D Vanmontfort

Developmental changes in immunoreactive inhibin and FSH in plasma of chickens from hatch to sexual maturity

1. The relationship between immunoreactive inhibin and follicle-stimulating hormone (FSH) was studied in male and female chickens from hatch to sexual maturity. Plasma inhibin was estimated by a heterologous radioimmunoassay validated for use in the chicken. FSH was measured by a recently developed homologous radioimmunoassay. 2. In a cross-sectional study, blood samples and gonads were collected from chickens of both sexes at 1, 3, 5, 7, 14, 21 and 28 d after hatching and subsequently at 14-day intervals until 182 d of age. 3. In the female, plasma progesterone concentration (P4) progressively increased during sexual development. The plasma luteinising hormone (LH) concentration rose during the first week after hatching, and fluctuated thereafter, with troughs at 6 and 14 weeks and peaks at weeks 10 and 18. The plasma inhibin and FSH concentrations remained low until the start of puberty and increased simultaneously thereafter. However, from week 18 on, plasma inhibin continued to rise while plasma FSH fell. Hence, FSH and inhibin were positively correlated before puberty, but developed a negative correlation during sexual maturation. 4. In the male, plasma testosterone and LH concentrations increased 38- and 3.7-fold respectively over the period studied. Inhibin and FSH followed similar time courses and were consequently positively correlated. 5. These results suggest sex differences in the role of inhibin in regulating FSH secretion during development. The FSH-inhibin feedback loop may become operational at the onset of sexual maturity in the hens. In male chickens, the similar pattern of inhibin and FSH secretion suggests that inhibin secretion is driven by FSH.

Evidence for the presence of immunoreactive inhibin in extragonadal tissues of ovariectomized ewes

Six ewes were ovariectomized to determine the immediate and long-term effects of removal of ovaries on the immunoreactive concentrations of FSH, LH and inhibin. Three months after ovariectomy, ewes were slaughtered and tissue samples of brain, pituitary, spleen, liver, perirenal fat, lung, kidney, adrenals and uterus were collected to determine the immunoreactive inhibin content. Both gonadotrophins, FSH and LH, increased significantly after ovariectomy. The increase of FSH, however, was more pronounced and remarkably faster than the changes of LH after ovariectomy. Immunoreactive concentrations of inhibin decreased sharply as early as 15 min after ovariectomy and subsequently decreased more gradually until 2 weeks after surgery. From this moment on, the level stabilized at 56% of the initial value. In control ewes, a considerable amount of immunoreactive inhibin is found in tissue samples of ovary, lung, kidney, pituitary and spleen. After ovariectomy, the level of immunoreactive inhibin decreased in spleen and lung samples while an important increase of immunoreactive inhibin is found in adrenals and pituitary. These results demonstrate a differential regulation of LH and FSH after ovariectomy and support an involvement of inhibin only in the immediate changes of FSH after ovariectomy in sheep. They further suggest that the adrenals and the pituitary may be extragonadal sources of inhibin. To explore the eventual contribution of the adrenals to circulating inhibin, dexamethasone (1.4 mg/ewe) and ACTH (200 IU/ewe) were in a following experiment injected intravenously in control and ovariectomized ewes. The lack of any effect of dexamethasone or ACTH on the plasma concentration of immunoreactive inhibin indicate that adrenal inhibin probably does not contribute to circulating inhibin.

Early prenatal survival in relation to the parental environment in sheep: A review

Abstract After multiple egg transfer litter size (LS) in recipient ewes from some breeds was greater than their potential natural size; Finnish Landrace, not Booroola Merino recipients, tended to be superior to recipient ewes from other breeds with a lower natural ovulation rate (OR). In Finnish Landrace and Merino ewes the difference in prenatal survival (PS) between purebred and crossbred litters was small. In Berrichone and Romanov breeds PS was higher in crossbred than in purebred ewes. A significant variation in PS was found between eggs from Finnish Landrace donors. A dam–embryo interaction on PS was present in high and low twinning Merino ewes. Embryos from Romney ewes selected against lamb faecal egg count (LFEC) were more likely to survive than embryos from Romney ewes selected for LFEC. Various translocation types in heterozygous and homozygous combinations in rams and ewes did not influence their overall fertility, probably because of prezygotic selection of gametes. Scrotal heating in Merino rams caused an increased loss of fetuses. Fetal survival in Merino ewes increased as both the number of spermatozoa and feeding level were higher. Lower service activity was linked to lower pregnancy rates (PR) and PS in 1.5-year-old Merino ewes, interacting with the mean duration of oestrus as compared to that in adult Merino ewes. Service activity per ewe, PR and PS in Merino flocks were lower as ram: ewe ratio decreased from 1.0 to 0.5 and 0.25%. In Merino flocks selected for skin folds the percentage of twin births per ewe lambing was lower in hot weather than in Merino flocks selected against skin folds. PR and PS tended to be higher in ewes exposed to Rambouillet rams selected for high prolificacy, compared to Rambouillet rams selected for low prolificacy. PR and PS were lower in Clun Forest ewe lambs than in Clun Forest ewes. Survival of ova from Galway and Romney ewes was greater than that of ewe lamb ova. Conditions in the uteri of both ages were equally favourable. In Galway ewe lambs plasma estrogen concentration 12–36 h after sponge removal was more than 100% greater than in adults. Progesterone levels were similar, also on day 12 of pregnancy. After day 13 progesterone concentration increased at a slower rate and remained lower on day 28 in Clun Forest ewe lambs than in Clun Forest adults. The smaller and more variable preovulatory LH surge in Clun Forest ewe lambs was considered to be evidence of inadequate progesterone priming. These and other data support the suggestion that conditions in the developing follicle and in the reproductive tract between ovulation and the 8–16 cell stage are related to the reduced fertility and PS in very young ewes. It is concluded that endogenous, paragenous and exogenous factors can have similar and interacting effects on PS in sheep.

