In vivo suppression of plasma IL-12 levels by acute and chronic stress paradigms: potential mediating mechanisms and sex differences.

Interleukin-12 (IL-12) is a major pro-inflammatory cytokine, which promotes cell-mediated immunity and T(H)1 differentiation. In vitro studies indicated suppression of IL-12 production by several stress-related factors, but no effects of behavioral stress were shown on plasma IL-12 levels. Therefore, in the current study we (i) examined the in vivo effects of various behavioral and pharmacological stress paradigms on baseline plasma IL-12 levels; (ii) compared these in vivo findings to those obtained following in vitro stimulation of leukocytes from the same rats; and (iii) assessed potential sexual dimorphism in these outcomes. The findings indicated that plasma IL-12 levels were significantly reduced by social confrontation, wet-cage exposure, surgery, and the administration of corticosterone, epinephrine, or prostaglandin-E(2). Notably, most in vivo impacts on plasma levels were not evident when assessed in vitro. The IL-12-reducing effects of wet-cage exposure, and of corticosterone and epinephrine administration, were significantly greater in males than in females, although females exhibited greater total corticosterone levels following stress. The duration of acute stressors predicted the degree of IL-12 reduction, but more prolonged stressors did not. Furthermore, seven days of alternating behavioral stressors reduced plasma IL-12 levels more than 14 days. These findings suggest animals' behavioral habituation to stress conditions, or a specific immune mechanism restricting the duration of IL-12 reduction. Overall, our findings indicate a generic and robust stress-induced reduction in plasma IL-12 levels, and suggest epinephrine, corticosterone, and prostaglandin-E(2), as potential mediators that should be scrutinized in vivo in the context of natural physiological stress responses.

Muscle fibre type and size, and muscle capillary density in young double-muscled blue Belgian cattle.

Bovine muscle biopsies were analysed for fiber type and capillary density by the acid ATP-ase and amylase-PAS methods respectively. Samples obtained from Belgian blue double muscled (DM) calves were compared for their fibre type, size and vascularization with samples from Friesian (F) calves. The animals were sampled both at 2 and 7 months of age. Changes in histochemical composition occurring with ageing, independently of the breed, and differences related to the muscle sampled by comparing biopsies obtained from the longissimus dorsi (LD) and gluteobiceps (GB) muscles in animals of both breed were also investigated. Independently of age and muscle, fibre type I percentage and area were significantly higher in F than in DM muscles. Type IIa area was significantly larger in F than in DM, while fibre type IIb percentage and area were higher in DM. The number of capillaries/mm2 was significantly higher in F than in DM. Fibre type IIa and IIb percentage as well as the diameter of the three fibre types was significantly higher in the oldest animals. Finally, independently of age and breed, fibre type I and IIb percentages were significantly higher in LD but lower in GB. The results mainly demonstrated that Belgian blue DM muscles present a higher proportion of IIb fibres and a lower capillary supply than F muscles.