Effect of vinblastine sulfate on the growth and histologic development of reaggregated Hydra

In vitro differential developmental toxicity of vitamin A congeners

Several forms of vitamin A were tested in the in vitro hydra assay for their developmental toxicity hazard potential and site of action on progressive ontogenesis. Retinol, retinyl acetate, retinaldehyde, all trans retinoic acid, and 13 cis retinoic acid were tested fully, and each was established clearly as being able to perturb development of artificial hydra "embryos" at, or near, adult toxic treatment levels. All forms of vitamin A tested interfered with differentiation, but, although the alcohol, acetate, and aldehyde forms (group I) prevented the initial stages of differentiation from occurring, the acid forms (group II) allowed the initial stages of differentiation to occur but not the final differentiation of tentacle buds. Group I compounds produced the developmental toxicity endpoint after as little as 24 h of transient exposure on the first day of development, but had no permanent effect on development at their minimal affective developmental concentration (D-MAC) when exposure began after the first day of development. In contrast, transient 24-h exposure to group II forms did not interfere with development. At, or even above, a concentration greater than the D-MAC, more continuous exposure to them was required to interfere with differentiation. Consistent with tests of other chemicals, the concentrations needed to produce effects in hydra bore no relation to those needed to produce effects in mammals.

A tier system for developmental toxicity evaluations based on considerations of exposure and effect relationships

The backlog of untested chemicals and the rate at which new substances enter the marketplace exceed our capacity for developmental effects testing by standard in vivo methods. However, conservative use of two observations in a manner consistent with present day understanding of abnormal developmental biology can more accurately focus attention and resources on those agents in greatest need of complex testing for effects on in utero development. These two observations are 1) most chemicals are no more toxic to embryonic development than they are to adult homeostasis and 2) most human exposure to chemicals is de minimus, i.e., so small that it is inconsequential. Recently devised in vitro assays to quantitatively rank chemicals according to their developmental hazard index, when used in conjunction with more conventional in vivo methods and appropriate considerations of exposure, permit evaluation of a significantly larger number of chemicals than is currently achieved. The methods described apply a tier approach to establish testing priorities that markedly reduce the time, cost, and number of laboratory animals needed for evaluation of developmental toxicity.

Relationship of developmental stage to effects of vinblastine on the artificial "embryo" of Hydra

Three milligrams of vinblastine sulfate per liter of culture medium prevented normal development of all reaggregated artificial hydra "embryos" at the 66-hour stage of regeneration. One milligram of vinblastine per liter of medium had no effect on development, and 100 mg did not markedly accelerate the developmental disruption beyond the pace of the 2 mg/liter concentration which was the lowest effective concentration. Treatment with vinblastine through the first few hours of development was sufficient to produce the toxic endpoint at 66 hours of incubation, but effects were delayed in appearance when treatment was initiated later in development. Early development of exposed preparations proceeded normally even in the presence of rather high concentrations of the test substance, and the pellet was resistant to the effects of vinblastine treatment begun after 24 hours of development. From these results, it would appear that interference with cell division is not the primary means by which vinblastine perturbs this developing system.