Search PubMed⌕ Search

Biomedical subjects

R H Smith

Publications and source records attributed to R H Smith.

At least 253 records · Page 14Linked to original sources
PubMed1966

Mineral composition and rates of flow of effluent from the distal ileum of liquid-fed calves.

1. Liquid-fed calves (aged 1(1/2)-4 months) examined more than five weeks after inserting a re-entrant fistula into the distal ileum, of normal sodium and potassium status and without abnormal gut infection, showed mean emergence rates from the ileum for sodium, potassium and water of 2.3 m-mole/hr, 0.38 m-mole/hr and 21 g/hr respectively after 16 hr fasting.2. Sodium and potassium emergence rates changed little when the residues from a milk or glucose-solution feed arrived at the distal ileum. When magnesium chloride was added to a glucose-solution feed an increase sometimes occurred but only in association with decreased small-intestine transit time.3. Widely differing sodium and potassium intakes had no appreciable direct effect on their emergence rates. Continued feeding of a diet deficient in either ion, however, altered the calf's metabolism and led to appropriate changes in the sodium/potassium ratio of ileal effluent. These changes were not simulated by injecting adrenal cortex hormones. The ratio also decreased when ileal effluent was allowed to discharge for several weeks without being returned to the colon. It was abnormally high in samples obtained less than five weeks after inserting cannulae.4. An increase in sodium and potassium emergence rates, which often occurred spontaneously at about 3 months of age, appeared to be due to infection and was usually prevented by giving aureomycin orally.5. Water emergence rate reflected changes in the emergence rates of osmotically effective constituents and isotonicity was maintained. In effluent after fasting, the cations involved were mainly sodium and potassium, and [Na] + [K] was approximately constant (mean 132 m-mole/l.). In effluent following feeds of milk or glucose, magnesium chloride solution, [Na] + [K] was depressed and [Na] + [K] + 1.5 [Mg] was approximately constant (mean 139 m-mole/l.). Magnesium behaved as it were mainly ionic. Calcium had no apparent osmotic effect and was probably insoluble.6. Bicarbonate was the major anion in ileal effluent after a milk feed with smaller amounts of chloride, phosphate and some other unknown anion(s).

Animals↗
PubMedDate not supplied

Sex differences in myocardial contractility in the rat.

We examined the intrinsic contractile performance of papillary muscles removed from the left ventricle of male and female Wistar rats. Muscles were studied isometrically and isotonically, stimulated at 0.1 Hz, perfused with Tyrode's solution having an external calcium concentration = 2.4 and maintained at 30 degrees C. In addition, we examined muscle response to changes in external calcium, added norepinephrine or verapamil and alterations in contraction frequency. No significant change in peak isometric development tension was observed between male and female preparations. However, muscles from male rats showed a significantly greater isometric time-to-peak tension and time to 1/2 relaxation with a depression of both the maximum rate of tension rise and maximum rate of tension decay. Isotonically, although peak shortening showed no difference between male and female preparations, the maximum velocities of shortening and relaxation were significantly depressed in muscles from male rats. Muscles from male animals also displayed significant prolongation of the time-to-peak shortening and time-to-peak velocity of shortening. These differences in papillary muscle performance were found over a wide range of muscle lengths, stimulus frequencies and bath concentrations of calcium, norepinephrine and verapamil. Thus differences in the intrinsic contractile performance between papillary muscle from male and female rats have been characterized.

Animals↗
PubMedDate not supplied

Sulfhydryl site-specific cross-linking and labeling of monoclonal antibodies by a fluorescent equilibrium transfer alkylation cross-link reagent.

The site-specific intramolecular cross-linking of sulfhydryls of monoclonal antibodies via a new class of "equilibrium transfer alkylation cross-link (ETAC) reagents" is described. Following complete or partial reduction of interchain disulfides with dithiothreitol (DTT), two murine IgG2a monoclonal antibodies, 225.28S and 5G6.4, were reacted with alpha,alpha-bis[(p-tolylsulfonyl)methyl]-m-aminoacetophenone (ETAC 1a) and a fluorescent conjugated derivative, sulforhodamine B m-(alpha,alpha-bis(p-tolysulfonylmethyl)acetyl)anilide derivative (ETAC 1b). Reducing SDS-polyacrylamide gel electrophoresis analysis of the products from 1b indicated the formation of S-ETAC-S interchain heavy and light chain cross-links (approximately 23-34% overall yield by video-camera densitometry) which do not undergo disulfide-thiol exchange with DTT at 100 degrees C. In contrast, no interchain cross-links were observed upon reaction of unreduced or reduced antibody wherein the thiols have been previously alkylated with iodoacetamide. These results indicated site-specific cross-linking of interchain sulfhydryls and places their distance within 3-4 A. Flow cytometry of the ETAC 1b 5G6.4 cross-linked product using 77 IP3 human ovarian carcinoma target cells showed positive binding and retention of immunoreactivity. The in vivo biodistributions of 131I-labeled intact 5G6.4 and 125I-labeled reduced 5G6.4 + ETAC 1a product in rats were essentially identical over a period of 24 h. The present study illustrates the potential applications of labelable ETAC reagents as thiol-specific probes for a wide variety of immunological studies.

