Acyclic Rats Research Articles

Acute sleep deprivation-induced hepatotoxicity and dyslipidemia in middle-aged female rats and its amelioration by butanol extract of Tinospora cordifolia

BackgroundSleep deprivation (SD) due to an unhealthy lifestyle poses an oxidative challenge and is closely associated with an increased risk and prevalence of different metabolic disorders. Although the negative consequences of SD are well reported on mental health little is known about its detrimental effects on liver function and lipid metabolism. Tinospora cordifolia is reported for its hepatoprotective activity in different pre-clinical model systems. The current study was designed to elucidate the cumulative effects of aging and acute SD on liver functions, oxidative stress, and lipid metabolism, and their management by butanol extract of T. cordifolia (B-TCE) using middle-aged female acyclic rats as the model system.ResultsRats were divided into 4 groups: (1) Vehicle-undisturbed (VUD) (2) Vehicle-sleep deprived (VSD) (3) B-TCE pre-treated sleep-deprived (TSD) (4) B-TCE pre-treated undisturbed sleep (TUD). TSD and TUD groups were given 35 mg/kg of B-TCE once daily for 15 days followed by 12 h of sleep deprivation (6 a.m.–6 p.m.) of VSD and TSD group animals using the gentle-handling method while VUD and TUD group animals were left undisturbed. SD of VSD group animals increased oxidative stress, liver function disruption, and dyslipidemia which were ameliorated by B-TCE pre-treatment. Further, B-TCE was observed to target AMPK and its downstream lipid metabolism pathways as well as the p-Akt/cyclinD1/p-bad pathway of cell survival as possible underlying mechanisms of its hepatoprotective activity.ConclusionsThese findings suggest that B-TCE being a multi-component extract may be a potential agent in curtailing sleep-related problems and preventing SD-associated hepatotoxicity and dyslipidemia in postmenopausal women.Graphical abstractGraphical abstract to depict mechanism of action of B-TCE on liver function and lipid metabolism.

A rodent model of human dose-equivalent progestin-only implantable contraception

BackgroundLong-acting, reversible contraceptives (LARC; progestin only) are an increasingly common hormonal contraceptive choice in reproductive aged women looking to suppress ovarian function and menstrual cyclicity. The overall objective was to develop and validate a rodent model of implanted etonogestrel (ENG) LARC, at body size equivalent doses to the average dose received by women during each of the first 3 years of ENG subdermal rod LARC use.MethodsIntact, virgin, female Sprague-Dawley rats (16-wk-old) were randomized to 1 of 4 groups (n = 8/group) of ENG LARC (high-0.30μg/d, medium-0.17μg/d, low-0.09μg/d, placebo-0.00μg/d) via a slow-release pellet implanted subcutaneously. Animals were monitored for 21 days before and 29 days following pellet implantation using vaginal smears, ultrasound biomicroscopy (UBM), saphenous blood draws, food consumption, and body weights. Data were analyzed by chi-square, non-parametric, univariate, and repeated measures 2-way ANOVA.ResultsPrior to pellet implantation there was no difference in time spent in estrus cycle phases among the treatment groups (p > 0.30). Following pellet implantation there was a dose-dependent impact on the time spent in diestrus and estrus (p < 0.05), with the high dose group spending more days in diestrus and fewer days in estrus. Prior to pellet insertion there was not an association between treatment group and estrus cycle classification (p = 0.57) but following pellet implantation there was a dose-dependent association with cycle classification (p < 0.02). Measurements from the UBM (ovarian volume, follicle count, corpora lutea count) indicate an alteration of ovarian function following pellet implantation.ConclusionAssessment of estrus cyclicity indicated a dose-response relationship in the shift to a larger number of acyclic rats and longer in duration spent in the diestrus phase. Therefore, each dose in this model mimics some of the changes observed in the ovaries of women using ENG LARC and provides an opportunity for investigating the impacts on non-reproductive tissues in the future.

