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The time- and dose-dependent effects of bovine activin A and bovine follicle stimulating hormone (FSH) suppressing protein (FSP) or follistatin on basal and FSH-induced steroidogenesis and inhibin production were studied in granulosa cells from immature, diethylstilbestrol (DES)-treated rats. In the presence of rat FSH (20 ng/ml) which stimulates aromatase activity and the production of progesterone and inhibin, activin (0.3-100 ng/ml) augmented all three parameters, whereas FSP (0.3-100 ng/ml) enhanced progesterone production and attenuated the other two parameters. In the absence of FSH, the basal parameters were unaffected by treatment with either activin or FSP alone, except for a statistically significant increase in basal inhibin in the presence of activin alone (P less than 0.05, at doses of 30 and 100 ng/ml). Neither activin nor FSP influenced the timing of the maxima of FSH-induced activities over 5 days. These findings suggest that activin and FSP, both present in follicular fluid, may play an important role in the local regulation of granulosa cell differentiation.

The functions of the ovary can be described as a storehouse for oocytes as well as a factory to produce mature oocytes at the appropriate time for fertilization and hormones at the appropriate time and in the appropriate quantities to assure fertility. A complex multiple-job specification such as this requires control processes which allow all facets to operate successfully at the same time, and in a co-ordinated manner. This can only be achieved by hypothesizing control at several levels, namely, externally via gonadotrophins (and perhaps GH and prolactin), and internally via local regulators, where the local regulators control the gonadotrophin-independent processes and fine tune the gonadotrophin-dependent processes. The available evidence is consistent with a role for local regulators in the control of follicular and luteal function in the ovary. In most cases, however, the nature of the local regulator involved in a particular process is not known. On the other hand, the list of candidates continues to increase (see Table 1). A priority for future research will be to firmly establish many of these substances as local regulators and to understand how and when they exert their actions, particularly in vivo. A particularly complex question concerns the potential interaction between the local regulators which have either similar or opposing actions. The clinical significance of local regulation in the ovary is yet to be fully appreciated. The addition of GH to gonadotrophin therapy for ovulation induction (Homburg et al, 1988) is the first example of the application of findings from basic research on local regulators in the ovary. It may be that clinical syndromes such as resistant ovary syndrome, polycystic ovarian disease and luteinized unruptured follicle have some perturbation of local regulator production or action, which, if defined, would underline the importance of local regulation and could offer a means of treatment.

Summary On the weight of the evidence presented above, it is concluded that regulation at a local, intragonadal level is an integral part of the overall regulation of gonadal function in both sexes. The interaction between cells within a gonad extends beyond the same cell type to include germ cell-somatic cell interactions as well. We believe this local interaction between cell types facilitates the differing requirements of the various developmental stages of germ cells within the gonad, which would not be possible by simply varying the afferent pituitary hormone supply. We re-emphasize that the local factors responsible for these interactions are acting in conjunction with the pituitary hormones, and, in some cases, may be their proximate regulators. A more controversial phenomenon is the possibility of an interaction between the gonads which does not involve the hypothalamic-pituitary axis. The little evidence which is available to support this hypothesis comes mainly from studies on ovarian function, particularly recruitment and selection of follicles. More research on this phenomenon is warranted. Not surprisingly there are many parallels between the testes and ovaries with respect to the nature and action of local regulators. For example, the intragonadal action of steroids, the local modulation of the response of target cells to FSH, the influence of macrophages on steroidogenesis and the presence of mitotic and meiotic regulators are common to both sexes. It would not be surprising if the chemical nature of these factors in the ovary and testes are similar. If the ever-increasing list of factors and activities being discovered in thegonads is any guide, the phenomena outlined in this review are just the beginning of an extensive list of cell-cell interactions occurring within and between the gonads. No doubt the gonads will share with other organs the same interactions between cells which are required for normal cellular function. The uniqueness of the gonads lies in their protection and production of germ cells. The challenge of the future for reproductive biologists will be to discover and describe the interactions within and between germ cells which are obligatory for normal reproductive function, and to apply that information to devising ways of overcoming infertility and regulating fertility.

Ovine trophoblast protein-1 (oTP-1), a protein secreted by the sheep conceptus immediately prior to implantation has sequence homology with alpha interferon. We have previously shown that, in parallel with human alpha interferon (IFN), oTP-1 reduces the release of prostaglandins (PG) E and F2 alpha from cultured ovine endometrial cells. Here we have examined the time and dose dependence of these actions and the possible site of action of the peptides. The concentrations of oTP-1 and IFN required for 50% inhibition of PGE release were 92 pg/ml and 0.88 pg/ml and for PGF2 alpha release, 165 pg/ml and 1.12 pg/ml respectively. Significant effects on PG release were not measured before 12 h after addition of peptide to culture dishes. Following removal of the peptides, the cells released less PGs for a further 18 h but then recovered. A large increase in PG synthesis and release occurred from cells cultured with added serum or arachidonic acid (AA) and an interactive effect was demonstrated between them, AA having a greater stimulatory effect on PG released in the presence of serum. However, in all cases oTP-1 and IFN continued to attenuate prostaglandin release. We conclude that the IFNs act directly or indirectly on the prostaglandin synthase enzyme.

