The ovarian-adrenal axis in the guinea pig: effects of photoperiod, cyclic state and ovarian steroids on serum cortisol levels

Steroid hormone concentrations and body mass are differently affected by polyunsaturated fatty acids during the oestrous cycle in guinea pigs

Reproductive functions in female mammals can be significantly affected by the actions of dietary polyunsaturated fatty acids (PUFAs) on steroid hormone secretion rates. Nevertheless, the effects of plasma free PUFAs on the oestrous cycle have seldom been considered. Therefore, in the present study, the diet of domestic guinea pigs was supplemented with high concentrations of different PUFAs and the effects of altered plasma PUFA patterns on steroid hormone concentrations, measured non-invasively, and body mass during oestrus and dioestrus were analysed. The oestrous cycle was characterised by increased oestrogen and cortisol concentrations in oestrus, corroborated by lowest bodyweight, whereas progesterone concentrations were highest in dioestrus. Plasma concentrations of the long-chain PUFAs docosahexaenoic acid (DHA; 22:6 ω3) and arachidonic acid (AA; 20:5 ω6) affected steroid hormone concentrations differently in oestrus and dioestrus. DHA positively affected oestrogen and progesterone concentrations and diminished cortisol concentrations only in oestrus. In contrast, AA negatively affected oestrogen and stimulated cortisol concentrations in oestrus and reduced progesterone concentrations in general. These findings imply selective and opposite contributions of DHA and AA to ovarian functions during different stages of the oestrous cycle, indicating a high biological relevance of plasma free PUFAs in female reproductive function.

Effects of prenatal stress on hypothalamic-pituitary-adrenal (HPA) axis function over two generations of guinea pigs (Cavia aperea f. porcellus)

Prenatal stress can alter hypothalamic-pituitary-adrenal axis function with potential consequences for later life. The aim of our study was to examine in guinea pigs (Cavia aperea f. porcellus) the effects of stress experienced during F0 pregnancy on glucocorticoid levels in plasma and feces, as well as challenge performance, in F1 offspring (n=44) and fecal glucocorticoid levels in F2 offspring (n=67). F1 animals were either born to F0 dams that had been stressed with strobe light during early to mid pregnancy, resulting in a short term increase but long-term down-regulation of maternal glucocorticoid levels, or to undisturbed F0 dams. The same stressor was used as a challenge for F1 offspring at age 26 days and around 100 days. Basal plasma cortisol concentrations during early F1 development, as well as overall glucocorticoid levels at challenge tests, were lower in F1 animals that were prenatally stressed than in control animals. Fecal cortisol metabolites were initially at lower levels in prenatally stressed F1 animals, relative to control animals, but shifted to higher levels around day 68, with an additional sex difference. Effects were also seen in the F2 generation, as male but not female offspring of prenatally stressed F1 animals had significantly higher levels of cortisol metabolites in feces after weaning. We conclude that stress exposure of F0 dams resulted in lower basal glucocorticoid levels in F1 offspring during the pre-pubertal phase and during stress exposure, but higher glucocorticoid levels in post-adolescent F1 animals. Also in males of F2 generation effects of stress exposure of F0 dams were detected.

Non-invasive measurement of adrenocortical and gonadal activity in male and female guinea pigs (Cavia aperea f. porcellus)

Taking blood samples is a common method in biomedical and biological research using guinea pigs. However, most blood sampling techniques are complicated and highly invasive and may therefore not be appropriate for certain research topics concerning stress and reproduction. Thus, a non-invasive method to measure steroid hormones is critically needed. The aim of this study was the biological validation of corresponding enzyme immunoassays for the measurement of fecal cortisol, progesterone, estrogen, and testosterone metabolites in guinea pigs. We examined the effect of subcutaneous injections of ACTH or saline on fecal cortisol metabolites to investigate the suitability of fecal samples to monitor adrenocortical activity. Furthermore, we investigated whether fecal sex steroid metabolites accurately reflected endocrine changes observed in plasma samples during female estrous cycles and male puberty, respectively. In addition, we compared fecal testosterone metabolites of intact males, castrated males, and females to investigate the reliability of fecal samples in discriminating gonadal status of males. Concentrations of fecal cortisol metabolites were significantly increased following ACTH challenge, indicating that adrenocortical activity can be monitored via fecal samples. Secondly, in females, plasma and fecal gonadal steroids were significantly correlated in most subjects. The assay for testosterone metabolites, on the other hand, could not clearly discriminate between test groups. From these findings we conclude that fecal samples can be used for the non-invasive assessment of adrenocortical and female reproductive status in guinea pigs. Testosterone metabolism seems to be more complex and further investigations are needed to establish a more suitable assay.