Intact Male Hamsters Research Articles

Daily melatonin injections mimic the short day-induced increase in negative feedback effects of testosterone on gonadotropin secretion in hamsters.

One of the mechanisms underlying short day-induced testicular regression in golden hamsters is an increase in hypothalamic-pituitary sensitivity to the negative feedback effects of gonadal steroids on gonadotropin secretion. Since pinealectomy abolishes this effect of short days, and daily afternoon melatonin injections given to hamsters maintained on long days lead to testicular regression, we investigated whether melatonin may exert its antigonadal effect by increasing hypothalamic-pituitary sensitivity to negative feedback effects of testosterone on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release. Intact and long-term castrated male golden hamsters were either exposed to 6L:18D for 14 weeks, or maintained on 14L:1OD for 14 weeks and injected daily with either oil or 25 �ig melatonin 4 h before lights off. During Weeks 1014, the castrated hamsters received various doses of testosterone by subcutaneous implantation of either a 2, 4, 8 or 20 mm-long testosterone-filled Silastic capsule. Both exposure to 6L:18D and daily melatonin injections led to testicular regression within 6-8 weeks in the intact hamsters. In castrated hamsters on a 14L: 1OD cycle receiving oil injections, serum LH and FSH were suppressed only by the 20 mm testosterone capsule. In castrated hamsters on a 14L: I OD cycle receiving melatonin injections, and in castrated hamsters exposed to 6L:18D, serum LH and FSH were suppressed to levels close to or below the limits of the assays by even the 2 mm capsule, as well as all other doses of testosterone administered. This study demonstrates that melatonin, like exposure to short days, can cause an increase in hypothalamic-pituitary sensitivity to the negative feedback effects of gonadal steroids. These results, along with those of other studies, suggest that short dayinduced testicular regression may be due to antigonadotropic actions of melatonin.

Daily 5-methoxytryptamine injections inhibit short-day-induced testicular atrophy in golden hamsters

Daily (6 days on 7) subcutaneous injections of 25μg of 5-methoxytryptamine in saline 0.9% into intact male hamsters given between 9.00 and 9.30 (lights on from 8.00 to 18.00; 10hL/14 hD) during 8 weeks block short photoperiodically induced testicular atrophy. Under these experimental conditions, however, this blockage is not total since the weight of the testes and of the accessory sex organs of the pinealectomized hamsters is higher than that of treated animals.

Adult sexual behavior deficits and altered hormone levels in male hamsters given steroids during development

Masculine sexual behavior and adult gonadotrophin and steroid hormone levels were assested in intact male hamsters (approximately 100 days old) which had received exogenous steroids on days 2–10 of postnatal life. Estradiol benzoate (EB), testosterone propionate (TP) or testosterone caused deficits in sexual behavior including elimination or decreases in ejaculatory capacity and intromission frequency. Androstenedione or progesterone had no effect on male sexual behavior. EB treatment caused increases in serum LH and FSH levels, normal serum androgen levels and reduced testis weight. TP neonatally administered resulted in decreased serum androgens and decreased testis weight but normal gonadotropin levels. Progesterone did not affect hormone levels or testis weight. Adult castration and TP replacement therapy in males treated neonatally with TP did not reinstate normal levels of ejaculation.

The independency of an intact pineal gland of the inhibition by 5-methoxytryptamine of the reproductive organs in the male hamster.

Subcutaneous injections fo 25 micrograms of 5-methoxytryptamine (5-MT) in oil into intact and pinealectomized male hamsters given between 4.30 p.m. and 5 p.m. (light on from 5 a.m. to 7 p.m.; 14 L/10 D) for 54 consecutive days caused involution of the testes. 5-MT, however, is more effective when the pineal is present. These results indicate that melatonin is not the only pineal factor inducing gonadal atrophy in the hamster. 5-MT seems even more effective than melatonin in so far as it is, contrary to melatonin under the same experimental conditions, also effective in the absence of the pineal. Like melatonin, 5-MT appears to be implicated in the control of the reproductive function.

Melatonin-induced suppression of gonadotropin titers in male golden hamsters: Effect on gonadal feedback mechanisms

Daily subcutaneous injections of melatonin cause testicular regression and a decline in circulating gonadotropin levels in male hamsters maintained on long photoperiods. We examine here if a reduction in gonadotropin levels also occurs in castrates administered melatonin and if melatonin-regressed hamsters respond to castration with an increased release of pituitary gonadotropins — a typical “castration response.” Groups of intact and castrated male hamsters maintained on a photoperiod of LD 14:10 received subcutaneous injections of 15 ug melatonin/day. Controls received vehicle only. After 7 weeks of injections the intact males were castrated. All animals were sacrificed a few days later and serum was assayed for gonadotropin titers. Melatonin injections caused a marked decline in serum gonadotropins in castrates and in intact males also caused testicular regression. In the latter, no “castration response” was observed upon removal of the testes. Thus, daily injections of melatonin depress serum gonadotropins in castrate and intact males and block the castration-associated rise in circulating gonadotropins in the latter.

