Individual rabbit cardiac myocytes have different thresholds for alpha myosin heavy chain regulation by thyroid hormone

Myocytes in adult rabbit ventricle express and alpha and a beta form of myosin heavy chain (MHC). The alpha-MHC distribution detected with indirect immunofluorescence has been found in different proportions in adjacent myocytes producing a mosaic staining pattern. The basis for cell-specific expression of the alpha-MHC isoform is not known. Since thyroid hormone is a major regulator of myosin gene expression, we varied the plasma thyroid level and followed the alpha-MHC content within a population of myocytes. Ventricular myocytes were induced to become 100% beta-MHC by placing the rabbits on a 0.15% propylthiouracil diet for 70 days. L-triiodothyronine (LT3) over a dose range of 1 to 10 micrograms/kg/day was delivered by an osmotic minipump for 5 days, with actual serum levels confirmed by LT3 radioimmunoassay to be in the range of from 115 to 1,230 ng/dl. The amount of alpha-MHC that returned was estimated in randomly selected cells by measuring the relative intensity of the fluorescence-tagged secondary antibody. The normal mosaic pattern of alpha-MHC expression in the left ventricle returned with an LT3 dose of 2-5 micrograms/kg/day. The first myocytes to express alpha-MHC were in the subepicardium and did so at a LT3 serum level of 115 of ng/dl. All myocytes of the ventricular wall expressed alpha-MHC at serum levels above 1,230 ng/dl. These data are interpreted to show that the variation of myosin isoform content seen in the adult heart is indicative of heterogeneity of thyroid sensitivity, with the threshold for serum LT3 being between 115 and 370 ng/dl.     

Single amino acid changes that alter the DNA sequence specificity of the DNA-[N6-adenine] methyltransferase (Dam) of bacteriophage T4.

Bacteriophage T4 codes for a DNA-[N6-adenine] methyltransferase (Dam) which recognizes primarily the sequence GATC in both cytosine- and hydroxymethylcytosine-containing DNA. Hypermethylating mutants, damh, exhibit a relaxation in sequence specificity, that is, they are readily able to methylate non-canonical sites. We have determined that the damh mutation produces a single amino acid change (Pro126 to Ser126) in a region of homology (III) shared by three DNA-adenine methyltransferases; viz, T4 Dam, Escherichia coli Dam, and the DpnII modification enzyme of Streptococcus pneumoniae. We also describe another mutant, damc, which methylates GATC in cytosine-containing DNA, but not in hydroxymethylcytosine-containing DNA. This mutation also alters a single amino acid (Phe127 to Val127). These results implicate homology region III as a domain involved in DNA sequence recognition. The effect of several different amino acids at residue 126 was examined by creating a polypeptide chain terminating codon at that position and comparing the methylation capability of partially purified enzymes produced in the presence of various suppressors. No enzyme activity is detected when phenylalanine, glutamic acid, or histidine is inserted at position 126. However, insertion of alanine, cysteine, or glycine at residue 126 produces enzymatic activity similar to Damh.     

Comparison of enzyme phenotypes in human bladder tumours and experimentally induced hyperplastic and neoplastic lesions of the rat urinary bladder. A combined histochemical and immunohistochemical approach

The expression of a number of enzymes involved in drug metabolism, membrane function etc. was compared in hyperplastic and neoplastic lesions of the rat bladder and in human bladder tumours. Transitional cell carcinomas (TCC) in both rat and Man were characterized by decreased alkaline phosphatase (ALP) and increased gamma-glutamyl transpeptidase (GGT), beta-glucuronidase (beta-G1), succinate dehydrogenase (SD) and glucose-6-phosphate dehydrogenase (G6PD) activities. In addition, binding for antibodies specific for different cytochrome P-450 species (UT50, PB3a, MC1, MC2) and microsomal epoxide hydrolase (mEHb) was elevated in both murine and human tumours. Comparison of the enzyme phenotype in hyperplastic lesions induced by freeze ulceration or uracil administration with that in preneoplastic papillary or nodular hyperplasia (PNH) and TCC suggested, however, that most of the alteration in enzyme content or activity was non-specific and related to requirements for epithelial cell proliferation. On the other hand, the decreased ALP, and increased GGT and beta-G1 activity appeared more directly related to neoplastic transformation. The results suggested that qualitative differences exist between reactive hyperplasia and preneoplastic or neoplastic lesions in the urinary bladder. The finding of increased cytochrome P-450, in clear contrast to the reduction characteristic of preneoplastic hepatic lesions, may be important with regard to the observed difference in neoplastic transformation between the bladder and liver in response to drug metabolising enzyme inducers.     

