Michael J.K. Harper

A rabbit model for bacteria-induced preterm pregnancy loss

Bacterial infection has been implicated in premature labor in humans. To elucidate mechanisms and potential intervention strategies, we sought to develop a model of infection-induced pregnancy loss in rabbits. On day 21 (70% of gestation), each uterine horn was inoculated hysteroscopically with 0.2 ml containing saline solution of 10(6) cfu Escherichia coli or Bacteroides bivius or Fusobacterium necrophorum. Fetal viability was assessed. Animals were sacrificed at various times or as delivery occurred. Serum progesterone and amniotic fluid prostaglandins were measured. Cultures and histologic sections were prepared. Compared with the saline solution group, E coli and F. necrophorum-inoculated rabbits were significantly more likely to deliver (16 of 16 and six of seven with mean times of 31.9 +/- 10.7 and 28.3 +/- 11.5 hours, respectively for E. coli and F. necrophorum). Positive amniotic fluid cultures for the E. coli group were found in 11 of 12 (92%) and for the F. necrophorum group in three of three cases (100%). Histologic inflammation was seen heavily in both the E. coli and F. necrophorum groups, whereas it was absent in the saline solution group. Inoculation with B. bivius led to a much lower pregnancy loss rate (eight of 32) and less histologic inflammation despite positive uterine cultures in most animals. This model may provide an opportunity to determine mechanisms of clinical or subclinical intraamniotic infection and to test intervention strategies.

Differential hormonal regulation of leukemia inhibitory factor (LIF) in rabbit and mouse uterus.

Leukemia inhibitory factor (LIF) has been shown to be essential for the implantation of mouse blastocysts. The present study was designed to determine how LIF protein was hormonally regulated in rabbit and mouse uterus using immunohistochemistry. In unmated rabbits, LIF protein was at a low level in the uterine epithelium and glands, and up‐regulated by progesterone alone or estradiol‐17β and progesterone combined. Estradiol‐17β alone had no apparent effect. In ovariectomized mice, the level of LIF protein was very low in the uterine epithelium and glands, and was up‐regulated by estradiol‐17β alone or estradiol‐17β and progesterone combined. Progesterone alone had no apparent effect. These results suggest that LIF protein is differentially regulated in rabbit and mouse uterus by progesterone and estrogen, respectively. This would explain the high level of LIF protein observed in uterine epithelium and glands prior to blastocyst implantation in the two species with different hormonal requirements for implantation.

Accelerated ovum transport in rabbits induced by endotoxin 1. Changes in prostaglandin levels and reversal of endotoxin effect

Abstract The effect of endotoxin ( Salmonella enteritidis -Boivin) on ovum transport in the rabbit was examined. A dose of 10 μg/kg intravenously (iv) given 24 h after an injection of human chorionic gonadotrophin (hCG) to induce ovulation caused expulsion of 87% of ova from the oviduct within 24 h. The ED50 and 95% probability limits were 3.1 (2.38–4.03) μg/kg. A dose of 20 μg/kg given at 24 h after hCG exerted its effect on ovum transport within 4 h. Concurrent treatment with indomethacin completely prevented the effect of endotoxin on ovum transport. Endotoxin caused an increase of prostaglandin-like material (PG) E, measured by radioimmunoassay, in uterine vein blood within 35 min and PGE levels continued to rise until 3 h after endotoxin and remained elevated until 8–9 ½ h. PGF in uterine vein blood was not elevated until 90 min after endotoxin and then increased more rapidly than PGE during the next 2.5 h: it was still elevated at 8–9 ½ h. The ratio of PGF:PGE in uterine vein blood decreased from 3:1 in 24 h control samples to 1:1 at 1 h after endotoxin, and then increased rapidly exceeding 5:1 at 2 h. In animals given both indomethacin and endotoxin PG levels in uterine vein blood declined. Phenoxybenzamine partially prevented the effect of endotoxin on ovum transport and in animals so treated PGE levels in uterine vein blood increased similarly to those in animals receiving endotoxin alone, but PGF values, while elevated, were suppressed compared to those in endotoxin animals and the PGF:PGE ratio never exceeded 2:1. It is concluded that endotoxin induces accelerated ovum transport by causing an initial relaxation of the oviductal isthmic musculature due to PGE dominance followed by stimulation of oviductal circular musculature due to PGF dominance.

Autoradiographic localization of platelet-activating factor (PAF) binding sites in the rabbit endometrium during the peri-implantation period

SummaryThis communication describes the use of in-vivo and in-vitro autoradiography to map specific platelet-activating factor (PAF) receptors in the rabbit uterus. Specific [3H]PAF uptake was predominantly localized on epithelial, but not on stromal or myometrial cells. Very few silver grains were associated with the luminal epithelial cells in the uterus of the estrous rabbit, primarily because of the non-differentiated state of the epithelium. In the differentiated pregnant uterus, significantly more [3H]PAF was bound to the glandular epithelial cells, with the stromal cells binding consistently significantly less. The highest density of silver grains was observed at the implantation sites on day 7 of pregnancy. There was no apparent difference in [3H]PAF C18:0 uptake between the epithelial cells at the inter-implantation zone on day 7 and on day 6. Bound [3H]PAF was displaceable by lyso-PAF, U66985, CV3988, but not U66982, L652,731, SRI 63,441 or the inactive PAF isomer, oleoyl PAF. Bovine serum albumin (BSA) significantly inhibited tissue uptake of [3H]PAF C18:0. Intraluminally administered [3H]PAF C18:0 and intravenously injected [3H]methylcarbamyl-PAF, a non-metabolizable PAF analog, penetrated the implanted blastocyst and bound to the embryoblast. This event was reproducible in vitro with pre-implantation blastocysts from day-6 pregnant rabbits, which suggests that uterine-derived PAF may translocate into the blastocyst after attachment.