Sexual discrimination by golden hamsters ( Mesocricetus auratus)

Experiments were designed to investigate variables that may be essential for the establishment of sexual discriminations by male and female golden hamsters. It was demonstrated that heterosexual contact experience of females is not an essential prerequisite for their ability to discriminate between males and females as adults. Males that had made physical contact with an alternate estrous hamster immediately prior to testing were found to be significantly more attractive to estrous hamsters than unprimed males. A past record of copulatory experience did not necessarily render males more attractive than sexually naive males. Whereas lordosis, tonic immobility, and maintenance of physical proximity served as measures of female sexual preference, flank marking by females against the cages confining hamsters did not serve as such a measure. Intact male hamsters reliably discriminated between an intact estrous hamster and an untreated overiectomized one only after they had contacted an alternate estrous hamster prior to testing. Male sexual discrimination between an intact estrous and an intact diestrous hamster was shown only when the stimulus females had been primed immediately prior to the test trial by allowing them to physically contact an alternate male. Upon simultaneous presentation of estrous vs diestrous vaginal secretions, intact males preferred to spend more time licking and sniffing the estrous sample in 50% of the test trials. However, only 10 sec more time was spent on average with the estrous sample. It is concluded that male hamsters probably rely more on a combination of visual, tactile, chemosensory, and auditory cues rather than solely on olfactory stimuli to discriminate between a sexually receptive and nonreceptive hamster. Furthermore, the strength of the cues appear to vary as a function of recent heterosexual contact.

Rhythmicity of hamster gnawing: Ease of measurement and similarity to running activity

Adult hamsters gnawed a wooden dowel which passively protruded into the cage. Gnawing was detected by a simple switch closed by movement of the dowel in the X-Y plane. Rhythmicity of the gnawing activity was circadian in nature and closely resembled the wheelrunning rhythm recorded simultaneously or sequentially under a variety of lighting conditions. Intact or castrated male or female hamsters did not differ in the mean number of switch closures generated per 24 hr by gnawing. There was a very large interindividual difference with this measure. The data indicated a tendency for the daily amplitude of gnawing to vary with the estrous cycle. The gnawbar may prove useful as a device for assessing effects of photoperiod on endocrine variables which can be obscured if hamsters have access to running wheels.

A Lipogenic Effect in Intact Male Hamsters Infected with Plerocercoids of the Tapeworm, Spirometra mansonoides

Plerocercoids of the tapeworm, Spirometra mansonoides, produce a potent growth stimulating substance which is active in several species of mammals. While most of the actions of the plerocercoid growth factor (PGF) are similar to those of growth hormone (GH), lipid metabolism is one area where their actions are not alike. This report demonstrates that plerocercoid infection not only stimulates growth of intact male hamsters but is lipogenic as well. The lipogenic effects of plerocercoid infection were demonstrated by increases in epididymal fat pad weights, serum triglycerides, cholesterol, and total lipid. The livers of the plerocercoid-infected hamsters also had more cholesterol and more lipid phosphorus than controls. Incorporation studies using [2-14C]acetate showed that infected hamsters incorporated significantly higher levels of the radionuclide in their livers and serum after 1 hr than the controls. The lipogenic effect of plerocercoid infection is distinctly unlike the reported lipolytic action of GH and the lack of any stimulation of [2-14C]acetate incorporation into the epididymal fat pads is unlike the reported acute actions of insulin as well.

Effects of chlordiazepoxide, oxazepam, chlorpromazine, andd-Amphetamine on sexual responses in male and female hamsters

The acute effects on sexual behavior of oxazepam (16--64 mg/kg), chlordiazepoxide (8--64 mg/kg), chlorpromazine (2--8 mg/kg), and d-amphetamine (0.8--3.2 mg/kg) were examined in intact male and female golden hamsters (Mesocricetus auratus). Intraperitoneal injections were given 45 min before the first behavioral test. In 10-min tests, lordosis was observed in estrous females both before and after copulation, and mounts, intromissions, and ejaculations were observed in males. Dose-response related decrements in male sexual behavior were observed following chlorpromazine and chlordiazepoxide. All dose levels of oxazepam depressed male sexual behavior. The highest dose of chlordiazepoxide and oxazepam attenuated the onset of female sexual behavior, and all dose levels reduced postcopulatory lordosis durations. Amphetamine did not interrupt either male or female sexual behavior, and chlorpromazine disrupted male but not female behavior.

