Serum testosterone and dihydrotestosterone changes with age in rat.

Serum testosterone (T) and 5alpha-dihydrotestosterone (DHT) were measured in young, adult and old Albino Wistar male rats using a sensitive and reliable radioimmunoassay, after separating T from DHT by thin layer chromatography. The mean plus or minus S.E.M. for T in young, adult and old rats were 62 plus or minus 11, 250 plus or minus 27 and 125 plus or minus 25 (ng/100 ml) respectively. Serum T was increased in adults (P less than 0.001) and decreased in old rats (P less than 0.01). The mean plus or minus S.E.M. for serum DHT was 8 plus or minus 2, 19 plus or minus 2 and 17 plus or minus 1 (ng/100 ml) for young, adult and old rats respectively. DHT was increased in adults (P less than 0.001), but did not change in old rats.     

LIGHT/DARK-PHASED CELL DIVISION IN EUGLENA GRACILIS (Z) (EUGLENOPHYCEAE) IN PO4-LIMITED CONTINUOUS CULTURE1

Eugene gracilis Klebs (Z) was grown in a cyclostat (continuous culture on a light/dark cycle) at growth limiting levels of phosphate. Cell division was restricted to the dark period regardless of the proportion of the cells dividing during each 24 h period. Growth rate, as reflected by the amplitude of the cell density oscillation, was correlated with dilution rate. The width of the division gate was analyzed using a phasing index and found to be narrowest at dilution rates where the mean generation time of the cell population was an even multiple of 24 h. The effect was attributed to enhanced phasing of the cell division process by the biological clock of Euglena. Residual phosphate levels in the cyclostat were less than 0.3 μM PO₄ at all submaximal growth rates. Cellular phosphorus concentration increased with dilution rate as described by a hyperbola saturating at D_max= 0.74 day⁻¹ with 8 × 10⁻⁸μM P/cell as the minimum intracellular phosphorus concentration for growth. The results are discussed, in terms of the inherent similarities and differences between a cyclostat and a steady state chemostat, and the advantages of the cyclostat for studies in phytoplankton ecology.     

Semisynthetic Coumermycins: Structure-Activity Relationships

The relative antimicrobial activity of a large series of semisynthetic coumermycins has been determined. Most of the derivatives, which were 3-substituted-4-hydroxy-8-methyl-7-[3-O-(5-methyl-2-pyrrolylcarbonyl) noviosyloxy] coumarins, had an in vitro antibacterial spectrum similar to that of the parent compound, coumermycin A(1), but were generally less potent in minimal inhibitory concentration (MIC) tests. Derivatives with an alkylcarboxamido, arylcarboxamido, or arylsulfonamido group in the 3 position had considerably greater in vitro activity than those possessing an amino-, aryl-, or alkyureido substituent. Efficacy in Staphylcoccous aureus Smith infections of mice was greater for those compounds with branched-chain alkylcarboxamido, unsubstituted, mono- or disubstituted aryl- and heteroaryl-carboxamido groups than for derivatives having an n-alkylcarboxamido, aralkyl-carboxamido, arylsulfonamido, or trisubstituted arylcarboxamido substituent. Significant in vitro activity against Klebsiella pneumoniae and other gram-negative species was restricted to those compounds having a 3-(3-n-alkyl-4-hydroxy-phenyl-carboxamido) group. Only the n-hexyl homologue demonstrated in vivo activity in a K. pneumoniae infection. Many derivatives were two- to threefold more active than coumermycin A(1) in orally treated mouse infections, despite the fact that their MIC values were considerably higher. This result was undoubtedly a reflection of the markedly greater oral absorbability possessed by many of the derivatives. Although peak oral mouse blood levels of some compounds were > 25 times higher than those of coumermycin A(1), their toxicity for the host was no greater. In addition, the semisynthetic coumermycins caused much less local irritation than coumermycin A(1) when administered parenterally.     

