The effect of photomirex on the in vitro perfused ovary of the rat.

Photomirex, a photodegradation product of the insecticide mirex, is an environmental contaminant that has been identified in Great Lakes fish, soil, and human adipose tissue. Because of the potential for human exposure, the present study was designed to investigate the short-term effects of photomirex on the in vitro perfused ovary of the rat. Adult Sprague-Dawley rat ovaries were isolated and perfused for a total of 6 h with Medium 199. Following a 2-h baseline period, 10(-4) M of photomirex was administered to the medium. Control ovaries received medium or DMSO (vehicle control). Significant effects of perfusion and chemical intervention were identified using lactate dehydrogenase enzyme, glucose utilization, lactate, pyruvate, and flow:pressure ratio as markers of toxicity (P < 0.05). Lactate:pyruvate ratio, glutathione, and oxygen consumption did not demonstrate significant effects. Post hoc tests showed that there were significant differences between the DMSO + photomirex group and the control group (M199) using lactate dehydrogenase as a marker of toxicity. Pyruvate concentration was also reduced significantly after perfusion with DMSO + photomirex compared to M199 only and DMSO only (P < 0.05). Histopathologic changes were not discernible by light microscopy. These results suggest that metabolic and respiratory processes of the ovary are acutely sensitive to perturbation with photomirex in the in vitro perfused rat ovary model.

The pituitary gonadotropin-releasing hormone (GnRH) receptor of the female rabbit: characterization and developmental aspects.

The aim of the present study was to characterize the pituitary gonadotropin-releasing hormone (GnRH) binding site in the rabbit and investigate its possible role in sexual maturation of the female rabbit. A radioligand binding assay was established, and the presence of specific 125I-labelled D-Ala6-des-Gly10-GnRH ethylamide (125I-DAl6EA) binding sites in the anterior pituitary gland of the rabbit was demonstrated. 125I-DAla6EA binding was saturable, specific, displaceable, reversible, correlated with increasing tissue concentrations, and susceptible to physiological manipulation. 125I-DAla6EA binding indicated the presence of two binding sites in the female adult rabbit pituitary: a high affinity, low capacity site (KD = 0.3-0.4 nM; Bmax = 100-200 fmol/mg protein) and a lower affinity, high capacity site (KD = 30 nM; Bmax = 5-8000 fmol/mg protein). Ontogeny of 125I-DAl6EA binding in the female rabbit (40-120 days of age) did not show a correlation between binding site number and serum luteinizing hormone (LH). In addition, the net serum LH response in female rabbits to a subcutaneous injection of DAla6EA (10 ng, 100 ng, and 1 microgram per kilogram body weight) was not significantly different between animals 40, 75, and 120 days of age. This suggests that a decrease in pituitary responsiveness to GnRH is not associated with sexual maturation in the female rabbit. Results indicate that factors other than and (or) in addition to GnRH binding site number, such as postreceptor events, play a role in gonadotropin secretion in the female rabbit.

Light-related melatonin changes in pituitary response to gonadotropin-releasing hormone during sexual development in the female rabbit.

Melatonin levels in the blood of female rabbits were determined from the time of weaning to adulthood in a longitudinal study. Blood samples were taken at 3 h after light onset and 1 h after dark onset and plasma was analysed for melatonin, LH and FSH by radioimmunoassay procedures. The animals were sacrificed on days 25, 32, 39, 51, 72, 91 and 120 days of life and pituitaries removed for in vitro incubation of slices to determine their response to GnRH. Circulating melatonin levels were significantly higher in the dark compared to the light phase and peaked on days 72 and 91 when gonadotropin levels were at a nadir. Melatonin levels on day 120 were lower than those on any other day examined. Basal secretion of LH and FSH by pituitary slices in vitro increased several-fold from day 25 of age to days 51-91 and then decreased by day 120. The pituitary gonadotropin responsiveness to GnRH in vitro was also different: while LH generally increased, FHS accumulation remained constant after GnRH stimulation. These data suggest that the female rabbit pituitary undergoes changes in sensitivity to GnRH during sexual maturation and that the pineal gland may play a role in this process.

Endurance exercise potentiates the stimulatory influence of oestrogen-progesterone on LH and FSH release in the rat.

Ovariectomized rats were treated with oestradiol benzoate and progesterone or GnRH. Prolonged exercise (running 4 days per week for 6 weeks) markedly potentiated the oestrogen/progesterone-induced release of LH and FSH, but the pituitary response to an injection of GnRH was unaffected. In contrast, at 24 h after a single exercise bout there was no apparent effect on steroid and GnRH stimulated LH and FSH responses although an acute exercise session given on the day of the LH surge inhibited steroid-induced LH release in some rats. We conclude that strenuous, prolonged exercise-training in the ovariectomized rat seems to modify the ability of the hypothalamus to release GnRH. The results were not attributable to a single bout of exercise since the gonadotrophin responses immediately or 24 h after such exercise did not parallel the results observed in the trained rats.