Macrophages of the rat thymus after cyclosporin treatment. Histochemical, enzymehistochemical and immunohistochemical study

Young adult Wistar rats received 40 mg/kg of cyclosporin perorally for 21 days. Cyclosporin induced almost total disappearance of thymic medulla, whereas the cortex remained preserved. Although the density of cortical macrophages did not change significantly, their characteristics altered markedly and they became enlarged and rounded. In addition to an increase in acid phosphatase and nonspecific esterase activities, cortical macrophages developed very strong succinic dehydrogenase and chloroacetate esterase activities and a fine, granular, aldehyde fuchsin-positive cytoplasmic content. However, these cytoplasmic granules were PAS-negative and were not sudanophilic. Cortical macrophages retained their normal antigenic properties (which were studied by the use of ED1, ED2 and R-MC 41 monoclonal antibodies). Phagocytic cells in the remaining medullary islands retained their usual characteristics. The changes in cortical macrophages after cyclosporin treatment are discussed, especially in relation to the characteristics of macrophages of the cortico-medullary zone in the normal rat thymus.     

Kinetic properties of transketolase from the rat liver in a reaction with xylulose-5-phosphate and ribose-5-phosphate

An analysis of steady-state kinetics of purified rat liver transketolase shows that the reaction proceeds according to a two-stroke substitution ("ping-pong") mechanism. Based on the kinetic data, a competitive relationship was shown to exist between xylulose-5-phosphate and ribose-5-phosphate for the sites of substrate binding by the substituted form of the enzyme with the formation of a non-productive abortive complex (kd = 125 microM). The values of constants of two monomolecular steps of the reaction (k2 = 42 s-1; k4 = 9.4 s-1) were determined. It was assumed that the maximum rate-limiting step of the transketolase reaction is the degradation of the substituted form of transketolase--ribose-5-phosphate complex having a rate constant of k4.     

Energy and plastic metabolism of the heart muscle in rabbits undergoing thyroid irradiation with decimeter waves

The functional state of myocardial mitochondria, the glycogen and nucleic acid contents in myocardium, and morphometry of structural elements of cardiomyocytes and myocardial capillary network were investigated in order to select the optimal regimen of decimeter wave exposures with power density of 10, 120 and 240 mW/cm2 on the area of thyroid gland. It was shown that the thyroid gland exposure to decimeter waves at these intensities resulted in functional shifts in energy and plastic processes in myocardium and capillary blood supply. These changes increased to a considerable extent as the intensity of exposure was increasing and reached the maximum at power density of 240 mW/cm2 but event at this intensity there was not found the injurious effect of decimeter waves on the myocardium.     

The electron microscopic characteristics of stress lung

The influence of long-term (6 hours) immobilization stress on morphofunctional state of lung air-blood barrier was studied in experiments of the rats. It was shown that stress provoked the marked ultrastructural changes in the lungs, which were as follows: lung tissue oedema, pronounced thickening of lung air-blood barrier and its separate layers, edema-hemorrhagic syndrome, alveolar epithelial injury, disturbance of lung surfactant systems. Such a pathological complex may be designated as a "stress lung".     

家兔中脑导水管周围灰质中注射八肽胆囊收缩素（CCK—8）拮抗吗啡镇痛和...

We have reported that intracerebroventricular (i. c. v.) injection of 1-4 ng of CCK-8 to the rat produced a remarkable antagonistic effect on morphine analgesia. In order to study the species specificity and the site of action, CCK-8 was microinjected into the PAG of the rabbit, and its influence on morphine analgesia and electroacupuncture analgesia was observed. The latency of the escape response (ERL) to radiant heat focused on the snout was measured as an index of the pain threshold. Microinjections were made via cannulae chronically implanted into the PAG. The drug solutions were delivered in a volume of 1 microliter, at a speed of 0.125 microliter/min. The ERL was measured for a period of 60 or 70 minutes at 10 min intervals. 1. CCK-8 administered unilaterally to the PAG of the rabbit at a dose of 3 ng antagonized the analgesia induced by morphine (4 mg/kg, i. v.) by 73% (P less than 0.001), and reduced the analgesic effect of electroacupuncture by 67% (P less than 0.001). These effects were dose-dependent within the range from 1.5 ng to 6.0 ng. The effect of CCK-8 was reversed by CCK receptor blocker proglumide (4 microliters, intra-PAG injection). Unsulfated CCK-8 (CCK-us) had no effect in this regard. These results indicate that in the PAG of the rabbit, exogenously administered CCK-8 was capable of antagonizing opioid analgesia by the activation of CCK receptors. 2. Two groups of rabbits were given with morphine (2 mg/kg, i. v.) and simultaneous injection of CCK-8 antiserum (CCK-AS, 1 microliter) or normal rabbit serum (NRS) into the PAG.(ABSTRACT TRUNCATED AT 250 WORDS)