Superovulation of Immature Rats by Continuous Infusion of Follicle-Stimulating Hormone1

Abstract

Immature female rats were infused s.c. continuously over a 60-h period with partially purified porcine pituitary follicle-stimulating hormone (FSH) preparations differing in degree of purity and having widely divergent luteinizing hormone (LH):FSH potency ratios as defined by radioreceptor assays. Rats infused with the more purified FSH preparation (FSH-A) ovulated a mean of 60-85 oocytes per rat on the morning of the third day (Day 1) after FSH infusion was begun (on Day-2). The same total dose of FSH administered as a single s.c. injection or as twice daily injections over the same 60-h period resulted in ovulation in only a minority of treated rats (3/16), with none achieving ovulation rates approaching those of rats infused continuously. High fertilization rates (80% of ovulated oocytes) were observed in superovulated rats joined with fertile males on the evening of the second day of infusion (Day 0). Of the 67 .+-. 7 fertilized ova per rat retrieved from oviducts flushed on Day 1, 52 .+-. 8, or 80%, were accounted for as morulae or blastocysts recovered when oviducts and uteri were flushed on the morning of Day 5, demonstrating essentially normal developmental rates and high survival rates in reproductive tracts of superovulated females during the preimplantation period. Infusion of rats with the same dose of a less well-purified FSH preparation (FSH-E) containing 20 times as much LH activity, or injection of rats with a superovulatory dose of pregnant mare''s serum gonadotropin (PMSG) (40 IU), were much less effective in causing superovulation, with ovulation rates of 17 .+-. 6 and 34 .+-. 8 oocytes/rat, respectively, compared to 79 .+-. 9 oocytes/rat infused with the FSH preparation (FSH-A) containing lower LH activity. The high rates of ovulation and of embryo development and recovery following infusion with a partially purified FSH preparation low in LH activity offers a convenient and effective alternative to PMSG as a means of superovulation of rats for the production of high yields of normal oocytes or embryos. The substantially lower ovulation rates observed after injection of PMSG or infusion of less purified FSH suggest a detrimental effect of high LH activity of gonadotropin used for superovulation of immature rats.