Nuclear maturation inhibitors in Bufo arenarum oocytes.

In Bufo arenarum, as in other amphibian species, nuclear maturation--characterized by germinal vesicle breakdown (GVBD) and meiosis resumption--is induced by progesterone. Seasonal variations in the sensitivity to progesterone were observed in Bufo arenarum oocytes. The gonadotropin FSH and drugs such as dbcAMP and xanthine did not affect nuclear maturation per se, although they acted as negative modulators of progesterone-induced nuclear maturation.

Effects of cytoplasmic components upon sperm aster development in Bufo arenarum eggs.

Bufo arenarum oocytes obtained during the winter period, presenting a metabolism similar to that of the differentiated tissues, are not able to form a sperm aster after spermatozoon injection. These oocytes may be considered immature, with respect to the state of their cytoplasm. In the present work, aster formation was induced in winter coelomic oocytes through injection of cytoplasm from summer oocytes, GTP, and EDTA.

Effects of the pineal gland and melatonin on the metabolism of oocytes in vitro and on ovulation in Bufo arenarum.

The pineal gland and the hormone melatonin appear to be responsible to some extent for the metabolic behaviour of Bufo arenarum oocytes during the winter. This assumption is supported by the observation that, in isolated mitochondria, both elements stimulate the rate of oxidation of citrate and inhibit that of fumarate, thus raising the oxidizing ratio that relates these parameters (C/F) to values close to or above 1, which is characteristic of these animals in winter. The sensitivity of oocytes to melatonin, in terms of the C/F ratio, varies throughout the year.

Effect of follicle-stimulating hormone on metabolism and maturation in Bufo arenarum oocytes.

In the fully grown Bufo arenarum oocyte, carbohydrate breakdown during the autumn-winter season is accomplished mainly through the glycolytic pathway followed by the Krebs cycle. During the breeding season (spring-summer), carbohydrates are used mainly through the pentose phosphate cycle and through the variant of the Krebs cycle known as the glutamic aspartic cycle. The metabolism operating in the oocytes was determined using the following parameters: 1) the capacity of isolated mitochondria to oxidize citrate and fumarate; 2) the enzymatic activities of phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase (G-6-PDH); and 3) citrate and ATP compartmentalization.

Sperm Nuclear Transformation and Aster Formation Related to Metabolic Behaviour in Amphibian Eggs.

Bufo arenarum oocyte maturation is related to important modifications in the metabolism of carbohydrates. Such changes involve a different relative participation of the main oxidative routes and are under the influence of seasonal variations of the pituitary activity. Ovulated coelomic oocytes obtained during the winter period, were unable to initiate cleavage after injection of a sperm suspension.