Acetophenones↗
PubMedDate not supplied

1,3-Dialkyltriazenes: reactive intermediates and DNA alkylation.

The reactions of calf thymus (ct) DNA with 1,3-dimethyltriazene (DMT), N-methyl-N-nitrosourea (MNU), 1,3-diethyltriazene (DET), N-ethyl-N-nitrosourea (ENU), and 1-ethyl-3-methyltriazene (MET) were studied as a function of concentration of the alkylating agents, of various buffers, and of ionic strength. The amount of alkylation at the 7- and O6-positions of guanine increased linearly with dose over a 10-fold concentration range. The slopes of the DMT and MNU curves were identical as were those of DET and ENU. These data suggest that both types of compounds alkylate DNA via a similar intermediate, presumably the corresponding alkanediazonium ion. MET methylates and ethylates DNA, the amount of each product being a function of the competitive formation of the two diazonium ions possible from MET. The MET product ratios could be reproduced by an appropriate mixture of DET and DMT. The alkylation of DNA by DMT and by MET is very sensitive to ionic strength, to the nature of the buffer, and to the identity of the salt used to balance ionic strength. In general, the reaction is favored by low ionic strength, by amine rather than oxy acid buffers, and by doubly charged inert anions. The alkylation of DNA is inversely proportional to the logarithm of the ionic strength over a wide range. The mutagenic activity of triazenes in Salmonella typhimurium is correlated very well with the ability of the triazenes to form adducts, particularly O6-guanine adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylation↗
PubMedDate not supplied

Alkylation of DNA by 1,3-dialkyl-3-acyltriazenes: correlation of biological activity with chemical behavior.

The reactions of calf thymus DNA with four 1,3-dialkyl-3-acyltriazenes were studied alone or in the presence of pig liver esterase in pH 7.4 phosphate buffer for varying lengths of time. The best alkylating agent in the absence of esterase was determined to be 1,3-dimethyl-3-carbethoxytriazene (DMC), followed in order by 1-(2-hydroxyethyl)-3-methyl-3-carbethoxytriazene (HMC), 1-(2-hydroxyethyl)-3-methyl-3-acetyltriazene (HMA), and 1-(2- chloroethyl)-3-methyl-3-carbethoxytriazene (CMC). This order is the same as that for the rate of decomposition of the various acyltriazenes in pH 7.5 phosphate buffer. The extent of calf thymus DNA alkylation by CMC was found to be dependent on both the reaction buffer and the ionic strength of the medium. Alkylation by CMC alone in low ionic strength glycine buffer produced large quantities of 7-(2-chloroethyl)guanine and 7-(2-hydroxyethyl)guanine. The products of DNA alkylation observed at neutral pH are consistent with N(2)-N(3) heterolysis of the triazene, resulting in the N(1) alkyldiazonium ion as the sole alkylating species. In the presence of esterase, CMC showed an enhanced rate of product formation. Furthermore, the product distribution shifted dramatically from mainly hydroxyethylation to predominantly methylation. CMC is postulated to undergo initial enzymatic deacylation, leading to two different alkyldiazonium ions which competitively alkylate DNA. HMC, on the other hand, was little affected by the esterase. The enzyme-catalyzed reaction showed a small increase in methylation and a smaller decrease in hydroxyethylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylating Agents↗
PubMedDate not supplied

Oxidative metabolism of 1-(2-chloroethyl)-3-alkyl-3- (methylcarbamoyl)triazenes: formation of chloroacetaldehyde and relevance to biological activity.

(Methylcarbamoyl)triazenes have been shown to be effective cancer chemotherapeutic agents in a number of biological systems. Because of their chemical stability, it is likely that their activity in vivo is the result of a metabolic activation process. Previous studies have shown that 1-(2-chloroethyl)-3-methyl-3-(methylcarbamoyl)triazene (CMM) and 1-(2-chloroethyl)-3-benzyl-3-(methylcarbamoyl)triazene (CBzM) are metabolized by rat liver microsomes in the presence of NADPH to yield the ((hydroxymethyl)carbamoyl)triazene analogs of the parent compounds. The present studies show that both compounds are also oxidized at the chloroethyl substituent to yield chloroacetaldehyde and a substituted urea. In the case of CBzM metabolism, 47% of the metabolized parent compound was recovered as benzylmethylurea, 8% was recovered as benzylurea, and 26% was recovered as the ((hydroxymethyl)carbamoyl)-triazene and carbamoyltriazene metabolites. These results suggest that the chloroethyl group is the favored initial site of metabolism. In reaction mixtures containing initial concentrations of 300 microM CBzM, 78 microM chloroacetaldehyde was produced, as compared to 58 microM chloroacetaldehyde produced from the metabolism of 300 microM CMM. The formation of chloroacetaldehyde, a known mutagenic DNA alkylating agent, may explain the biological activity of these compounds.

