Regulation of alternative oxidase activity in six wild monocotyledonous species. An in vivo study at the whole root level

The activity of the alternative pathway is affected by a number of factors, including the level and reduction state of the alternative oxidase (AOX) protein, and the reduction state of the ubiquinone pool. To investigate the significance of these factors for the rate of alternative respiration in vivo, we studied root respiration of six wild monocotyledonous grass species that were grown under identical controlled conditions. The activity of the alternative pathway was determined using the oxygen isotope fractionation technique. In all species, the AOX protein was invariably in its reduced (high activity) state. There was no correlation between AOX activity and AOX protein concentration, ubiquinone (total, reduced, or oxidized) concentration, or the reduction state of the ubiquinone pool. However, when some of these factors are combined in a linear regression model, a good fit to AOX activity is obtained. The function of the AOX is still not fully understood. It is interesting that we found a positive correlation between the activity of the alternative pathway and relative growth rate; a possible explanation for this correlation is discussed. Inhibition of the AOX (with salicylhydroxamic acid) decreases respiration rates less than the activity present before inhibition (i.e. measured with the 18O-fractionation technique).

Possible involvement of inhibin in the interrelationship between numbers of antral follicles and peripheral FSH concentrations in female rats

The possible dependence of peripheral concentrations of FSH on a non-steroidal, ovarian factor, was studied in adult female rats. Increases in FSH levels during the periovulatory period were not correlated with decreases of steroid concentrations, and administration of steroids did not result in a reduction of FSH levels to basal values. However, a negative correlation between FSH levels and numbers of large follicles (volume greater than or equal to 200 x 10(5) micron 3) was demonstrated, and injection of steroid-free bovine follicular fluid, which contains inhibin-like activity, suppressed FSH levels to basal values. These results suggest that an ovarian, inhibin-like factor is involved in the fast regulation of FSH concentrations in the periovulatory period, and that this inhibin-mediated control of FSH might play a role in the regulation of the number of follicles maturing in female rats.

Follicle growth in the immature rat ovary

In ovaries of immature rats the following parameters were estimated from autoradiographs prepared after pulse labelling with tritiated thymidine: 1) The time it takes follicles to grow from one stage of development to another. This could be derived from the total number of granulosa cells in these stages and from their doubling times. The doubling time of granulosa cells was determined from their labelling index and the duration of their DNA-synthesis phase. 2) The number of follicles present in the ovary at different ages. 3) The number of follicles, which start on their development at different ages. It was found, that more follicles start to grow in 8 and 16 days old rats (2.0/h) than in 28 days old ones (1.0/h). Moreover, the follicles grow somewhat faster earlier in life than later. The development from a follicle with one layer of granulosa cells to one with several layers and antrum formation takes about 15 days in the first half of the period of immaturity while it takes about 17 days as the animal approaches maturity.

Administration of antiserum against ovine follicle-stimulating hormone or ovine luteinizing hormone at pro-poestrus in the rat: effects on follicular development during the oncoming cycle

Cyclic rats received at 13.00 h on the day of pro-oestrus a single i.v. injection of one of the following antiserum preparations: AOLH (raised in rabbits against NIH-LH-S17); AOFSH (raised against NIH-FSH-S9) or pAOFSH (AOFSH preincubated with 195 mug NIH-LH-S16/ml). Rats were killed at day 1, 3 or 5 after injection, and the ovaries prepared for histological study of the antral follicles. After AOLH, ovulation and resumption of meiosis in oocytes in pre-ovulatory follicles were prevented but follicular development during the following cycle appeared undisturbed. After either AOFSH or pAOFSH, blockade of ovulation was never observed but the formation of antral follicles normally occurring between mid-pro-oestrus and mid-oestrus was postponed by about one day. The later development of antral follicles might reflect a supranormal compensatory secretion of endogenous gonadotrophin because the development does not occur in AOFSH- or pAOFSH-treated rats hypophysectomized 24 h after injection and subsequently treated with pregnant mare serum gonadotrophin in dosage approximating the amount of gonadotrophin secreted endogenously during dioestrus. The results imply (1) that the pre-ovulatory surge of LH release is not essential for follicular development during the oncoming cycle whereas (2) a surge of FSH release is required for the formation of the new cohort of antral follicles that is normally seen at the start of a new cycle.

