Effects of chronic exposure to estradiol on ovarian cyclicity in C57BL/6J mice: potentiation at low doses and only partial suppression at high doses

Long-term exposure to ovarian hormones contributes to age-related changes in estrous cyclicity in rodents. Estrogens are implicated in this process, but the concentration of estrogen required to exert these effects is not well established. Also, although estrogens are presumed to alter vaginal cyclicity by affecting the hypothalamic-pituitary axis, they may also impair the ability of the vaginal epithelium to cornify. To address these issues, young and middle-aged ovariectomized (ovx) C57BL/6J mice were exposed for 7-10 wk to plasma levels of estradiol (E2) at one of three ranges (30-40, 50-80, or 120-160 pg/ml). Ovaries from young mice were then transplanted under the renal capsule, and vaginal cyclicity was monitored for 4 mo. Mice exposed to the lowest level of E2 not only failed to stop cycling, but had a higher monthly frequency of estrous cycles than did controls (nearly 1 extra cycle/mo). Mice exposed to the intermediate level of E2 showed no impairment in cyclicity. Although mice exposed to the highest concentrations of E2 showed no vaginal cyclicity, they continued to ovulate as evidenced by fresh, albeit reduced, numbers of corpora lutea. These results indicate that, in ovx mice, (1) chronic exposure to relatively low concentrations of E2 potentiates cyclicity, (2) very high levels of E2 are required to induce acyclicity, and (3) this acyclicity reflects vaginal as well as neuroendocrine alterations. The results also indicate that vaginal acylicity may be a poor indicator of ovulatory acyclicity in mice that have been chronically exposed to E2.     

Early treatment of young female rats with progesterone delays the aging-associated reproductive decline: a counteraction by estradiol

We have recently reported that successive treatments of young virgin rats with progesterone (P) implants produce elevated circulating P and consistently low estradiol (E2) concentrations, and subsequently delay the aging-associated reproductive decline. Inasmuch as E2 has been implicated in causing the loss of regular estrous cyclicity in aging rats, the present study examined if the concomitant presence of moderately increased circulating E2 levels could counteract the effects of P implants on reproductive aging. Starting at 3 1/2 mo and continuing to 8 mo of age, regularly cyclic, virgin rats received either s.c. Silastic implants of P (P-implanted), blank Silastic implants (virgin controls), or P + E2 implants (P + E2-implanted) for 3 wk, followed by implant removal for 1 wk. Each of these implant treatments was repeated in the same female rats 5 times. Blood samples were obtained on different days of the estrous cycle from the control group and on Day 11 of successive treatments with P or P + E2 implants for measurements of serum P and E2 values. At 8 1/2 and 10 mo of age, estrous cyclicity of these same virgin rats was again monitored, and 10-mo-old regularly cyclic females from each treatment group were mated with young fertile males to complete term pregnancies. While virgin controls showed cyclic increases in E2 and P secretion during the estrous cycle, P-implanted virgins exhibited consistently low serum E2 and moderately increased P levels during 5 successive treatments. The latter indicates a potent inhibition of ovarian E2 secretion by P implants.(ABSTRACT TRUNCATED AT 250 WORDS)     

Length of prolactin priming differentially affects maternal behavior in female rats

Prolonged exposure to prolactin (Prl) or to ectopic pituitary grafts that secrete Prl has been shown to stimulate maternal behavior in steroid-treated, hypophysectomized female rats. Since Prl levels in the blood of pregnant rats increase beginning 2-3 days prepartum, it was of interest to determine whether acute Prl priming prior to exposure to rat young would also stimulate full maternal behavior. Hypophysectomized, ovariectomized nulliparous rats were assigned to one of three treatments: Group 1, prolonged Prl; Group 2, acute Prl; or Group 3, controls/no Prl. All groups were implanted with 3 X 30 mm progesterone (P)-filled Silastic capsules s.c. at the time of ovariectomy (ovx) on Treatment Day 1. After ovx, Group 1 rats (prolonged Prl) were injected twice daily with 0.5 mg Ovine (o) Prl throughout the course of the study. Group 2 (acute Prl) and 3 (controls/no Prl) females were injected with vehicle alone or noninjected from Day 1-10. On Day 11 of Treatment, P implants were removed from all rats and each female was given a 2 mm estradiol-17 beta (E2)-filled Silastic implant. Starting on Day 11, Group 2 females were injected twice daily with oPrl. Group 3 rats continued to receive vehicle only. Behavioral testing began on Day 12 and was conducted daily through Day 22. Prolonged Prl priming (Group 1) stimulated a rapid onset of all aspects of maternal behavior (latencies less than 1 day, all p less than 0.05-0.001 vs. Group 3 controls). Control latencies ranged from 4-10 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Delayed anovulatory syndrome induced by estradiol in female C57BL/6J mice: age-like neuroendocrine, but not ovarian, impairments

