Paul A. Wright

Induction of ovulation in vitro in Rana pipiens with steroids

Abstract Ovulation induced by pituitary extracts in vitro was enhanced by addition of certain androgenic, progestational, and cortical steroids, but inhibited by estrogens. A number of nonestrogenic steroids also had potent ovulatory capacity in vitro in the absence of pituitary factors, progesterone being the most effective of those tested. A greater ovulatory efficiency was demonstrated for progesterone than for pituitary extract. It is proposed that the principal function of pituitary gonadotropins in ovulation may be to stimulate steroid production by ovarian tissue, and that steroids are the real agents responsible for ovulation.

Facilitation of Pituitary-Induced Frog Ovulation by Progesterone in Early Fall.

Summary In October, when Rana pipiens ovaries are notoriously insensitive to ovulatory influences, injection of one frog pituitary gland in combination with small dosages of progesterone induced nearly complete ovulation within 24 hours. Progesterone, and to a lesser extent testosterone, also exerted some ovulatory effect when injected alone.

3-Keto-Δ4 steroid: Requirement for ovulation in Rana pipiens

Abstract Evidence is presented supporting the hypothesis that frog pituitary gonadotropins effect ovulation by stimulating synthesis of an ovulatory steroid. Lymph sac injection of 200 μg/50 g body weight of cyanoketone (2α-cyano,4,4,17α-trimethyl-17β-hydroxyandrost-5-en-3-one), a specific inhibitor of 3β-hydroxysteroid dehydrogenase, 12–16 hours prior to excising the ovary, results in total inhibition of pituitary gonadotropin-induced ovulation in vitro, but does not affect ovulation induced by progesterone or by combinations of progesterone and pituitary extract. Pregnenolone, the normal substrate for 3β-hydroxysteroid dehydrogenase, induced ovulation in vitro in normal frog ovary, but not in ovaries from cyanoketonetreated animals. Simultaneous administration of pituitary gonadotropins and cyanoketone in vitro, using normal ovarian tissue, results in much reduced ovulatory response, but not complete inhibition. It is apparent, then, that inhibition of the capacity to form 3-keto-Δ4-steroid, presumably from a 3-hydroxy-Δ5 precursor, prevents the event of ovulation.

Influence of estrogens on induction of ovulation in vitro in Rana pipiens.

In the fall estrogens exerted 70–100% inhibition on pituitary-induced ovulation in vitro, but enhanced ovulation induced by progesterone and combinations of pituitary extract and progesterone. Estrogens also diminished the sensitizing capacity of pituitary extracts in vivo. It is proposed that estrogens act as antimetabolites in the biosynthesis of some ovulatory steroid, but augment the action of ovulatory steroids once they are formed.

Infertility in rabbits induced by feeding Ladino clover.

Summary Feeding Ladino to female rabbits impaired reproductive performance, infertility being complete when clover was fed both prior to and during gestation periods. Cause is unknown but failure of ovulation and implantation was observed, and evidence indicates that infertility may be unrelated to estrogenic content of the clover.

Tissue fatty acid composition in four diverse vertebrate species.

Abstract 1. 1. Fatty acids of seven tissues from the mouse (Mus musculus), quail (Coturnix coturnix japonica), bullfrog (Rana clamitans), and sunfish (Lepomis gibbosus) were analyzed by gas-liquid chromatography. Twenty-seven fatty acids were separated as their methyl esters and identified. 2. 2. A higher degree of unsaturation was found in all tissues from the aquatic species (bullfrog and sunfish) than in those from terrestrial species (mouse and quail). 3. 3. High levels of 22:6 were found in tissues which are metabolically active in energy production, particularly in mouse heart, where it comprised approximately one-third of the fatty acids present. 4. 4. Brain fatty acid composition was similar in all four species, indicating a tissue specificity; whereas, the distribution of testicular fatty acids, particularly the C22 series, suggested a species specify. The predominance of 18:1 in depot fat confirmed that this fatty acid is the preferred form of reserve energy storage in animals. 5. 5. Branched-chain fatty acids were found in all tissues analyzed.

The influence of colchicine on ovulation in vitro in the frog, Rana pipiens

Abstract Colchicine (10 −5 M ) potentiates pituitary-induced ovulation in vitro by a factor of about 3, a phenomenon noted previously by other workers. Colchiceine, lacking one of the colchicine methoxy radicals, had a much reduced potentiating activity on pituitary-induced ovulation. Colchicine augmented ovulation induced by progesterone by a factor of about 3, increased ovulatory activity of testosterone by a factor of only 1.25, and did not potentiate ovulation induced by cortisone and hydrocortisone at all. Testosterone further augmented ovulation induced by mixtures of pituitary extract and colchicine, but progesterone, cortisone, corticosterone, hydrocortisone, and pregnenolone did not. Colchicine reversed a part of the inhibition imposed by dicumarol on pituitary-induced ovulation, but was ineffective against inhibition by nicotinic acid analogs. A possible explanation for the action of colchicine is discussed.

Influence of Certain B-Vitamin Antimetabolites on Ovulation in vitro in the Frog, Rana pipiens.

Summary Ovulation in vitro, as induced by pituitary extracts, was inhibited by antimetabolites of nicotinic acid in December experiments but not in April. Results suggest that metabolism of nicotinic acid may participate in sensitization of frog ovary which occurs gradually during the hibernation months from December to April, but not directly in ovulation itself. Other B vitamins were not implicated.

Non-specificity of pituitary-induced anuran ovulation in vitro.

Summary Ovulation in vitro has been induced in a variety of anurans using homoplastic and heteroplastic pituitary extracts, indicating (1) that the reaction as induced in excised ovarian tissue is truly physiological and normal, and (2) that there is a general lack of specificity of pituitary hormones for this response.