Generation of estradiol within the pregnant guinea pig uterine compartment with special reference to the myometrium

Species differences in developmental toxicity of epoxiconazole and its relevance to humans

Epoxiconazole, a triazole-based fungicide, was tested in toxicokinetic, prenatal and pre-postnatal toxicity studies in guinea pigs, following oral (gavage) administration at several dose levels (high dose: 90 mg/kg body weight per day). Maternal toxicity was evidenced by slightly increased abortion rates and by histopathological changes in adrenal glands, suggesting maternal stress. No compound-related increase in the incidence of malformations or variations was observed in the prenatal study. In the pre-postnatal study, epoxiconazole did not adversely affect gestation length, parturition, or postnatal growth and development. Administration of epoxiconazole did not alter circulating estradiol levels. Histopathological examination of the placentas did not reveal compound-related effects. The results in guinea pigs are strikingly different to those observed in pregnant rats, in which maternal estrogen depletion, pathological alteration of placentas, increased gestation length, late fetal death, and dystocia were observed after administration of epoxiconazole. In the studies reported here, analysis of maternal plasma concentrations and metabolism after administration of radiolabeled epoxiconazole demonstrated that the different results in rats and guinea pigs were not due to different exposures of the animals. A comprehensive comparison of hormonal regulation of pregnancy and birth in murid rodents and primates indicates that the effects on pregnancy and parturition observed in rats are not applicable to humans. In contrast, the pregnant guinea pig shares many similarities to pregnant humans regarding hormonal regulation and is therefore considered to be a suitable species for extrapolation of related effects to humans.

Are animal models relevant to key aspects of human parturition?

Preterm birth remains the most serious complication of pregnancy and is associated with increased rates of infant death or permanent neurodevelopmental disability. Our understanding of the regulation of parturition remains inadequate. The scientific literature, largely derived from rodent animal models, suggests two major mechanisms regulating the timing of parturition: the withdrawal of the steroid hormone progesterone and a proinflammatory response by the immune system. However, available evidence strongly suggests that parturition in the human has significantly different regulators and mediators from those in most of the animal models. Our objectives are to critically review the data and concepts that have arisen from use of animal models for parturition and to rationalize the use of a new model. Many animal models have contributed to advances in our understanding of the regulation of parturition. However, we suggest that those animals dependent on progesterone withdrawal to initiate parturition clearly have a limitation to their translation to the human. In such models, a linear sequence of events (e.g., luteolysis, progesterone withdrawal, uterine activation, parturition) gives rise to the concept of a "trigger" mechanism. Conversely, we propose that human parturition may arise from the concomitant maturation of several systems in parallel. We have termed this novel concept "modular accumulation of physiological systems" (MAPS). We also emphasize the urgency to determine the precise role of the immune system in the process of parturition in situations other than intrauterine infection. Finally, we accentuate the need to develop a nonprimate animal model whose physiology is more relevant to human parturition. We suggest that the guinea pig displays several key physiological characteristics of gestation that more closely resemble human pregnancy than do currently favored animal models. We conclude that the application of novel concepts and new models are required to advance translational research in parturition.

Transfer of [3H]estrone-[35S]sulfate across guinea pig fetal membranes

The possible role of fetal membrane deconjugating activity in the movement of a charged steroid conjugate between fetal and maternal compartments was investigated. The ability of amnion and chorion laeve to transfer [3H]estrone-[35S]sulfate was assessed in both orientations of guinea pig tissue at 45 days and near parturition. While early amnion was impermeable, late tissue transferred approximately 50% (w/w) of the substrate in a bidirectional process that was non-saturable and independent of either deconjugation or ATP. Transfer across early chorion was similar to late amnion. Saturation curves from each tissue were superimposable, as were those of the time course. Transfer across both early and late chorion proceeded in the absence of deconjugation, with no effect of tissue orientation or ATP depletion. However, late chorion exhibited a decrease in estrone-sulfate transfer, as verified by concentration dependency and time course analyses, though transport across the tissue remained non-saturable. The results in amnion were congruous with the presence and absence of tight junctions in the epithelium of early and late tissue, respectively. However, sulfoconjugate transfer across early chorion proceeded in the presence of a paracellular barrier, suggesting specialized regulation of the transport process which extended late into gestation.