Ovulation rate (OR) was studied in two experiments using mature Border Leicester × Merino ewes in which oestrous cycles were synchronized using a prostaglandin analogue. In both experiments a basal ration of 500 g of lucerne/barley pellets was provided. In the first experiment, ewes were fed individually iso-energy supplements of 500 g of either peas, lupins, soybean pellets or lucerne/barley pellets. The ovulation studied at laparoscopy occurred approximately 34 days after starting the supplementary feeding. Ewes fed lupins or soybean pellets had higher (P < 0.05) OR's than the ewes fed the other diets. In the second experiment, ewes were fed either iso-protein supplements of peas or lupins or casein supplement (170 or 100 g of protein) either formalin treated or untreated. The ovulations studied at laparoscopy occurred approximately either 17 or 34 days after the first feeding of the supplement. Follicle stimulating hormone (FSH) levels in plasma were measured over the 8 days prior to the second ovulation. There were no differences (P < 0.05) in OR's at the first ovulation. However, by the second, ewes fed peas had the highest (P < 0.05) OR while those fed lupins or protected casein had similar OR's. These tended to be higher than in the ewes fed untreated casein. FSH levels were generally higher from 8 days to 3 days prior to ovulation in ewes which were to have twin ovulations compared to those having single ovulations. The results confirm that feeding high energy or high protein will increase OR. There are independent effects of energy and protein. The results suggested that the ovulation rate may be related to FSH levels.

The effect of prostaglandin F2alpha (PGF2alpha) on the sperm output of six boars was investigated in two studies. Although PGF2alpha did not significantly affect sperm numbers in the ejaculate, a significantly longer (P less than 0.05) ejaculation of the sperm rich fraction occurred following injection of PGF2alpha. In the second study it was found that PGF2alpha produced a 49% increase (P less than 0.05) in the number of sperm in the sperm rich fraction of the ejaculate. The implications of these results on artificial breeding are discussed.

Publisher Summary This chapter discusses selective binding of gonadotrophins and the control of follicular growth and atresia. The number of ovarian follicles developing to a stage, at which ovulation is possible, is determined by the interaction of the rate at which primordial or nonproliferative follicles are induced to enter the proliferative phase of growth and the proportion of proliferative follicles that undergo the degenerative process—atresia. The rate at which follicles are influenced by the hormonal milieu to progress through the various growth phases to become capable of ovulation can also be an important determinant at particular stages of the reproductive cycle. Changes within the follicular components or environment will alter the growth and maturation of the follicle and can lead to atresia. Atresia can represent many different processes depending on the stage of follicular development and the follicular tissue being examined. Follicular growth and maturation, particularly from the time of antrum formation, depends on the support of pituitary gonadotrophins.

Publisher Summary This chapter discusses the hormonal control of lactation. Lactation is an essential part of the total reproductive process in mammals so it is important that the onset and duration of lactation is timed to coincide with the demands of the offspring. Many of the hormones controlling pregnancy and parturition also play an important role in the establishment and maintenance of lactation. There are three important phases of lactation: (1) mammogenesis—the development and proliferation of the mammary apparatus in preparation for milk secretion; (2) lactogenesis—the initiation of milk secretion; and (3) galactopoiesis—the maintenance of milk secretion. All these processes are under endocrine control and the transition from one lactational phase to another coincides with an alteration of the relative proportions of various hormones. The chapter discusses a study to examine the importance of the various hormones implicated in the control of lactation in ewe. This study used the ewe that was artificially induced to lactate by a combination of estrogen, progesterone and glucocorticoid treatment as a model to study the hormonal control of lactation.

Publisher Summary The blastocysts of quite a number of species can produce a variety of agents capable of influencing endometrial and ovarian function in the preimplantation period. However, definitive involvement of those agents in the endometrial processes prior to and during implantation remains conjectural. It is paradoxical that in the rat, there is good evidence for an influence of prostaglandins and estradiol on the endometrium, yet the blastocysts of rat apparently lack the capacity to produce those agents. A relatively passive role of the blastocyst is suggested in the rat. By contrast, in ungulates, where there is considerable growth and expansion of the blastocyst prior to attachment, there is good evidence for an influence of the blastocyst on endometrial metabolism and secretion but the nature of the agents responsible is not known. Of the blastocyst factors, the luteotrophic properties of estradiol in pigs and CG in primates and the antiluteolysin, trophoblastin, in sheep seem best established. The chapter discusses the relationship of the blastocyst and endometrium in primates.

The luteotrophic properties of LH were examined by determining whether this hormone could overcome the luteolytic action of Prostaglandin F 2α (PGF 2α ) in vivo . Sheep with ovarian autotransplants were given intra-arterial infusions of LH (10 μg/h for 6 h). PGF 2α (5 μg/h) was then added to the infusate and the infusion continued for 6 hours. In all cases, LH failed to counteract the effect of PGF 2α and luteolysis resulted.

Sheep fetal blood cells contain an active 17β-hydroxy steroid oxidoreductase which catalyses the interconversion of estrone and estradiol-17β and may play an important role in the metabolism of estrogens in the sheep fetal-placental unit.

NAD dependent 20α-hydroxysteroid-dehydrogenase activity has been localized using a histochemical method in the walls of the foetal blood vessels which ramify through the tertiary villi of the human term placenta. The physiological significance of this finding with respect to the foetal placental circulation of gestagens is discussed.