Oxygen dependency of preovulatory follicles from pregnant mare serum gonadotropin-treated immature rats

A novel follicle culture system markedly increases follicle volume, cell number and oestradiol secretion

This study reports a novel, simple method for culture of mouse follicles which results in follicles with cell numbers similar toin vivofully grown follicles. Using this method, follicles (180–240 μm in diameter) were cultured in a 100 μl inverted drop of medium without oil and compared with culture in upright drops with and without a mineral oil overlay. Follicles, isolated from C57BL/6 × CBA/ca crossbred and MF1 inbred mice, were cultured individually at 37 °C in 96-well round-bottomed suspension cell tissue culture plates for 6 days. Follicles grown in the inverted drop culture system reached a markedly higher final diameter (means±s.e.m.; 471 ± 6.0 μm) as compared with the upright with oil (363 ± 2.7 μm) and without oil (358 ± 4.0) systems. There was no significant effect of mouse strain on follicle diameter. Follicular secretion of oestradiol and lactate into the medium was measured on days 2, 4 and 6 of culture. Secretion of oestradiol per follicle on day 6 was 2.49 ± 0.45 ng in the inverted and 0.90 ± 0.17 ng in the upright without oil system (P< 0.001). Follicular secretion of lactate on a per unit of follicle volume basis remained constant in the inverted system over days 2, 4 and 6 and was less (P< 0.001) than secretion in both the upright with and without oil systems. Follicle cell proliferation was markedly increased in the inverted as compared with the upright with oil system; the increases in cell numbers were significant on day 3 (P< 0.01) and on all subsequent days (P< 0.001). These results are discussed in relation to the supply of oxygen to the follicle in culture.

Interaction between 17 beta-oestradiol and 3 alpha-hydroxy-5 alpha-pregnane-20-one in the control of neuronal excitability in slices from the CA1 hippocampus in vitro of guinea-pigs and rats

The effect of 17 beta-oestradiol and 3 alpha-hydroxy-5 alpha-pregnane-20-one (allopregnanolone) on the action potentials in the Schaffer collateral pathway was investigated in hippocampus CA1. Slices from male and female guinea-pigs and female rats were used. In the rat three groups were studied: (a) untreated prepubertal rats at day 25 after partus; (b) rats injected on day 26 with 10 IU of equine serum gonadotropin studied on day 28, when in the pro-oestrus follicular phase; and (c) on day 32 when in the luteal phase. The allopregnanolone (12.6 microM, 0.5 nL) was applied locally in stratum orienspyramidale. the 17 beta-oestradiol (0.7 nM) was perfused (4 mL min-1) or applied locally. The amplitude of the population spike in stratum pyramidale was increased by oestradiol in guinea-pigs of both sexes and in all the three groups of rats. Allopregnanolone decreased the amplitude of the population spike in the guinea-pigs and in the luteal phase rats. The effect appeared within seconds after the application of the drugs. The allopregnanolone inhibition of the population spike was increased by perfusion with oestradiol in the guinea-pigs and in the luteal phase rats. This effect appeared within 7 min, and improved with increasing length of the perfusion (7-71 min). It remained for 55 min after return to perfusion with artificial cerebrospinal fluid. In prepubertal and follicular phase rats the allopregnanolone inhibition was seen only after perfusion with oestradiol for more than 15 min. The results show that 17 beta-oestradiol increases the allopregnanolone inhibition and that this inhibition is most efficient during the luteal phase of the rat.

The in vitro perifused rat ovary: II. Role of oxygen tension in the whole and quartered ovary

In vitro perifusion of whole ovaries raises questions about tissue viability and its effects on the observed ovarian steroid secretion. To assess effects of tissue degeneration, whole and quartered ovaries from pregnant mare serum gonadotropin (PMSG-) treated immature rats were perifused for 8 h, employing various levels of pO2. Histological examination of both the whole and quartered ovary showed signs of degeneration in centrally located follicles but not in follicles located near the surface. However, basal and gonadotropin-stimulated (luteinizing hormone plus follicle stimulating hormone) secretion of estradiol, testosterone and progesterone were not significantly different in the whole ovary whether in the presence of high or low pO2 (n = 8; p > 0.05). Similarly, although the quartered ovary secreted greater amounts of steroids than did the whole ovaries (p < 0.05, n = 8), pO2 levels did not affect the steroid output. We conclude that during in vitro perifusion, minimal oxygen supply is sufficient for ovarian steroidogenesis to proceed. In addition, although quartered ovaries displayed some evidence of tissue degeneration, they were more responsive in terms of steroid output per mg ovary than were whole ovaries.

The effect of reduced oxygen tension on progesterone accumulation in rat granulosa cell cultures

Studies were carried out on the effect of oxygen tension on progesterone (P) accumulation in rat granulosa cell cultures. At 1-2% oxygen, basal, luteinizing hormone (LH)-stimulated, and follicle stimulating hormone (FSH)-stimulated P accumulations were 20, 18, and 11%, respectively, of P levels at 20% oxygen. Basal P accumulation was also inhibited at 5% oxygen, but LH- and FSH-stimulated P levels were 50% and 40% higher, respectively, than at 20% oxygen. P levels at 10% oxygen were intermediate between those at 5% and 20% oxygen. The inhibitory effect of 1-2% oxygen on P accumulation was reversible: LH-stimulated P accumulation was inhibited in cultures incubated in 1-2% oxygen for 24 h, but rebounded during a subsequent 24 h period in 20% oxygen to the same level as that in cultures maintained continuously in 20% oxygen. We conclude that oxygen tension does influence granulosa cell steroidogenesis in vitro. Changes in blood flow and oxygen delivery to the ovary before and after ovulation could, therefore, effect the pattern of steroidogenesis during this period.