These studies describe induction of a delayed anovulatory syndrome (DAS) by estradiol (E2) in female C57BL/6J mice. Six days after birth, female mice were injected s.c. with 0.1 micrograms estradiol benzoate or oil. Over 90% of the oil-injected controls exhibited estrous cycles from 2 to 9 mo of age. In contrast, 60% of the E2-injected mice exhibited estrous cycles at 2 mo of age but were acyclic by 9 mo; these mice were considered to have exhibited a DAS, and had longer cycles than controls. At 12 mo, ovarian impairments were assessed by examining 1) ovulation after s.c. injection of 5 IU human chorionic gonadotropin (hCG), and 2) estrous cycles after grafting into young (3-mo-old) hosts. Simultaneously, neuroendocrine impairments were assessed by examining 1) the surge of luteinizing hormone (LH) induced by E2 implants after ovariectomy, and 2) estrous cycles after receiving ovarian grafts from 3-mo-old mice. Ovaries from DAS and control mice ovulated equally in response to hCG. Ovaries from DAS mice grafted into young ovariectomized hosts supported 30% more cycles, of shorter period, compared with ovaries from control donors. However, the E2-induced LH surge was 50% smaller in DAS mice than in controls. Ovariectomized DAS hosts with ovarian grafts from young mice supported 70% fewer estrous cycles, of longer period, compared with ovariectomized control hosts with young grafts. We conclude that the E2-induced DAS in female mice is not due to ovarian impairments, but seems to result from neuroendocrine impairments.     

Disruption of pubertal onset by exogenous testosterone and estrogen in two species of rodents

The administration of adult physiological levels of testosterone (T) and 17beta-estradiol (E(2)) to male Siberian hamsters was previously shown to delay the onset of puberty. To examine whether this is a response common to other rodents, we investigated whether exogenous steroids also alter the onset of puberty in Syrian hamsters and mice. Juvenile male Syrian hamsters and mice were implanted with Silastic capsules containing T, E(2), or cholesterol control. After 15 days, plasma, pituitaries, and testes were processed for histological analysis or measurements of gonadotropins and circulating steroid hormones. T and E(2) implants reduced testis mass and gonadotropin stores in both species and arrested spermatogenesis in Syrian hamsters. In contrast, spermatogenesis in mice was unaffected by T and only modestly affected by E(2). Although E(2) inhibited circulating follicle-stimulating hormone (FSH) in both species, T inhibited circulating FSH in mice only. Overall, our results demonstrate that the hypothalamic-pituitary-gonadal axis of each rodent species responds uniquely to T and E(2) during the pubertal transition. Despite the highly varied effects of T and E(2) in these two species, the ability of steroid hormones to disrupt the onset of puberty appears to be a feature common to many rodents.     

Exercise training-induced adaptations of immune response are mediated by beta-adrenergic receptors in aged but not young mice.

Beta-adrenergic blockade was used to determine whether the exercise training-induced adaptations of immune response to viral infection were mediated by catecholamines in young and old mice. Young (2 mo) and older (16 mo) male BALB/c mice were randomly assigned to an exercise or control group, and half of the mice in each group received the beta-adrenergic receptor antagonist nadolol. After 8 wk of moderate exercise training, mice were challenged with herpes simplex virus (HSV) 24 h postexercise. The results showed that exercise treatment increased anti-HSV IgM antibody, enhanced IL-10, and altered the kinetics of IFN-gamma and IL-2 production in young and old mice. Unique to older mice, exercise decreased mitogen-induced proliferation, increased splenocytes, and tended to decrease memory cells (CD44(hi+)). In contrast, exercise increased mitogen-induced proliferation but decreased the number of splenic lymphocyte and CD4+ cells in young mice. beta-Adrenergic blockade blunted the exercise-induced changes in anti-HSV IgM, IL-2, IFNgamma, and mitogen-induced proliferation in old but not young mice. The findings suggest that some of the immunomodulatory effects of chronic exercise are mediated via beta-adrenergic receptors and that the role of beta-adrenergic receptors is age dependent.     

