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  • Author or Editor: Shu-Hua Zhang x
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SUMMARY

A study was conducted to determine whether differences in adrenocortical response to exogenous adrenocorticotropin (acth) were an accurate reflection of an animal's perception of and response to stressful stimuli, or whether the pituitary gland might modulate adrenocortical responsiveness. Sixteen Large White × Landrace female pigs, of which 8 had high adrenocortical response to acth and the other 8 had low response, were administered iv a bolus of synthetic human corticotropin-releasing factor (hcrf) at dose rates ranging from 0.002 to 2 μg/kg of body weight. Blood samples were collected at known times for up to 2 hours after administration of hcrf. Plasma acth and cortisol concentrations were measured by radioimmunoassay. Results indicate that hcrf stimulated the pituitary gland of high- and low-responding pigs to secrete acth, which in turn stimulated the adrenal cortex to secrete cortisol. Plasma acth concentration, before or after hcrf administration, was not significantly different between the high and low responders. However, high-responding pigs had higher cortisol concentration after hcrf administration than did low-responding pigs. Thus, the differences in adrenocortical response to acth between the 2 groups of pigs were not attenuated by variation in pituitary response. It is concluded that adrenocortical responsiveness to acth is an accurate indicator of the perception of and the response to stress.

Free access
in American Journal of Veterinary Research

SUMMARY

A study was conducted to determine whether within-breed differences in adrenocortical response to exogenous adrenocorticotropin (acth) might be accounted for by differences in responsiveness of the adrenocortical cells per se. Large White × Landrace male pigs (n = 20) were used; 10 had high adrenocortical response to acth administration and 10 had low response. Five high and 5 low responders were euthanatized at 15 weeks of age, and the remaining 5 high and 5 low responders were euthanatized at 21 weeks of age. Adrenal glands were removed and weighed, and adrenocortical cells were dispersed by tryptic digestion and incubated for 2 hours with synthetic acth at concentrations ranging from 0.5 to 10,000 pg/ml. Samples were taken at 30-minute intervals, and cortisol concentration was determined by use of a radioimmunoassay. Results indicate that for pigs of both age groups, high responders had heavier adrenal glands, with higher adrenocortical cell density and higher cell yield than did low responders. Synthetic acth had a stimulatory effect on dispersed porcine adrenocortical cells, as indicated by changes in cortisol concentration in vitro. Adrenocortical cells from high responders produced less cortisol, on a per-cell basis, than did those from low responders. However, when corrected for total cell yield, the potential cortisol production by each pair of adrenal glands was significantly (P < 0.05) higher in the high responders than in the low responders. Thus, high-responding pigs have larger adrenal glands and higher adrenocortical cell density, which may result in higher output of cortisol after acth administration or exposure to stressors.

For high- and low-responding groups, 15-week-old pigs had higher adrenal gland weight to body weight ratio, higher adrenocortical cell density, and higher steroidogenic function per adrenocortical cell than did 21-week-old pigs.

Free access
in American Journal of Veterinary Research