Timing of Ovulation Following Progesterone Withdrawal in the Rat1

The Effect of Progesterone on Serum Luteinizing Hormone Concentrations in the Ewe

“…Although the increases are not large they are found consistently in both the intact and ovariectomized animals and occur at similar times in relation to the withdrawal of progesterone. In support of these data, recent work in the rat (Hoffman & Schwartz, 1965) (Ellington et al, 1964) indicates that the effect is associated with the progesterone treatment and is not due to a synergism with other gonadal steroids. In the rabbit it has been shown that progesterone can both raise and lower arousal thresholds in the reticular formation of the brain (Kawakami & Sawyer, 1959).…”

“…To date, the majority of workers have taken samples 1 to 3 days after the cessation of progesterone treatment On the basis of some recent observations (Ellington, Contopoulos & Clegg, 1964;Hoffman & Schwartz, 1965) Mindlin & Butler (1938) and expressed in terms of mg/100 mg ovary weight. In each assay two dose levels of nih lh s-7 were included with a four-fold dose difference between the levels.…”

Effects of Norethynodrel and Mestranol on Pituitary Luteinizing Hormone in the Female Rat

“…The mechanism by which norethynodrel enhances pituitary lh stores is speculative. The effect appears to be reminiscent of increase in the pituitary lh level in response to administration of natural progestagen-progesterone (Hoffman 8c Schwartz, 1965;Van Rees & de Groot, 1965). This increase could result from an inhibition of lh release, a stimulation of lh synthesis, or both.…”

The Synchronization of Ovulation in the Adult Female Rat by Oral Administration of Megestrol Acetate

“…The Hoffman & Schwartz (1964, 1965 (Everett, 1961;Peterson, Edgren & Jones, 1964;Kaufman & Rothchild, 1966). Support for this conclusion is afforded by the work of Greep & Jones (1950) (Bennett, Vallance & Vickery, 1968 …”