Acetaldehyde↗
PubMedDate not supplied

Base sequence selectivity in the alkylation of DNA by 1,3-dialkyl-3-acyltriazenes.

The base sequence selectivity of DNA alkylation for a series of structurally related 1,3-dialkyl-3-acyltriazenes was examined with calf thymus DNA or polymers containing the sequences GGG, CGC, TGT, and AGA. The reaction products at the N7 and the O6 positions of guanine were identified, quantitated, and then correlated with the decomposition rates of the triazenes, 1-(2-chloroethyl)-3-methyl-3-carbethoxy- (CMC), 1-(2-chloroethyl)-3-methyl-3-acetyl- (CMA), 1-(2-hydroxyethyl)-3-methyl-3-carbethoxy- (HMC), 1-(2-hydroxyethyl)-3-methyl-3-acetyl- (HMA), and 1,3-dimethyl-3-acetyl- (DMA). The results of these studies revealed that DNA sequences with runs of purines were more reactive toward alkylation by all of the triazenes tested, irrespective of whether the alkylation was measured by N7, O6, or total guanine adducts. Within this generalization, the (hydroxyethyl)triazenes showed a preference for the AGA sequence, while the (chloroethyl)triazenes favored the GGG sequence. The structure of the 3-acyl group of the triazene also played a role in the extent of alkylation of a particular sequence of DNA. Both the (chloroethyl)- and the (hydroxyethyl)triazenes produced higher alkylation product yields for the 3-carbethoxytriazenes as compared with the 3-acetyl derivatives for most of the sequences examined. These overall patterns correlated well with the order of decomposition of the triazenes at 37 degrees C: HMC > DMA > HMA > CMC > CMA. This study has demonstrated how varying the structure of 1,3-dialkyl-3-acyltriazenes can modulate DNA alkylation, a finding which may be important in the design of new triazene antitumor agents.

Alkylation↗
PubMedDate not supplied

The effects of different sources of nitrogen supplementation on the post ruminal flows of organic matter and different nitrogenous constituents in steers.

Friesian steers, virtually protozoa free, were equipped with simple rumen and abomasal cannulas. They were given diets consisting of approximately equal proportions of ground, pelleted alkali treated straw and a rolled barley, tapioca mixture supplemented with urea + casein (UC), soybean meal (SBM), 'normal' white fishmeal (NDF) or white fishmeal designated as being of 'low' rumen degradability (LDF). The diets were isoenergetic (the protein sources replacing part of the tapioca) and they were given in amounts to supply sufficient metabolizable energy (ME) to support an average growth rate of 0.5 kg/d. Rumen degradable nitrogen (RDN): ME values were estimated to be 2.08, 1.40, 1.90 and 1.66 for diets UC, SBM, NDF and LDF respectively. RNA, alpha-epsilon-diaminopimelic acid and 35S (added as sulphate) were used as bacterial markers. Chromic oxide and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Rumen volumes and ruminal liquid fractional outflow rates were measured using PEG. Samples of mixed rumen bacteria separated from strained rumen digesta from animals receiving diet UC contained significantly less DAP-N (0.322 g/kg DM) than those from animals receiving diets SBM, NDF or LDF (0.530 g/kg DM). Mean rumen volume (approximately 15 l) and liquid fractional outflow rates (approximately 0.105/h) were similar on all diets but there was appreciable variation between animals. The proportion of OM intake digested in the rumen was similar on all diets. The proportional contribution of bacterial-N to the total non-ammonia-N passing the abomasum based on mean values derived from DAP and 35S as markers was 0.57, 0.47, 0.39 and 0.31 for diets UC, SBM, NDF and LDF respectively. Corresponding values based on RNA were 0.71, 0.50, 0.48 and 0.35 respectively. Bacterial-N (RNA) flows at the abomasum were 31, 25, 26 and 20 g/d for diets UC, SBM, NDF and LDF respectively. Corresponding values for 35S and DAP were 26, 24, 21 and 18 g/d respectively. Values derived from RNA flows were consistently and significantly higher (P less than 0.01) than those based on DAP or 35S. Mean estimated efficiencies of bacterial protein synthesis (g bacterial-N/kg OM truly digested) were 15, 15, 14 and 12 for diets UC, SBM, NDF and LDF respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Abomasum↗