Levels of follicle-stimulating hormone, luteinizing hormone, oestradiol-17 beta and progesterone, and follicular growth in the pseudopregnant rat

Throughout a period of pseudopregnancy the peripheral blood levels of progesterone, oestradiol-17 beta, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), as well as the size-distribution of ovarian antral follicles were estimated in the rat. The progesterone concentrations, as measured by a competitive protein-binding technique, exceeded metoestrous values (25 ng/ml plasma) from day 3 of pseudopregnancy onwards. The highest levels were found on days 6 and 8 (91 ng/ml). From day 8 onwards the levels decreased gradually but were still above metoestrous values on the day of pro-oestrus after pseudopregnancy. Concentrations of oestradiol-17 beta, as measured by radioimmunoassay, were within the range of those at metoestrus (about 5 pg/ml plasma) until day 10. Thereafter levels increased to a value of 57 pg/ml. Concentrations of FSH, measured by radioimmunoassay, were within the range of metoestrous values until day 10 (about 100 ngNIAMD-rat-FSH RP-1/ml serum), but declined to a level of 33 ng/ml on day 12. Concentrations of LH, measured by radioimmunoassay, were generally within the wide range of metoestrous values (9-60 ng NIAMD-rat-LH RP-1/ml serum), but concentrations found on days 4, 8 and 10 were significantly lower than those found on preceding or subsequent days. Histological determination of the number of follicles present in various volume-classes, showed an increase in antral follicles on days 1 and 2, comparable to the increase observed during metoestrus and dioestrus 1 of the normal cycle. There was no change in the follicles between days 3 and 10 and they resembled those of early dioestrus. Preovulatory growth had occurred by day 12. Injection of human chorionic gonadotrophin (HCG) on days 2, 4 or 6 showed that ovulation could be induced only in some of the larger follicles. On the basis of these results it is suggested that during pseudopregnancy the high progesterone levels present result in a decreased plasma LH level which is insufficient to cause full maturation of the follicles and to stimulate oestrogen secretion to the levels required for induction of an ovulatory surge of LH release.

Plasma oestradiol-17beta and its relationship to serum follicle-stimulating hormone in immature female rats

SUMMARY

Oestradiol-17β (E2) was measured by radioimmunoassay in the plasma of immature female rats. Maximal E2 levels of 55–60 pg/ml were found at 10–15 days of age; from day 25 to day 35 E2 levels were low to undetectable. The E2 measured appeared to be of ovarian origin: ovariectomy performed on day 13 resulted in a decreased E2 level 2 days later (13 pg/ml) as compared with the value from the control litter mates (46 pg/ml); after adrenalectomy the level of circulating E2 remained normal (54 pg/ml). The effects of ovariectomy and adrenalectomy on uterine weights followed a similar pattern: ovariectomy resulted in a decrease and adrenalectomy in no change in uterine weight.

In the strain of rat used, levels of follicle-stimulating hormone (FSH) in the serum (measured by radioimmunoassay) were high from day 10 to day 20 and showed a steep decrease on day 21. After ovariectomy on day 15 this decrease in serum FSH was not observed.

The influence of circulating E2 on serum levels of FSH was studied after ovariectomy followed by treatment with varying doses of oestradiol benzoate. Ovariectomy on day 13 resulted in a significantly increased FSH level 2 days later (1770 ng NIAMD-rat-FSH RP-1/ml) as compared with the value obtained from control animals (1033 ng/ml). This increase was not observed after daily injections of 0·1 μg oestradiol benzoate/100 g body weight.

The results indicate that E2 and FSH concentrations show a similar pattern between 5 and 35 days of age. Furthermore, an inhibitory feedback mechanism between oestrogens and FSH concentrations was found to be operative. The implications of these findings are discussed.

Amounts of gonadotrophins required for normal follicular growth in hypophysectomized adult rats

Rats were hypophysectomized at oestrus, at days 1, 2 and 3 of dioestrus or at pro-oestrus. They were injected with various doses of PMS only, or with combinations of PMS and HCG, in such a way that fairly constant blood levels could be expected, and killed 24 h later.

It was found that the minimal doses of substitutional gonadotrophins, required to maintain normal follicular growth, were considerably higher during the period from pro-oestrus to oestrus (when a new generation of follicles begin to develop) than during all the other periods investigated. This peak requirement primarily concerned PMS. The minimal requirements during other periods showed only minor variations. The maximal doses which still caused normal follicular growth were higher during the period from dioestrus −1 to −3 than during the period from oestrus to dioestrus −1 and the period from dioestrus −3 to pro-oestrus.

The data suggest that during pro-oestrus very high amounts of FSH are required to recruite a new crop of follicles, whereas during the other phases, low levels of both FSH and LH are generally needed for normal follicular growth.

Compensatory ovarian growth and compensatory ovulation after unilateral ovariectomy in rats with an ovarian autograft in the region of the portal vein

Compensatory growth and the compensatory increase of the number of ovulations in the remaining ovary after unilateral ovariectomy were compared in three groups of rats:

I. Rats with no ovarian graft. II. Rats with an ovarian autograft in the region of the portal vein. III. Rats with an ovarian autograft in a region draining into the general circulation.

Compensatory growth was not inhibited by ovarian grafts placed in the region of the portal vein, whereas this was inhibited with grafts of the same volume but draining into the general circulation. This finding supports the view that compensatory ovarian growth after unilateral ovariectomy is at least partially the result of an increase in the gonadotrophin level in the blood, following the decrease in oestrogen level.

In contrast, the total number of ovulations did not differ significantly in the three groups. The number of ovulations in the ovary in situ was in most cases decreased, when ovulations had occurred in the grafts, even in animals with a graft in the region of the portal vein. These findings are discussed.