Abstract
Glucocorticoids act upon the hypothalamus and pituitary to regulate both corticotropin-releasing factors and adrenocorticotropin (ACTH) in a classical negative feedback loop. There are two distinct receptor systems in the central nervous system for glucocorticoids: type I corticosterone/cortisol-preferring, predominantly hippocampal receptors, and type II dexamethasone-binding receptors with a much broader distribution. To determine the relative roles played by these two receptors in determining basal and stress-induced ACTH/cortisol levels in the sheep, we have conducted two series of experiments. In the first, we infused 4 sheep with cortisol (50 μg/h), or dexamethasone (20 μg/h) for 17 h, collected 10-min blood samples for 3 h for basal hormone levels, and then subjected the sheep to an audiovisual stress (barking dog), 10 μg of ovine corticotropin-releasing factor (oCRF) 1 h later, and 100 U of insulin another 2 h later. Dexamethasone reduced ACTH and cortisol levels, both basal and in response to stress; cortisol infusion had no effect on any parameters; oCRF did not raise ACTH levels. In the second experiment, cortisol (100 μg/h) alone was infused into 4 sheep for 17 h, and blood samples were collected for 3 h for basal hormone levels; this was followed by the injection of 10 μg oCRF, and 2 h later a barking dog was introduced into the sheep shed. Again, cortisol infusion did not affect basal ACTH or cortisol levels, though both cortisol-infused and control animals had ACTH responses to oCRF when it was not preceded by the audiovisual stress. ACTH and cortisol levels were higher in the 2 h following oCRF injection. Subsequent responses to the stress brought on by the dog were not altered. We conclude: (i) with the caveat that cortisol levels did not rise post-infusion, that negative feedback effects of glucocorticoids on the hypothalamo-pituitary adrenal axis in intact sheep are primarily via type II and not type I receptors; (ii) that physiologically induced elevations in cortisol are capable of inhibiting pituitary responsiveness to oCRF in the sheep via an intermediate duration (minutes-to-hours) feedback mechanism, and (iii) that oCRF may play a role in priming the hypothalamo-pituitary-adrenal axis.
| Original language | English |
|---|---|
| Pages (from-to) | 181-189 |
| Number of pages | 9 |
| Journal | Neuroendocrinology |
| Volume | 51 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 1 Jan 1990 |
| Externally published | Yes |
Keywords
- adrenocorticotropin
- corticotropin- releasing factor
- cortisol
- dexamethasone
- glucocorticoid receptors
- negative feedback
- pituitary
Cite this
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Adrenocorticotropin responses to endogenous and exogenous secretagogues in the sheep : Specificity of glucocorticoid action. / Canny, B. J.; Clarke, I. J.; Funder, J. W.
In: Neuroendocrinology, Vol. 51, No. 2, 01.01.1990, p. 181-189.Research output: Contribution to journal › Article › Research › peer-review
TY - JOUR
T1 - Adrenocorticotropin responses to endogenous and exogenous secretagogues in the sheep
T2 - Specificity of glucocorticoid action
AU - Canny, B. J.
AU - Clarke, I. J.
AU - Funder, J. W.
