Effects of the opioid antagonist naloxone on concentrations of LH and FSH in plasma were measured in mares during different stages of the oestrous cycle. During the follicular phase of the cycle, naloxone (300 mg i.v.) had no discernible effects on basal concentrations of LH and FSH. A significant increase in plasma LH (P < 0.01) and FSH (P < 0.05) concentrations was observed after naloxone in mares during the luteal phase. This response was not different between suckled and non-suckled mares. The gonadotrophin-releasing hormone analogue buserelin (0.02 mg i.v.) caused a significant (P < 0.05) LH and FSH release irrespective of the stage of the oestrous cycle and a previous naloxone treatment. The results of this study indicate that endogenous opioid peptides are involved in the inhibition of LH and FSH release during the luteal phase of the oestrous cycle in mares and may partially mediate the suppressive influence of progesterone on gonadotrophin secretion. The opioid-mediated suppression of LH and FSH release does not seem to be affected by suckling.
The protein disulfide isomerase (PDI) is a ubiquitous protein, which contributes in building disulfide bridges. In the work presented here, the expression of the PDI in different stages of the canine hookworm Ancylostoma caninum was investigated. Third-stage larvae (L3), adults, as well as serum-stimulated and hypobiotic L3 were used. For quantification of the PDI gene transcription, a real-time PCR was used establishing a hybridization probe (TaqMantrade mark probes) for detection of PDI copy numbers in different populations. 18S ribosomal ribonucleic acid (rRNA) was used as a housekeeping gene for normalization. The results show differences in the transcription level of the investigated A. caninum populations: The serum-stimulated larvae representing the switch to parasitism showed the highest PDI expression. The hypobiotic larvae representing a resting stage showed the lowest expression level. Male adults showed an elevated expression compared to female adult worms. The L3 expression level was just below the serum-stimulated population. This work confirms the upregulated gene expression of PDI during host penetration and invasion.
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