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At least 919 records · Page 51Linked to original sources
PubMed1991

Suprachiasmatic nucleus lesions abolish photoperiod-induced changes in the testis function and GnRH immunoreactivity in the mink, a short-day breeder.

Testicular activity (testis volume and plasma testosterone) and immunoreactive GnRH hypothalamic system were examined after suprachiasmatic nucleus (SCN) lesion in the mink, a short-day breeding mammal, whose sexual activity is inhibited by day lengths exceeding 10 h. In animals maintained under a natural photoperiod, SCN destruction performed during the period of maximum sexual activity (February) was shown to have no effect on onset of the testicular inactive period which begins at the end of winter and continues through spring. On the other hand, while gonadal activity began again at the end of autumn in intact animals, minks that had undergone SCN destruction remained sexually inactive until the end of the experiment period (February). The SCN could thus be crucial to the onset of sexual activity triggered by the reduction of day length, whereas onset of sexual inactivity is a spontaneous phenomenon. This was confirmed in a second experiment demonstrating that a short photoperiod (4 L:20 D), highly gonadostimulatory in intact animals, had no effect on testicular activity after SCN destruction. An immunocytochemical study of the hypothalamic GnRH system (staining intensity and number of labeled perikarya and immunoreactive endings in the external layer of the median eminence) also showed consistent by very low rates of immunoreactivity and number of labeled perikarya and endings in operated animals.

Animals↗
PubMed2005

Seasonal changes in the activity of 11 beta-hydroxysteroid dehydrogenase in toad testes.

In mammals, glucocorticoids (GC) are inactivated by the oxidative activity of 11beta-hydroxysteroid dehydrogenase (11beta-HSD). To study that mechanism in the testes of Bufo arenarum, 11beta-HSD activity and plasma corticosterone (B) were determined in toads from pre- (PR), post- (P), and reproductive (R) periods. Toad 11beta-HSD is NAD(+)-dependent and strongly inhibited by glycyrrhetinic acid. V(max) is higher in the P period (1.37 vs. R: 0.13 and PR: 0.26 pmol/min-mg protein), whereas K(m) values (around 200 nM) remain constant. Plasma B concentrations (R: 178; PR: 61; P: 114 nM) are close to K(m) values, suggesting that, under baseline conditions, 11beta-HSD could protect testes against GC action.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2006

Adverse effects of the model environmental estrogen diethylstilbestrol are transmitted to subsequent generations.

The synthetic estrogen diethylstilbestrol (DES) is a potent perinatal endocrine disruptor. In humans and experimental animals, exposure to DES during critical periods of reproductive tract differentiation permanently alters estrogen target tissues and results in long-term abnormalities such as uterine neoplasia that are not manifested until later in life. Using the developmentally exposed DES mouse, multiple mechanisms have been identified that play a role in its carcinogenic and toxic effects. Analysis of the DES murine uterus reveals altered gene expression pathways that include an estrogen-regulated component. Thus, perinatal DES exposure, especially at low doses, offers the opportunity to study effects caused by weaker environmental estrogens and provides an example of the emerging scientific field termed the developmental origin of adult disease. As a model endocrine disruptor, it is of particular interest that even low doses of DES increase uterine tumor incidence. Additional studies have verified that DES is not unique; when other environmental estrogens are tested at equal estrogenic doses, developmental exposure results in increased incidence of uterine neoplasia similar to that caused by DES. Interestingly, our data suggest that this increased susceptibility for tumors is passed on from the maternal lineage to subsequent generations of male and female descendants; the mechanisms involved in these transgenerational events include genetic and epigenetic events. Together, our data point out the unique sensitivity of the developing organism to endocrine-disrupting chemicals, the occurrence of long-term effects after developmental exposure, and the possibility for adverse effects to be transmitted to subsequent generations.

Animals↗
PubMed2004

In vitro delayed senescence of extirpated buds from zooids of the colonial tunicate Botryllus schlosseri.