Estradiol-induced adult anovulatory syndrome in female C57BL/6J mice: age-like neuroendocrine, but not ovarian, impairments

Long-term effects of elevated plasma estradiol (E2) on ovarian and neuroendocrine functions were examined in 4-month-old cycling female C57BL/6J mice injected s.c. with 0.2 or 0.05 mg estradiol valerate (EV), or oil. Within 7 days, EV-injected mice became permanently acyclic, exhibiting the persistent vaginal cornification (PVC) characteristic of reproductive senescence in rodents. Four months after injection, ovaries from EV-injected mice exhibited no corpora lutea, but ovulated in response to an injection of human chorionic gonadotropin (hCG) (as do older, spontaneously PVC mice). When grafted into young mice, ovaries from EV-injected mice supported as many estrous cycles as ovaries from oil-injected controls. EV did not alter the suppression of luteinizing hormone (LH) by E2, LH response to injected LH releasing hormone (LHRH), or plasma prolactin (Prl). However, EV-injected mice exhibited impairments in LH regulation similar to those seen in old, acyclic mice. Plasma LH 30 days after ovariectomy was 40% lower, and E2-induced LH surges were 60% lower, in EV-injected mice versus controls. Furthermore, EV-injected mice were unable to support estrous cycles given young ovarian grafts, in contrast to controls. Effects of sustained but physiological levels (15-20 pg/ml) of plasma E2, were examined in intact cycling mice given sham or E2 implants. Six weeks after implantation, the implants were removed; only 50% of the E2-implanted mice subsequently exhibited estrous cycles, compared with 100% of sham-implanted controls. Furthermore, those E2-implanted mice which did cycle had fewer cycles than controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decreased inhibitory influences from forebrain on proceptivity and receptivity in old female rats

Female rats of Long-Evans strain were divided into a young group (3 to 4 months of age, mo) and an aged group (over 19 mo). Rats were ovariectomized and implanted subcutaneously with 14%, 20% or 33% estradiol benzoate (E2)-cholesterol mixture-filled Silastic capsules. Proceptivity and receptivity were compared between young rats and aged rats. There was no age difference in the lordosis quotient (LQ) or in the incidence of lordosis, but the incidence of solicitation was lower in aged rats than in young rats. Proceptivity and receptivity were examined again after anterior roof deafferentation (ARD) of the brain. ARD enhanced LQ in young rats and old prolonged vaginal cornification (PVC) rats but not in old anestrous (ANE) rats. ARD also increased the incidence of solicitation in both young and aged rats. However, the extent of enhancement of these two behaviors was smaller in the aged rats than in the young rats. These results demonstrate that there is decreased inhibitory influence from the forebrain on solicitation and lordosis following induction by exogenous estradiol in advancing age and that the disinhibition of lordosis is more prominent in ANE rats than in PVC rats.     

Growth hormone is secreted by ectopic pituitary grafts and stimulates maternal behavior in rats

The onset of maternal behavior at parturition in rats is hormonally regulated. Recently, we reported that treatment of behaviorally inexperienced, hypophysectomized (hypox), ovariectomized (ovx) rats with a sequential steroid treatment of progesterone (P) and estradiol (E2), and either ectopic anterior pituitary grafts or prolactin (PRL), stimulated maternal responsiveness toward foster young. That growth hormone (GH) has a number of PRL-like activities led us to ask whether the actions of PRL on maternal behavior were specific to PRL or might be shared by other PRL-like protein hormone, i.e., GH. In Experiment 1 we quantified plasma concentrations of GH and PRL by RIA in groups of hypox female rats that were ovariectomized and treated with a combination of ectopic pituitary grafts (Days 1-23) and Silastic capsules filled with P (Days 1-11) and E2 (Days 11-23). Blood samples were collected from Days 1 to 23 of treatment. Both plasma PRL and GH levels increased after grafting, initially rising 10- to 60-fold by Day 4 and gradually declining throughout the remainder of the 23-day sampling period. Throughout the 3-week period after grafting plasma GH levels were as high or higher than those of PRL. In Experiment 2 the behavioral effects of exogenously administered ovine (o)-GH were measured in groups of hypox, ovx rats that were treated with P and E2 as in Experiment 1. Experimental rats were injected twice daily with 0.25 mg oGH beginning on Day 1. Testing for maternal behavior toward foster young was conducted daily from Day 12 to Day 22. In steroid-treated rats, GH treatment stimulated a more rapid onset of maternal behavior (latencies of 3 vs greater than 10 days for vehicle-injected controls). These data indicate that GH, like PRL, is secreted by ectopic pituitary grafts and is capable of stimulating maternal behavior.     