Uterine venous, peripheral venous, and radial arterial levels of prostaglandins E and F in women with pregnancy-induced hypertension

Patients with pregnancy-induced hypertension have higher prostaglandin (PG) F concentrations in radial arterial blood (0.39 +/- 0.03 ng/ml) than control subjects (0.24 +/- 0.03 ng/ml) and higher (PGE plus PGF) concentrations in uterine venous blood obtained at the time of cesarean section (1.62 +/- 0.18 versus 1.03 +/- 0.12 ng/ml in the control group). The present results suggest that both PGE and PGF production by the uterus in patients with pregnancy-induced hypertension is increased but that catabolism of PGF by the lung is compromised; this permits larger quantities of the vasoconstrictor PG to pass into the systemic circulation, where it may cause hypertension directly or indirectly, by association with other vasoactive substances.

Effect of inhibitors of prostaglandin synthesis and metabolism on ovum transport in the rabbit.

Several drugs known to affect prostaglandin synthesis, release, or metabolism have been tested for their effects on ovum transport in the rabbit after systemic or local administration. Acceleration of transport was obtained with several drugs; among the most effective were benzydamine, a blocker of thromboxane production, and L11204, an inhibitor of prostaglandin metabolism.

Studies on peroxidase-catalyzed formation of progesterone

Subcellular fractions of pregnant rabbit ovary at day six of gestation catalysed the formation of progesterone from pregnenolone (3 beta-hydroxy-5-pregnen-20-one). The microsomal fraction was found to have maximum activity. The enzyme needed hydrogen peroxide for its activity. In vitro studies using horseradish peroxidase also showed similar conversion and this was stimulated 200% in the presence of ascorbic acid. Ascorbate thus appears to perform a catalytic role in this conversion. The importance of peroxidase in luteal steroidogenesis is indicated.

Effect of indomethacin in vivo on prostaglandin content of several rabbit tissues.

The prostaglandin (PG) content of several tissues and fluids from 6 day pregnant rabbits was evaluated following treatment with indomethacin or vehicle in vivo. PGE and PGF were measured by radioimmunoassay. More complete depletion of PGE and PGF was accomplished by 3 injections of indomethacin (s.c.) given during the 18 h before sacrifice at a dose of 10 mg indomethacin per kg body weight than was accomplished by 1 injection of the same amount of indomethacin (i.v.) 1.5 h before sacrifice. Levels of PGF were more easily depressed by indomethacin than were those of PGE. PG levels in the kidney and blastocysts were depressed to a greater extent by indomethacin than were those in the uterus, uterine fluid or peritoneal fluid. Evaluation of the effect of indomethacin on a particular physiological function should be interpreted with caution unless the extent of PG depletion in that tissue is also measured.

Contraceptive properties of endotoxin in rabbits.

Endotoxin derived from Salmonella enteritidis-Boivin at a dose of 20 micrograms/kg intravenously interfered with follicular rupture normally induced by human chorionic gonadotropin (hCG) in rabbits. This action was greatest when the endotoxin was given 5 to 6 hours after the administration of hCG. The failure of follicular rupture resulted in entrapment of ova. Endotoxin (5 micrograms/kg) given intravenously to rabbits on day 4 of pregnancy resulted in failure of implantation. Indomethacin (2 micrograms/kg) given intramuscularly concomitantly was unable to reverse this action. Endotoxin (5 micrograms/kg) given intravenously to rabbits on day 8 of pregnancy had an immediate lethal action on embryonic development, and this effect was inhibited by concomitant indomethacin treatment. Nevertheless, most fetuses died after the indomethacin treatment. Whether this was due to a direct toxic action of indomethacin or to a secondary action of endotoxin not blocked by indomethacin is not clear. Endotoxin did not exert its antifertility actions through a luteolytic mechanism.

Contraception — retrospect and prospect

Contraception as a socially aceptable custom is by and large a 20th century phenomenon and is now perceived by many as a solution to a pressing world problem - that of overpopulation. As Shakespeare states in quotations above, we can define accurately what we would like to accomplish, but the achievement is often easier said than done. Such sentiments describe very well the state of the art as far as contraception is concerned. Most thinking people, and indeed many governments, see a reduction of the birth rate as the most significant way to achieve economic progress and to raise the standard of living in their countries commensurate with the expectations of their citizens. It is clear that we, the peoples of the world, have a choice, either we can reproduce until resources become insufficient to support us or we can take steps to control reproduction and achieve the desirable goal of zero population growth. Zero growth is defined as that state where the number of births and deaths are equal.