Kenneth M. Pruitt

A theory of growth

Abstract A generalized theory of growth is presented based upon three postulates. The first asserts that the rate of growth is jointly proportional to a monotonic function of the generalized distance from the origin to present size (“reproductive capability”), and to a monotonic function of the generalized distance from present size to ultimate size (“limiting factor”). The second postulate restricts the monotonic function to power (or “mass action”) functions. The third postulate constrains the model to a mathematically tractable set which never-the-less is sufficiently general to include the cases of Malthusian, Gompertz, logistic and Bertalanffy-Richards Growth. The most general case is termed the “generic growth model”. Other special cases are termed hyperGompertzian and hyperlogistic growth. Generic growth is illustrated by rat weight data from the literature.

Specific assays for peroxidases in human saliva

The peroxidase activity in human whole saliva is due to salivary peroxidase and, in some cases, myeloperoxidase; it is usually determined by spectrophotometric methods based on the rate of oxidation of chromogen substrates. Thiocyanate ion, a normal component of saliva, interferes with these kinetic assays by competing with the chromogen for the available oxidizing equivalents; this results in underestimation of peroxidase activity. Both salivary peroxidase and myeloperoxidase will catalyse the peroxidation of the thiocyanate ion; the product, hypothiocyanite ion, is a reactive oxidizing agent. We have developed an assay for total peroxidase activity in saliva, based on the rate of formation of hypothiocyanite, which is not affected by the concentrations of thiocyanate found in saliva. Myeloperoxidase will catalyse the peroxidation of the chloride ion but salivary peroxidase will not; the product of this in neutral solution is the hypochlorite ion, which is also a reactive oxidizing agent. The specific contribution was determined of myeloperoxidase to total peroxidase activity in saliva by measuring the rate of both hypochlorite and hypothiocyanite formation. Because the thiocyanate ion will compete with the chloride ion, the concentration of thiocyanate in saliva samples must be reduced below 0.05 mM prior to measurements of the rate of hypochlorite formation.

An Improved Amylase Assay

An improved amylase assay has been developed by modifying the method of Bernfeld (Advances Enzym 12:379-424, 1951), to increase accuracy and sensitivity. The method described here differs from that of Bernfeld as follows: (1) The color reagent contained 1 mg/ml of 3,5-dinitrosalicylic acid instead of 10 mg/ml. (2) Incubation was performed at 25 C instead of 20 C as a matter of convenience. (3) Samples for spectrophotometric observations were diluted 1: 10 instead of 1:5 to reduce the total amount of light energy absorbed. (4) Spectrophotometric readings were made at wavelength 470 mjA instead of 540 m~t because the absorbance peak of the reaction product occurs at 470 mg (Fig 1). REAGENTS EMPLOYED.-Enzyme.-Aqueous solutions of amylase (crystalline product of Aspergillus oryzeae with concentrations from 1 to 20 Ag/ml). Substrate.-One percent soluble starch solution (10 gm/i) in 0.02M sodium phosphate buffer, pH 6.9, containing 0.006M NaCl. The starch solution was heated to boiling and filtered using Whatman no. 1 filter paper. COLOR REAGENT.-One hundred milligrams

The interactions of human complement with interfacially aggregated preparations of human secretory IgA

Abstract Solutions of human secretory IgA (S-IgA) did not interact with complement. When S-IgA solms were lyophilized, and resuspended with gentle stirring only 50–70 per cent of the resulting powder dould be redissolved subsequently. Incubation of the insoluble residue with human serum remove complement activity. Simple freezing and thawing of S-IgA solns did not produce anticomplementary activity. Solution of human S-IgA, IgG, and albumin were evaporated on a rotary evaporator at 37°C. The residues were resuspended and analyzed for anticomplementary activity using a method which measures rate of cell lysis by following turbidity changes in suspensions of sensitized red cells to which complement has been added. On a relative scale, the quantities of the individual human residues required to remove one half of the complement offered were: IgG = 1, IgA = 5, albumin = 27. Aggregated human Fabα fragments of secretory IgA as well as aggregated serum myeloma IgA were also found to be complement reactive. Aggregated secretory IgA was found to reduce the hemolytic activity of human C3–9 but not that of human C1. the IgA aggregates were probably not held together with covalent bonds since they readily dissolved at alkaline pH. The results suggest that the Fab region of S-IgA may be involved in the complement interactions of S-IgA aggregates and that secretory component is not necessary of these interactions.

Mathematical models of bacterial growth, inhibition and death under combined stress conditions

SummaryIn this report we review the history of growth theories. We show how classical growth models may be derived as special cases of a generic growth rate equation. We show how growth models may be modified to represent survival data. We use linear combinations of growth and survival models to represent complex growth/survival curves and give practical examples utilizing nonlinear regression analysis. We show that traditional methods of estimating D values are inappropriate for complex, multiphasic growth/survival data. We show how such data may be modeled mathematically and illustrate methods for estimating true D values from such data.

