Concentration-dependent Delay Research Articles

The block to sperm penetration in zona-free mouse eggs

The rate of sperm penetration and the number of sperm penetrating zona-free mouse eggs were found to be dependent on sperm concentration. At the lowest sperm concentrations examined (10 2 cells/ml, sperm-egg ratios of approximately 1:1), most eggs were penetrated (75%), and polyspermy was low (19%) following 3 hr of incubation. The number of sperm penetrating the egg was logarithmically related to sperm concentration. All eggs showed a delay of at least 20 min between insemination and penetration, and penetration was complete in approximately 2 hr at 10 4 sperm/ml; this penetration block was attributed to egg-related changes. The existence and timing of the egg plasma membrane block to polyspermy were evaluated by reinsemination experiments. In this approach, the block was triggered in zona-free eggs with a low concentration of capacitated epididymal sperm at time 0, and the eggs were subsequently challenged with high sperm concentrations. The presence or absence of a block was inferred from the degree of polyspermy observed in these eggs after 3 hr of incubation. Adjusting for sperm concentration-dependent delays between insemination and sperm penetration, a blocking time of approximately 40 min was obtained.

Effects of 3′-deoxy-3′-fluorothymidine on proliferation kinetics of Ehrlich ascites tumour cells in vitro (comparison with other cytostatic drugs)

Treatment of Ehrlich ascites carcinoma cells in vitro with cytosine-arabinoside, 5-fluoro- 2′-deoxyuridine and hydroxyurea in concentrations just completely inhibiting cell proliferation, results, in agreement with data published for other cells, in progressive loss of viability if the treatment exceeds a period of one generation time (about 14hr). Pulse cytophotometric analysis of the treated cells showed them to be located mainly in the G 1 -phase of the cell cycle. In contrast, cell proliferation can be inhibited for about 32hr (more than 2 generation times), without loss of viability, if the treatment is done with 3′-deoxy- 3′-fluorothymidine ( 3′-FTdR). Pulse cytophotometric analysis revealed a concentration-dependent delay of progression through the S-phase. At a concentration just completely inhibiting cell proliferation, discontinuation of proliferation was predominant in late S-phase at the G 2 -boundary. These properties recommend 3′-FTdR for experiments aimed at improving cancer chemotherapy by a non-toxic accumulation of cells in the S-phase followed by treatment with a second, S-phase specific agent.