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Plasma Testosterone Concentrations (plasma + testosterone_concentration)
Selected AbstractsShort periods of prenatal stress affect growth, behaviour and hypothalamo,pituitary,adrenal axis activity in male guinea pig offspringTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Amita Kapoor Prenatal stress can have profound long-term influences on physiological function throughout the course of life. We hypothesized that focused periods of moderate prenatal stress at discrete time points in late gestation have differential effects on hypothalamo,pituitary,adrenal (HPA) axis function in adult guinea pig offspring, and that changes in HPA axis function will be associated with modification of anxiety-related behaviour. Pregnant guinea pigs were exposed to a strobe light for 2 h on gestational days (GD) 50, 51, 52 (PS50) or 60, 61, 62 (PS60) (gestation length ,70 days). A control group was left undisturbed throughout pregnancy. Behaviour was assessed in male offspring on postnatal day (PND)25 and PND70 by measurement of ambulatory activity and thigmotaxis (wall-seeking behaviour) in a novel open field environment. Subsequent to behavioural testing, male offspring were cannulated (PND75) to evaluate basal and activated HPA axis function. Body weight was significantly decreased in adult PS50 and PS60 offspring and this effect was apparent soon after weaning. The brain-to-body-weight ratio was significantly increased in adult PS50 males. Basal plasma cortisol levels were elevated in PS50 male offspring throughout the 24 h sampling period compared with controls. In response to an ACTH challenge and to exposure to an acute stressor, PS60 male offspring exhibited elevated plasma cortisol responses. Plasma testosterone concentrations were strikingly decreased in PS50 offspring. Thigmotaxis in the novel environment was increased in PS50 male offspring at PND25 and PND70, suggesting increased anxiety in these animals. In conclusion, prenatal stress during critical windows of neuroendocrine development programs growth, HPA axis function, and stress-related behaviour in adult male guinea pig offspring. Further, the nature of the effect is dependant on the timing of the maternal stress during pregnancy. [source] Hypothalamic Expression of Human Growth Hormone Induces Post-Pubertal Hypergonadotrophism in Male Transgenic Growth Retarded RatsJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2006J. S. Davies Growth hormone (GH) is known to regulate peripheral components of the hypothalamo-pituitary gonadal (HPG) axis, but it remains unclear whether GH exerts a significant influence on the activity of the hypothalamo-pituitary components of the HPG axis. In this study, we investigated the development of HPG axis function in the male transgenic growth retarded (Tgr) rat, a model of moderate systemic GH deficiency caused by hypothalamic expression of human (h)GH. Impaired postnatal somatotroph expansion and moderate GH deficiency in male Tgr rats were accompanied by a two- to three-fold increase in pituitary gonadotrophin content, but without a significant change in the pituitary gonadotroph population. A three- to nine-fold elevation in basal circulating luteinising hormone concentration was seen in postpubertal Tgr rats, with a smaller increase in follicle-stimulating hormone. Despite this hypergonadotrophism, there was no corresponding increase in steroidogenic (circulating testosterone and seminal vesicle weights) or gametogenic (spermatozoa counts in seminiferous tubules) activity in the postpubertal Tgr testis. Following puberty, the plasma leptin concentration also became progressively elevated in Tgr males. Circulating gonadotrophin and leptin levels were normalised in Tgr rats by peripheral physiological replacement of rat GH, but plasma testosterone concentration was unaffected. These results confirm that hGH exerts a positive influence on the central control of gonadotrophin secretion in the Tgr rat, but the absence of a corresponding elevation in the steroidogenic or gametogenic function of the Tgr testis implies that the peripheral GH/insulin-like growth factor I axis may also exert a permissive influence on testicular function. The relative contribution of somatogenic and lactogenic mechanisms and the potential influence of elevated leptin and decreased sensitivity to androgen feedback to the development of postpubertal hypergonadotrophism in Tgr males remain to be determined. [source] Evaluation of the methoxytriazine herbicide prometon using a short-term fathead minnow reproduction test and a suite of in vitro bioassaysENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2006Daniel L. Villeneuve Abstract Prometon is one of the most consistently detected herbicides in the U.S. environment. However, no previous assessment of the potential for prometon or related methoxytriazine herbicides to act as endocrine-disrupting chemicals has been conducted. This study used an array of in vitro bioassays to assess whether prometon, atraton, terbumeton, or secbumeton might act as potent (ant)agonists of the aryl hydrocarbon, estrogen, androgen, or glucocorticoid receptors or as aromatase inhibitors or inducers in vitro. Potential effects of prometon were also evaluated using a 21-d fathead minnow reproduction assay. Concentrations of methoxytriazines, as great as 1 mg/L (4.4 ,M), did not induce significant dioxin-like responses in H4IIE-luc cells, estrogenic responses in MVLN cells, or androgen or glucocorticoid receptor,mediated responses in MDA-kb2 cells, nor did the methoxytriazines significantly affect aromatase activity in vitro. In the fathead minnow assay, exposure to 20, 200, or 1,000 ,g prometon/L significantly reduced the weight of the male fat pad (an androgen-responsive tissue) relative to body weight. Exposure to 20 ,g prometon/L significantly increased female plasma testosterone concentrations, but the effect was not observed at greater concentrations. Overall, prometon did not significantly reduce fecundity over the 21-d exposure, nor were other endpoints, including plasma vitellogenin and estradiol concentrations, brain and ovary aromatase activity, and male tubercle index, significantly affected. Evidence from our work suggests that prometon may cause subtle endocrine and/or reproductive effects in fathead minnows, but no clear mechanism of action was observed. The relevance of these effects to hazard assessment for the pesticide is uncertain. [source] Reproductive seasonality in the Tete veld rat (Aethomys ineptus) (Rodentia: Muridae) from southern AfricaJOURNAL OF ZOOLOGY, Issue 2 2006S. P. Muteka Abstract Very little is known about the reproductive biology of the recently recognized Tete veld rat Aethomys ineptus. In the present study, we investigated the seasonality of reproduction in this newly recognized rodent using a number of histological and endocrinological parameters. Body mass, reproductive tract morphometrics, gonadal histology, and plasma testosterone concentrations in males and plasma oestradiol-17, and progesterone concentrations in females were assessed from a population in the north-central part of South Africa over a 12-month period in order to ascertain the pattern of reproduction in the species. Seminiferous tubule diameters in 59 males were significantly larger between September and February relative to between March and August. Although spermatogenesis was prevalent in the southern hemisphere winter (June,August), the number of spermatozoa in the epididymides decreased in the southern hemisphere spring (September,November), summer (December,February) and autumn (March,May). Testicular mass relative to body mass and testicular volume regressed between May and September but exhibited recrudescence between September and April, whereas plasma testosterone concentrations increased significantly between September and February relative to between March and August. Ovarian histology of 67 females showed corpora lutea to be present throughout the year, but decreased in number during winter, whereas mean plasma progesterone concentration increased significantly between August and November and again between February and April. This bimodal pattern of progesterone concentration suggests that up to two litters per breeding season may be raised by the Tete veld rat. Gravid females were found between October and April, whereas gravid or lactating females were conspicuously absent between May and September. Collation of all these data suggests that the Tete veld rat is a seasonal breeder with reproduction confined predominantly to summer and autumn months of the southern hemisphere. However, the presence of follicular development in females and the presence of corpora lutea outside the breeding season imply that the Tete veld rat may undergo spontaneous ovulation. [source] | ||||||||||