Transfer of steroidal and nonsteroidal compounds across guinea pig fetal membranes

Transfer of steroidal and nonsteroidal compounds across guinea pig amnion and chorion laeve was investigated as a function of stage of gestation, tissue orientation, steroid specificity, and molecular size. Each fetal membrane was examined at early and late stages of gestation, before and after pubic symphysis relaxation. Early amnion was impermeable to macromolecules and small charged molecules while [3H]estrone and [3H]pregnenolone were transferred, the latter depending on tissue orientation and involving conjugation at the basolateral interface. After symphysis dilation, amnion transferred all substrates tested with the exception of BSA; the molecular weight cutoff was approximately 5,000. Unlike amnion, early chorion transferred both free and conjugated steroids as well as inorganic sulfate. Transfer of estrone involved conjugation and depended on tissue orientation. Transfer of [3H]estrone-sulfate, [3H]estrone-glucuronide, and [3H]pregnenolone-sulfate was similar despite selective deconjugating activity toward estrone-sulfate. Near term, chorion was impermeable to inorganic sulfate and transfer of estrone-glucuronide depended on tissue orientation, involving deconjugation in the maternal to fetal direction. At no stage of gestation did chorion transfer macromolecules. These results suggest that the transfer of free and conjugated steroids across fetal membranes is differentially regulated by tissue, its stage of development, and direction of transfer.

Regulation of sulfotransferase mRNA expression in male and female rats of various ages

Sulfotransferases (SULTs) are Phase II drug-metabolizing enzymes that catalyze the addition of a sulfuryl moiety to both endogenous compounds, including steroids and neurotransmitters, and certain xenobiotics, including N-hydroxy-2-acetylaminoflourine and phenolic compounds, like alpha-naphthol. In contrast to certain Phase I drug-metabolizing enzymes, little is known about the regulation of the sulfotransferases. These series of studies were designed to analyze SULT mRNA expression and hormonal regulation in male and female rats. The hepatic expression of six different SULT isoforms was examined including three phenol SULTs and three hydroxysteroid SULTs. SULT mRNA expression was examined in adult and developing rats, as well as, in hypophysectomized (HX) and growth hormone-supplemented HX animals. SULT1A1 is thought to be important for the sulfation of simple phenols and its mRNA expression is about twice as high in adult male as in female rats. This difference in SULT1A1 mRNA levels is largely due to a greater decrease in mRNA levels after puberty in female than in male rats. Hypophysectomy resulted in a decrease in expression of SULT1A1 mRNA in both male and female rats. Replacement of growth hormone (GH) by either intermittent injection (male pattern) or infusion (female pattern) failed to restore SULT1A1 expression. Sulfotransferase SULT1C1 has been implicated in activation of N-hydroxyacetylaminoflourine. In contrast to SULT1A1, SULT1C1 mRNA expression is about 10-fold higher in adult males than in adult female rats. This male-dominant expression pattern emerges at 40-50 days of age and is due to an increase in SULT1C1 mRNA in males. Hypophysectomy abolished SULT1C1 expression in male rats. Interestingly, replacement of GH by injection (male pattern) restored SULT1C1 mRNA expression in males and enhanced SULT1C1 expression in female rats to levels observed in adult male rats. GH infusion (female pattern) did not affect SULT1C1 mRNA expression in either male or female rats. Estrogen sulfotransferase (SULT1E2) may play a role in estrogen homeostasis. Adult male rats express SULTIE2 mRNA at levels 10-fold higher than those observed in adult females and similar to SULT1C1, this is due to an increase in SULT1E2 mRNA occurring during puberty in the male rat. Hypophysectomy did not appreciably affect SULT1E2 expression in male rats, however in contrast to males, hypophysectomy markedly enhanced SULT1E2 expression in female rats. GH infusion suppressed SULT1E2 levels in HX male rats. The expression of hydroxysteroid sulfotransferases was also examined. The SULT-20/21 isoform was expressed in both male and female rats. Male expression of this isoform peaked at 30 days of age and then declined to approximately 30% of the level observed in adult females. SULT-20/21 mRNA expression increased sharply at 45 days of age in female rats and remained elevated. Expression of SULT-20/21 mRNA was decreased markedly by hypophysectomy in both male and female rats. GH injection did not affect SULT-20/21 mRNA expression in HX males, however this treatment resulted in a 4-fold increase in SULT-20/21 mRNA in HX females. GH infusion restored SULT-20/21 expression in HX-male rats. GH infusion did elevate SULT-20/21 mRNA expression in female-HX rats, but not to the level observed in intact females. Hydroxysteroid SULT isoform SULT-40/41 was expressed in adult female but not adult male rats. SULT-40/41 expression peaked at 15 days of age in both male and female rats and decreased thereafter. The decrease in expression was more pronounced in male rats. SULT-60 mRNA, like SULT-40/41, was expressed only in adult female rats. Male rats express SULT-60 at 30 days of age, but SULT-60 mRNA is undetectable at 60 days. SULT-60 mRNA was expressed in females only after day 30 and female SULT-60 mRNA expression remains high thereafter. SULT-40/41 and SULT-60 mRNA expression was increased by HX in male rats and decreased by HX in female rats. (ABSTRACT TRUNCATED)

