Estrogens and progesterone during gestation in Dolichotis patagona.

During pregnancy, a progesterone-binding plasma protein is present and is similar in several respects to the binding protein reported in other hystricomorphs. These findings establish estradiol-17 beta as the predominant estrogen of pregnancy and that progesterone rises during pregnancy and does not decline until after parturition. Gestation length is 96 days. This study establishes similarities between the mara and its closest relative, the guinea pig.

Regional variations in uterine blood flow in the guinea pig: relationship to pregnancy site distribution.

The alterations which occur in the total uterine blood flow (UBF) during early pregnancy in the guinea pig were determined using electromagnetic blood flow probes. Between days 4 and 6 postcoitum, UBF rose from basal levels of 1.2 ml/min to peak levels of 3.0 ml/min. The elevated levels corresponded temporally with the onset of blastocyst implantation. Between days 7 and 8, UBF declined to basal levels. In guinea pigs possessing three pregnancy sites per uterine horn on days 10-20, obvious regional differences in UBF were observed. Consistently higher UBF measurements were monitored from uterine segmental arteries supplying the tubal and cervical thirds of the uterus than from those distributed to the middle third of the uterus. These data indicate that regional variations in UBF exist in the guinea pig which may be involved in the regulation of pregnancy site selection or subsequent placental-fetal growth.

In vitro mycotoxin binding to bovine uterine steroid hormone receptors.

The mycotoxins, aflatoxin B(1), aflatoxin M(1), aflatoxicol and zearalenone were tested for binding to bovine endometrial estrogen and progestin receptors. Radioinert estradiol-17beta, estrone, testosterone, and cholesterol were evaluated for binding to the estrogen receptor. Zearalenone and aflatoxicol but not aflatoxins B(1) and M(1) competed with estradiol-17beta for the estrogen receptor. The order of binding affinities for the estrogen receptor were zearalenone > estradiol-17beta > estrone > aflatoxicol. The affinity of zearalenone for the estrogen receptor was 2-3 times that of estradiol-17beta. Progesterone, cortisol, radioinert R 5020, and cholesterol were evaluated for binding to the progestin receptor. None of the tested compounds except R 5020 and progesterone competed for the progestin receptor. The significance of aflatoxicol binding to the estrogen receptor is unclear. It is proposed that aflatoxicol binding to the receptor may alter gene expression in target tissues or act at the level of the hypothalamus to inhibit gonadotropin secretion and ovulation. These effects could explain reports of reduced fertility in domestic animals following ingestion of aflatoxin contaminated feedstuffs. It is also suggested that the mechanism of adverse effects on fertility of chronic aflatoxin ingestion in cattle and other livestock should be more thoroughly investigated.