Effects of secretin on insulin secretion and glucose tolerance.

Effects of intravenous (IV) infusion of secretin during IV infusion of glucose were examined in normal men. Secretin was administered according to three schedules: with each schedule a comparable priming dose was delivered in the first minute, but this was followed by a maintained (120 min) infusion of secretin at a relatively high rate, or by maintained infusion at one-third that rate, or by brief (15 min) infusion at the lower rate. The lower infusion rate produced increments in secretin in the blood within the range attainable during endogenous secretion. By comparison with effects of glucose alone each secretin infusion enhanced the increments of immunoreactive insulin in the blood. Enhancement of the early release (0-5 min) of insulin was similar with each type of secretin infusion, but the integrated changes in insulin levels through the total infusion period were related to the total doses of secretin. With each dose of secretin glucose tolerance was improved but the three mean glucose curves observed during infusions of secretin were not distinguishable from one another in spite of widely different integrated insulin responses. Secretin did not modify suppression of immunoreactive glucagon or free fatty acids in the blood during hyperglycemia. The results suggest that the effect of continuous administration of secretin on glucose tolerance is not simply related to its integrated insulinotropic action. It is suggested that the effect may be highly dependent on enhancement of insulin secretion early in the response to glycemia, or that it may be due to effects of secretin on glucose production or disposal which are not mediated by insulin.     

Regulation of allantoate transport in wild-type and mutant strains of Saccharomyces cerevisiae.

Accumulation of intracellular allantoin and allantoate is mediated by two distinct active transport systems in Saccharomyces cerevisiae. Allantoin transport (DAL4 gene) is inducible, while allantoate uptake is constitutive (it occurs at full levels in the absence of any allantoate-related compounds from the culture medium). Both systems appear to be sensitive to nitrogen catabolite repression, feedback inhibition, and trans-inhibition. Mutants (dal5) that lack allantoate transport have been isolated. These strains also exhibit a 60% loss of allantoin transport capability. Conversely, dal4 mutants previously described are unable to transport allantoin and exhibit a 50% loss of allantoate transport. We interpret the pleiotropic behavior of the dal4 and dal5 mutations as deriving from a functional interaction between elements of the two transport systems.     

A 113-amino acid fragment of CD4 produced in Escherichia coli blocks human immunodeficiency virus-induced cell fusion

A gene encoding a 113-amino acid, NH2-terminal fragment of CD4, rsT4.113, was constructed and expressed in Escherichia coli under the control of the tryptophan operon promoter. Following induction, rsT4.113 is produced at 5-10% of total E. coli protein, and it is found in inclusion bodies. The protein is purified in two steps under denaturing and reducing conditions. Solubilized rsT4.113 is first purified on a column of Q-Sepharose to remove low molecular weight contaminants and then purified to greater than 95% homogeneity by gel filtration. Renaturation of rsT4.113 is achieved at approximately 20% yield by dilution and dialysis. High performance liquid chromatography analysis of renatured rsT4.113 reveals a less than 15% contaminant of reduced protein. Purified and renatured rsT4.113 contains epitopes for both OKT4a and Leu3a, anti-CD4 monoclonal antibodies which block CD4-gp 120 association, but lacks measurable affinity toward a nonblocking anti-CD4 monoclonal antibody, OKT4. By comparison to a longer form (375 amino acids) of recombinant soluble T4 produced in mammalian cells that contains the entire extracellular domain, rsT4.113 has a comparable affinity for binding to OKT4a and Leu3a in a radioimmunoassay. Analysis of antiviral activity of rsT4.113 demonstrates that the E. coli-derived protein inhibits human immunodeficiency virus-induced syncytium formation with an IC50 of 5-10 micrograms/ml. These data demonstrate that the human immunodeficiency virus-binding domain of CD4 is localized within the NH2-terminal 113 amino acids of CD4 and is contained within a structure homologous to the kappa variable-like domain of immunoglobulins.