Testicular prolactin receptors and serum growth hormone in golden hamsters: effects of photoperiod and time of day

Investigations were conducted to determine effects of exposure to short photoperiod--with its accompanying reductions in serum prolactin (Prl) concentrations--for various durations on testicular Prl receptors. An additional study investigated the possibility of nyctohemeral fluctuations in testicular Prl receptors and serum growth hormone (GH) concentrations and their alteration by photoperiod. After 10 and 28 days of exposure to a short photoperiod consisting of 5 h of light and 19 h darkness (5L:19D) (and prior to changes in testicular weight), there were progressive and significant reductions in the concentration of testicular Prl receptors (fmol/mg protein) when compared with long-photoperiod controls (14L:10D). After 12 weeks of 5L:19D, when testicular weights were dramatically decreased, Prl receptor concentration was reduced to 39% of long-photoperiod controls in one study, without alteration of affinity of Prl receptors for their labeled ligand. When measured at 6-h intervals in hamsters on 14L:10D, and on 5L:19D for 12 weeks, there were no significant changes in concentration or total content (fmol/testes) of testicular Prl receptors throughout the day. Although serum GH concentrations fluctuated markedly in hamsters on both photoperiods, no definitive nyctohemeral patterns were detected. These data provide indirect evidence for the ability of Prl to regulate its own testicular receptors, and demonstrate that diurnal fluctuations in testicular sensitivity to injected Prl are not a consequence of changes in Prl receptors. The data also suggest the absence of effects of photoperiod on serum GH concentrations in male golden hamsters.     

Characterization of serum dehydroepiandrosterone secretion in golden hamsters

Dehydroepiandrosterone (DHEA) is an adrenal androgen whose function is poorly understood. Although DHEA and DHEA sulfate (DHEAS) are secreted in relatively high quantities by the human adrenal, the laboratory rat secretes very little, thus hindering experimental studies of the hormone. In this paper, we measured the changes in serum DHEA and DHEAS under various physiological conditions in golden hamsters. Evening serum DHEAS fell from 6.30 +/- 0.78 microg/dl (mean +/- SE) before surgery to 3.03 +/- 0.23 microg/dl 12 days after bilateral adrenalectomy. Hamsters had higher levels of DHEA and DHEAS in the evening than in the morning, but removal of the gonads did not consistently decrease serum DHEA or DHEAS in males or females. Evening levels of DHEA and DHEAS reached a peak around 7 weeks of age and then gradually decreased to about one-third of these levels by one year of age. These results suggest that DHEA and DHEAS are secreted at least in part from the hamster adrenal, that they do not originate from the gonads, and that there is a daily rhythm with peak levels at a time of day just preceding the active phase. In addition, the levels of these hormones decrease with aging.     

Hormonal regulation of testicular prolactin receptors and testosterone synthesis in golden hamsters

A study was conducted with hypophysectomized hamsters to determine effects of administration of prolactin (PRL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)-alone or in combination-on testicular PRL receptors and in vitro testosterone production. Hormonal injections commenced the second day after hypophysectomy, and hamsters were killed on Day 5, approximately 13 h after the last hormonal injection. PRL receptor numbers were reduced by hypophysectomy, and PRL administration alone lessened the extent of this decrease. By themselves, neither LH nor FSH affected PRL receptors, but a combination of PRL + FSH + LH produced the greatest effect on these receptors. Receptor affinity was only modestly affected by any treatments. In vitro testosterone synthesis was measured after addition of 0, 2, 10, and 50 mIU of human chorionic gonadotropin (hCG) to incubations of testicular tissue. Neither PRL nor FSH by themselves in vivo affected basal or hCG-stimulated testosterone production. However, PRL + FSH increased (p less than 0.05) the magnitude of the in vitro testosterone response to hCG, as well as the sensitivity of that response (slope of the dose-response curve). LH alone increased both basal and hCG-stimulated testosterone production. PRL + LH provided no additional increase in the magnitude of the testosterone response, but increased (p less than 0.05) the sensitivity. PRL + FSH + LH in vivo provided for the greatest sensitivity of the testosterone response to hCG.(ABSTRACT TRUNCATED AT 250 WORDS)     

A magnetic field effect on learning in male golden hamsters

The aim of this experiment was to investigate the influence of repeated exposure to 10, 20, 30 or 40 Hz magnetic fields at 0.1 T on the learning of male golden hamsters in a Skinner box, in which the animals learned to press a lever to receive a food reward. The latency of the first response was not affected by exposure to the magnetic fields used in this experiment. No significant field-dependent effects on the performance of the task were observed in males exposed to 10 and 20 Hz magnetic fields at 0.1 T. However, exposure significantly improved the learning of the task in animals exposed to 30 and 40 Hz magnetic fields at 0.1 T.     

