Effects of 8-Arginine Vasotocin on Plasma Prolactin and Follicle-Stimulating Hormone Surges in the Proestrous Rat

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Abstract
Previous findings that AVT [8-arginine vasotocin] inhibited the preovulatory surge of LH [luteinizing hormone] and subsequent ovulation prompted this study demonstrating that AVT effects a marked suppression of the prolactin surge during proestrus, but does not affect the concurrent surge of FSH [follicle stimulating hormone]. Microgram amounts of AVT (administered from 1300-1600 h on the afternoon of proestrus) suppressed the prolactin surge significantly, relative to saline-treated controls and comparable doses of antidiuretic hormone and oxytocin (P < 0.001); and prolonged administration with increased amounts of AVT (up to 16 .mu.g over the period from 0900 through 1600 h) had no effect on the FSH surge. Different mechanisms may be involved in the cyclic release of LH and FSH, and the surge of FSH is minimally involved in ovulation in the cycling rat.