The effect of chorion-uterine interaction upon free progesterone metabolism during advanced gestation in the guinea pig

The in vitro fate of [3H]progesterone was studied after incubation with guinea pig tissues at 58/59 days (before pubic symphysis relaxation) and in the final week (post relaxation) of gestation. Buffered steroid was added to the fetal surface of chorion attached to the uterus or to the uterus alone. Neither the amount of recovered progesterone nor its metabolites (6.2% average conversion) differed between the two stages when only uterus was incubated. With chorion present, conversion averaged 28.3% at 58/59 days and 63.4% at the late stage. A 4.6-fold decrease in progesterone concentration, and 3.0-, 2.4- and 3.1-fold increases in the concentrations of 3alpha-hydroxy-5alpha-pregnan-20-one, 3beta-hydroxy-5alpha-pregnan-20-one and 5alpha-pregnane-3,20-dione, respectively, were found in the uterus in the late stage vs 58/59 days. Also, 2.8- and 6.4-fold decreases in progesterone concentration occurred in the myometrium and endometrium, respectively, from 58/59 days to the late stage. In endometrium, the concentrations of the 3alpha- and 3beta-isomers, and 5alpha-pregnane-3,20-dione, increased 2.6-, 2.6- and 5.0-fold, respectively. The above changes were all significant at P < 0.05 or better. Changes in the 3alpha-, 3beta- isomers and dione in the myometrium were not significant. The chorion-uterine interaction and gestation time thus affect the degree of progesterone conversion, and the amounts of metabolites reaching the uterus in the chorion-uterine in vitro system.

Sulfation by guinea pig chorion and uterus: differential action towards estrone and estradiol

The activities of estrogen sulfotransferase, estrogen sulfatase and estradiol 17beta-dehydrogenase change considerably in the guinea pig uterine compartment during gestation. This study was undertaken to inquire if the chorion membrane could influence the pattern of estrogen resulting when substrates were applied to the fetal surface of the chorion while it was attached, late in gestation, to the uterine wall. This tissue system resulted in a differential handling of estrone and estradiol. Estrone was largely excluded from the tissue, remaining mainly in free steroidal form. Estradiol was considerably converted to its 3-sulfate which was mainly retained by the chorion. Parallel experiments with chorion and uterus separately failed to discriminate between the two substrates. Hydrolysis of estrone sulfate and estradiol 3-sulfate was similar in all three tissue systems. It appears that the interaction of chorion with uterus late in gestation causes a difference in tissue action towards the two steroid substrates of closely related structure. The results suggest a limitation in tissue uptake of estrone compared with estradiol, or a much greater sulfotransferase activity towards estradiol. Whole cytosols of late gestational chorion catalyzed sulfation of estradiol at about double the velocity of estrone. This may only partly account for the difference in the intact chorion-uterine tissue system.

Steroid sulfation Current concepts

Formation of steroid sulfates is catalyzed by sulfotransferase enzymes that are widely distributed and frequently of high specificity. Steroid sulfates cannot be described as being active hormones, but some serve in tissue sites as precursors of active steroids formed by enzymic cleavage of the sulfate group by sulfatase enzymes. There is increasing evidence that intracellular sulfation and desulfation can play a role in regulating the availability of active steroid hormones near target sites. There are strong indications for this regulation in the uterine compartment, in the liver, and in mammary cancer cells.