Gonadal responses to food restriction in intact and pinealectomized male golden hamsters

Male golden hamsters underfed for 11-16 weeks showed a 30% decrease in body weight accompanied by significant testicular regression. Pinealectomy did not prevent underfeeding-induced gonadal regression. Resumption of ad-libitum feeding restored body weights to near control levels and permitted testicular redevelopment in animals with previously regressed tests. These data indicate that chronic food restriction can affect the reproductive status of hamsters and that this effect does not depend on an intact pineal gland. Body weight changes may serve as a secondary proximate cue in addition to photoperiod for timing the hamster seasonal breeding cycle.     

Photoperiodic influences on sexual behavior in male Syrian hamsters

The effect of photoperiodic conditions on sexual behavior was investigated in male Syrian hamsters that were either gonadally intact, or castrated and treated with low doses of testosterone throughout the experiment. Hamsters were exposed to long (LD 16:8) or short (LD 8:16) days for 7 weeks; for the next 8 weeks, either they were exposed to an intermediate daylength (LD 12:12), or daylength conditions remained unchanged. Sexual behavior was affected by photoperiod conditions in both gonadally intact animals and testosterone-treated castrates, but to different degrees. Intact males exposed to short days for 15 weeks exhibited gonadal regression, and their copulatory performance was impaired. The percentage of animals that intromitted or ejaculated was significantly reduced. Additional measures of sexual performance among the copulating males were also affected. In contrast, among the castrates with testosterone clamped at low but stable levels, the proportion of males that mounted, intromitted, or ejaculated was not affected by photoperiod. However, among the males that continued to copulate, sexual performance changes were present in the short-day castrates that resembled those displayed by the intact males. We infer that these behavioral effects in both hormonal conditions reflect primarily a difficulty in the attainment of intromission. Gonadal regression alone cannot easily account for the behavioral deficits of the intact males, because circulating testosterone levels at the end of the experiment were not significantly different between the gonadally intact hamsters and the castrated, testosterone-treated hamsters exposed continuously to short days. Males transferred from either long or short days to the intermediate-daylength condition responded behaviorally to this photoperiod as if it were a short day, that is, their ejaculatory frequency declined. We conclude that male hamsters exposed to photoinhibitory daylengths exhibit deficits in their sexual behavior, not only because endogenous levels of testosterone decrease, but also because the substrates on which this hormone acts become less responsive. We hypothesize that under physiological conditions, the episodic secretion of testosterone imposes constraints on the maintenance or restoration of copulation, and that the potent behavioral effects achieved by constant-release implants of testosterone may mask the presence of photoperiodically induced alterations in the hamster's sensitivity to this gonadal hormone.     

Sexual behavior of male golden hamsters receiving diverse androgen treatments

Four androgens were compared for their effectiveness in maintaining the sexual behavior of castrated male golden hamsters. Sexually experienced males were divided into 4 experimental treatment groups which received 500 μg daily of testosterone, androstenedione, dihydrotestosterone or androsterone. Control castrates were given oil. All animals were tested for sexual behavior every 2 wk for 10 wk following the onset of experimental treatment. Testosterone and androstenedione were the only androgens that maintained intromissions above the oil control level. However, testosterone, androstenedione and androsterone, but not dihydrotestosterone were effective in maintaining mounting behavior above the oil control level. No differences were detected between these 4 androgens in their maintenance of penile papillae.     

Acute and repeated exposure to social conflict in male golden hamsters: increases in plasma POMC-peptides and cortisol and decreases in plasma testosterone.

The purpose of the present study was to characterize the hormonal response of dominant and submissive male hamsters to acute and repeated exposure to social conflict. We found that submissive, but not dominant, males exhibited elevated plasma levels of adrenocorticotropin (ACTH), cortisol, and beta-endorphin (beta-EP) following one exposure to an agonistic encounter. After five exposures to a dominant opponent, submissive males showed smaller, but still significant, elevations in these plasma hormones. After nine exposures, submissive hamsters showed significant elevations only in plasma ACTH and beta-EP. Plasma testosterone was significantly suppressed in submissive males that fought nine times. We conclude that hamsters are a useful species with which to study the neuroendocrine correlates of social behavior.     

