Orsini and Panski (1952) used colchicine in their investigations on the proliferative growth of hamster tissue. They found that injected doses of colchicine varying from O· 1 up to 2 mg per 100 g body weight did not cause any significant v4riation from the normal number of mitoses, and the presence of anaphase and telophase stages with normal spindles in normal ratio suggested that these doses were ineffective. They stated that effective doses in other rodents (mice, rats, guinea-pigs, and rabbits) are usually below the lethal level. In an attempt to establish the effective dose, they injected colchicine intraperitoneally at concentrations ranging from 0·13 to 7 mg per 100 g body weight into a series of hamsters, rats, mice, and a rabbit. At these levels colchicine was lethal for the latter three series of animals, but was not lethal for hamsters, even up to a concentration of 10 mg per 100 g body weight. They concluded that the hamster possesses a natural resistance to this compound.The present study has been made to find out the effect of colchicine on different stages of development of golden hamster embryos.
Material and MethodsHamsters were maintained in a colony receiving artificial lighting from 6 a.m. to 6 p.m. each day. From other evidence (Austin and Braden 1956), it was presumed that ovulation occurred in the colony between 1 and 3 a.m. The stage of the cycle was determined by daily examination using the method described by Orsini (1964). Mating was carried out by penning females overnight, singly, with fertile males.The occurrence of mating was checked by examination of vaginal smears for the presence of spermatozoa. The day of presumed ovulation is referred to here as day 1. In an attempt to increase the number of eggs shed some females received a subcutaneous injection of 25 i. u. pregnant mare serum gonadotropin (PMSG) 4 days before oestrus.In order to increase the number of mitotic figures available for examination in embryos studied before implantation, females were injected intraperitoneally with 0·25 ml of O· 03% (w/v) solution of colcemid (CIBA) 77-84 hr after ovulation.Eggs were recovered at autopsy at various times after mating. After removal of the ovaries and genital tract, counts were made of the corpora lutea in each ovary and the contents of the uterine horns were flushed onto a watch glass with warm (37°0) saline. Stained preparations of air-dried whole egg mounts were prepared by modification of the method described by Tarkowky (1966) as follows. The eggs were first treated by exposure to a hypotonic (1 %) solution of sodium citrate, swelling of the eggs being observed visually under a dissecting microscope. The eggs were then pipetted onto clean dry slides. After removal of excess hypotonic solution the eggs were fixed by cautious addition to the slide of a drop of acetic acid-methanol (1 : 3). Fixation was completed by evaporation of the fixative, the process being observed by microscopical examination.Embryos (10 days old) recovered after implantation were incubated for 90 min at...