Estrone, estradiol, progesterone and 17 -hydroxyprogesterone in the ovarian venous plasma during the estrous cycle of the hamster

RFamide-related Peptide-3 and the Trade-off between Reproductive and Ingestive Behavior

Ingestive and sex behaviors are important for individual survival and reproductive success, but when environmental energy availability is limited, individuals of many different species make a trade-off, forfeiting sex for ingestive behavior. For example, food-deprived female Syrian hamsters (Mesocricetus auratus) forego vaginal scent marking and lordosis (sex behaviors) in favor of foraging, hoarding, and eating food (ingestive behavior). Reproductive processes tend to be energetically costly, and individual survival requires homeostasis in metabolic energy. Thus, during energetic challenges, the chances of survival are enhanced by decreasing the energy expended on reproductive processes. The entire hypothalamic-pituitary-gonadal (HPG) system is inhibited by severe energetic challenges, but comparatively little is known about the effects of mild energetic challenges. We hypothesized that (1) a trade-off is made between sex and ingestive behavior even when the level of food restriction is insufficient to inhibit the HPG system; (2) mild energetic challenges force a trade-off between appetitive ingestive and sex behaviors, but not consummatory versions of the same behaviors; and (3) the trade-off is orchestrated by ovarian steroid modulation of RFamide-related peptide 3 (RFRP-3). In other species, RFRP-3, an ortholog of avian gonadotropin-inhibitory hormone, is implicated in control of behavior in response to energetic challenges and stressful stimuli. In support of our three hypotheses, there is a "dose-response" effect of food restriction and re-feeding on the activation of RFRP-3-immunoreactive cells in the dorsomedial hypothalamus and on appetitive behaviors (food hoarding and sexual motivation), but not on consummatory behaviors (food intake and lordosis), with no significant effect on circulating levels of estradiol or progesterone. The effect of food restriction on the activation of RFRP-3 cells is modulated at the time of estrus in gonadally-intact females and in ovariectomized females treated with progesterone alone or with estradiol plus progesterone. Intracerebral treatment with RFRP-3 results in significant decreases in sexual motivation and results in significant but small increases in food hoarding in hamsters fed ad libitum. These and other results are consistent with the idea that ovarian steroids and RFRP-3 are part of a system that orchestrates trade-offs in appetitive behaviors in environments where energy availability fluctuates.

Estrous cycle fluctuations in sex and ingestive behavior are accentuated by exercise or cold ambient temperatures

This article is part of a Special Issue "Energy Balance". In female Syrian hamsters (Mesocricetus auratus), low circulating levels of ovarian steroids are associated with increased food hoarding and decreased sexual motivation, but these effects are exaggerated in food-restricted females. To determine whether cold ambient temperature has the same effects as food restriction, groups of hamsters were fed ad libitum while they were housed at either 5 °C or 22 °C, and then tested for behavior for 90 min on each day of the estrous cycle. In females housed at 22 °C, high levels of sexual motivation and low levels of food hoarding were seen every day of the estrous cycle. In females housed at 5 °C, high levels of sexual motivation were restricted to the periovulatory day. On the three nonestrous days, these females showed high levels of food hoarding, but not food intake. A separate cohort of females were provided with access to running wheels and housed at 22 °C. They showed high levels of sexual motivation restricted to the periovulatory day, similar to the pattern of sexual motivation seen in cold-housed females. Unlike cold-housed females, those with running wheels showed low levels of food hoarding and high levels of food intake. Food restriction, cold housing, and access to wheels had no significant effect on plasma estradiol or progesterone concentrations, but significantly decreased plasma leptin concentrations. All three energetic challenges unmask estrous cycle fluctuations in sexual motivation that are obscured in laboratory conditions, i.e., isolation in a small cage with an overabundance of food.