SAT-LB039 Development of an Animal Model of Long-acting, Reversible Contraception at Physiologic Equivalent Doses

Hormonal contraception is used routinely by premenopausal women to suppress ovarian function and menstrual cyclicity for various reasons. The most commonly chosen hormonal contraceptive types are combined oral contraceptive pills (ethinyl estradiol and a progestin) and long-acting, reversible contraceptives (LARC; progestin only). The overall objective was to develop and validate a rodent model of implanted LARC, using etonogestrel (ENG) doses at physiologic equivalents to the average dose received by women during the first 3 years of LARC use. Intact, virgin, female Sprague-Dawley rats (n=32; 16-wk-old) were randomized to 1 of 4 groups (n=8/group) of ENG LARC use (high-0.30ug/d, medium-0.17ug/d, low-0.09ug/d, placebo-0.00ug/d) via a slow-release pellet inserted under the skin. Animals were monitored for 21 days prior to pellet insertion and 29 days following pellet insertion using vaginal smears, ultrasound biomicroscopy, saphenous blood draws, food consumption, and body weights. At termination, serum and ovarian/uterine weights were collected. Data were analyzed by chi-square, non-parametric, univariate, and repeated measures 2-way ANOVA. Weekly average body weight and daily food consumption did not differ among groups across the study (p>0.63). Weekly blood sampling did not reveal differences in serum estradiol among groups across the study (p=0.22). Ovarian volume and number of ovulatory sized follicles, assessed by ultrasound biomicroscopy, did not differ among groups across the study (p>0.071). Ovarian and uterine weights did not differ among groups at termination (p>0.16). The percentage of time spent in diestrus, proestrus, estrus, and metestrus prior to pellet insertion did not differ among groups (p>0.30). Following pellet insertion, the percentage of time spent in proestrus and metestrus did not differ among groups (p>0.08). The medium dose group spent more time in diestrus than the placebo group and the high dose group spent more time in diestrus than the placebo and low dose groups (p<0.05). Low and medium dose groups spent less time in estrus than the placebo group; the high dose group spent less time in estrus than placebo and low dose groups (p<0.05). An association between LARC dose group and estrus cycle classification was not observed prior to pellet insertion (p=0.57). Following pellet insertion, there was an association between LARC dose and estrus cycle classification (p<0.02). Further, the high dose group had a significantly greater proportion of acyclic animals and a smaller proportion of cyclic animals (p<0.05) compared to the placebo group. The every-other-day ultrasound assessment used in this investigation was unable to detect differences in ovarian function. Assessment of estrus cyclicity indicated a dose-response relationship based on the shift to a larger number of acyclic rats and longer in duration of time spent in the diestrus phase. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

The transition to reproductive senescence is characterized by increase in A6 and AVPV neuron activity with attenuation of noradrenaline content

During the course of life, cyclic females face a state of midlife transition that occurs in a fully functioning neurological system, and results in reproductive senescence. The authors' hypothesis was that changes in the activity noradrenergic neurons may be one of the factors involved in this phenomenon. The aim of this study was to investigate the activity of the neurons in the anteroventral periventricular nucleus (AVPV) and locus coeruleus (LC), to analyze their role in determining reproductive senescence. Adult female Wistar rats in the diestrus phase (4months/cyclic) and old females (18–20months/acyclic) in persistent diestrus, were decapitated or perfused at three different time intervals (10, 14 and 18h) throughout the day. In acyclic rats, the gonadotropin-releasing hormone (GnRH) and noradrenaline (NE) content were reduced; Fos-related antigen (FRA) in AVPV and Fos-related antigen/Tyrosine hydroxylase (FRA/TH) in LC showed immunolabeling of a higher number of neurons in these animals. The 3-methoxy-4-hydroxyphenylglycol/noradrenaline (MHPG/NE) ratio was higher and plasma LH was lower in the acyclic rats. Furthermore, the estradiol level was higher, and the progesterone level was lower after 14h of persistent diestrus. These findings suggested that during the periestropause, there was a higher level of POA/AVPV and NE neuronal activity in the LC of acyclic rats, associated with a lower capacity of synthesis and storage of neurotransmitters and neurohormones contributed to changes in the temporal pattern of neuroendocrine signaling, thereby compromising the accuracy of inhibitory and stimulatory effects, causing irregularity in the estrous cycle and determining reproductive senescence

