Experiments with fibroblasts in culture demonstrated that collagen fibrilsstrongly inhibited DNA synthesis, and suppressed cell growth. Collagen fibrils also induced a specific cell shape with abundant cytoplasmic protrusions. The rate of DNA synthesis on collagen was less than 20% of that on tissue culture plastic. The extent of the suppression of DNA synthesis was strictly dependent upon the quantity of collagen available to cells. 60 pg/cell, which differed from that for the induction of a collagen-mediated change in the cell shape (5.3 ng/cell). The extent of suppression of DNA synthesis on collagen fibrils decreased as the length of culture period increased, suggesting that fibroblasts interact with collagen during culture and induce changes in the properties of collagen. Native collagen which loses ability to form a fibril in the culture condition was prepared by modifying ε-amino groups of lysyl residues. The chemically modified collagen didnot induce any collagen-mediated changes in fibroblasts, indicating the importance of a polymeric form of collagen for collagen to cell interaction.
Using skinned muscle fibers, the response to caffeine was compared between malignant hyperthermia susceptible (MHS) and control swines. The caffeine concentration for the threshold and halfmaximum contracture was markedly lower in MHS swines than in controls. These results agree with those in human malignant hyperthermia (MH). Dantrolene did not exhibit any effect on the dose-response relationship ofcaffeine contracture in the skinned fiber from MHS swines. The muscle fiber diameter was significantly increased in every fiber type of MHS swines. The pathogenesis of porcine MH and effect of dantrolene were discussed.
Increase in tetraploid nuclei in relation to age was analyzed based on sedimentaion profiles of liver nuclei labeled with [3H]thymidine in vivo. On centrifugation, nuclei synthesizing DNA sedimented faster than theresting nuclei. Among the nuclei from rats of 3 weeks old, most of the labeled nuclei became diploid again, but in rats of 4 weeks old half of the labeled nuclei remained tetraploid. During week 5, the tetraploid nuclei were formed from diploid nuclei; these tetraploid nuclei did not show the ability to synthesize DNA yet. However, no further conversion of diploid to tetraploid cells occurred during week 6, whereas the percentage of cells with tetraploid nuclei was still increasing. Therefore, a definitive change in nuclear segregation after DNA replication seems to occur during weeks 4 and 5 after birth.
Procainamide (PA), an anti-arrhythmic agent, was recently found to be a specific inhibitor of suppressor T cells. The effects of PA and X-ray irradiation were studied on both plaque forming cells (PFC) and antibody titer using sheep red blood cells and vaccinia virus as antigens. A single injection of PA (50μg) augmented both PFC and antibody titer; the increase was more than twice that seen after X-ray irradiation. A single injection of higher doses and repeated PA injections did not further augment antibody production. These data indicate that PA could be introduced as the sensitizing step in some experimental antibody-dependent anticancer regimens.
Actomyosin isolated from the bovine adrenal medulla was capable of Ca2+-dependent superprecipitation, and retained the actin-stimulated Mg2+-ATPase activity. A half maximum activation was attained with Ca2+ at about 4 μM. The superprecipitation was inhibited by agents interacting with calmodulin, i.e. trifluoperazine, chlorpromazine, W-7 and promethazine with I50 values of 15, 70, 85 and 440 μM, respectively, suggesting the involvement of calmodulin in the Ca2+-dependent actin-myosin interaction in medullary actomyosin. About 8-10 mg of myosin was obtained from 200 mg of medullary actomyosin isolated from 100g of the bovine adrenal medulla. Caldesmons (caldesmon150 and caldesmon77), actin-linked regulatory proteins, were identified in our actomyosin preparation by immunoblotting using anti-gizzard caldesmon IgG. The medullary actinmyosin interaction was inhibited by caldesmons in a dose-dependent manner. Myosin light chain kinase, a myosin-linked regulatory protein, was also identified in our medullary actomyosin preparation by immunoblotting. Actin-stimulated Mg2+-ATPase activity of medullary myosin was enhanced 2.5-fold when the myosin light chain was phosphorylated in the presence of Ca2+ and calmodulin. We suggest that the actin-myosin interaction in medullary actomyosin is dually regulated by Ca2+ via the actin-linked and myosin-linked systems.
The effects of neonatal thymectomy on insulitis in non-obese diabetes (NOD) mice,which suffer from destruction of B cells in the pancreas, were studied histopathologically. Complete neonatal thymectomy reduced the incidence of insulitis in NOD mice, from 100% to 53% in males and from 100% to 69% in females at day 60; and from 100% to 44% in males and from 100% to 54% in females at day 100. The results suggest that the pathogenesis of insulitis in NOD mice may depend on an autoimmune mechanism related to the thymus, through which destruction of B cells in the pancreatic islets is mediated. NOD mice can therefore be useful as an animal model for studying the autoimmune etiology of type I diabetes in humans.
The marked structural homology of human pancreatic growth hormone releasing factor (hpGRF) with peptide histidine-isoleucine (PHI) and vasoactive intestinal polypeptide (VIP), members of the glucagon-secretin family that stimulate pancreatic exocrine secretion, suggested that hpGRF should be tested for this activity. Synthetic hpGRF-44, shown to be active in releasing growth hormone in human volunteers, had no effect on the volume or protein content of pancreatic juice in anaesthetized rats at intravenous bolus doses from 20 to 1,840 pmol. GRF seems unlikely to have a physiological role as a pancreatic secretagogue.
We have synthesized twelve CCK7 and CCK8 analogues with a substituted glycine at position 3 or 4. The most interesting analogues studied were Nα-carboxyacylated CCK7 or CCK8 with D-tryptophan or D-alanine substitution, i.e. Nα-carboxyacylated [D-Trp3]- and [D-Ala3]-CCK7 and Nα-carboxyacylated [D-Trp4]- and [D-Ala4]-CCK8. These analogues stimulated pancreatic exocrine secretion in anesthetized rats to almost the same extent as CCK8, but their guinea pig gall bladder contracting activity was substantially diminished. The selective stimulation of pancreatic secretion was also confirmed in vivo in anesthetized dogs with the D-amino acid-substituted CCK7 analogues.