Antigonadal effect of melatonin in pinealectomized and intact male hamsters.

2 studies were performed in order to determine whether exogenous melatonin can inhibit gonadal activity independently from the pineal gland. In Experiment 1, complete testicular atrophy was induced by exposing male golden hamsters to a nonstimulatory photoperiod (LD 6:18). Animals were either sacrificed and testes weight determined, or sham-pinealectomized (intact) or pinealectomized (Px) and implanted with empty or melatonin-filled Silastic capsules (25, 100, or 300 mm long). Animals were then moved to stimulatory LD 14:10 and sacrificed 45 days later. In a 2nd study, 10-week-old male hamsters maintained on LD 14:10, were either left intact of PX and implanted with melatonin-filled 300 mm Silastic capsules. At surgery 5 animals were sacrificed and paired testes weight determined. LD 6:18 resulted in complete testicular regression. Transfer from LD 6:18 to LD 14:10 resulted in the expected testicular weight increase. Testicular growth occurred to the same degree in intact and Px hamsters receiving empty Silastic capsules. Photo-induced testicular recrudescence was prevented or supressed in both intact and Px animals at all doses. Melatonin-treated hamsters had significantly smaller testes (p less than .01) than intact and Px hamsters receiving empty capsules. In the 2nd study melatonin provoked testicular atrophy in sexually mature intact and Px maintained at LD 14:10. It is suggested that the antigonadal action of melatonin occurs by means other than the pineal gland.

The Effects of A Nonsteroid Antiandrogen, Flutamide, on Sebaceous Gland Activity

Flutamide (alpha,alpha,alpha-trifluoro-2-methyl-4'-nitro-m-propionotoluidide), at daily oral doses of 20 mg/day for 24 days, reduced the number and size of skin sebaceous gland cells, and reduced sebum production in ovariectomized, testosterone-stimulated rats. The weight of the preputial glands was also reduced. Unilateral topical application of flutamide (0.1-3.0 mg/day) to flank organs (androgen-sensitive cutaneous sebaceous structures) of testosterone propionate-treated female hamsters for 14 days resulted in bilateral reductions in flank organ weight and in inhibition of in vitro incorporation of 14-C from sodium [1--14C]acetate into lipids. Flutamide inhibition of flank organ weight paralleled the drug effect on lipogenesis. Unilateral topical application of flutamide to flank organs of intact male hamsters for 14 days resulted in significant bilateral reductions of flank organ weight at doses as low as 0.375 mg/day (the lowest dose tested). These weight changes were marked by reduction in sebaceous gland size, accompanied by focal cytoplasmic degeneration, and reductions in cytoplasmic organelles and in the size of the lipid bodies. Flutamide did not, however, seemingly alter the pattern of endogenous total lipids in sebaceous glands, nor did it alter the pattern of 14-C-incorporation into the lipids of male flank organ epidermis and isolated sebaceous glands, when compared to control, untreated preparations.

The interaction of castration and photoperiod in the regulation of hypophyseal and serum gonadotropin levels in male golden hamsters.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in intact and castrate adult male hamsters maintained on photostimulatory (LD 14:10) and non-photostimulatory (LD 6:18) light:dark cycles to assess the interaction of photic stimuli and gonadal hormones on pituitary gonadotropin release. Immunoreactive serum LH and FSH levels increased 1.6- and 8-fold respectively, within 3 days after photostimulated hamsters were castrated. In contrast, castration failed to alter serum LH concentration and had only a slight, if any, effect on FSH concentration in hamsters exposed to nonstimulatory photoperiods that induced testicular atrophy. In a second experiment, male hamsters previously maintained on LD 14:10 were castrated, transferred with intact animals to LD 6:18, and killed periodically over 60 days. In intact animals, pituitary content and serum levels of LH and FSH declined substantially during exposure to the non-stimulatory LD 6:18 cycle. In castrated animals, serum LH and FSH levels which had increased 2- and 8-fold in response to the castration eventually declined to about the levels found in the intact initial control animals. In contrast to serum gonadotropins, the increased hypophyseal content of LH and FSH following castration was not reduced during exposure to LD 6:18. Exposure to nonstimulatory photoperiods does not alter the increased hypophyseal LH and FSH content observed after castration. However, our results indicate that exposure to short days renders the hypothalamic-hypophyseal neuroendocrine system governing gonadotropin release relatively insensitive to gonadal steroid hormone feedback.

