Abstract
Concerning effects of post-ovulatory anti-LH serum (aLH) administration on luteal progesterone (P) secretion and reactivity to prolactin (PRL), comparisons were made between 4-and 5-day cycles. Plasma P declined by 6:00 hr on diestrus (D) in control 4-day cycling rats and by 18:00 hr on day D in control 5-day cycling rats. Daily injections of aLH from 8:00 hr on estrus (E) in 4-day cycles did not alter P secretion. However, aLH injections from 8:00 hr on metestrus (M) prolonged P secretion up to 18:00 hr on day D, while aLH injections from 19:00 hr on day M failed to prolong P secretion. In 5-day cycles, aLH injections from 8:00 hr on day E or 19:00 hr on day M prolonged P secretion. Control 4-day cycling rats responded to PRL injections from 8:00 hr on day M with elevated P secretion and persistent leukocytic vaginal smears for 9-10 days, but they failed to respond to PRL injections from 19:00 hr on day D. Control 5-day cycling rats also failed to respond to PRL injections from 19:00 hr on day D. Injections of aLH from 8:00 hr on day M in 4-day cycles preserved the full luteal re-activity at 19:00 hr on day D. The aLH injections from 19:00 hr on day M maintained the full luteal reactivity at 19:00 hr on day D in 5-day cycles, but not in 4-day cycles. At 18:00 hr on day D, changes in the fine structure of the lutein cells from control and aLH-treated 4-day cycling rats were correlated to those in plasma P levels. These results indicate (1) tonic LH levels on day E of 4-day cycles "enhance" luteal P secretion, (2) tonic levels of LH secreted on day M suppress luteal function, which has a structural basis, (3) the suppressive effect is imposed at least 11 hr later in 5-day cycles than in 4-day cycles.