Decreased nuclear binding of estrogen receptors in the pituitary of mice: correlation with biological effects throughout aging

We have determined the biological impact of our previously reported decreased activation of pituitary E2 receptors (PER) in mice. Young (4-8 months), middle-aged (10-14 months) and aged (15-18 months) female mice were studied either intact (metestrous) or gonadectomized (ovx) for 2 weeks prior to decapitation. Recombination studies using heat-treated cytosolic PER and enriched nuclear fractions of various age groups showed a markedly reduced ability for nuclear binding with advancing age, despite unchanged affinity of activated PER for nuclear acceptor sites. Cross incubation studies of heat-activated cytosolic PER with nuclei from mice of various age groups suggested that the activation defect followed the onset of anestrous whereas a reduced nuclear ability to support receptor binding preceded this manifestation. In parallel with these endocrine changes we observed a decrease in baseline cytosolic progesterone receptor (RcP) concentration and in the activity of the enzyme G6PDH in intact aging mice. Ovx induced a further decrease of both markers in young and middle-aged, but not in old mice, while E2 administration induced a decreased pituitary response in RcP but not in G6PDH in aged mice. Our results suggest functional changes in cytosolic nuclear interactions in the pituitary of aging female mice.     

Prepubertal treatment with estrogen or testosterone precipitates the loss of regular estrous cyclicity and normal gonadotropin secretion in adult female rats

To examine the effects of prepubertal steroid environment on subsequent estrous cyclicity and gonadotropin secretion, Silastic implants containing 25, 50 or 100% 17 beta-estradiol (E2;n=34), 50% diethylstilbestrol (DES; n=16) or 50% testosterone (T; n=17) were placed into female rats at 12 days of age and removed on the day of vaginal opening (18-24 days of age). At 80 days of age, the percentages of regularly cycling females in the E2-(three groups combined), DES- and T-implanted groups were 59%, 0% and 59%, respectively. By 110 days of age, the percentages were reduced to 24%, 0% and 0%, and at 140 days of age 6%, 0% and 0%, respectively. Many of these females displayed irregular estrous cycles followed by a persistent estrous (PE) state. By contrast, 89% of the control females (blank implants or no implant) maintained regular cycles up to 140 days of age. At 150 days of age, an i.p. injection of gonadotropin-releasing hormone (GnRH; 100 ng/100 g BW) markedly increased serum luteinizing hormone (LH), but not follicle-stimulating hormone (FSH), in intact PE females treated prepubertally with E2 implants. After the test with GnRH, PE rats were ovariectomized (OVX). Thirty days after OVX, similar GnRH administration significantly increased serum levels of both LH and FSH, but these responses were significantly (P less than 0.01) reduced when compared with those in OVX controls. Progesterone administration to estradiol benzoate-primed, acutely (3 days) OVX, or long-term (43 days) OVX-PE females did not increase LH or FSH release. These results indicate that exposure to exogenous estrogen or T prior to puberty precipitates the decline in estrous cyclicity associated with the loss of gonadotropin surge response, presumably due to an alteration in hypothalamic GnRH release.     