The development of aggressive and marking behavior in intact and castrated male hamsters

In pairs consisting of two intact or two castrated male hamsters, the level of aggressive and flank-marking behavior increased with age. Dominance relationships were established early and remained stable. Castration prevented the appearance of the flank gland but did not alter the development of aggression, dominance, and marking. After the formation of intact-castrate pairs, the level of performance of the intacts was significantly higher than the castrates only for marking behavior. In a second experiment involving 49 intact-castrate pairs, there were no differences between intacts and castrates for any behavioral variables measured. Although testicular integrity may influence agonistic behavior in certain situations, these data indicate that it must be only one of several influences in determining the occurrence and outcome of an agonistic encounter.

A comparison of the aggressive behaviour of isolated intact and castrated male golden hamsters towards intruders introduced into the home cage

Intact and castrated adult male golden hamsters were isolated into individual cages. Six weeks later their aggressive response was observed towards an intact male of the same body weight placed into their home cages for a 10 min test period. Both groups of isolated resident males attacked, and showed more aggression than, the intruders. However, intact residents exhibited significantly more aggression than castrated residents, and showed a significantly lower latency to attack. Because of this, and the relatively high levels of aggression generated by the test situation, it is considered a particularly useful one in which to examine the possible effects of hormonal manipulation.

牧草中のエストロジェン様物質の投与によるハムスターの正常雄と去勢雌の体成分の変化

牧草中のエストロジェン様物質の投与によるハムスターの正常雄と去勢雌の体成分の変化

Serum LH levels in intact and castrated golden hamsters.

The concentrations of LH in serum have been measured by radioimmunoassay in golden hamsters maintained in an environment with controlled lighting (on at 5 AM; off at 7 PM, CST). The maximal concentration of LH in serum of cycling hamsters occurred between 3 and 4 PM on the proestrous day, at which time the LH concentration increased as much as 50- to 100-fold within a short time. The pattern of LH release in the cycling hamster is very similar to that in the rat. Ovulation occurs 9–10 hr after the LH surge. In contrast to intact female hamsters during diestrus in which the concentration of LH in serum is quite low, female hamsters ovariectomized during diestrus have markedly increased serum LH levels within 3.5 hr following removal of the ovaries. Intact males showed great variability in serum LH levels, and the average LH concentration in intact male hamsters was much higher than that observed in diestrous females. Serum LH concentrations in males were noticeably elevated 24 hr after removal of the teste...

The effect of testosterone on chemical carcinogenesis in the buccal pouches of castrated and intact male hamsters.

Tumors were induced in the cheek pouches of intact and castrated male Syrian golden hamsters by repeated topical application of 9,10-dimethyl-1,2-benzanthracene (DMBA). Half of the animals received in addition intramuscular injections of testosterone propionate throughout the treatment with DMBA. After 9 and 12 weeks of treatment, squamous cell carcinomas were reduced in number among intact animals receiving DMBA combined with testosterone. Among castrated animals treated with DMBA and testosterone, there were less tumors after 9 weeks than in castrated animals treated with DMBA only, but not after 12 weeks. The tumor incidence in intact and castrated animals treated with DMBA only was similar throughout the experiment. Thus in the present model testosterone appeared to decrease carcinoma formation in intact male animals.

Some effects of copulatory experience on postcastration mating behavior in the male hamster

Intact male hamsters were first rated on sexual activity and then assigned to high and low experience conditions. Animals in the high experience condition received nine additional sexual activity trials while those in the low experience condition were placed with nonestrus females. The animals were then further divided into high experience gonadectomy (HG) and control (HC) groups and low experience gonadectomy (LG) and control (LC) groups. Early in postoperative testing, group HG showed significantly more sexual activity than group LG and group HC outperformed group LC.

DISSOZIATION DER BIOLOGISCHEN UND ENZYMINDUZIERENDEN AKTIVITÄTEN VON PREDNISON-21-GLYCYLGLYCINAT UND ANDROST-4-EN-3-ON-17-AMINO

ABSTRACT 1. The biological effects and the induction of the glutamic-pyruvic-transaminase (G. P. T.) of the liver and of the carbonic-acid-anhydratase (C. A.) of the seminal vesicle produced by the administration of prednisone-21-glycylglycinate (PGG), androst-4-en-3-one-17-amino (aminotestosterone) and the corresponding free steroid alcohols has been investigated in intact and adrenalectomized male golden hamsters and in intact male rats. 2. The administration of PGG has no effect on the survival period in adrenalectomized animals and does not lead to adrenal cortex atrophy in intact animals. However, it increases the weight of the liver and induces an increase of the G. P. T. of the liver significantly. 3. Although aminotestosterone and testosterone increase the concentration of the C. A. of the seminal vesicles to the same degree, aminotestosterone was found to have only very weak androgenic and anabolic activity. 4. The significance of the dissoziation between the enzyme inducing and the biological activities of the compounds studied is discussed.