Identification of follicles with fertilizable oocytes by sequential ultrasound measurements during follicular development

Delayed ovulation and pregnancy outcome: effect of environmental toxicants on the neuroendocrine control of the ovary(1)

In the female rat, we have shown that a burst exposure to environmental toxicants known to alter noradrenergic function will block the ovulatory surge of LH when administered during a sensitive period on the day of vaginal proestrus. Such treatments will delay ovulation by 24 h and affect embryo survival. These results demonstrate clearly that brief, appropriately timed, toxicant exposure can initiate a cascade of changes that can alter reproductive outcome. However, we also found that continued exposure to the same compound is without an apparent influence on the reproductive capacity of the female, indicating that the female can become tolerant to such adverse reproductive effects. These observations raise a number of questions concerning the approaches currently used to examine potential reproductive toxicants. In this review, we describe the consequences of appropriately timed exposures to chlordimeform and dithiocarbamates on the timing of ovulation and subsequent alterations in pregnancy outcome. We also review the available literature on phenobarbital delays in ovulation and oocyte function in the rodent and the relevance to ovulatory delays in the human.

The dithiocarbamate fungicide thiram disrupts the hormonal control of ovulation in the female rat

Thiram has been reported to inhibit dopamine-beta-hydroxylase (D beta H), thereby affecting norepinephrine (NE) synthesis. Because NE is a neurotransmitter that is known to play an important role in the hypothalamic regulation of pituitary function, the acute effects of the thiram on the hormonal control of ovulation in the rat were investigated. Ovariectomized, estrogen-primed female rats were given a single injection of thiram (0, 6, 12, 25, 50, and 100 mg/kg, i.p.) at 1100 h and serum LH was measured in serial bleeds. Thiram at 100 and 50 mg/kg completely blocked the LH surge in all rats tested, while 12 and 25 mg/kg blocked the surge in 40 and 75% of the treated animals, respectively. Six mg/kg had no effect. Ovulation was then assessed in intact, proestrous females in response to thiram administration (0, 12, 25, or 50 mg/kg) at 0900, 1100, 1300, or 1800 h. Ovulation was blocked by 25 and 50 mg/kg at 1300 h in all rats, but when injected at 1100 h only the 50 mg/kg dose was effective. No such blockade was found with 50 mg/kg injected at 0900 and 1800 h. To assess the influence of thiram on the LH surge in intact rats, additional females were dosed at 1300 h on the day of proestrus and blood collected over that same day. Thiram at 50 mg/kg blocked the LH surge in all rats, while 25 mg/kg blocked the surge in 60% of the females tested. No effect occurred with 12 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)