5-Azacytidine affects the programming of expression of the somatic nucleus of Paramecium.

This report introduces a new system in the study of programming of genomic function during development of the somatic nucleus of Paramecium tetraurelia. Previous works have established a definite, but replaceable, role of the germ nuclei (micronuclei) in oral development in the asexual cycle; their removal from the cell generates viable amicronucleate cell lines, which characteristically suffer a transient period of growth depression marked by abnormal oral development. Such cell lines gradually recover, showing that a compensatory mechanism is activated in the absence of the germ nuclei to bring the cell back to near-normal. To test the notion that the somatic nucleus (macronucleus) is involved in this compensation, cells possessing micronuclei were treated with 5-azacytidine during sexual reproduction when new somatic nuclei develop. These cells were then propagated asexually for a number of fissions in the absence of the drug, and thereafter micronuclei were removed from them. The amicronucleate cell lines generated in this manner clearly did not suffer a depression as severe as the untreated controls did in terms of growth rate and oral development, and they recovered much sooner. This supports the notion that the somatic nucleus is the physical basis of the compensatory mechanism. This study suggests that the stomatogenic sequences in question normally become repressed in the somatic nucleus developing in sexual reproduction, and that 5-azacytidine administered to the cells at this time could alter this programme which then persists during subsequent asexual propagation. The possibility that the somatic nucleus is programmed by methylation of cytosine at the 5' position is discussed.

Pharmacokinetics of piperacillin in subjects with various degrees of renal function.

The pharmacokinetics of piperacillin were examined after single intravenous doses to three groups of male patients with creatinine clearances of greater than or equal to 60 (group I), greater than or equal to 20 but less than 60 (group II), and less than 20 (group III) ml/min per 1.73 m2. Each of 32 patients received either 1 or 4 g of piperacillin as a bolus injection. Three patients received both doses. After a rapid 0.5- to 1-h distribution phase, antibiotic levels in serum declined monoexponentially. After the 1-g dose, mean peak piperacillin levels in serum were 60, 103, and 67 micrograms/ml and the beta phase elimination half-lives were 1.0, 1.6, and 3.9 h in groups I, II, and III, respectively. After the 4-g dose, the respective mean peak piperacillin levels in serum were 329, 232, and 262 micrograms/ml and beta phase half-lives were 1.4, 2.3, and 2.6 h in the three groups. There was no clear evidence of significant dose-dependent effects on any pharmacokinetic parameters in any of the groups. Piperacillin levels in urine were far higher than those in serum, generally exceeding the minimal inhibitory concentrations for susceptible organisms during the 24 h after both the 1- and the 4-g dose. Piperacillin dosage modification is required only in patients with severe renal impairment.