Activity of neurons in the preoptic area and their participation in reproductive senescence: Preliminary findings

Alterations in the hypothalamic–pituitary–gonadal axis in females determine the transition from regular to irregular reproductive cycles, with loss of fertility. Stimulation of noradrenergic neurons of the anteroventral periventricular neurons (AVPV) is essential for regular reproductive cycles. Therefore, we examined the activity of neurons of the AVPV and measure the noradrenaline (NE) of acyclic rats, in constant estrus, and compared it with that of cyclic rats in estrus. Female cyclic (4–5months) and acyclic (17–18months) rats were euthanized at 10, 14, and 18h in estrus. Brains were processed for immunoreactivity to antigens related to Fos (FRA) in AVPV, and the NE was determined by HPLC-ED. Plasma concentrations of LH, FSH, E2 and P4 were determined. In the acyclic animals, plasma LH was higher but the FSH was lower. There was decreasing P4 at different times, while the E2 was constant and lower in acyclic rats. FRA-ir expression in AVPV neurons of acyclic rats as well as turnover of NE was higher when compared with cyclic group. The preliminary findings showed increased activity in AVPV neurons in aging contribute to changes in the temporal pattern of neuroendocrine signaling, compromising the accuracy of inhibitory and stimulatory effects, causing irregularity in the estrous cycle and determining reproductive senescence.

Involvement of hyaluronan synthesis in ovarian follicle growth in rats

Most of the previous studies on ovarian hyaluronan (HA) have focused on mature antral follicles or corpora lutea, but scarcely on small preantral follicles. Moreover, the origin of follicular HA is unknown. To clarify the localization of HA and its synthases in small growing follicles, involvement of HA in follicle growth, and gonadotropin regulation of HA synthase (Has) gene expression, in this study, perinatal, immature, and adult ovaries of Wistar-Imamichi rats were examined histologically and biochemically and by in vitro follicle culture. HA was detected in the extracellular matrix of granulosa and theca cell layers of primary follicles and more advanced follicles. Ovarian HA accumulation ontogenetically started in the sex cords of perinatal rats, and its primary site shifted to the intrafollicular region of primary follicles within 5 days of birth. The Has1-3 mRNAs were expressed in the ovaries of perinatal, prepubertal, and adult rats, and the expression levels of Has1 and Has2 genes were modulated during the estrous cycle in adult rats and following administration of exogenous gonadotropins in immature acyclic rats. The Has1 and Has2 mRNAs were predominantly localized in the theca and granulosa cell layers of growing follicles respectively. Treatments with chemicals known to reduce ovarian HA synthesis induced follicular atresia. More directly, the addition of Streptomyces hyaluronidase, which specifically degrades HA, induced the arrest of follicle growth in an in vitro culture system. These results indicate that gonadotropin-regulated HA synthesis is involved in normal follicle growth.

Ovarian Aging: Melatonin Regulation of the Cytometric and Endocrine Evolutive Pattern

We have investigated the effect of melatonin administration on the cytometric and endocrine functions of the ovary during aging. Young cyclic (3 months old), middle-aged pre-acyclic (13 months old), and old acyclic (22 months old) female Wistar rats were used for two months, in both control and melatonin-treated groups. Cell cycle by flow cytometry: the percentage of ovarian cells in the G0-G1 phase was the highest in both control and melatonin-treated rats. However, melatonin treatment significantly reduced (P< 0.05) the percentage of cells in the G0-G1 phase compared to control rats. This reduction of cells in the G0-G1 phase is derived to the S phase in cyclic and acyclic rats. The possibility that a tumoral process leads to a proliferative effect observed in young and acyclic melatonin-treated rats was ruled out because no significant differences were found for p53 and Ki67 expression levels between control and melatonin groups. Density of oocytes: the oocyte number per ovary unit volume was not affected by melatonin treatment in the three age ranges studied. Melatonin treatment in middle-aged (pre-acyclic) rats resulted in significantly higher (P< 0.05) ovarian volume; higher oocyte volume, without significant differences, and oocytes in circular form were significantly (P< 0.05) higher than in control rats. Melatonin treatment during pre-acyclic age range could resynchronize the estrous cycle periodicity. Melatonin treatment was able to maintain the same levels of estradiol in the pre-acyclic age groups studied as those observed in the young cyclic rats. The present results indicate that melatonin administration to middle-aged female rats produces beneficial effects that extend the reproductive function of the ovary.

