Inhibition of fertilization in rabbits during treatment with progesterone

• Published in: Biology of reproduction Vol. 2; no. 2; pp. 230 - 238
• Main Authors: Nutting, E.F, Mares, S.E
• Format: Journal Article
• Language: English
• Published: United States Society for the Study of Reproduction 01-04-1970
• Subjects: animal science; Animals; Cell Movement; Cervix Mucus; Contraceptives, Oral - pharmacology; Female; Fertilization - drug effects; Insemination, Artificial; Male; Oviducts; Ovum - drug effects; Oxytocin - pharmacology; Pregnancy; Progesterone - pharmacology; Rabbits; Semen; Spermatozoa; Time Factors; zoology
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod2.2.230

Adult female rabbits (Dutch strain) were artificially inseminated with 0.5 ml of diluted
semen (10 x 10 6 to 40 x 10 6 spermatozoa) and ovulated with 100 to 200 IU of HCG.
Corn oil or progesterone in corn oil was injected daily subcutaneously for various periods,
ranging from 0 to 6 days before insemination and continuing until sacrifice 48 hr after
insemination. Fertilization of ova was inhibited when 1 mg progesterone was injected
daily for 2 or 6 days before insemination but not when the treatment began on the day
of insemination or 4 days before insemination. An increase in the transport rate of ova
occurred only when treatment was initiated 2 days before insemination. The fertilization-inhibitory response to progesterone
was dose dependent between doses of 0.05 and 4
mg/day and the ED 50 was 0.4 mg. Although none of the levels employed was 100%
effective, only 2% of the ova recovered from the group given 4 mg/day were fertilized.
A sperm index with values ranging from 0 to 3 was employed to indicate the total
number of sperm counted in the mucin layer, zona pellucida, or perivitelline space of ova.
Values in all three areas were low in ova recovered from animals given 0.5 mg progesterone/day and were reduced to 0 or near
zero with all higher doses. When semen was
deposited into the uterus of animals given 1 mg progesterone/day for 6 days, nearly all
ova were fertilized. In animals given 1 mg progesterone/day, an increase in the
semen concentration from 10 to 100% failed to significantly increase the percentage of
ova fertilized, but successive injections of 50 U.S.P. units of oxytocin 1 hr before
insemination and 1 and 4 hr afterwards increased the percentage of ova fertilized from
0 to 45% and increased the sperm index values approximately 50% in each of the layers
of the ovum. Spermatozoa were recovered from the cervix and serial segments of the
uterus and oviducts at 4, 8, 16, and 24 hr following insemination; they were counted
using a micropore filtration technique. The numbers of sperm in all segments of the
uterus and oviducts of the progesterone-treated animals were consistently less than in
corresponding segments of control organs; they were absent from the anterior 2/3 of
the oviduct until 16 hr after insemination at which time only a few in the middle
oviducal segment were found. Progesterone inhibited fertilization of ova, we conclude,
primarily by interference with sperm transport mechanisms in the uterus and/or oviduct.