Effects of unilateral ovariectomy on growth of oocytes in the ovaries of adult toads (Bufo bufo bufo L.).

Abstract

Sexually mature female toads were unilaterally ovariectomized at various stages in the annual ovarian cycle and the effects were studied on numbers of oocytes in the various stages of growth in the remaining ovary. Three size groups of oocytes were distinguished: small oocytes, 0.1-0.3 mm in diameter; medium sized oocytes, 0.4-0.7 mm and large oocytes, 0.8-1.5 mm or more. The latter are in the final growth stage. Medium sized oocytes constitute the immediate source of oocytes for recruitment to the final growth stage, but smaller oocytes can presumably also be recruited. Excision of 1 ovary late in the final growth stage, or after completed growth of the oocytes, had no effects on any of the pools of oocytes (Experiment 1). Excision of 1 ovary during or just after the period of recruitment of oocytes to the stage of final growth resulted in the recruitment within the remaining ovary of numbers of oocytes normal for 2 ovaries (Experiments 2, 3). This compensatory response was practically complete within 1 month after the operation (Experiment 3). Unilateral ovariectomy caused marked depletion of the pool of medium sized oocytes. Reestablishment of the original pool size was slow and it was complete in only 5 out of 8 toads even 5 months after operation. Replenishment of the pool was correlated with increase in body weight. Reestablishment of a normal sized pool of small oocytes was also slow and it was erratic. In some ovaries, no increase in the number of oocytes was observed even 5 months after the operation; in others, the remaining ovary had produced oocytes in numbers that were high even for 2 ovaries in the control toads. There was no correlation between the reestablishment of the pools of small and medium sized oocytes (Experiment 3). The results indicate that there are different types of growth patterns and regulatory mechanisms for the various stages of oocyte development.