Tyrosine administration decreases serum prolactin levels in chronically reserpinized rats

The injection of tyrosine, 200 mg/kg, decreased serum prolactin levels and elevated hypothalamic (and striatal) concentrations of two dopamine metabolites, dihydroxyphenylacetic acid and homovanillic acid, in chronically reserpinized rats. Tyrosine administration had none of these effects in otherwise untreated rats, and did not block the increase in serum prolactin that occurred 4 hours after a single injection of reserpine. As anticipated, the injection of dopa decreased serum prolactin in all rats. Valine, another large neutral amino acid, did not modify serum prolactin in chronically reserpinized animals. Since prolactin secretion is normally inhibited by dopamine released from the hypothalamus, reserpine treatment probably elevates serum prolactin by depleting the hypothalamus of dopamine. Our data suggest that tyrosine injection suppresses serum prolactin levels in chronically reserpinized rats by enhancing the synthesis and release of hypothalamic dopamine. Thus, administration of tyrosine, dopamine's dietary precursor, can alter physiologic functions that depend on dopamine.     

Pituitary function during the sexual maturation of the male rat: inhibition of prolactin secretion by exogenous dopamine

Experiments were designed to determine if the responsiveness of the anterior pituitary to the prolactin (Prl) inhibiting effects of dopamine were altered during the sexual maturation of the male rat. Initial experiments established that bolus injection of dopamine HCl into cannulated (left carotid) rats pretreated with alpha-methyl-p -tyrosine (MPT) resulted in an appropriate reduction of serum Prl and that the MPT treatment did not significantly alter testosterone or luteinizing hormone (LH). Immature (25-30 days), pubertal (50-55 days), and young adult (75-80 days) rats were studied. One hour after MPT administration a blood sample was collected, followed by administration via the cannula of 2.5, 10, 40 or 160 micrograms dopamine/100 g BW or the 5% glucose vehicle. Additional blood samples were collected 15, 30, 45 and 60 min after dopamine. MPT administration resulted in a significant increase in serum Prl compared to saline-treated controls at all ages; however, the absolute value of these increases varied significantly with age. Subsequent data were calculated in terms of the decrement in serum Prl versus Time O. In immature rats the 160-micrograms dose of dopamine resulted in a significant inhibition of Prl at 15 and 30 min when compared to glucose-treated controls. In pubertal animals, 40 micrograms dopamine was effective in inhibiting Prl at both 15 and 30 min. In young adult rats, 10 micrograms dopamine was effective at 15 and 30 min; 160 micrograms lowered Prl through 45 min. These data suggest that the responsiveness of the pituitary to the Prl inhibiting effects of dopamine increases during the sexual maturation of the male rat.     

Lack of endothelial nitric oxide synthase decreases cardiomyocyte proliferation and delays cardiac maturation

We recently demonstrated that deficiency in endothelial nitric oxide synthase (eNOS) results in congenital septal defects and postnatal heart failure. The aim of this study was to investigate the role of eNOS in cardiomyocyte proliferation and maturation during postnatal development. Cultured eNOS knockout (eNOS^–/–) cardiomyocytes displayed fewer cells and lower bromodeoxyuridine (BrdU) incorporation in vitro compared with wild-type (WT) cardiomyocytes (P < 0.05). Treatment with the nitric oxide (NO) donor diethylenetriamine NONOate increased BrdU incorporation and cell counts in eNOS^–/– cardiomyocytes (P < 0.05). Inhibition of nitric oxide synthase activity using N^G-nitro-L-arginine methyl ester decreased the level of BrdU incorporation and cell counts in WT cardiomyocytes (P < 0.05). Vascular endothelial growth factor (VEGF) increased the level of BrdU incorporation in cultured WT cardiomyocytes in a dose- and time-dependent manner (P < 0.05). Conversely, VEGF did not alter BrdU incorporation in eNOS^–/– cardiomyocytes (P = not significant). Furthermore, deficiency in eNOS significantly decreased BrdU labeling indexes in neonatal hearts in vivo. Although WT hearts displayed a rapid decrease in atrial natriuretic peptide (ANP) expression in the first week of neonatal life, ANP expression in eNOS^–/– hearts remain elevated. Our study demonstrated that NO production from eNOS is necessary for postnatal cardiomyocyte proliferation and maturation, suggesting that eNOS plays an important role during postnatal heart development. proliferation; heart development     

Development and sexual maturation of Taenia crassiceps (Cestoda) in the golden hamster

