Breed-Specific Stress Coping Characteristics In Pigs During Transport And Molecular Mechanisms Underlying The Breed Differences In Adrenocortical Function

This study was aimed to analyze the breed-specific characteristics of pigs in response to transport stress, through comparison of the dynamic changes of behavior, plasma physiological and biochemical measures between Erhualian(EHL) and Pietrain(PIE) pigs, during 2 h of transportation. In order to testify the hypothesis that the breed difference in plasma cortisol levels is of adrenocortical origin, the expression pattern of proteins. involved in adrenal ACTH signaling pathway, including MC2R, CREB and pCREB, StAR, as well as that of the key enzymes involved in steroidogenesis in EHL and PIE pigs was characterized, both in vivo and in vitro.1 Dynamic changes of behavior, plasma enzymes activities and hormone levels in Erhualian and Pietrain pigs during transportEHL and PIE pigs equipped with chronic catheters in jugular vein were subjected to 2 h transport. Behavioral exhibition of the pigs was recorded with a video camera and dynamic changes of the activities of creatine kinase(CK) and lactate dehydrogenase(LDH), as well as the plasma concentrations of stress and metabolic hormones were investigated in EHL and PIE pigs during 2 h transport. The majority of the behavior of EHL pigs consisted of oral/nasal/facial(ONF) and fit behaviors during the initial observations(first 15 min after start), and these behaviors were replaced by increased time sitting and lying in later observations(middle and last 15 min of transport). In contrast, PIE pigs showed high levels of ONF behaviors in initial observation, followed by high frequency and duration of standing during the middle and the last observation period. PIE pigs demonstrated significantly higher plasma CK(P＜0.01) and LDH activities(P＜0.05). There were significant effects of time and time×breed interaction on CK activities(P＜0.01) in both breeds. Plasma ACTH levels did not differ between breeds, yet a significant effect of time (P＜0.05) was shown during transport. Plasma cortisol levels of both breeds rose in parallel rapidly after loading, peaked at 15 min after the start, and EHL pigs exhibited consistently higher basal and stimulated plasma cortisol levels(P＜0.05). There were significant time effects on metabolic hormones(insulin, T3 and T4) (P＜0.01), Whereas no significant breed effect for these hormones were found. These results indicate that different coping strategies apply in EHL pigs, as compared with PIE pigs, reflected by different behavioural, endocrine and biochemical responses during transport. No significant difference in plasma ACTH levels, whereas significantly higher cortisol levels in EHL indicate that the difference is probably of adrenal origin.2 Molecular mechanisms underlying the breed difference in adrenal ACTH signaling pathway and steroidogenic enzymes in pigsThe objectives of the present study were to characterize the expression pattern of proteins involved in adrenal ACTH signaling, including MC2R, CREB and pCREB, StAR, as well as that of the key enzymes involved in steroidogenesis, in order to elucidate the difference of adrenocortical function between EHL and PIE pigs. The plasma concentrations of the substrates for adrenal steroidogenesis, cholesterol and low-density lipoprotein(LDL) cholesterol, did not differ between breeds; plasma concentration of ACTH and the adrenal contents of MC2R mRNA and protein were similar in two breeds of pigs; no significant differences were found in MC2R mRNA and protein levels, CREB content and 3β-HSD mRNA between breeds; adrenal cAMP content tended to be higher in EHL than in PIE pigs; adrenal pCREB, StAR, P450scc contents and P450_17a, P450c21 and P450_11β mRNA levels were all significantly higher in EHL pigs than in PIE pigs. These results indicate that the enhanced cAMP/PKA/pCREB Signaling system and augniented expression of StAR and steroidogenic enzymes are major attributes to the higher basal plasma cortisol concentrations in pigs.3 Signal transduction pathway for cortisol production in isolated adrenocortical cells responding to ACTH-influence of halothane geneTo determine the contribution of halothane genotype on the breed difference in adrenocortical function between EHL (Hal^NN) and PIE (Haⁿⁿ) pigs, adrenocortical cells was isolated from PIE×EHL F2 piglets of Hal^NN and Halⁿⁿ, respectively. Cortisol levels in culture medium, the content of StAR, P450scc, MC2R, cAMP, CREB and pCREB in adrenocortical cell lysates after ACTH treatment was determined. Adrenocortical cells isolated from Hal^NN pigs showed higher basal cortisol levels in control(not treated with ACTH) group, which was accompanied with the higher expression of ACTH post-receptor signaling components, cAMP, StAR and P450scc, as compared with the adrenocortical cells from Halⁿⁿ pigs. ACTH treatment resulted in significant increases in cortisol, MC2R, cAMP, StAR and P450scc levels both in Halⁿⁿ and Hal^NN cells. No significant difference was observed in MC2R content under basal conditions, CREB content under basal or ACTH-stimulated conditions, while pCREB content tended to be higher in Hal^NN, compared with that in Halⁿⁿ under basal condition. These results indicate that the different cortisol levels between Halⁿⁿ and Hal^NN adrenocortical cells are associated with the distinct cAMP/PKA/pCREB signaling system and expression of StAR and P450scc. The difference of adrenocortical function between EHL and PIE pigs is attributed largely to the difference of halothane genotypes, whether different breeds of pigs with the same halothane genotype would differ in adrenocortical functions awaits further study.