Date of Award


Degree Type


Degree Name

Doctor of Philosophy


This study examined the possible causes of infertility in immature rats following superovulation (SOV) with pregnant mares' serum gonadotrophin (PMSG). The areas looked at included the timing of ovulation, oocyte normality, fertilization, oviductal transport, early embryo development and implantation.;SOV with a single injection of PMSG or continuous infusion of follicle-stimulating hormone (FSH) was compared and in some rats the period of action of PMSG was restricted to (TURN) 58 h by use of a specific antiserum (a/s). Pregnancy was observed in most FSH-infused rats whereas following SOV with PMSG pregnancy failed prior to day 5. Increased ovarian oestradiol secretion was implicated in the infertility associated with PMSG. Pregnancy continued to term in some a/s-treated animals.;Ovulation in SOV rats occurred from 22 h after PMSG onwards with a burst of ovulations at 64 - 70 h; the latter time was comparable to that seen in control rats. In vivo fertilization rates of oocytes in cumulus from SOV rats were lower, probably due to the long time span of ovulation. However the developmental capacity of oocytes collected from the oviduct of SOV rats shortly after ovulation was equal to that of oocytes from control rats, when assessed by transfer to a synchronized recipient.;In SOV rats the majority of embryos was lost between days 1 and 3 of pregnancy. Use of PMSG a/s ensured the presence of blastocysts in the uterus on day 5 of pregnancy but implementation only occurred in (TURN) 50% of rats. The ability of the uteri to undergo decidualization was frequently impaired but transfer studies showed that the blastocysts were normal.;The results of this research suggest that the infertility seen after SOV results primarily from changes in the maternal environment resulting from excessive gonadotrophic stimulation. Excessive oestrogen secretion was particularly implicated. The preovulatory elevation in oestrogen concentrations appeared to prevent implantation in many rats and elevated postovulatory oestrogen concentrations caused loss of embryos by accelerated transport. Oocytes and blastocysts from SOV rats were normal if transferred to suitable recipients.



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