Plasma arginine vasotocin, progesterone, and luteal development during pregnancy in the viviparous lizard Tiliqua rugosa.

The relationship between plasma levels of arginine vasotocin (AVT), progesterone, and corpus luteum formation and degeneration was studied in the viviparous lizard Tiliqua rugosa. Hormone levels were monitored in free-ranging, pregnant females which were located for sampling by means of attached radio transmitters. There was an increase in plasma AVT levels in the 30 days immediately prior to parturition. Concurrent with this event was a decline in plasma progesterone levels from relatively high levels in mid-term to basal levels prior to parturition. This is associated with degenerative changes in the corpus luteum which include pyknosis of the nuclei of the cells of the cell mass and increasing prevalence of intercellular spaces, while the thecal layer became increasingly compacted. Ovariectomy experiments indicate that the major source of progesterone during pregnancy in T. rugosa is ovarian.