Bone microtomography and immunohistochemistry of acyclic rats post antiresorptive therapy and resistance training

Searchable abstracts of presentations at key conferences on calcified tissues ISSN 2052-1219 (online)

Hypothalamic IGF-I Gene Therapy Prolongs Estrous Cyclicity and Protects Ovarian Structure in Middle-Aged Female Rats

There is substantial evidence that age-related ovarian failure in rats is preceded by abnormal responsiveness of the neuroendocrine axis to estrogen positive feedback. Because IGF-I seems to act as a permissive factor for proper GnRH neuronal response to estrogen positive feedback and considering that the hypothalamic content of IGF-I declines in middle-aged (M-A) rats, we assessed the effectiveness of long-term IGF-I gene therapy in the mediobasal hypothalamus (MBH) of M-A female rats to extend regular cyclicity and preserve ovarian structure. We used 3 groups of M-A rats: 1 group of intact animals and 2 groups injected, at 36.2 weeks of age, in the MBH with either a bicistronic recombinant adeno-associated virus (rAAV) harboring the genes for IGF-I and the red fluorescent protein DsRed2, or a control rAAV expressing only DsRed2. Daily vaginal smears were taken throughout the study, which ended at 49.5 weeks of age. We measured serum levels of reproductive hormones and assessed ovarian histology at the end of the study. Although most of the rats injected with the IGF-I rAAV had, on the average, well-preserved estrous cyclicity as well as a generally normal ovarian histology, the intact and control rAAV groups showed a high percentage of acyclic rats at the end of the study and ovaries with numerous enlarged cysts and scarce corpora lutea. Serum LH was higher and hyperprolactinemia lower in the treated animals. These results suggest that overexpression of IGF-I in the MBH prolongs normal ovarian function in M-A female rats.

N-Methyl-D-aspartate receptor subunit expression in GnRH neurons changes during reproductive senescence in the female rat.

During reproductive senescence in females, the function of GnRH neurons becomes compromised, and this may play a role in the transition from normal estrous cycles to acyclicity. One hypothalamic component of this dysregulation is an alteration in the stimulatory effects of glutamate, acting via N-methyl-D-aspartate receptors (NMDARs), on GnRH release. The present study examined whether GnRH neurons express the subunits necessary to make functional NMDARs, and how subunit expression may change during aging in association with compromised reproductive physiology. Colocalization of the three NMDAR subunits that are most abundant in the hypothalamus (NR1, NR2A, or NR2B) with GnRH perikarya was determined in female rats at different stages of the reproductive life cycle: young (3-4 months) rats with regular estrous cycles, middle-aged (8-10 months) rats with regular estrous cycles, middle-aged rats with irregular estrous cycles, and middle-aged acyclic rats in persistent estrus. The number, percent, and localization of GnRH perikarya expressing NR1, NR2A, or NR2B were mapped and quantified by double label immunofluorescence microscopy. Overall, each of the NMDAR subunits was present in a majority of GnRH neurons. There were no age- or reproductive status-related changes in coexpression of NR1 or NR2A subunits in GnRH neurons. However, coexpression of the NR2B subunit, which affects several functional channel characteristics, was significantly lower in young compared with middle-aged rats, irrespective of reproductive status. This may result in an age-related increase in the ratio of the NR2B to the NR1 and NR2A subunits on GnRH neurons. These data indicate that the majority of GnRH neurons express the proteins needed to receive direct NMDAR-mediated glutamatergic input, and that a change in the stoichiometry of the NMDAR pentamer occurs during aging that precedes, and may have consequences for, altered neuroendocrine function.

Neuroendocrine aging in the female rat: the changing relationship of hypothalamic gonadotropin-releasing hormone neurons and N-methyl-D-aspartate receptors.

