title: Cyclic variation of oxytocin in the blood of pituitary portal vessels of rats.
abstract: The release of oxytocin (OT) into pituitary portal blood during the estrous cycle was studied in female rats under Althesin anesthesia. On each afternoon of the 4-day estrous cycle, animals were anesthetized with Althesin, and pituitary portal blood samples were collected. The concentration of OT in portal plasma collected between 14.00 and 16.00 h of proestrus (1,079 +/- 185 pg/ml) was significantly higher than that at any other time studied. There were no appreciable differences between the mean OT concentration on the days of estrus (198 +/- 29 pg/ml), metestrus (283 +/- 55 pg/ml), and diestrus (267 +/- 49 pg/ml). The concentration of OT in pituitary portal plasma was also greater than that in blood withdrawn from the external jugular vein (less than 41-67 pg/ml). Comparison of the portal plasma OT with peripheral plasma prolactin in Althesin-anesthetized rats indicated an association between the release of these hormones during the estrous cycle.
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000294:innervation; D004971:Estrus; D005260:Female; D008473:Median Eminence / Q000502:physiology; D010121:Oxytocin / Q000097:blood*; D010286:Paraventricular Hypothalamic Nucleus / Q000502:physiology*; D010902:Pituitary Gland / Q000098:blood supply*; D010903:Pituitary Gland, Anterior / Q000502:physiology; D011247:Pregnancy; D011388:Prolactin / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010121:Oxytocin; D011388:Prolactin