Counter current transfer of beta-endorphin in the perihypophyseal cavernous sinus--carotid rete vascular complex of sheep.

Abstract

This study was performed to answer the question of whether counter current retrograde transfer of beta-endorphin in the perihypophyseal cavernous sinus-carotid rete vascular complex depends on the reproductive activity of sheep and if this transfer depends on membrane Na+ K+ ATP-ase blocking by ouabain. Sheep were anaesthetised and the jugular vein and the carotid artery were cannulated on both sides. Multielectrolitical liquids (Solfin, Polfa "Kutno", Poland): 500 ml of Solfin with heparin (25,000 IU), or Solfin with heparin and ouabain (Sigma, St. Louis, USA) in concentrations of 10(-5) or 10(-4) mol 1(-1) were infused into the brain through the carotid artery. Heparinized blood was collected through the carotid artery. After exsanguination, the head with the neck was removed. The isolated head was supplied with oxygenated, heated, autologous blood diluted with Solfin (4:1) without or with ouabain in concentration of 10(-5) or 10(-4) mol 1(-1). Blood pressure and temperature were measured throughout the duration of the experiment. During the experiment 125I-beta-endorphin (7.9 x 107 dpm) dissolved in 10 ml of Solfin was infused for 5 min (5 ml) into each cavernous sinus through the angularis oculi veins. Blood samples for radioactivity measurements were collected each min from the carotid rete (through the opposite carotid artery to the artery supplying the brain with arterial blood) and from both jugular veins. In all the experiments significant 125I-beta-endorphin radioactivity was found in arterial blood supplying the brain and hypophysis in the early luteal phase in sheep. No radioactivity was found (with the exception of one animal) in sheep during seasonal anoestrus. A blockage of Na+ K+ ATP-ase by ouabain administered during exsanguination and during head perfusion with dose of 10(-4) mol 1(-1) reduced beta-endorphin counter current transfer to arterial blood, but this effect was not evident with the dose of 10(-5) mol 1(-1). Increased blood pressure was observed in all the experiments with either dose of ouabain.