Masanao Hirai

Effects of Norethynodrel on Progestins in Ovaries and Ovarian Venous Blood of Rats

France and Pincus [i] reported that administration of I7a-ethynyl5(io)-estrene-i7/3-ol-3-one (norethynodrel) resulted in the inhibition of gonadotropin-induced ovulation, as determined by the significant decrease in the mean number of ova recovered from the fallopian tubes of rats, and ovarian weight was decreased in hypophysectomized, gonadotropin-primed rats treated with norethynodrel suggesting a direct inhibitory action on the follicular growth induced by exogenous gonadotropins. Since Zanders observation [2-4], workers have demonstrated the presence of 4-pregnen-2oa-ol-3-one (2Oa-OH-P) in different species [5-7]. Recently, Hilliard, Penardi, and Sawyer [8] suggested that this 2Oa-OH-P acts as a positive feedback agent to prolong and heighten LH discharge in the mated rabbit. The secretion of progesterone by ovarian corpora lutea and the essential role of this steroid in implantation and maintenance of fertilized ova have been well established. In addition to this progestogen, the mammarian ovary synthesizes and releases two structurally similar compounds, 2Oa-OH-P and/or its 0-isomer (20/3-OH-P), to which no specific physiological functions have yet been assigned. The present experiments were carried out to define the effect of norethynodrel on ovulation and to determine whether the norethynodreltreated rat would have altered progestins in ovarian venous blood and the ovaries in vivo.

Isolation of 4-Pregnen-20α-ol-3-one from Rats' Ovarian Venous Blood and Ovaries

Ovulation can be inhibited by both progesterone and testosterone, but certain newer synthetic compounds related to these are extremely effective and produce fewer undesirable side effects. Among these are: norethindrone, which is also classified as a 19-nortestosterone, and norethynodrel, which is more closely related to the estrogens. Fairly large scale studies in Puerto Rico [1] and Haiti [2] have revealed that these compounds when taken by mouth prevent ovulation, and therefore conception, in a very high proportion of sexually active women. Field trials of these and similar oral contraceptive substances are currently proceeding in a number ofheavily populated parts of the world, and they are being watched with interest by all those who are concerned with the problems raised by our worldwide population explosion. Biochemical control of contraception as most widely practiced is attained by means of the orally active ovulation inhibitors. The problem of the mechanisms of action of the synthetic progestins has been extensively discussed in numerous publications [3]. However, fundamental significance of norethynodrel as ovulation inhibitor remains unknown. In rabbits the steroidogenic response of the ovaries to LH, mating, or electrical stimulation of the hypothalamus or medial amygdala [4] is extremely rapid and appears to have a lower threshold than the ovulatory response [5]. The marked stimulus by FSH of follicle growth seen in * A preliminary report of this paper was presented at the 3d Asian and Oceanic Congress ofEndocrinology at Manila, January, 1967. t Department of Pharmacology, Jikei University School of Medicine, Tokyo, Japan. We are grateful to: Yoshiko Masubuchi for technical assistance; Dr. Gregory Pincus for his advice and for a gift of 4-pregnen-2oa-ol-3-one; Drs. Yoshihito Omori and Sumio Shima for infrared spectra analysis; and Dr. Tomojy Yanagita, Central Laboratory for Experimental Animals, Tokyo, for the Sprague-Dawley rats.