The reproductive axis undergoes alterations during aging, resulting in acyclicity and the loss of reproductive function. In the hypothalamus, changes intrinsic to GnRH neurons may play a critical role in this process, as may changes in inputs to GnRH neurons from neurotransmitters such as glutamate. We investigated the effects of age and reproductive status on neuroendocrine glutamatergic NMDA receptors (NRs), their regulation of GnRH neurons, and their expression on GnRH neurons, in female rats. First, we quantified NR subunit messenger RNAs (mRNAs) in preoptic area-anterior hypothalamus (POA-AH) and medial basal hypothalamus (MBH), the sites of GnRH perikarya and neuroterminals, respectively. In POA-AH, NR1 mRNA levels varied little with age or reproductive status. NR2a and NR2b mRNA levels decreased significantly between cycling and acyclic rats. In MBH, NR mRNAs all increased with aging, particularly in acyclic animals. Second, we tested the effects of N-methyl-D,L-aspartate (NMA) on GnRH mRNA levels in POA-AH of aging rats. NMA elevated GnRH mRNA levels in young rats, but decreased them in middle-aged rats. Third, we quantified expression of the NR1 subunit on GnRH perikarya in aging rats using double label immunocytochemistry. NR1 expression on GnRH cell bodies varied with age and reproductive status, with 30%, 19%, and 46% of GnRH somata double labeled with NR1 in young proestrous, middle-aged proestrous, and middle-aged persistent estrous rats, respectively. Thus, 1) the expression of hypothalamic NR subunit mRNAs correlates with reproductive status; 2) changes in NR subunit mRNA levels, if reflected by changes in protein levels, may result in alterations in the stoichiometry of the NR during aging, with possible physiological consequences; 3) the effects of NR activation on GnRH mRNA switches from stimulatory to inhibitory during reproductive aging; and 4) expression of the NR1 subunit on GnRH perikarya changes with reproductive status. These molecular, physiological, and cellular neuroendocrine changes are proposed to be involved in the transition to acyclicity in aging female rats.

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in rats

The effect of age and melatonin on the activity of the neuroendocrine reproductive system was studied in young cyclic (3-5 months-old), and old acyclic (23-25 month-old) female rats. Pituitary responsiveness to a bolus of GnRH (50 ng per 100 g body weight) was assessed at both reproductive stages in control and melatonin-treated (150 micrograms melatonin per 100 g body weight each day for 1 month) groups. After this experiment, female rats were treated for another month to study the influence of ageing and melatonin on the reproductive axis. Plasma LH, FSH, prolactin, oestradiol and progesterone were measured. A positive LH response to GnRH was observed in both control groups (cyclic and acyclic). However, a response of greater magnitude was observed in old acyclic rats. Melatonin treatment reduced this increased response in acyclic rats and produced a pituitary responsiveness similar to that of young cyclic rats. FSH secretion was independent of GnRH administration in all groups, indicating desynchronization between LH and FSH secretion in response to GnRH in young animals and during senescence. No effect on prolactin was observed. Significantly higher LH (3009.11 +/- 1275.08 pg ml(-1); P &lt; 0.05) and FSH concentrations (5879.28 +/- 1631.68 pg ml(-1); P &lt; 0.01) were seen in acyclic control rats. After melatonin treatment, LH (811.11 +/- 89.71 pg ml(-1)) and FSH concentrations (2070 +/- 301.62 pg ml(-1)) decreased to amounts similar to those observed in young cyclic rats. However, plasma concentrations of oestradiol and progesterone were not reduced. In conclusion, the results of the present study indicate that, during ageing, the effect of melatonin is exerted primarily at the hypothalamo-pituitary axis rather than on the ovary. Melatonin restored the basal concentrations of pituitary hormones and pituitary responsiveness to similar values to those observed in young rats.

