In vitro metabolism of progesterone by canine hair follicle cells

Relationships between age, diet, and stress-related hormones and reproduction in American marten (Martes americana)

American marten (Martes americana) in Interior Alaska are at the northwestern limit of their North American range. To investigate factors that may be associated with reproduction we determined the cementum age and the presence or absence of blastocysts in 118 female martens for 3 years (2012, 2014, and 2016) in two regions. For each marten we collected fur samples and measured steroid hormone concentrations (cortisol, testosterone, and progesterone) and stable isotopes (δ15N and δ13C values, a proxy for diet). These parameters reflect the diet and endocrine activity between June and October when fur is grown. We also collected two claws from a subset of 39 female marten from one region in 2012 and 2014. Progesterone concentrations were measured in one whole claw and from a second claw divided into proximal (recent growth) and distal sections. Differences in the probability of blastocysts being present were associated with geographic region and sample year suggesting that reproduction in female marten varies on a fine scale. We found the that presence of blastocysts was positively associated with marten age and δ15N values in fur but negatively associated with fur cortisol concentrations. These findings suggest that the likelihood a female marten will reproduce in a given year is influenced, in part, by the proportion of protein in their diet and stressors encountered during late summer and fall, months before active gestation begins.

Do follicles matter? Testing the effect of follicles on hair cortisol levels

Cortisol concentrations in hair are used increasingly as a biomarker of long-term stress in free-ranging wildlife. Cortisol is believed to be integrated into hair primarily during its active growth phase, typically occurring over weeks to months or longer periods, depending on latitude. Cortisol concentrations in hair thus reflect the activity of the hypothalamic-pituitary-adrenal axis over this time. However, local, independent cortisol secretion within the skin, which includes hair follicles, may also contribute to cortisol levels in growing hair. Methodological differences between studies include the measurement of cortisol in only the hair shaft (i.e. follicle absent, as with shaved hair) versus the whole hair (i.e. follicle present, as with plucked hair). If the concentration of cortisol in the follicle is high enough to influence the overall hair cortisol concentration (HCC), this could confound comparisons between studies using different types of hair samples (hair shafts vs. whole hair) and collection methods. Here, we test the hypothesis that cortisol present in follicles influences HCC. We compared HCC in paired subsamples of hair with and without follicles from 30 free-ranging Scandinavian brown bears (Ursus arctos) and observed significantly greater HCC in samples with follicles present. The effect of follicles remained significant also with sex and age of sampled bears taken into account in a linear mixed model. Finally, we provide an overview of collection methods and types of hair samples used for HCC analysis in 77 studies dealing with stress in wild mammal species. Our findings highlight the need to unify methods of hair collection and preparation to allow for valid comparisons, and to optimize labour input in ecophysiological studies.

Influence of external factors on hair cortisol concentrations

Measuring hair cortisol has attracted interest as a long term parameter for chronic stress evaluation. However, some studies support the hypothesis that locally produced cortisol, originating from the hair follicle or skin cells, affects concentrations in the hair. In an animal model the influence of different treatments (extensive brushing, administration of a hyperemising fluid that enhances blood circulation or a synthetic glucocorticoid) on the local cortisol production of hair was evaluated. Therefore eight sheep were sheared and the area of the skin surface of the back was quartered, with three quarters being daily subjected to a certain treatment and one quarter remaining untreated. The skin areas were sheared again after three weeks and cortisol concentrations of all wool samples were determined by immunoassay. Systemic cortisol concentrations were additionally monitored with faecal samples, indicating a significant decline in concentrations of glucocorticoid metabolites between week 1 and 2 or 3, respectively. We found no significant difference in hair cortisol concentrations between fields before treatment (p=0.310). Comparing matched fields before and after treatment, we found no significant differences in wool cortisol concentrations for fields treated with hyperemising fluid as well as for the control fields (p=0.329, p=0.097). Hairs exposed to either extensive brushing or dexamethasone fluid had significantly higher immunoreactive cortisol concentrations after three weeks of treatment (p=0.016, p=0.01). We therefore advise cautious interpretation when measuring hair cortisol concentrations as a parameter for chronic stress, because external factors may have a significant influence on the results.

Measurement of cortisol in dog hair: a noninvasive tool for the diagnosis of hypercortisolism

BACKGROUND

The clinical signs of hyperadrenocorticism (hypercortisolism) in dogs are known to be caused by chronic overexposure to glucocorticoids. The quantification of cortisol in serum, saliva or urine reflects the cortisol concentration at the time of sample collection, but in suspected hyperadrenocorticism it may be preferable to examine a long-term parameter of cortisol production.

HYPOTHESIS/OBJECTIVES

There is a need for a noninvasive method to monitor the long-term production of cortisol in dogs. It seems possible that measuring cortisol levels in hair could represent such a method.

ANIMALS

Hair was collected from 12 dogs with hyperadrenocorticism and from 10 healthy control dogs.

METHODS

Immunoreactive cortisol, cortisone and corticosterone concentrations were determined by enzyme immunoassay. High-performance liquid chromatography was performed to test the validity of the cortisol assay.

RESULTS

Levels of immunoreactive cortisol, cortisone and corticosterone were significantly higher in dogs with hyperadrenocorticism than in control dogs. The difference was most pronounced for the cortisol level.

CONCLUSIONS AND CLINICAL IMPORTANCE

The determination of cortisol in hair offers the advantage that sampling is easier and less invasive than taking blood, urine, faeces or saliva. Measuring cortisol in hair may represent a valuable tool for the diagnosis of hyperadrenocorticism in dogs.

Hair cortisol: a parameter of chronic stress? Insights from a radiometabolism study in guinea pigs

Measurement of hair cortisol has become popular in the evaluation of chronic stress in various species. However, a sound validation is still missing. Therefore, deposition of radioactivity in hair and excretion into feces and urine after repeated injection of (3)H-cortisol was studied in guinea pigs (n = 8). Each animal was given intraperitoneally 243.6 kBq (3)H-cortisol/day on 3 successive days. After the first injection, all voided excreta were collected for 3 days. After the second injection, hair was shaved off the animals' back and newly grown hair was obtained on day 7. Following methanol extraction, radiolabeled and unlabeled glucocorticoid metabolites (GCM) in fecal and hair samples were characterized by high-performance liquid chromatography (HPLC) and enzyme immunoassays (EIA). In feces, maximum radioactivity was reached 8 h (median) post each injection, whereas maxima in urine were detected in the first samples (median 2.5 h). Metabolites excreted into feces (13.3% ± 3.7) or urine (86.7%) returned nearly to background levels. HPLC of fecal extracts showed minor variation between individuals and sexes. In hair, small amounts of radioactivity were present. However, two EIAs detected large amounts of unlabeled GCM, including high levels at the position of the cortisol standard; radioactivity was absent in this fraction, demonstrating that (3)H-cortisol was metabolized. Furthermore, large amounts of immunoreactivity coinciding with a radioactive peak at the elution position of cortisone were found. These results show for the first time that only small amounts of systemically administered radioactive glucocorticoids are deposited in hair of guinea pigs, while measurement of large amounts of unlabeled GCM strongly suggests local production of glucocorticoids in hair follicles.