Concentrations of β-endorphin and oxytocin were measured in plasma of cows before, during and after parturition. The effect of the PGF2α analogue cloprostenol on β-endorphin and oxytocin release was investigated. During parturition, there were marked, parallel increases in β-endorphin and oxytocin concentrations. Both hormones were released in an episodic manner in conjunction with uterine and abdominal contractions. It is therefore likely that factors stimulating oxytocin release also enhance β-endorphin secretion. This suggests a role of labour or labour-associated hormones in stimulating peripheral β-endorphin release. Cloprostenol caused an immediate, pronounced increase in plasma β-endorphin and oxytocin concentrations.
J. E. Aurich, I. Dobrinski, H-O. Hoppen and E. Grunert
J. E. Aurich, I. Dobrinski, H.-O. Hoppen and E. Grunert
Summary. Plasma concentrations of β-endorphin and met-enkephalin were measured, with appropriate radioimmunoassays, in cows during gestation and at parturition and in newborn calves. During pregnancy β-endorphin immunoreactivity (IR) concentration increased, but values during the last month of gestation were not different from those at parturition. Highest met-enkephalin IR levels were obtained in cows during calving. A term Caesarean section caused an increase in plasma β-endorphin and metenkephalin IR concentrations, but no such increase occurred in cases of a preterm Caesarean section. In calves β-endorphin IR values were lower before umbilical cord rupture than immediately after birth. Values decreased continuously thereafter. This was also the case for met-enkephalin IR concentrations in calves born at term. In preterm calves met-enkephalin IR values were low immediately after delivery and increased during the first hour of life. A significant correlation existed between the degree of acidosis and plasma levels of both opioid peptides in the calves. We conclude that a direct stimulation of peripheral β-endorphin release by the pain or stress associated with calving does not seem to exist in cattle, whereas met-enkephalin seems to be more directly related to parturition. In calves the change to the extrauterine environment causes an immediate, increased release of both opioids.
Keywords: β-endorphin; met-enkephalin; cattle; parturition; neonate
C. Behrens, J. E. Aurich, E. Klug, H. Naumann and H-O. Hoppen
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.