Serologic response of Rio Grande wild turkeys to experimental infections of Mycoplasma gallisepticum

The serologic response of Rio Grande wild turkeys (Meleagris gallopavo intermedia) to Mycoplasma gallisepticum (MG) was determined. Free-ranging turkeys were caught in southern Texas, shipped to the University of Wisconsin, Madison, and housed in isolation facilities. Fourteen birds were exposed to MG, by intratracheal and intranasal inoculation. Eight birds received sterile broth only. Two wk prior to the end of the experiment, MG exposed turkeys were stressed by challenge with a serologically unrelated mycoplasma. Serum from all exposed birds reacted positively for MG antibody by the rapid plate agglutination (RPA) procedure within 2 mo postexposure (PE) and all but one remained positive for 14 mo PE. Less than one half of the exposed birds developed positive MG antibody titers detectable by the hemagglutination inhibition (HI) test within 2 mo PE, and by 10 mo PE, none had positive titers. Antibody was detected by the HI test in two of 11 infected turkeys, 14 mo PE, and titers increased significantly within 2 wk. MG was isolated from tracheal swabs from two infected birds 2 mo PE, but attempts thereafter failed. However, at the termination of the experiment 15 mo later, MG was isolated from lung tissue of three of 11 exposed turkeys and from a blood clot found in the lower trachea of one bird.     

Enhancing effect of IFN-gamma on helper T cell activity and IL 2 production

A single injection of young murine immune interferon (IFN-gamma) in young (3 mo) or old (14 to 24 mo) mice 3 days before carrier-priming significantly enhances helper T cell activity of their spleen cells. Maximal enhancement is attained when IFN-gamma is injected once immediately before priming or for 4 consecutive days from the time of priming. Helper activity for anti-TNP antibody response was titrated in vitro by adding graded numbers of spleen cells from HRBC-primed mice of a given age to cultures containing a constant number of spleen cells from 3-mo-old normal mice and TNP-HRBC. When T cell-enriched spleen cells from HRBC-primed young or old mice, uninjected or injected with IFN-gamma, were separated by nylon wool filtration into passed (Thi) and adherent (Th2) cells, the helper activity of both T cell subpopulations was found to be enhanced by IFN-gamma injection. Helper activity of purified Th1 and Th2 cells was also increased by their in vitro preincubation with IFN-gamma. Furthermore, interleukin 2 (IL 2) production by mitogen-activated spleen cells from young and old mice is enhanced by addition of IFN-gamma to cultures. These data altogether indicate that IFN-gamma plays an important role in immunoregulation of helper T cell activity.     

Suppression of viral specific primary T-cell response following intense physical exercise in young but not old mice.

Intense exercise to exhaustion leads to increased susceptibility and severity of infections. T cells play an essential role in control of viral infections. Whereas immune suppression is considered as a likely mechanism for exhaustive exercise-induced susceptibility to infection, we know little about viral-specific T-cell response following exhaustive exercise in young or old mice. In this study, one group of female young (10-12 wk) and old (22-24 mo) C57BL/6 mice was exposed to a single bout of intense exercise to exhaustion and immediately infected with lymphocytic choriomeningitis virus (LCMV). Eight days later, at the peak of expansion phase of T-cell response, we used tetramers of MHC class I molecules containing viral peptides to directly visualize antigen-specific CD8 T cells and a sensitive functional assay measuring interferon-gamma production at the single-cell level to quantitate the CD8 and CD4 T-cell response. To evaluate the impact of intense exercise during both the initiation and evolution of the expansion phase of the T-cell response, a second group of young and old mice continued their daily bouts of intense exercise to exhaustion over the next 8 days. Our data show that, in young mice, LCMV infection following exhaustive exercise leads to suppression of LCMV-specific CD8 and CD4 T-cell responses, and this suppression effect occurs at the initiation of the expansion phase of viral-specific T cells. However, in old mice, unlike young mice, exhaustive exercise does not cause suppression of LCMV-specific T-cell responses.     

Hormonal modulation of responses to thymus-independent and thymus-dependent antigens in autoimmune NZB/W mice