Ageing and melatonin influence on in vitro gonadotropins and prolactin secretion from pituitary and median eminence

The effect of ageing and/or melatonin (MEL) on in vitro gonadotropins, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) release and tissue content from pituitary and median eminence (ME) were investigated. Gonadotropins and PRL basal release (I-1) from hemipituitaries of young cyclic-rats was decreased by MEL to levels shown in old acyclic rats. Pituitary tissue content of LH and PRL were not affected by ageing or MEL treatment. However, pituitary FSH tissue content was decreased by ageing and MEL, suggesting a different regulatory mechanism. MEL inhibitory influence on pituitary hormones is mainly exerted on the secretory process. This effect is only exerted in young rats. ME LH and PRL release and content were significantly lower than in pituitary. However, FSH release and content in ME showed values similar to those found in the pituitary. This study confirms that the functional capacities of pituitary gland and ME are maintained during reproductive senescence.

Neuroendocrine mechanisms for reproductive senescence in the female rat: gonadotropin-releasing hormone neurons.

Reproductive aging in female rats is characterized by profound alterations in the neuroendocrine axis. The preovulatory luteinizing hormone (LH) surge is attenuated, and preovulatory expression of the immediate early gene fos in gonadotropin-releasing hormone (GnRH) neurons is substantially reduced in middle-aged compared with young rats. We tested the hypothesis that alterations in GnRH gene expression may be correlated with the attenuation of the LH surge and may be a possible mechanism involved in neuroendocrine senescent changes. Sprague-Dawley rats ages 4 to 5 mo (young), 12-14 mo (middle-aged), or 25 to 26 mo (old) were killed at 10:00 AM or 3:00 PM on proestrus, the day of the LH surge, or diestrus I in cycling rats, and on persistent estrus or persistent diestrus in acyclic rats. RNase protection assays of GnRH mRNA and GnRH primary transcript were performed. GnRH mRNA levels increased significantly with age, whereas GnRH primary transcript levels, an index of GnRH gene transcription, decreased in old compared to young and middle-aged rats. This latter result suggests that an age-related change in GnRH mRNA levels occurs independently of a change in gene transcription, indicating a potential posttranscriptional mechanism. On proestrus, GnRH mRNA levels increased significantly from 10:00 AM to 3:00 PM in young rats. This was in contrast to proestrous middle-aged rats, in which this afternoon increase in GnRH mRNA levels was not observed. Thus, the normal afternoon increase in GnRH mRNA levels on proestrus is disrupted by middle age and may represent a substrate for the attenuation of the preovulatory GnRH/LH surge that occurs in rats of this age, prior to reproductive failure.

In vitro pituitary responsiveness to LHRH in young and old female rats. Influence of melatonin

The effect of aging and melatonin on in vitro pituitary responsiveness to luteinizing hormone-releasing hormone (LHRH) was studied. Young cyclic (3-months-old) control (cyclic-control, N=15), and melatonin (MEL) treated for 2 months (150 μg/100 g BW) (cyclic-MEL, N=15), old acyclic (23-months-old) control (acyclic-control, N=13), and MEL-treated (acyclic-MEL, N=18) rats were used. The hormones analyzed were luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL). The results showed a different influence of the reproductive status as well as of melatonin on the basal secretion rate of both gonadotropins, i.e. LH and FSH. Only the basal FSH release was significantly reduced in cyclic-MEL and acyclic-controls compared to cyclic-controls. The hemipitutary FSH content raised to values similar to those observed for FSH secretion and only the cyclic-MEL group showed significantly higher FSH pituitary content than for release. LHRH addition to the incubation medium resulted in increased LH release for both cyclic and acyclic rats, but FSH release was only stimulated in acyclic rats. Melatonin treatment blunted this response in both cases. In addition, melatonin treatment inhibited prolactin release in acyclic-MEL group after LHRH stimulation but not the basal levels. Pituitary LH and prolactin contents, were significantly higher than the pituitary LH and prolactin levels released from all groups studied, and were not affected by reproductive senescence nor by exogenous melatonin. These data indicate that aging influences more the secretory than the biosynthetic processes. Melatonin influences is endocrine status-dependent, being inhibitory when pituitary hormones reach their higher values.

L-deprenyl inhibits tumor growth, reduces serum prolactin, and suppresses brain monoamine metabolism in rats with carcinogen-induced mammary tumors.