In the colonial growth of botryllid ascidians, blastogenesis (bud formation) is a cyclical and synchronized developmental process characterized by a weekly rhythm of budding and apoptotic events. Very little is known about this cycle regulation and its control. In this study, the in vitro fate of developing buds and regressing zooids extirpated from Botryllus schlosseri colonies at different blastogenic stages were examined, revealing that stages 'B' to 'D' buds (but not stage 'A' buds) developed new structures under in vitro conditions. These were mainly spheres (up to 1 mm in diameter) and epithelial monolayers around the attached buds. We also found that: (1) when attached spheres and epithelial monolayers appeared, the life expectancy of an isolated bud in vitro reached 50-60 days, five times the life expectancy of intact, in vivo developing zooids; (2) the life expectancy of in vitro buds that remained unattached to the substrates was at least 150 days; (3) after attaching to the substrates, buds obeyed a newly imposed developmental clock dictating up to 35 survival days for spheres and up to 14 days for epithelial monolayers; (4) the prevailing mode of death in vitro was necrotic, in contrast to the apoptotic mode of zooidal deterioration at the takeover phase of blastogenesis; (5) under in vitro conditions, degenerating zooids surprisingly produced epithelial monolayers within 3 weeks of culturing. Monolayers survived for up to 10 additional days, extending the lifespan of the degenerating zooids from a few hours to up to 1 month. We conclude that under in vitro conditions, not only are the underlying colonial growth mechanisms replaced by different developmental pathways, but also the internal colonial-level clocks programming death, are replaced by a new biological mechanism with different timetables.

Aging↗
PubMed1989

Post-natal patterns of plasma androgen-binding activity in Djungarian (Phodopus sungorus) and golden (Mesocricetus auratus) hamsters.

The binding of sex steroids to plasma proteins was examined in post-natal Djungarian and golden hamsters. With dihydrotestosterone or testosterone as ligands, steady-state polyacrylamide gel electrophoresis revealed 2 androgen binding components in the plasma of young Djungarian hamsters of both sexes. The fast-moving component exhibited a low affinity and high capacity for androgens and corresponded to albumin in stained gels. In contrast, the slow moving component was a beta-globulin with high affinity (Ka = 10(9) M-1) and low capacity for androgens, and was identified as a specific sex steroid-binding protein (SBP; also SHBG). This SBP did not bind oestrogens or corticosteroids and was electrophoretically distinct from corticosteroid-binding globulin (CBG). In addition, this protein did not appear to be of testicular origin because it was present in immature females and in immature males that had been castrated for 8 days. Plasma concentrations of SBP in males as measured by a diethyl-aminoethyl-cellulose binding assay were low at birth, became significantly elevated shortly thereafter when plasma androgen values were also elevated, and subsequently fell to low levels during puberty. These changes follow the same general pattern that has been described for other mammals, including humans, during this period of reproductive development. Although the significance of elevated SBP concentrations during prepuberty has yet to be determined, it appears that the increased concentrations of high-affinity androgen binding in the plasma of Djungarian hamsters plays a role in the asynchronous pubertal development of the testes and accessory organs which occurs in this species. The post-natal SBP pattern in females was similar to that observed in males. Plasma SBP levels were low or undetectable in adults of both sexes. As previously described for adult golden hamsters, the plasma of post-natal male and female golden hamsters lacked a specific SBP: androgen binding in this species is apparently limited to albumin and CBG.

Androgen-Binding Protein↗
PubMed2000

Vector competence of two species of mosquitoes (Diptera: Culicidae) from southern California for Dirofilaria immitis (Filariidea: Onchocercidae).

Two species of mosquitoes reared to adults from field-collected larvae or egg rafts in or near Los Angeles County, CA, were exposed to dogs with known levels of Dirofilaria immitis (Leidy) microfilariae per 20 cubic millimeters of blood. Aedes taeniorhynchus (Wiedemann) readily blood fed on an infected dog ingested microfilariae but did not become infected. Culiseta incidens (Thomson) also fed on an infected dog became infected, and 10% of the microfilariae developed to the L3 stage. Cs. incidens is a peridomestic species broadly distributed in Los Angeles County and abundant from February through December. The wide distribution of this species as well as its long annual period of reproductive activity in Los Angeles County may contribute to its potential as a vector of D. immitis.

Aedes↗
PubMed1975

The role of short days in the termination of photorefractoriness in female canaries (Serinus canarius).

Photorefractory intact female canaries were exposed to a photoperiod of 8 h light: 16 h darkness (8L: 16D) for 0, 2, 4 or 6 weeks before photostimulation with 14L: 10D for 4 weeks. Photoresponsiveness was measured in terms of plasma immunoreactive LH, ovary and oviduct weights, follicle size and nest-building behaviour. Birds not exposed to 8L: 16D were unresponsive to photostimulation while those exposed for 6 weeks to 8L: 16D were as fully photosensitive as females similarly treated immediately before their first breeding season. Birds exposed for 2 or 4 weeks to 8L: 16D responded to subsequent photostimulation but were not as responsive as birds exposed to short days for 6 weeks. Positive correlations between the two ovarian parameters and between these ovarian parameters and oviductal weight existed in all groups exposed to short days, but not in birds not exposed to short days. It is concluded that the restoration of photosensitivity at the end of the refractory period is a function of the number of short days experienced; about 6 weeks of short days are needed for its completion. In another experiment photorefractory birds exposed for 6 weeks to short days without subsequent photostimulation, although potentially photosensitive, were indistinguishable (in terms of the above parameters) from refractory birds kept on long days for the same period; in these birds refractoriness was not broken.

