Inhibin‐like activities in charcoal‐treated bovine follicular fluid (FF) and medium from cultured Sertoli cells (SCCM) were assayed in an in vitro bioassay system, using cultured pituitary cells. Addition of both fluids resulted in parallel dose‐dependent decreases of the concentration of follicle‐stimulating hormone (FSH) in the medium, both in the presence or absence of luteinizing hormone‐releasing hormone (LH‐RH). A single injection of FF into immature and adult male and female rats resulted in decreased peripheral levels of FSH, but not of LH, after 4 or 8 h. This decrease was larger and occurred faster in adult female rats than in prepubertal female animals. Injection of FF into adult female rats, immediately after unilateral ovariectomy (ULO) prevented the specific increase of FSH levels, occurring in control animals. This suppression could not be obtained after treatment with steroids. Daily treatment of adult female or immature male rats for periods longer than 5 days did not result in prolonged suppression of circulating FSH concentrations; LH levels were significantly increased. The female animals showed cyclic vaginal smear changes and normal ovulation; in the male rats testis weight and numbers of spermatogenic cells were reduced. It is concluded that testicular and ovarian inhibin‐like activities have similar properties. Injections of FF into male and female rats cause similar effects on FSH and LH. The effect of FF in ULO‐animals suggests that inhibin could play a role in the short‐term regulation of the number of developing follicles in the ovary. Injection of FF into male rats causes a probably transient impairment of spermatogenesis through an initial suppression of FSH.
Administration of steroid-free bovine follicular fluid (bFF), containing inhibin-like activity, depressed levels of FSH measured 4 h after injection in intact adult and 35-day-old female rats, but not in younger females. Suppression of FSH was also observed in intact male rats, aged 55 days, but not in older and younger male rats. Eight hours after injection of bFF, FSH levels were depressed in 15-day-old and older immature and adult rats of both sexes. Male and female rats, gonadectomized 2 days earlier, responded similarly to bFF treatment as did the intact animals. In a second experiment it was found that the rise of FSH levels, occurring within 8 h of gonadectomy, decreased with age in male and increased with age in female rats. Steroid treatment was found to prevent the rise in FSH levels partially in 15-day-old male and completely in 25-day-old female rats, whereas treatment with bFF was fully effective in blocking the FSH rise in both immature and adult rats of both sexes. It is concluded that inhibin might be a major physiological factor in a fast-acting control of FSH concentrations from at least the age of 25 days onwards in female rats. In male rats its physiological significance might be limited to the prepubertal period, despite the fact that pituitary secretion of FSH is suppressed by exogenous inhibin-like activity at all ages studied.
A single injection of steroid-free bovine follicular fluid (bFF), which contains inhibin-like activity, was given to adult female rats at 09.00 h on dioestrus-2 (the day after metoestrus), dioestrus-3, pro-oestrus or oestrus. peripheral concentrations of gonadotrophins were measured at 2-h intervals after injection. Compared with values in control animals treated with bovine plasma, injection of bFF did not influence concentrations of LH. In contrast, at all days studied injection of bFF resulted in suppressed concentrations of FSH, during a period which started between 4 and 10 h after injection and lasted 4-12 h, depending on the day of the cycle. With the exception of pro-oestrus, the period of suppression was followed by one in which fluctuating levels of FSH were found; in general, resulting levels were higher though not significantly increased. This latter effect was most pronounced on dioestrus-2 and dioestrus-3, when levels of FSH, which were already low in control animals, were first suppressed during the 6 h after injection of bFF. These data, in conjunction with results from an earlier study in rats at dioestrus-1, showed that administration of bFF induces a fast and selective suppression of FSH secretion on all days of the cycle. This period of suppression was followed by one with fluctuating levels of FSH which showed a tendency to be higher, indicating that disturbances in FSH secretion, such as are caused by bFF, can be compensated for quickly. In this way the process of follicular maturation might be protected.
textabstractFertility in mammals ~as recei~ed considerable attention as far back as written
reports exist. In the last centennium, the study of fertility has surpassed the
level of merely descriptive and empirical science and has been applied to solve
some problems of the regulation of fertility. This has contributed to the treatment
of fertility disorders arid to birth control in man, as well as to improvement
of animal husbandry.