Previous work suggested that gonadal steroids influence immunity through the thymus, but the mechanisms were unclear. To investigate the effects of these hormones on immune responses to T1 and TD antigens in autoimmune mice, we studied hybrid NZB/W mice and the nonautoimmune DBA/2 strain. Mice castrated at 14 days of age were implanted with Silastic capsules releasing, in adults, physiologic levels of E2 in males or Te in females. Sham-operated controls received empty capsules. Splenic PFC were quantified 4 to 5 days after challenge with the TI2 antigen TNP-Ficoll, the TI1 antigen TNP-LPS, or the TD antigen SRBC. Young castrated NZB/W males implanted with E2 had striking enhancement of IgM responses to TNP-Ficoll when compared to castrated Te-treated females and comparable sham-operated controls of both sexes. E2 also stimulated responses to TNP-LPS. In response to challenge with SRBC, young E2-treated NZB/W males had a consistent trend to increased IgM PFC, and the stimulatory effect of E2 on IgG plaques was variable. Physiologic doses of Te had no consistent effect on responses in young mice. In old female NZB/W mice, Te caused PFC response after immunization with TNP-Ficoll to resemble age-matched NZB/W males. As sham-operated NZB/W females grew older, PFC responses to SRBC fell. This age-related phenomenon was delayed, however, in female castrates implanted with Te. In contrast, Te clearly suppressed responses to TNP-LPS. Implantation of E2 did not alter responses to TNP-Ficoll, TNP-LPS, or SRBC in nonautoimmune DBA/2 males. This finding suggested that exogenous E2 given in physiologic doses did not influence immunologic responsiveness in a normal strain to the degree seen in hormone-sensitive NZB/W mice. It was concluded that E2 enhanced responses to a variety of exogenous antigens in autoimmune NZB/W mice. The most consistent E2-induced increase in PFC response was observed with TI antigens, suggesting that E2 exerted its effects on B cells or Ts.     

Developmental exposure to noninherited maternal antigens induces CD4+ T regulatory cells: relevance to mechanism of heart allograft tolerance

We hypothesize that developmental exposure to noninherited maternal Ags (NIMA) results in alloantigen-specific natural and adaptive T regulatory (T(R)) cells. We compared offspring exposed to maternal H-2(d) (NIMA(d)) with nonexposed controls. In vitro assays did not reveal any differences in T cell responses pretransplant. Adoptive transfer assays revealed lower lymphoproliferation and greater cell surface TGF-beta expression on CD4(+) T cells of NIMA(d)-exposed vs control splenocytes. NIMA(d)-exposed splenocytes exhibited bystander suppression of tetanus-specific delayed-type hypersensitivity responses, which was reversed with Abs to TGF-beta and IL-10. Allospecific T effector cells were induced in all mice upon i.v. challenge with B6D2F1 splenocytes or a DBA/2 heart transplant, but were controlled in NIMA(d)-exposed mice by T(R) cells to varying degrees. Some (40%) NIMA(d)-exposed mice accepted a DBA/2 allograft while others (60%) rejected in delayed fashion. Rejector and acceptor NIMA(d)-exposed mice had reduced T effector responses and increased Foxp3(+) T(R) cells (CD4(+)CD25(+)Foxp3(+) T(R)) in spleen and lymph nodes compared with controls. The key features distinguishing NIMA(d)-exposed acceptors from all other mice were: 1) higher frequency of IL-10- and TGF-beta-producing cells primarily in the CD4(+)CD25(+) T cell subset within lymph nodes and allografts, 2) a suppressed delayed-type hypersensitivity response to B6D2F1 Ags, and 3) allografts enriched in LAP(+), Foxp3(+), and CD4(+) T cells, with few CD8(+) T cells. We conclude that the beneficial NIMA effect is due to induction of NIMA-specific T(R) cells during ontogeny. Their persistence in the adult, and the ability of the host to mobilize them to the graft, may determine whether NIMA-specific tolerance is achieved.     

Age restriction in antigen-specific immunosuppression

Age-related alterations of antigen-specific T cell-mediated suppression have been examined in the 4-hydroxy-3-nitrophenyl acetyl (NP) system. Inducer suppressor T cells (Tsi) were activated in mice at the age of 3 mo (young) or 18 mo (old) by i.v. injection of NP-conjugated syngeneic spleen cells (SC). Spleen cells from the NP-SC-injected mice were subcultured in vitro with spleen cells from normal young or old mice to generate transducer suppressor T cells (Tst). Four days later subcultured cells were added to responder cell cultures 1 day before the PFC assays to trigger effector suppressor T cells (Tse). Responder cell cultures, containing NP-conjugated horse red blood cells (HRBC) and spleen cells from HRBC-primed young or old mice, were assayed on day 4 for anti-NP and anti-HRBC PFC. Suppression was found to be antigen specific and age restricted. NP-specific suppressor cells are easily induced in subculture if the Tsi and Tst cell populations are both derived from young or old mice. Conversely, if Tsi cells from young or old mice are subcultured with Tst cells from mice of a different age, suppression of the anti-NP PFC response is hardly observed. Age restriction was also found to operate in the interactions between subcultured and responder cell populations, indicating that age-matching is required for effective triggering of Tse cells by Tst cells. These results altogether suggest that aging may affect the recognition repertoire expressed in suppressor T cell subsets. Moreover, the finding that suppression is less efficient when exerted on responder spleen cells from old than from young mice provides an explanation for the increased frequency of autoimmune disorders in aging.     

