Arterial-Venous Differences in Gonadotropin Concentration Across the Ovary of Sheep During Different Reproductive States 1

Summary

Concentrations of gonadotropins in arterial, systemic venous, and ovarian venous plasma were determined by radioimmunoassay in order to assess the role of “utilization” of these hormones in the regulation of ovarian function. Samples were collected at frequent intervals (0.5–2 hr) for periods ranging from 18 to 52 hr from ewes beginning on Days 7 and 14 of the cycle and Day 14 of pregnancy. The functional state of the corpus luteum was assessed by concentrations of progesterone in ovarian venous blood and by histology. There was no evidence that the corpus luteum “utilizes” any gonadotropin during periods of active luteal function nor was there evidence of “utilization” of any gonadotropin during periods of active follicular growth. The data did suggest that serum levels of LH and possibly prolactin and FSH are regulated by periodic episodic releases of these hormones. Episodic “bursts” of LH were particularly apparent in ewes in which sampling was begun on Day 14 of the cycle.