Our knowledge of the processes controlling fertility has increased due to
clinical observations and the use of experimental techniques ranging from para-
biosis experiments, castration and hypophysectomy to brain l~sions and 'implantations
of materials such as tissue fragments. Information has been obtained about
the interplay between central nervous structures, pituitary gland and the gonads,
and about the role of hormones secreted by these organs. In the most simple scheme,
these interactions firstly involve the control and release of hypothalamic releasing
factors, which reach the anterior pituitary gland by way of the portal vessels.
In turn, the pituitary gland releases in both male and female animals gonadotrophic
hormones: follicle stimulating hormone (FSH) and luteinizing hormone
(LH). These hormones enter the circulation and reach their end-organs, testes or
ovaries, in which they influence both morphology and function. The testes and ovaries,
apart from producing gametes, respond with the production of gonadal hormones,
which do not only control the secretion of hypothalamic releasing factors and
the pituitary secretion of FSR and LH, but also influence the development and maintainance
of acces_sory sex organs, secondary sex characteristics and sexual behaviour.
One of the problems in testicular and ovarian (patho)physiology is the nature
and action of these gonadal hormones.
Ovariectomized rats were treated with follicular fluid isolated from cows and pigs in order to assess the effect on gonadotropin levels. Bovine follicular fluid (BFF) was pooled according to size of the follicle (less than 5, 5-10, 11-20, more than 20), while porcine follicular fluid (PFF) samples were pooled without regard to follicular size. Steroids were removed from fluids. Concentration of progesterone and estradiol-17beta were less than .5% of values before extraction with charcoal. Wistar rats with at least 2 regular 5-day cycles were used. In the 1st experiment the animals were bilaterally overiectomized or sham operated. At 900 hours on the 12th day following surgery, 250 mcl saline, bovine plasma, or charcoal-treated BFF 11-20 were injected. Follicle stimulating hormone (FSH) increased 1700% and luteinizing hormone (LH) increased 500-900% in BFF-treated animals. Bovine plasma was without effect on gonadotropin levels but BFF injection was followed by a reduction in FSH levels which reached significance at 8 hours. In a 2nd experiment, rats were unilaterally ovariectomiezed or sham operated and injected with either 60 or 250 mcl saline, bovine plasma, or 1 of the 5 follicular fluid preparations. 4 hours following injection, unilaterally ovariectomized rats showed an increase in FSH levels to 183 + 10 or -10% (at 4 hours) and 334 + 21 or -21% (at 8 hours) of control values at the low dosage and 140 + 8 or -8% and 323 + 21 or -21% at the higher dosage. Changes in LH values were insignificant. Treatment with bovine plasma was without influence on gonadotropin levels after unilateral ovariectomy. 60 mcl of any follicular fluid preparation resulted in significantly reduced FH levels at 4 hours and at 8 hours were still reduced in animals receiving BFF 5-10 or BFF 11-20. 250 mcl resulted in more marked reduction of FSH but still BFF 20 and PFF failed to prevent the increase of FSH levels over 8 hours. An inhibinlike factor in bovine and porcine follicular fluid is suggested.
The time-related changes in gonadotrophin concentrations after a single injection of steroid-free bovine follicular fluid (bFF), which contains material with inhibin-like activity, were studied in 25-day-old and adult female rats which either were intact or had been ovariectomized 2 days before. In ovariectomized and intact rats administration of bFF caused a selective suppression of FSH after 4–8 h in 25-day-old rats and after 3–4 h in adult rats. No systematic changes in concentrations of LH after bFF injection were observed. Relative suppression of FSH levels in adult rats was more pronounced and of longer duration than in 25-day-old rats. Moreover, the total period of suppression lasted longer in ovariectomized than in intact rats (12 and 8 h for 25-day-old and 24 and 15 h for adult rats respectively). Hypersecretion of FSH was found in intact rats after the initial suppression; this phenomenon was more pronounced and of longer duration in adult than in 25-day-old rats. No clear change in the numbers of healthy growing follicles was observed after injection of bFF into intact rats. These results indicate that the pituitary secretion of FSH responds quickly and selectively after administration of bFF to intact and ovariectomized, 25-day-old and adult female rats. The hypersecretion of FSH in intact rats might compensate for the initial suppression of this gonadotrophin, and may thus ensure the maturation of a normal number of follicles.
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.
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