Lipid dynamics in goldfish (Carassius auratus) during a period of gonadal recrudescence: Effects of beta-sitosterol and 17beta-estradiol exposure

The potential for contaminants to alter lipid or cholesterol dynamics in fish is rarely investigated and may include critical physiological endpoints that are impacted by exposure to endocrine-active substances. The current study investigated plasma and tissue lipid dynamics over a period of recrudescence in goldfish, while also examining the potential for beta-sitosterol (beta-sit), a phytosterol and 17beta-estradiol (E(2)), an endogenous estrogen, to alter lipid homeostasis. Goldfish were exposed to 0 microg/g (no chemical; control), 200 microg/g beta-sit (72.3% sitosterol mixture) or 10 microg/g 17beta-estradiol (E2) via Silastic implants for a period of five months. Plasma lipids peaked in control fish coincident with maximum liver size, while gonadal cholesterol concentration was highest concomitant with maximum gonad size. Plasma lipid concentrations were highly affected by E2 but not beta-sit exposure; E2 elevated total cholesterol (p<0.001) and triglyceride (TG; p<0.001) and decreased high-density lipoprotein (HDL) concentration (p<0.001) in male fish. Tissue cholesterol concentrations were minimally affected by beta-sit exposure, while hepatic cholesterol concentrations were increased in E2 exposed females (p=0.041), indicating elevated liver lipogenesis in response to E2, but not beta-sit, exposure. The present study demonstrates differential effects by beta-sit and E2 on plasma lipoprotein profile and TG concentration and indicates estrogen-specific effects on hepatic lipid metabolism during gonadal development.     

The relation of ovarian steroid levels in young female rats to subsequent estrous cyclicity and reproductive function during aging

In multiparous rats, the incidence of regular estrous cyclicity and fertility decreases markedly at middle age. However, recent studies have shown that repeated pregnancies or progesterone (P) implants can subsequently cause retired breeder females to maintain regular cyclicity for an extended period of time; these results suggest a P-mediated deceleration of reproductive aging. In the present study, we examined the relation of ovarian steroid levels in young virgin females to their subsequent estrous cyclicity and reproductive function during aging as compared to multiparous females. Beginning at 4 mo of age and continuing to 6 mo of age, regularly cyclic virgin rats received either consecutive P implants (n = 41) or no implants (controls, n = 45) for 3 wk, followed by implant removal for 1 wk. Additional females (n = 72) were mated and allowed to undergo repeated pregnancies at 4, 6 1/2, and 8 mo of age. Blood samples were obtained throughout the estrous cycle (virgin females), during pregnancy (multiparous rats), and on Day 11 of successive treatments with P implants (virgins with P implants) for P, estradiol (E2), and testosterone (T) measurements. Subsequently, regularly cyclic females from all three groups were mated with fertile males to undergo term pregnancies at 10 and 12 mo of age. While the virgin controls showed cyclic increases in P, T, and E2 secretion during their estrous cycles, the P-implanted females had persistently low E2 and high P and T levels during treatment, which indicates an inhibition of ovarian E2 synthesis by P.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mice: progesterone stimulates aggression in pregnancy-terminated females

Three experiments were conducted in order to assess the role of progesterone (P) in the aggressive behavior displayed by late pregnant Rockland-Swiss mice toward adult male intruders. In Experiment 1, hysterectomy on the 15th day of gestation reduced the aggressive behavior normally displayed by pregnant mice toward male intruders. In Experiment 2, Silastic implants of P stimulated aggression in hysterectomized mice but did not fully restore the behavior to the level of fighting normally observed in pregnant animals. In Experiment 3, aggressive behavior in P-treated hysterectomized animals was inhibited by simultaneous exposure to estradiol (E). Also, treatment with E alone did not stimulate aggression in hysterectomized mice. While pregnancy-induced aggression is promoted by P, other neuroendocrine factors may act in concert with the steroid to fully stimulate aggression in gravid mice.