DECREASED BINDING OF GROWTH-HORMONE IN THE RAT HYPOTHALAMUS AND CHOROID-PLEXUS FOLLOWING MORPHINE TREATMENT

Male Sprague-Dawley rats were continuously infused with morphine throu gh subcutaneously implanted mini-osmotic pumps over a period of 5 days . The binding of rat growth hormone (rGH) to specific sites in choroid plexus, cortex, hypothalamus, hippocampus and striatum was determined . It was found that in the acute phase of morphine administration the density of growth hormone-binding sites was significantly decreased in choroid plexus and in hypothalamus, but not in any other of the tissu es studied. When tolerance to morphine was developed, the level of gro wth hormone-binding was restored to control level. In the acute phase, the plasma levels of GH, as measured by radioimmunoassay, correlated negatively with the density of the binding sites in choroid plexus and hypothalamus. The decrease in growth hormone-binding in these regions of the rat brain was also confirmed by SDS-polyacrylamide gel electro phoresis of cross-linked complexes of the binding entities to I-125-la belled rGH as visualized by autoradiography. In experiments, where mor phine was administrated by intermittent injections, a similar decrease in rGH-binding was observed. However, the time-course of this decreas e seemed to be dependent upon the route of administration. Following i ntracerebroventricular (i.c.v.) injections, the binding of the hormone was already affected after 30 min, whereas the binding of rGH in brai n areas after subcutaneous (s.c.) injections was affected at a later s tage.