Animals↗
PubMed1986

A testosterone-independent reduction in net photoperiodic drive triggers photorefractoriness in male tree sparrows (Spizella arborea).

An experiment was performed to determine whether photorefractoriness in male tree sparrows is triggered by a testosterone-independent reduction in net photoperiodic drive or by a photoperiod-induced hypersensitivity of the hypothalamic-pituitary axis to testosterone negative feedback. Photosensitive male tree sparrows were transferred from 8 h light:16 h darkness (8L:16D) to 20L:4D. Birds were castrated bilaterally on day 28 of photostimulation. Beginning on day 33 and weekly thereafter until day 54, birds were given replacement testosterone (0-1.49 mumol) in s.c. polydimethylsiloxane capsules. Plasma samples collected on days 36, 43, 50 and 57 were assayed for LH. Plasma LH concentrations in birds without replacement testosterone were regarded as reflecting net photoperiodic drive in the absence of testosterone feedback, and the slopes of curves relating the logarithm of plasma LH concentration to dose of replacement testosterone were taken as quantitative measures of testosterone feedback sensitivity. The results showed that a testosterone-independent reduction in net photoperiodic drive beginning between days 43 and 50 preceded any change in sensitivity to testosterone negative feedback. Such results provide compelling evidence that a testosterone-independent mechanism triggers the photorefractory state in male tree sparrows.

Animals↗
PubMed1999

Ultradian, circadian and seasonal rhythms in cortisol secretion and adrenal responsiveness to ACTH and yarding in unrestrained red deer (Cervus elaphus) stags.

Seasonal changes in the activity and responsiveness of the adrenal gland in red deer (Cervus elaphus) stags were quantified by measuring 24 h endogenous cortisol secretory profiles and plasma cortisol responses to either administration of exogenous ACTH or a standardised stressor during November (period of velvet growth), February (pre-rut), April (mid-rut) and July (post-rut) (southern hemisphere) using a remote blood sampling device (DracPac). Ultradian rhythms in the concentration of plasma cortisol were observed resulting from the episodic secretion of cortisol from the adrenal cortex at a mean rate of 0.8 pulses/h. Circadian rhythms in plasma cortisol concentrations were also found in 11 out of the 20 complete 24 h profiles (mean amplitude, 3.8+/-1.4 ng/ml). Seasonal rhythms in mean 24 h plasma cortisol concentrations and cortisol pulse parameters were also observed. Mean 24 h plasma cortisol concentrations were higher in November (12.5+/-1.0 ng/ml) than in February (6.3+/-1.0 ng/ml), April (4.0+/-1.0 ng/ml) or July (4.2+/-1. 0 ng/ml). Cortisol pulse height, nadir and amplitude were all significantly higher in November than at other times of the year (P<0.01). Peak cortisol concentrations following infusion of ACTH(1-24) (0.04 IU kg(-1)) were higher (P<0.05) in November (55.8+/-2.7 ng/ml) and lower (P<0.001) in April (33.7+/-1.8 ng/ml) than those in February and July (48.7+/-2.0 ng/ml and 45.4+/-2.0 ng/ml respectively). The area under the cortisol response curve was significantly smaller (P<0.05) in April (266.6+/-15.3 ng/ml/190 min) than at other times of the year (February, 366.1+/-15.3 ng/ml/190 min; July, 340.7+/-15.3 ng/ml/190 min and November, 387.8+/-21.2 ng/ml/190 min). These data demonstrate that the adrenal gland of the red deer stag exhibits ultradian, circadian and seasonal rhythms in activity, and that its responsiveness to ACTH varies with season. November, a period of reproductive quiescence in the southern hemisphere, with new antler growth and rapid weight gain, is associated with higher mean plasma cortisol concentrations and a greater responsiveness to exogenous ACTH. In contrast, the breeding season is associated with lower adrenal activity and responsiveness.

Adrenocorticotropic Hormone↗
PubMed1982

Dietary Calcium and phosphorus levels for reproducing sows.