The development of cysticerci of Taenia crassiceps to mature tapeworms in the intestinal tract of cortisone-treated and untreated golden hamsters is described. The development of the worms in untreated hamsters is as follows. Maturation and branching of the uterus and the presence of ova in the uterus were observed on day 15 postinfection (PI). By day 21 PI, fertilization had taken place, as evidenced by the presence of sperm in the seminal receptacle. On day 28 PI, shelled eggs were observed in feces. The rate of development of the worms in cortisone-treated hamsters was similar to that observed in untreated hamsters. More worm recovery and a longer period of worm survival were seen in the cortisone-treated than in the untreated hamsters. Thus, both cortisone-treated and untreated golden hamsters can produce normal gravid individuals of T. crassiceps.     

己烯雌酚对成年雄性金色中仓鼠的生殖毒性与氧化损伤的关系

为研究环境雌激素己烯雌酚(DES)的生殖毒性与活性氧(ROS)的关系,连续7天给成年金色中仓鼠皮下注射0、0.01、0.1、1mg/kgBWDES,称量睾丸重量、计算睾丸相对重量,光镜观察睾丸组织结构的变化,分光光度法检测睾丸组织和血浆中超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、总抗氧化能力(T-AOC)和丙二醛(MDA)的含量。结果表明:1mg/kgBWDES导致睾丸萎缩、重量下降,曲细精管中生精细胞排列紊乱,管腔内几乎没有成熟精子;随着DES剂量的增加,睾丸组织中SOD、GSH-Px和T-AOC含量显著下降,MDA显著上升。提示DES的生殖毒性与ROS密切相关,DES通过降低抗氧化酶水平,增加ROS含量,干扰生精细胞正常功能,导致细胞死亡,表明氧化损伤可能是环境雌激素生殖毒性的作用机理之一。     

Effects of light deprivation on prolactin cells in golden hamsters: an immunoelectron microscopic study.

In the golden hamster light deprivation has been shown to induce gonadal regression and reduction of pituitary and plasma levels of prolactin (PRL). In the present study we examined changes in morphology and population ratios of three types of PRL cells 8 weeks after light deprivation, by means of blinding or exposure of hamsters to continuous darkness. In the pituitary of intact hamsters of either sex, which were entrained to a 14-h light: 10-h dark cycle, Type C cells with large secretory granules were the most numerous and Type A with smaller granules the least. After light deprivation the pituitary was found to contain remarkably atrophic PRL cells and showed a profound change in population ratio of PRL cell types, i.e., Type A cells prevailed over the other two types. Pituitary glands from light-deprived and concurrently pinealectomized hamsters exhibited structures and a population ratio of three types of PRL cells similar to those from intact animals. It is suggested that small-granule-containing PRL cells represent an inactive stage of PRL cells, whereas medium- and large-granule-containing cells are functionally active cells. The atrophy of PRL cells can account for the decreased pituitary level of PRL in light-deprived hamsters reported previously.     

Aromatization and the induction of male sexual behavior in male, female, and androgenized female hamsters

Eight weeks after gonadectomy male, female, and androgenized [10 μg testosterone propionate (TP), 24 hr after birth] female hamsters were given daily treatment with: 150 μg dihydrotestosterone (DHT), 5 μg estradiol benzoate (EB), 150 μg DHT + 5 μg EB, 150 μg DHT + 1 μg EB, 30 μg DHT + 5 μg EB, 30 μg DHT + 1 μg EB, or the oil vehicle. Treatment of castrated male hamsters with 5 μg EB fully restored mounting but relatively few of these animals intromitted and none ejaculated. Treatment with 150 μg DHT restored all components of male sexual behavior but only in a small proportion of the males. Combined treatment with EB and DHT restored mounts, intromissions, and ejaculations in the majority of the males. Although as little as 30 μg DHT + 1 μg EB restored the full complement of male behavior, the males which received 150 μg DHT + 5 μg EB or 150 μg DHT + 1 μg EB required fewer intromissions to achieve ejaculation than the males which received 30 μg DHT + either dose of EB. The response of the androgenized females was similar to that of the males except that the androgenized females had lower intromission rates and none ejaculated. Relatively few of the nonandrogenized females responded to EB and DHT treatment and those that did mounted only a few times each test. These results demonstrate that both EB and DHT can stimulate male sexual behavior in the hamster and that the sensitivity to EB and DHT for copulatory behavior is determined by early postnatal androgen exposure.