Development and application of a micro-capillary rheometer for in-vitro evaluation of parenteral injectability.

A micro-capillary rheometer was developed to determine the rheology and injectability of parenteral formulations. The rheometer consisted of a micro-capillary and a glass syringe attached to an Instron that drove the syringe plunger at predetermined speeds and measured resulting forces on the plunger. The cross-head speed and the measured force were used to calculate the shear rate and the shear stress respectively, according to the Hagen-Poiseuille equation. The resulting rheograms of several Newtonian standards showed excellent linearity over a broad range of about 10 x 10(3) to 160 x 10(3) s(-1) and produced accurate and reproducible viscosity determinations over the viscosity range of about 10 x 10(-3) to 100 x 10(-3) Pa.s. The developed methodology focussed primarily on the minimization of errors associated with the determination of the wall frictional force using both direct measurement and linear regression to determine this parameter from the data. The effect of micro-capillary diameter, syringe cross-sectional area and micro-capillary length was explored in an effort to increase the measured force so that wall frictional force errors could be minimized. The micro-capillary rheometer gave reproducible and accurate rheograms over a range of shear rates consistent with the shear rate range used in clinical practice, and showed that Newtonian and non-Newtonian rheological behaviours could be evaluated quantitatively.

Effect of pH on hen egg white lysozyme production and evolution of a recombinant strain of Aspergillus niger.

An Aspergillus niger strain (B1) transformed to produce mature hen egg white lysozyme (HEWL) from a glucoamylase fusion protein under control of the A. niger glucoamylase promoter was grown in glucose-limited chemostat culture at a dilution rate of 0.07 h-1 at various pH values. Maximum HEWL production (9.3 mg g-1; specific production rate = 0.65 mg g-1 per h) was obtained at pH 4.5. However, in chemostat culture, HEWL production was not stable at any pH tested. After 240 h in steady state, specific production decreased to only 0.03 +/- 0.01 and 0.24 +/- 0.02 mg g-1 per h at pH 6.5 and 4.5, respectively. Some isolates removed from the chemostat cultures had lost copies of the HEWL gene and when grown in shake flask cultures all of the isolates produced less HEWL than the parental strain. Morphological mutants with similar phenotypes were isolated at all pHs, but their rate of increase in the population was pH dependent, with cultures at low pH (< 4.5) being more morphologically stable than cultures at high (> 4.5) pH. The selective advantage of these mutants was also generally dependent on pH. Both yellow pigment producing mutants and brown sporulation mutants had higher selective advantages over the parental strain at high than at low pH, regardless of the pH at which they were isolated. However, the selective advantage of densely sporulating mutants was independent of pH.

Acid phosphatase positional correlations in solid surface fungal cultivation: a fractal interpretation of biochemical differentiation.

Colour image analysis was used to measure the positional correlation between acid phosphatase intracellular concentration and hyphal cellular differentiation which leads to concentric circular zonal activity patterns. Acid phosphatase is strongly implicated in the biochemical control of hyphal branching, and exo-enzyme secretion, such as laccase in fungi, occurs predominately via the hyphal tips. Different concentrations of an organic dye were used to effect substrate induction of the enzyme response, which was shown to be statistically correlated according to a fractal power law (H approximately 0.39). A self-organized critical state for the molecular responsivity of dissipative enzyme expression is hypothesized as an efficient mechanism for hyphal adaptation, also accounting for the underlying biophysics of the observed pattern formations.

Enteropathy complicating maintenance therapy in acute lymphoblastic leukaemia.

Seven patients being treated for acute lymphoblastic leukaemia between March 1976 and March 1981, in accordance with Medical Research Council protocols, developed clinical malabsorption while on maintenance chemotherapy. All of them received weekly methotrexate and 6 of the 7 were given co-trimoxazole. Five patients had folate deficiency. Stopping the anti-leukaemic therapy led to a resolution of gastrointestinal symptoms. A combined effect of methotrexate and co-trimoxazole is postulated.

Management of leukaemic infiltration of the testis.

Of 95 boys treated for acute lymphoblastic leukaemia 25 have developed leukaemic infiltration of the testes. In 15 children relapse was apparently confined to the testes, and since treatment 7 of these boys remain in remission. The median duration of remission after testicular relapse was 72 weeks, considerably longer than that reported after other forms of leukaemic relapse.