Temperature relationship to distance and flow rate of warmed IV fluids

STUDY OBJECTIVE To determine whether therapeutic benefit is obtained by administering warmed IV fluid to hypothermic children. DESIGN Saline at 37 C in standard IV tubing was subjected to temperature measurements within a fluid warmer and at 5, 25, 45, 65, 85, and 105 cm distally. Flow rates varied from 20 to 1,000 mL/hr. SETTING The Childrens Hospital of Alabama emergency department. TYPE OF PARTICIPANTS None. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Temperature readings were made every minute until the volume required to flush the tubing had infused. Only at rates of 750 and 1,000 mL/hr did the fluid remain warmer than 32 C more than 25 cm from the warmer. CONCLUSION At flow rates usual in pediatrics, hypothermic patients must be connected to fluid warmers by lengths of IV tubing shorter than customary or practical in the ED to benefit from this treatment modality.

Detection of the hypothiocyanite (OSCN−) ion in human parotid saliva and the effect of pH on OSCN− generation in the salivary peroxidase antimicrobial system

Human whole saliva contains the hypothiocyanite ion (OSCN-) which is the principal antimicrobial product of the salivary peroxidase system. The peroxidase system requires a source of peroxide in order to produce OSCN- and in the human mouth this source has been assumed to be primarily the peroxidogenic oral bacteria. However, we report here studies which show that samples of stimulated human parotid saliva collected directly from Stensons duct have concentrations of OSCN- which are similar to those found in human whole saliva. Thus, the peroxidogenic bacteria are not an absolute requirement for the generation of significant levels of OSCN- in the human mouth. Supplementation of human whole saliva with components [thiocyanite (SCN-), hydrogen peroxide (H2O2)] of the peroxidase system produces a 10-fold or greater increase in OSCN- concentration. However, the magnitude of this increase is critically dependent upon pH and upon the relative and absolute concentrations of SCN- and H2O2. The pH dependence of OSCN- generation is similar for human whole saliva and for the lactoperoxidase/SCN-/H2O2 system. The optimum is in the range 6.5-7.0. Samples of parotid saliva adjusted to pH 6.5 and supplemented with appropriate amounts of SCN- and H2O2 show increases in OSCN- concentrations which are similar to those observed with whole saliva. The results show that there is a significant source of H2O2 within the parotid gland, that the OSCN- generating potential of parotid saliva is similar to that of whole saliva and that the enhancement of OSCN- levels in saliva by addition of SCN- and H2O2 is critically dependent upon pH and upon the relative and absolute concentrations of H2O2 and SCN-.

The Interaction of Salivary Proteins with Tooth Surface

Studies of the adsorption of human salivary proteins, in general, and the enzymes amylase, lysozyme, and neuraminidase, in particular, reveal that these proteins differ in their affinities for the surface of enamel. The enzymes studied retained their enzyme activity in the adsorbed state. Only amylase was desorbed by water; lysozyme was desorbed by its substrate; and all three enzymes, as well as most other adsorbed proteins, were desorbed by phosphate.

Is thiocyanate peroxidation at equilibrium in vivo

The peroxidase-catalyzed oxidation of SCN- by H2O2 is an important in vivo reaction because it limits the accumulation of toxic H2O2 and provides significant concentrations of the antimicrobial agents, HOSCN and OSCN-. Data presented in this report suggest that the reaction: (Formula: see text) is in a state of dynamic equilibrium in vivo. Since OSCN- can form the weak acid HOSCN (pKa = 5.3), the equilibrium constant expression (Kox) for thiocyanate peroxidation is dependent on the concentration of hydrogen ions as well as the concentrations of H2O2, SCN-, HOSCN, OSCN- and water, and on the HOSCN ionization constant, Ka: (Formula: see text). The concentration of water is assumed to be constant and unaffected by the other components and is omitted from the Kox equation. The value of Kox was estimated from in vitro data to be 3.7 X 10(3) M-1 (S.D. = 0.8 X 10(3) M-1, n = 8). Using this value for Kox and observations of salivary concentrations of SCN- and HOSCN + OSCN- from several previous reports, the equilibrium concentrations of H2O2 in whole saliva were calculated to range from 8 to 13 microM. This range is consistent with reported estimates of 10 microM as the hydrogen peroxide tolerance limit for human cells.

Limiting Factors for the Generation of Hypothiocyanite Ion, an Antimicrobial Agent, in Human Saliva

The limiting factors for the generation of the bacterial inhibitor, hypothiocyanite OSCN- ion, in human whole saliva were studied. Significant increase in OSCN- production could be achieved both in vitro and in vivo by supplementing saliva with peroxide alone or with a combination of peroxide and SCN-. The most effective initial H2O2 concentration was 700 μM. Higher concentrations caused a rapid loss in the amount of OSCN-. In contrast to expectations, supplementation of saliva with excess lactoperoxidase resulted in decreased generation of OSCN- ions. From these results we conclude that the enhancement of this naturally occurring antimicrobial system is possible by a combination of peroxide and SCN- ions added to human saliva in the appropriate ratios.