Thirty-six gilts were used to evaluate three dietary Ca/P levels over a three parity period on reproductive performance. Diets formulated to contain 14% protein with total Ca/P levels of .65/.50, .80/.60 or .90/.70%, respectively, were provided during both gestation and lactation. In each group, 10 gilts were bred and two remained unbred with diets fed at 1.8 kg/d during gestation and ad libitum during lactation. Nongravid gilts were fed 1.8 kg daily during the trial. Blood samples were collected at 60 and 100 d postcoitum and both blood and milk samples at 14 and 28 d postpartum. From each lactation and each sow group, three pigs were killed at birth and six pigs at 14 and 28 d postpartum. The rib was collected for bone ash analyses with the rib, humerus and femur collected from the progeny and examined for histopathologic lesions during the second parity. After three reproductive cycles, four sows and two unbred females/group were sacrificed and bone ash determined on femur, humerus, rib and vertebrae. The results indicated no significant difference in any sow reproductive of litter performance measurement during gestation or lactation or in milk Ca and P concentration. No histopathologic bone lesions were presented in the progeny. Sow bone ash values at the end of three reproductive cycles suggested that bone demineralization from lactating animals occurred, but not uniformly for all bones. The rib, vertebrae and humerus demineralized at a greater rate than the femur. Bone ash values for reproducing sows fed the .90/.70% Ca/p treatment for three parities were similar to those of nongravid females, which were similar for all treatment groups. The results suggested an average daily intake of 50 to 55 g Ca and 40 g P to maintain bone homeostasis in lactating sows.

Animals↗
PubMed1980

Seasonal changes in the thyroid hormones of the male squirrel monkey.

The serum of male squirrel monkeys was analyzed for levels of thyroxine (T4) and triiodothyronine (T3) at intervals corresponding to (1) preparations for breeding, (2) termination of breeding, and (3) well after the breeding season. Highest concentrations of hormones were found prior to breeding when body weight was also highest. Significant differences in hormone levels were found across sampling period. The interaction between gonadotropins and thyroid hormones is discussed.

Animals↗
PubMed1996

Seasonal rhythm of semen characteristics of a Brazilian breed ("Mangalarga") stallion.

An attempt has been made to define semen seasonality in a horse in the Southern Hemisphere. Repeated measurements of three variables in the semen were made for 36 months (Jan/90-Dec/92) in a 21-year old "Mangalarga" stallion living under natural photoperiod and temperature conditions in a farm situated in São José do Rio Pardo, São Paulo, Brazil (latitude 21 degrees) 36'S; longitude 46 degrees 53' W). The horse fed on natural pasture and a nutritionally balanced feed twice a day (11:00 and 17:00 h). Water and mineral supplement were available ad libitum. Semen was collected almost daily by an artificial vagina and showed annual changes in volume of ejaculate, sperm motility, and sperm concentration. Spectral and rhythmometric analyses of the semen data were performed according to the fast Fourier transform (FFT) and cosinor techniques (tau = 365 days). Statistically significant annual rhythms for semen volume, motility, and concentration of sperm were present. Acrophases occurred in the spring (October) for ejaculate volume and in autumn (May) for sperm concentration and motility.

Animals↗
PubMed1989

A prospective study on corpus luteum function and breast cancer risk.

A case-control study incorporated within a cohort study was undertaken to test the hypothesis that anovulation or decreased luteal function is associated with increased risk of breast cancer. A large population (n = 12,000) of apparently healthy women aged 40-49 collected a specimen of urine on day 22 of 3 consecutive menstrual cycles, or, in cases of amenorrhea, on 3 arbitrarily chosen days. These samples were stored at -20 degrees C. Subsequent screening of the women by mammography revealed 34 cases of breast cancer, and over the next 4 years a further 34 cases were reported to the cancer registry. Urine samples from 53 of these cases were assayed for pregnanediol and creatinine, and the results were compared with those for an equal number of matched controls. No differences between these groups were found in the pregnanediol/creatinine ratio. We conclude that our results do not support the hypothesis that women with luteal insufficiency are at increased risk for breast cancer. However, since breast cancer patients tend to have a later menopause than controls, the possibility cannot be excluded that breast cancer patients continue to have ovulatory cycles for a longer period during reproductive life. Such a finding--opposite to the working hypothesis--would complicate the interpretation of the results.

Adult↗
PubMed1980

Participation of the eyes in the photostimulation of chickens.

This study examined the participation of the eyes in the photosexual response of chickens to incandescent and fluorescent light. Intact and blinded female chickens were exposed to short photoperiods (8L:16D) of incandescent and fluorescent light and the age at first egg and the early rate of egg production. Blinding prevented this response. It was concluded that the eye is not essential to the photosexual response of chickens but that it may modify the response to light in certain conditions.

Animals↗