PY - 1990/1/1
Y1 - 1990/1/1
N2 - Glucocorticoids act upon the hypothalamus and pituitary to regulate both corticotropin-releasing factors and adrenocorticotropin (ACTH) in a classical negative feedback loop. There are two distinct receptor systems in the central nervous system for glucocorticoids: type I corticosterone/cortisol-preferring, predominantly hippocampal receptors, and type II dexamethasone-binding receptors with a much broader distribution. To determine the relative roles played by these two receptors in determining basal and stress-induced ACTH/cortisol levels in the sheep, we have conducted two series of experiments. In the first, we infused 4 sheep with cortisol (50 μg/h), or dexamethasone (20 μg/h) for 17 h, collected 10-min blood samples for 3 h for basal hormone levels, and then subjected the sheep to an audiovisual stress (barking dog), 10 μg of ovine corticotropin-releasing factor (oCRF) 1 h later, and 100 U of insulin another 2 h later. Dexamethasone reduced ACTH and cortisol levels, both basal and in response to stress; cortisol infusion had no effect on any parameters; oCRF did not raise ACTH levels. In the second experiment, cortisol (100 μg/h) alone was infused into 4 sheep for 17 h, and blood samples were collected for 3 h for basal hormone levels; this was followed by the injection of 10 μg oCRF, and 2 h later a barking dog was introduced into the sheep shed. Again, cortisol infusion did not affect basal ACTH or cortisol levels, though both cortisol-infused and control animals had ACTH responses to oCRF when it was not preceded by the audiovisual stress. ACTH and cortisol levels were higher in the 2 h following oCRF injection. Subsequent responses to the stress brought on by the dog were not altered. We conclude: (i) with the caveat that cortisol levels did not rise post-infusion, that negative feedback effects of glucocorticoids on the hypothalamo-pituitary adrenal axis in intact sheep are primarily via type II and not type I receptors; (ii) that physiologically induced elevations in cortisol are capable of inhibiting pituitary responsiveness to oCRF in the sheep via an intermediate duration (minutes-to-hours) feedback mechanism, and (iii) that oCRF may play a role in priming the hypothalamo-pituitary-adrenal axis.
AB - Glucocorticoids act upon the hypothalamus and pituitary to regulate both corticotropin-releasing factors and adrenocorticotropin (ACTH) in a classical negative feedback loop. There are two distinct receptor systems in the central nervous system for glucocorticoids: type I corticosterone/cortisol-preferring, predominantly hippocampal receptors, and type II dexamethasone-binding receptors with a much broader distribution. To determine the relative roles played by these two receptors in determining basal and stress-induced ACTH/cortisol levels in the sheep, we have conducted two series of experiments. In the first, we infused 4 sheep with cortisol (50 μg/h), or dexamethasone (20 μg/h) for 17 h, collected 10-min blood samples for 3 h for basal hormone levels, and then subjected the sheep to an audiovisual stress (barking dog), 10 μg of ovine corticotropin-releasing factor (oCRF) 1 h later, and 100 U of insulin another 2 h later. Dexamethasone reduced ACTH and cortisol levels, both basal and in response to stress; cortisol infusion had no effect on any parameters; oCRF did not raise ACTH levels. In the second experiment, cortisol (100 μg/h) alone was infused into 4 sheep for 17 h, and blood samples were collected for 3 h for basal hormone levels; this was followed by the injection of 10 μg oCRF, and 2 h later a barking dog was introduced into the sheep shed. Again, cortisol infusion did not affect basal ACTH or cortisol levels, though both cortisol-infused and control animals had ACTH responses to oCRF when it was not preceded by the audiovisual stress. ACTH and cortisol levels were higher in the 2 h following oCRF injection. Subsequent responses to the stress brought on by the dog were not altered. We conclude: (i) with the caveat that cortisol levels did not rise post-infusion, that negative feedback effects of glucocorticoids on the hypothalamo-pituitary adrenal axis in intact sheep are primarily via type II and not type I receptors; (ii) that physiologically induced elevations in cortisol are capable of inhibiting pituitary responsiveness to oCRF in the sheep via an intermediate duration (minutes-to-hours) feedback mechanism, and (iii) that oCRF may play a role in priming the hypothalamo-pituitary-adrenal axis.
KW - adrenocorticotropin
KW - corticotropin- releasing factor
KW - cortisol
KW - dexamethasone
KW - glucocorticoid receptors
KW - negative feedback
KW - pituitary
UR - http://www.scopus.com/inward/record.url?scp=0025020218&partnerID=8YFLogxK
U2 - 10.1159/000125335
DO - 10.1159/000125335
M3 - Article
VL - 51
SP - 181
EP - 189
JO - Neuroendocrinology
JF - Neuroendocrinology
SN - 0028-3835
IS - 2
ER -