Previously, we have reported that L-deprenyl decreased the incidence of mammary tumors and pituitary tumors in old acyclic rats. The objective of the present study was to investigate the effects of L-deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, treatment on the development and growth of tumors and on the metabolism of catecholamines and indoleamine in the medial basal hypothalamus (MBH) and the striatum (ST) of rats bearing 7,12-dimethylbenzanthracene (DMBA)-induced mammary tumors. Female Sprague-Dawley rats with DMBA-induced mammary tumors were injected (sc) daily with 0.25 mg or 5.0 mg of deprenyl/kg BW or the vehicle (saline; control) for 12 wk. Tumor diameter, tumor number, body weight, and feed intake were measured every week of the treatment period. Serum PRL and the concentrations of catecholamines, indoleamine, and their metabolites were measured by RIA and HPLC, respectively. Treatment with 5.0 mg deprenyl decreased the tumor diameter, tumor number, and serum prolactin (PRL) level. Although the body weight increased in all three groups, the body weight gain in the 5.0 mg group was smaller than that in the control and 0.25 mg groups. Deprenyl treatment had no effect on feed intake. The concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased in the MBH and the ST, and the concentration of 5-hydroxyindoleacetic acid (5-HIAA) was decreased in the MBH of deprenyl-treated rats. Treatment with 5.0 mg deprenyl enhanced the concentrations of norepinephrine (NE) and serotonin (5-HT) in the MBH and in the ST, and the concentration of dopamine (DA) in the MBH. These results suggest that the suppression of the development and growth of DMBA-induced mammary tumors by chronic deprenyl treatment may be mediated through alterations in the synthesis and metabolism of catecholamines and indoleamine in the MBH and inhibition of PRL secretion.

Atrial natriuretic factor release during pregnancy in rats.

1. We investigated the control of atrial natriuretic factor (ANF) secretion during pregnancy. 2. Plasma ANF levels were measured in conscious virgin female rats under basal conditions, and after atrial distension with an indwelling balloon catheter. The rats were then mated, and the measurements repeated at 7, 14 and 21 days of pregnancy, and at 1 week postpartum. Plasma ANF levels were also measured in ovariectomized rats injected with progesterone, oestradiol, or oestradiol plus progesterone. 3. Basal plasma ANF levels were elevated at 7 and 14 days of pregnancy, but returned to prepregnant levels by 21 days. At 1 week postpartum, they were again elevated. 4. In response to atrial stretch, plasma ANF increased significantly in virgin rats (from 100 +/- 10 to 148 +/- 13 pg ml-1, P < 0.001, n = 20). In contrast, there was no such secretory response observed in the pregnant and postpartum animals i.e. stretch-induced secretion of ANF was markedly attenuated. 5. Treatment with exogenous oestradiol caused a significant increase in plasma ANF levels in acyclic rats. However, neither progesterone nor a combination of oestradiol plus progesterone had any effect. 6. It is concluded that basal and stretch-induced ANF secretion are differentially influenced by pregnancy; oestradiol is identified as a potential stimulatory factor.

Deprenyl reinitiates estrous cycles, reduces serum prolactin, and decreases the incidence of mammary and pituitary tumors in old acyclic rats

The purpose of this study was to investigate the effects of long term treatment with deprenyl, a monoamine oxidase-B inhibitor, on estrous cyclicity, serum PRL, incidence of mammary and pituitary tumors, and monoamine metabolism in the medial basal hypothalamus (MBH) and striatum (ST) of old female rats. Acyclic female Sprague-Dawley rats (15-16 months old) were treated sc with 0, 0.25, or 2.5 mg deprenyl/kg BW.day for more than 8 months. Body weight and food intake were measured every week, and the estrous cycles and development of mammary tumors were monitored throughout the treatment period. At the end of the treatment period, the concentrations of catecholamines, serotonin, and their metabolites in the MBH and ST were determined by HPLC with electrochemical detection. The wet weights of the pituitary, heart, liver, lung, kidney, adrenals, uterus, and ovaries were recorded. Trunk blood was collected for measurement of serum PRL concentrations by RIA. Deprenyl treatment temporarily reestablished estrous cycles in most of the rats. The incidence of pituitary and mammary tumors was markedly reduced in the deprenyl-treated rats compared with that in the saline-treated control rats. Deprenyl had no significant effect on the weights of internal organs. The high dose of deprenyl (2.5 mg/kg) decreased serum PRL concentrations significantly. There were no significant differences in body weight or food intake between the control and deprenyl-treated groups. Deprenyl decreased the concentrations of the monoamine metabolites, dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid, in both the MBH and ST. It had no effect on the concentrations of norepinephrine and dopamine in the MBH, but significantly increased norepinephrine concentrations in the ST and serotonin concentrations in both the MBH and ST (P < 0.05). It is concluded that deprenyl treatment exerted these effects via suppression of monoamine metabolism.

