Date of Award

5-2003

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Abstract

Reproductive malformations such as hypospadias, cryptorchidism and testicular cancer appear to be on the rise in certain human male populations. Declining sperm counts have also been reported in certain regions of the world, but these findings remain widely debated. Similar reproductive disorders have been seen in wildlife species and have been linked to highly contaminated ecosystems. A unifying mechanism was proposed to explain the decline in male reproductive health.1 According to this hypothesis, all the alleged increases in male reproductive deficits in humans could be linked to disruption of critical developmental events occurring in utero and during the neonatal period when the fetal testes and particularly the Sertoli cells, are undergoing differentiation and replication. Thus, this theory centers on the disruption of the endocrine system during development by chemicals with hormone-like activities such as estrogens and anti-androgens.

The objective of this study was to determine the effects of endocrine disrupters on the reproductive system in male rats. In this study, Di-n-butyl phthalate (DBP), a known endocrine disrupter and a plasticizer was used. Male rats were fed with DBP for the duration of one month both at maturity (3 months) and when they were 1 month of age. After being fed the DPB for one month, some of the experimental animals were necropsied. A second objective was to extend this model to a continuous multi-generation breeding protocol, and to assess if the effects of DBP would be multiplied over the generations. The remaining rats of the original protocol were then bred with control female rats to obtain offsprings which would then be subjected to the same feeding protocol. At necropsy, all animals were sacrificed to obtain serum levels for testosterone (T) measurement, and tissues of testes, accessory sex organs including prostate, seminal vesicles and epididymis were fixed for histological examination. The findings as observed in the first generation of treated rats were consistent with those reported in the literature for DBP. These include minor changes in occasional undescended testis, underdeveloped epididymis, prostate and/or seminal vesicles. However, these changes were observed to have amplified progressively in the successive generation of rats. In particular, the effects were much more pronounced when the feeding protocol were initiated in the immature (one month old) rats as compared to the sexually mature (3 months old) rats. The results clearly indicated that sexually immature rats at one month of age, even well passed the neonatal period, are more susceptible than the older rats at the time when DBP in food is administered; this period of susceptibility extends to the time the development of both the testes and the accessory sex organs are still being formed. Mature rats of the continuous multi-generation breeding protocol, when fed DPB, however, are by comparison quite resistant to the effects of DBP.

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