick crusty lesions on both ears, the nose, one forelimb and tail-base of a free-living naked-tailed rat, Melomys cervinipes, on North Stradbroke Island, Queensland, Australia. The source of infestation was obscure.     

Effects of fourH-2K mutations on virus-induced antigens recognized by cytotoxic T cells

Lysis of ectromelia- or LCM virus-infected macrophage target cells by virus-specific cytotoxic T cells from mice immunized with the homologous virus occurred only where donors of T cells and target cells shared eitherH-2K orH-2D genes. With both viruses, use of T cell or target cell donors bearing mutations (B6.C-H-2^ba, B6-H-2^bh, B6-H-2^bg1, and B6-H-2^bg2), all of which apparently occurred in the same single genetic element in theH-2K^b region, abolished (H-2^ba) or impaired (H-2^bh,H-2^bg1 andH-2^bg2) lysis in T cell-target cell combinations that shared (apart from the mutations) all other genes in theK, I-A, orI-B regions of theH-2 complex. The data suggest that virus-induced antigenic patterns on infected B6.C-H- 2^ba (mutant) cells are more different antigenically from those on C57BL/6 (wild type) cells than are those on infected cells from the other mutants -B6-H-2^bh, B6-H-2^bg1, and B6-H-2^bg2. (B6.C-H-2^ba× B6 -H-2^bh)F₁ mice behaved like B6-H-2^bh, indicating no complementation, and confirming that theH-2K gene(s) involved in recognition of virus-infected cells by virus-specific T cells behave as a single element. These findings are discussed in relation to the nature of virus-induced antigenic patterns that are recognized by virus-specific cytotoxic T cells.     

A histocompatibility region (H-2IC) in theIC region of theH-2 complex of the mouse

Skin graft rejection in congenic pairs of mice differing only at theH-2 complex appears to be influenced by at least 3 genes (H-2K, H-2D, H-2I); we now describe a fourth,H- 2IC: Grafts transplanted across anIC difference are sometimes rejected. TheI-C regions of three differentH-2 haplotypes (d,k,s) were studied in different combinations, and variable patterns emerged: (a)IC ^d : B10.S(7R) show delayed or no rejection of first B10.S(9R) grafts, but grafts to immunized recipients were usually rejected in 20 days; (b)IC ^k : in two combinations (A.AL A and B10.HTT B10.S[9R]) first grafts were rejected by day 30, although grafts to immunized mice showed a different pattern. In the third combination (B10.HTTB10.S[7R]) first grafts were retained but immunized mice rejected their grafts, (c)IC ^s : B10.S(9R) regularly reject B10.S(7R) first grafts, but immunized mice retain their grafts. In two other combinations first grafts were retained but grafts to immunized recipients were rejected; while in a third combination rejection did not occur at all. The background of the recipient appeared to be important in determining the variable pattern of rejection, and there is evidence for a similarity of the H-genes inIC ^s andIC ^k , and inIC ^k andIC ^p . Graft rejection occurred independently of known differences in Ia specificities, indicating thatH-2IC and the genes determining Ia specificities are probably different, although when grafts were performed in the presence of known la differences, graft rejection usually occurred.     

Serological and complementation studies in four C57BL/6H-2 mutants

C57BL/6 (H-2 ^b ) mice, and four mutants (B6.C-H-2 ^ba , B6-H-2 ^bg1 , B6-H-2 ^bg2 , B6-H-2 ^bh ) derived from this strain after separate mutations had occurred at the same locus within theH-2 complex, were analyzed to determine whether the mutations had led to anyH-2 (or Ia) difference which could be detected serologically. The strains were typed directly with antisera specific for H-2K and H-2D public and private specificities and for the Ia specificities; quantitative absorption studies were also performed for the relevant H-2K^b, H-2D^d and Ia^b specificities. In no case was any quantitative or qualitative difference detected serologically between any of the strains. In addition, by using a variety of techniques to produce and assay for antibody, we failed to produce any antisera between the parental strains and the four mutants. TheH-2 mutations therefore appear to give rise to a type of antigenic specificity which is recognized byT cells and which generateT, but notB cell responses; nor are they recognized by H-2 or Ia alloantisera. The location of the mutating locus within theH-2 complex was shown by the complementation method to be within theK orIA region and not in theIB region, since crosses of the mutant strains with B10.A(4R) or D2.GD failed to complement for a subsequent C57BL/6 skin graft.     

Gene Flow and Selection in a Natural Population of DROSOPHILA MELANOGASTER

A marked genetic differentiation to the presence of alcohol in the environment has been shown to occur between inside cellar and adjacent outside sections of a vineyard population of D. melanogaster ( McKenzie and Parsons 1974). Estimates of migration during the vintage period suggest considerable movement occurs from outside into the cellar and that the most tolerant genotypes are the most successful migrants. A quantitative model of this system suggests that the selection intensity may not be a limiting factor in maintaining the differentiation. It also suggests that gene flow must be restricted between sections of the population at all but vintage periods if this differentiation is to persist.