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Summary.
Progesterone was administered to male rats (4 mg/day) for 10 or 13 days in two different experiments and pituitary lh stores were determined by a modified ovarian ascorbic acid depletion method. The steroid administration resulted, in both experiments, in involution of seminal vesicles and significant decreases in pituitary lh stores.
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Summary.
A possible synergistic participation of lh and fsh in the ovulatory process was explored by intravenous administration of subthreshold doses of lh and/or fsh to rats with 4-day oestrous cycles, in which ovulation was blocked by a potent anti-oestrogen—ICI 46,474. The individual gonadotrophins in the doses used were only marginally active in restoring ovulation but, when given in combination, they potentiated the incidence of ovulation in four different experiments. It is postulated that both lh and fsh synergize with each other in the induction of ovulation as they do in causing growth of follicle.
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Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545, U.S.A.
(Received 15th August 1974)
Barbiturates, notably sodium pentobarbital (Nembutal), have provided a useful tool for studying the neuroendocrine mechanism mediating ovulation. Everett & Sawyer (1950) first used barbiturates to confirm the existence of the `critical period' which they had earlier detected by using atropine and Dibenamine, an α-adrenergic blocking agent (Everett, Sawyer & Markee, 1949). It has been generally assumed that pentobarbital (PB) and related barbiturates interfere with ovulation by acting on the central nervous system. Hagino (1969) reported inhibition of PMSG-induced ovulation in immature rats by PB injected directly into the hypothalamus although the pituitary was not excluded as a possible site of action of the drug. Cross & Dyer (1971) reported reduced unit activity of hypothalamic neurons following intravenous injection of subanaesthetic doses of sodium methohexitone (Brietal: Eli Lilly Co. Ltd) but response to urethane was variable. Using a
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Methallibure (ICI 33828) is a non-steroidal compound which has been found to inhibit secretion of gonadotrophins from the pituitary in a wide variety of species (Walpole, 1965). Decrease in pituitary gonadotrophin stores and/or secretion following treatment with methallibure has been found in the rat (Brown, 1963; W. R. Russell and A. L. Walpole, unpublished observations), pig (Garbers & First, 1969; Stormshak, Leverage, Kelley, Gerrits & Howland, 1970) and human (Loraine, Bell & Foss, 1965). The compound is also known to cause restriction of food intake with a consequent loss in body weight. It is not known whether a decrease in the gonadotrophin synthesis and/or release following the methallibure treatment stems from the specific effects of the compound or is secondary to a restriction of food intake. In the present communication, pituitary and serum lh
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Summary.
Crystalline progesterone or cholesterol (50 μg/rat) was implanted stereotaxically into the anterior pituitary gland or median eminence region on the day before pro-oestrus in the 4-day cyclic rat, and the effects of these steroids on ovulation were studied by examining tubal ova at autopsy on the expected day of oestrus. Progesterone (at 1/10 the effective subcutaneous dose) implanted at either location proved significantly more active in interfering with ovulation than cholesterol (P<0·01). The data provide evidence that progesterone acts at both the hypothalamic and pituitary levels to interfere with ovulation.
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Summary.
A total of forty-nine samples of ovarian venous blood from pregnant hamsters was analysed by radioimmunoassay for oestradiol and oestrone. The secretion rate (ng/hr/ovary) and the concentration (ng/ml blood) of oestradiol were low on Day 1 of pregnancy, showed a significant rise before implantation on Day 3, and remained elevated on the day of implantation (Day 4) with no significant changes until after Day 9. Between Days 10 and 12, the values rose sharply to peak levels (P<0·01) which were followed by a significant (P<0·05) decline during the last 3 days of gestation. The secretion of oestrone paralleled that of oestradiol. The secretion of both oestrogens was very low during the post-partum period.
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Summary.
A silk suture inserted in one uterine horn significantly decreased the secretion of progesterone on Day 4 of pregnancy from the adjacent as compared to contralateral ovary. The concentration of oestradiol was similarly depressed on the IUD side. These results provide evidence for the local effect of an IUD on the ovary in the pregnant rat.
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The guinea-pig has an oestrous cycle of 16 to 18 days. Many original observations in reproductive endocrinology such as formation of deciduoma in response to trauma (Loeb, 1907), existence of the oestrous cycle (Stockard & Papanicolaou, 1917) and the ability of the uterus to modify luteal function (Loeb, 1923) involved the guinea-pig as the experimental animal. Several studies have delineated the pattern of progesterone secretion during the oestrous cycle of guinea-pigs (Heap, Perry & Rowlands, 1967; Feder, Resko & Goy, 1968; Challis, Heap & Illingworth, 1971; Blatchley, Donovan, Horton & Poyser, 1972) but comparative changes in the secretion of oestrogens have received very little attention. Challis et al. (1971) attempted to measure total oestrogens by radioimmunoassay in the peripheral plasma, but failed to detect any due to their very low levels. In the present study, we determined