Serum and tissue levels of estradiol during estrogen-induced renal tumorigenesis in the Syrian hamster

The estrogen-induced renal tumor in the hamster has emerged as a major animal model in hormonal carcinogenesis. However, a fundamental aspect of this experimental model has as yet not been investigated. In the present study, comparisons between the serum and tissue 17 beta-estradiol (E2) levels in cyclic female hamsters and corresponding hormone levels in E2-treated castrated male hamsters have been made. Data is provided concerning the concentration of estrogenic hormones in the serum and target tissue typically required to elicit renal tumorigenesis in this species. Serum E2 levels in the cyclic female hamster average 79 pg/ml on days 1-2 and 311 pg/ml on days 3-4, attaining a maximum of 358 pg/ml on day 4 of the cycle. Elevation in uterine, renal and hepatic E2 tissue levels during days 3-4 of the cycle reflect increases in serum E2 levels which were 3.0-, 2.0-, and 2.6-fold higher when compared to day 1 of the cycle in these tissues. As expected, serum E2 levels of untreated castrated male hamsters did not appreciably vary over a 6 month period of aging and averaged about 32 pg/ml. Under conditions which produced essentially 100% renal tumor incidence, a rapid rise in serum E2 levels, averaging 71.0-fold higher than untreated castrated levels, was seen. A steady state serum E2 level of 2400 to 2700 pg/ml was maintained from 45-180 days of continuous estrogen treatment. Compared to kidneys of untreated hamsters, renal E2 levels in E2-treated hamsters rose only on average 5.4-fold between 15-180 days of hormone exposure. Serum levels of E2-treated hamsters were 5.7- to 8.0-fold higher than those observed in cyclic female hamsters on days 3 and 4. However, at these higher E2-treated serum levels there was no apparent effect either on weight loss or mortality of the animals.

Gonadotropin-induced ovarian carbonyl reductase in mice and hamsters: comparison with carbonyl reductase in rats

We investigated the effects of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) on ovarian carbonyl reductase activities towards 13,14-dihydro-15-ketoprostaglandin F2 alpha (15KD-PGF2 alpha), p-nitroacetophenone (PNAP) and p-nitrobenzaldehyde (PNBA) in mice and hamsters, and compared with their effects on those we observed previously in rats. The treatment with PMSG and hCG caused a significant increase in ovarian weights and superovulation in both mice and hamsters. Hamster ovary possessed appreciable carbonyl reductase activities towards all three substrates, whereas the activities were lower than those in rat ovary. The reductase activities were not increased by the treatment with gonadotropins, differing from rat ovarian carbonyl reductase. In untreated mice, carbonyl reductase activity towards 15KD-PGF2 alpha was not detected, whereas the activities towards PNAP and PNBA were detected, which activities were lower than those in rats and hamsters. The PNAP and PNBA reductase activities in mouse ovary were significantly increased up to 7.1- and 1.7-fold, respectively, by the treatment with gonadotropins. These results show that there are species differences in ovarian carbonyl reductase and response of the enzyme to gonadotropins.

An in vitro method to determine the selective inhibition of estrogen biosynthesis by aromatase inhibitors

Potency and selectivity of aromatase inhibition are parameters which ultimately influence the therapeutic efficacy of aromatase inhibitors. This report describes an in vitro model which allows an assessment of the selectivity with which aromatase inhibitors inhibit estrogen biosynthesis. Estrogen production was stimulated by incubating adult female hamster ovarian tissue with ovine LH. The production rates of estrogens (E), testosterone (T) and progesterone (P) were determined using radioimmunoassays to measure the amount of these steroids released into the incubation medium over a 4-hour incubation period. The selectivity of aromatase inhibition was assessed by determining the IC50S with which each inhibitor inhibited the production of E (end product), T (immediate precursor of E) and P (early precursor of E). Selectivity was studied for each of the 4 aromatase inhibitors, CGS 16949A (a new non-steroidal compound), 4-OH-androstenedione, aminoglutethimide and testolactone. CGS 16949A was the most potent of the four, followed by 4-OH-androstenedione, aminoglutethimide and testolactone. As far as selectivity was concerned, both CGS 16949A and 4-OH-androstenedione selectively inhibited aromatase judging from the IC50s for E and P production (CGS 16949A: IC50 for E & P = 0.03 & 160 microM, resp.; 4-OH-androstenedione: IC50 for E & P = 0.88 & greater than or equal to 330 microM, resp.). Aminoglutethimide was the least selective inhibitor of aromatase (IC50 for E & P = 13 & 60 microM, resp.). For testolactone, the least potent of the four (IC50 for E = 130 microM), no conclusive data were obtained concerning the selectivity of aromatase inhibition. Thus a simple, effective and reproducible method is described for assessing the selectivity with which aromatase inhibitors inhibit aromatase.

