Thesis (MSc (Physiological Sciences))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Bi-directional communication exists between HPA-axis activation and interleukin-6
(IL-6). However, the relative contribution of centrally versus peripherally secreted IL-
6 remains unclear, especially under psychological stress conditions. We
hypothesised that the HPA response to mild psychological stress is dependent on IL-
6, both centrally and peripherally.
120 male Wistar rats were divided into four groups, depending on whether they
received an anti-IL-6 antibody (Ab) (2μg/ml/kg body weight) or a placebo (sterile
saline) injection and whether or not they were subjected to 1 hour of restraint stress
for 1, 2 or 3 days. Rats were euthanized 24 hours after stress exposure.
Plasma corticosteroid (GC) levels remained significantly increased 24 hours after a
single stress exposure (control placebo (CP) versus stress placebo (SP): p < 0.05).
The undetectable plasma IL-6 levels evident across all groups may be explained by
the short half-life of IL-6. Plasma IL-1β levels decreased when IL-6 was blocked in
unstressed animals (CP versus CAb: p < 0.05), suggesting a role for IL-6 in the
maintenance of IL-1β levels under tonic physiological conditions.
At tissue level, pituitary gland mass increased significantly at time point 2,
independently of stress when blocking IL-6 (CAb: p < 0.05). This suggests that when
normal homeostasis is threatened, immediate adaption or at least compensation
may occur. It was observed that GR, IL-1β, IL-1βR, IL-6, IL-6R and GABAARα1
showed no response to stress alone in the pituitary. It is therefore more likely that
resistance to adaptation exists centrally. IL-1β and IL-1βR (p < 0.05) and
GABAARα1 (p < 0.005) expression increased in the CAb group in the pituitary, again
suggesting a role for IL-6 under control conditions. In terms of the adrenal, blocking IL-6 resulted in decreased glandular mass at time point 1, independent of stress
(CAb and SAb: p < 0.005). The up-regulation in GR expression seen in CAb and
SAb (p < 0.05) may be the effect of a compensatory mechanism to increase IL-6
dependent bioactivity of GCs. The fact that expression of IL-6, IL-6R, IL-1β and IL-
1βR consistently increased in the Ab groups, and mostly in the zona fasciculata and
zona reticularis, suggests that lack of local direct negative cytokine feedback
occurred in response to very low plasma IL-6 levels and that this contributes more
than GCs in the down-regulation of inflammatory cytokine release.
In conclusion, consistent effects of the Ab were apparent in the tissues investigated,
even in control conditions, suggesting that IL-6 plays a role in the maintenance of
basal homeostasis, including its regulation of the response to psychological stress.
We found differential regulation in terms of cytokines and GCs when comparing
peripheral versus central effects of stress and Ab, as well as the levels of cytokines
in the blood compartment, compared to within tissues. / AFRIKAANSE OPSOMMING: Daar bestaan twee-rigting kommunikasie tussen HPA-as aktivering en interleukin-6
(IL-6), allhoewel die relatiewe bydrae van sentraal versus perifeer afgeskeide IL-6
nog onduidelik is, veral gedurende sielkundige strestoestande. Ons hipotese is dat
die HPA reaksie tot sielkundige stres afhanklik van IL-6 is, beide sentraal en in die
periferie.
120 manlike Wistar rotte is in vier groepe verdeel, afhangende van of hulle ‘n anti-IL-
6 teenliggaampie (Ab) (2μg/ml/kg liggaamsgewig) of ‘n plasebo (steriele
soutoplossing) inspuiting gekry het, en of hulle onderworpe was aan 1 uur van
vaskeer-stres vir 1, 2 of 3 dae. Rotte is 24 uur na blootstelling aan stres aan
genadedood onderwerp.
Bloed kortikosteroïed (GC) vlakke het beduidend toegeneem binne 24 uur na ‘n
eenmalige stres blootstelling (kontrole plasebo (CP) versus stres plasebo (SP): p <
0.05). Die onmeetbaar lae vlakke van IL-6 regoor al die groepe, kan verduidelik
word na aanleiding van die kort half-leeftyd van IL-6. Bloed IL-1β vlakke het
afgeneem in kontrole rotte wanneer IL-6 geblok is (CP versus CAb: p < 0.05). Dit kan
beteken dat IL-6 noodsaaklik is vir die onderhoud van IL-1β vlakke gedurende
basale toestande.
Op weefselvlak het die hipofise massa toegeneem by tydpunt 2 toe IL-6 geblok is,
onafhanklik van stres (CAb: p < 0.05). Dit dui aan dat wanneer normale homeostase
bedreig word, daar onmiddelike aanpassing of kompensasie plaasvind. Dit is
opvallend dat GR, IL-1β, IL-1βR, IL-6, IL-6R en GABAARα1 geen respons in terme
van stres alleen in die hipofise getoon het nie. Na aanleiding daarvan is dit meer
waarskynlik dat weerstand tot aanpassing sentraal bestaan. IL-1β and IL-1βR (p <0.05) en GABAARα1 (p < 0.005) uitdrukking in die hipofise het toegeneem in die CAb
groep, wat weereens ‘n rol vir IL-6 onder kontrole toestande uitwys. In terme van die
bynier, het die blok van IL-6 ‘n afname in massa veroorsaak by tydpunt 1, wat weer
onafhanklik van stres was (CAb en SAb: p < 0.005). Die opregulering in die CAb en
SAb groepe (p < 0.05), kan wees as gevolg van ‘n kompensasie meganisme om IL-6
afhanklike GC aktiwiteit te verhoog. Die feit dat die uitdrukking van IL-6, IL-6R, IL-1β
and IL-1βR in die Ab groepe deurlopend verhoog was, en meeste in die zona
fasciculata en zona reticularis, stel voor dat daar ‘n tekort aan plaaslike, direkte
sitokien negatiewe terugvoering was, as gevolg van die merkwaardige lae bloed IL-6
vlakke en dat dit meer bydra as GCs in die afregulering van inflammatoriese sitokien
vrystelling.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4365 |
| Date | 12 1900 |
| Creators | Viljoen, Monet |
| Contributors | Smith, C., University of Stellenbosch. Faculty of Science. Dept. of Physiological Sciences. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 97 p. : ill. |
| Rights | University of Stellenbosch |
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