Arginine vasotocin (AVT) release in relation to uterine contractility in the hen.

The relationship between plasma levels of arginine vasotocin (AVT) and factors associated with increases in uterine contractility was studied in the domestic hen. Plasma AVT levels increased from 3.3 +/- 0.3 microU/ml 15 min before a midsequence oviposition (OP) to 14.8 +/- 0.6 microU/ml at OP and then decreased to 5.2 +/- 0.6 microU/ml 15 min following OP. A ninefold increase in plasma AVT concentration was observed in hens laying a terminal egg of a sequence, which is not immediately followed by ovulation (OV). AVT levels also increased approximately 1 hr before the time of the first ovulation (C1OV) of the next sequence in association with an increase in uterine contractility. When OP was induced 2 hr before an expected OP by intrauterine administration of prostaglandin F2 alpha (PGF2 alpha, 1.0 microgram), plasma AVT levels immediately increased threefold (P less than 0.001) and then returned to basal levels within 30 min. In PGF2 alpha-treated hens AVT levels rose at the expected time of OP (P less than 0.05) in association with an increase in uterine contractility without OP actually occurring. When C1OV was induced by LH-RH (25 micrograms, iv), a small but significant increase of AVT similar to levels during spontaneous C1OV was observed. These results suggest that plasma AVT levels increase with every ovulation and oviposition in the absence of an egg in the uterus and that AVT is released in association with induced ovulation and oviposition.