The kinetics of metaphase arrest in human psoriatic epidermis: an examination of optimal experimental conditions for determining the birth rate.
The optimum experimental conditions have been investigated for the measurement of the birth-rate in human psoriatic epidermis using the vinca alkaloids vinblastine and vincristine. The dose response characteristics of the two drugs were assessed over a 2.5 h collection period; although the dose response characteristics differed between the two agents, a dose of 1 microgram injected intradermally was considered to be optimal for both. The linearity of metaphase correction was assessed for both agents, taking biopsies for up to 10 h after injection. It was found that there was a delay period for up to an hour which must be avoided during the analysis to prevent an underestimate of the birth rate. However, linearity was then demonstrated for up to 4 h after injection. Metaphase degeneration was assessed by isolating a cohort of unlabelled cells in the G2 phase and tracing their fate over the next 10 h. It was found that the minimum life of an arrested metaphase was of the order of 4 h, and then metaphases degenerated at the rate of approximately 0.4% per hour. It is recommended that metaphase arrest experiments in psoriatic epidermis be confined to 4 h although, if required, correction factors are available to correct for experiments which are lengthened. Finally it is shown that flux into DNA synthesis exceeds the flux into mitosis by four or five times; several explanations are considered, and it is thought that the most likely explanation involves the death of psoriatic cells in the G2 phase.
D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D008677:Metaphase / Q000187:drug effects*; D008938:Mitosis; D011565:Psoriasis / Q000378:metabolism / Q000473:pathology*; D012867:Skin / Q000378:metabolism / Q000473:pathology*; D013997:Time Factors; D014747:Vinblastine / Q000494:pharmacology; D014750:Vincristine / Q000494:pharmacology
D014750:Vincristine; D014747:Vinblastine; D004247:DNA