Ovarian steroids and modulation of morphine-induced analgesia and catalepsy in female rats

The influence of ovarian steroids on modulation of antinociceptive and cataleptic responses to morphine in female rats was evaluated. The sensitivity of the animals to morphine varied at different stages of the estrous cycle. The responses of postpartum and ovariectomized rats to morphine was attenuated. The test doses of estradiol-17 beta or progesterone, either alone or in combination, did not alter this attenuated morphine sensitivity. Testosterone, however, sensitized post-partum as well as ovariectomized rats to morphine. Unlike progesterone, 17-alpha-hydroxy progesterone antagonized testosterone. Collectively these data implicate ovarian testosterone as a physiological modulator of actions of morphine in female rats.

Ovulation, ovum transport and implantation in the adult golden hamster

The time of ovulation in various hamster colonies and its relationship with the period of light as reported in the literature was compared with the observations made in this study. Ovulation and transport of ova to the oviduct was studied during days 4 and 1 of the estrous cycle. Microscopical examination of the various oviducal segments for the presence of ova resulted in a detailed description of physiological ovum transport for the adult golden hamster. Simultaneously the developmental stages of ova were checked together with the occurrence of unfertilized ova and the percentage of ova implanted in the uterus. Finally, the contractility of the oviduct in vitro was observed for groups of animals at different times in the pre- and postovulatory period. The presented data indicate that the golden hamster is useful for the study of ovum transport processes. This is due to the regularity of its estrous cycle including multiple ovulations, and because ovum transport can easily be monitored microscopically with a high degree of reliability.

Prostaglandins E and F in uterine venous plasma in relation to peripheral plasma levels of progesterone and 20alpha-hydroxyprogesterone in the rat throughout pregnancy and parturition

Prostaglandins E and F in uterine venous plasma and progesterone (P) and 20alpha-hydroxyprogesterone (20alpha-OH-P) in peripheral plasma were measured by radioimmunoassays throughout pregnancy and parturition in the rat. E Prostaglandins are low (approx. 2 ng/ml) and maintain a more or less constant level throughout most of the pregnancy except just before parturition when they rise to 3.8 ng/ml on day 20. F Prostaglandin levels are always higher than E prostaglandins and show distinct peaks around day 5 (5 ng/ml), day 11 (7 ng/ml), and before parturition (8.4 ng/ml). Progesterone levels are higher than 20alpha-OH-P levels throughout most of the pregnancy (day 6-20); however, during early pregnancy (day 1-5) and before parturition more 20alpha-OH-P than P is present in peripheral blood. The possible role of uterine venous prostaglandin levels in altering the 20alpha-OH-P/P ratio during pregnancy and parturition is discussed.

The differential effects of estrogen and progesterone on the uterus of the ovariectomized golden hamster

The effects of estrogen and progesterone on incorporation of 3H-thymidine by the uterus of the ovariectomized hamster are reported. In the ovariectomized hamster progesterone alone did not induce incorporation of 3H-thymidine. Estrogen alone caused significant incorporation of 3H-thymidine, predominantly in the luminal epithelium wheras a prior or subsequent treatment with progesterone activated DNA synthesis in the stroma and muscualris. These results indicate the role of estrogen in priming the uterus of the hamster for the subsequent action of progesterone.