Deprenyl reinitiates estrous cycles, reduces serum prolactin, and decreases the incidence of mammary and pituitary tumors in old acyclic rats.

The purpose of this study was to investigate the effects of long term treatment with deprenyl, a monoamine oxidase-B inhibitor, on estrous cyclicity, serum PRL, incidence of mammary and pituitary tumors, and monoamine metabolism in the medial basal hypothalamus (MBH) and striatum (ST) of old female rats. Acyclic female Sprague-Dawley rats (15-16 months old) were treated sc with 0, 0.25, or 2.5 mg deprenyl/kg BW.day for more than 8 months. Body weight and food intake were measured every week, and the estrous cycles and development of mammary tumors were monitored throughout the treatment period. At the end of the treatment period, the concentrations of catecholamines, serotonin, and their metabolites in the MBH and ST were determined by HPLC with electrochemical detection. The wet weights of the pituitary, heart, liver, lung, kidney, adrenals, uterus, and ovaries were recorded. Trunk blood was collected for measurement of serum PRL concentrations by RIA. Deprenyl treatment temporarily reestablished estrous cycles in most of the rats. The incidence of pituitary and mammary tumors was markedly reduced in the deprenyl-treated rats compared with that in the saline-treated control rats. Deprenyl had no significant effect on the weights of internal organs. The high dose of deprenyl (2.5 mg/kg) decreased serum PRL concentrations significantly. There were no significant differences in body weight or food intake between the control and deprenyl-treated groups. Deprenyl decreased the concentrations of the monoamine metabolites, dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid, in both the MBH and ST. It had no effect on the concentrations of norepinephrine and dopamine in the MBH, but significantly increased norepinephrine concentrations in the ST and serotonin concentrations in both the MBH and ST (P < 0.05). It is concluded that deprenyl treatment exerted these effects via suppression of monoamine metabolism.

Transient shortening of estrous cycles in aging C57BL/6J mice: effects of spontaneous pseudopregnancy, progesterone, L-dihydroxyphenylalanine, and hydergine.

Regular estrous cycles can be reinitiated in old acyclic female rats by pharmacologic, hormonal, and environmental manipulations. The most responsive acyclic states are persistent vaginal cornification (PVC) and spontaneous pseudopregnancy (SP). However, it is not known if the irregular cyclicity that precedes acyclicity during aging can also be alleviated. We found that transient shortening of estrous cycles follows smear sequences indicative of pseudopregnancy in C57BL/6J mice, aged 9-15 mo, suggesting a role for progesterone. This phenomenon was investigated through a limited model of pseudopregnancy in which intact aging mice with lengthened cycles were given progesterone implants (yielding 70 ng progesterone/ml plasma) that suppressed estrous cycles; upon removal of the implants, cycles were transiently shortened in aging mice. Therefore, we hypothesize that withdrawal from the progesterone elevations associated with SP is the mechanism in shortening subsequent estrous cycles. Effects of central-acting drugs, similar to those used to reinitiate cyclicity in acyclic old rats, were also examined. Hydergine, an ergot mixture with partial dopaminergic and serotonergic agonist activities, suppressed SP when fed to 10- to 12-mo-old, middle-aged mice. Hydergine did not otherwise affect estrous cycle length, prevent PVC, or reinitiate cycling in acyclic PVC mice. Feeding L-dihydroxyphenylalanine to middle-aged mice did not suppress SP, affect estrous cycle lengths, or reinitiate cycles from PVC.