Induced Stop of Egg Laying Results in a Transient LH-Sensitivity of the Progesterone Producing Cells Both in Vitro and in Vivo

In laying hens, the primary sources of progesterone (P4) are the granulosa cells of the 4-5 largest follicles in the hierarchy of the ovary. During forced moulting, cessation of egg production occurs with ovarian atrophy and a decrease in P4 as well as in luteinizing hormone. While it is reported that follicular atresia as well as the P4 decrease are the result of a reduced luteinizing hormone (LH) stimulation, P4 decrease occurred already during the second or third day after food withdrawal while atresia occurred only several days later. Since P4 decrease at the beginning of moult induction cannot simply be explained by the lack of large follicles the aim of this study was to determine whether the rapid decrease in P4 after food withdrawal is only related to a decreased hypophyseal stimulus and/or a concomitant change in follicular sensitivity as well. Granulosa cells from follicles F, to F4 were collected according to the method of Gilbert et al. (1977). Cell number was estimated with a haemocytometer and viability by trypan blue exclusion technique. Cell suspension was diluted to 105 cells ml-1 in M199 and incubated for 0.5, 1, 2, 4, 8 and 24 h with or without oLH, and P4 secretion in the medium was assayed by RIA. Short-term starvation increased P4 response in vitro to oLH indicating a higher sensitivity of granulosa cells of follicles from all classes to oLH. In an additional experiment, in vivo injections of different doses of LH also showed an enhanced increase in P4 the first days of food restriction. Therefore, the rapid decrease in P4 after feed withdrawal is not due to a decreased follicular sensitivity but to a decrease in stimulatory factor(s).

Autocrine/paracrine effects of inhibin and activin in chicken ovary

inhibin and/or activin and if this relative contribution to molecules with an opposing biological activity is mathematically dependent on the a / b A ratio. SAFI, M., BUYS, N., ONAGBESAN, O.M., BLEUGELS, B. & DECUYPERE, E. (1998) Quantification of inhibin/activin a and b A subunit messenger ribonucleic acid by competitive reverse transcription-polymerase chain reaction in chicken granulosa cells during follicular development. Biology of Reproduction, 59: 1047–1054.

Circulating levels of inhibin and FSH during the oestrous cycle in 4 genotypes of sheep with different reproductive performances

Abstract Two relatively fecund genotypes (Flemish Milksheep and KU-Lovenaar—an F 2 cross-bred originating from pure-bred Suffolk and Flemish Milksheep) and two meat-type breeds (Texel and Suffolk) were compared regarding their plasma inhibin and FSH levels. Oestrus was synchronised by progestagen-impregnated sponges. Blood sampling, starting 12 h after the sponge removal, continued twice daily for 21 consecutive days. To localise the pre-ovulatory LH peak and to determine the cycle length, sampling at 2 h intervals was carried out during the first 3 days and the last 4 days of the 21-day period. Immunoreactive inhibin was measured by a 5-24 α -subunit inhibin assay as well as by an assay based on an antiserum against native bovine 31-kDa inhibin (Monash assay). Changes in plasma concentration of immunoreactive FSH and LH during the oestrous cycle agree with the literature data. The profiles generated by the two different inhibin RIAs were different and showed a negative correlation during the periovulatory phase and on days 9–11. No characteristic pattern could be observed during the oestrous cycle. Significant breed differences were observed for 5-24 α -subunit inhibin as well as for inhibin, measured by the Monash assay. The significantly higher ( P α -subunit inhibin and lower inhibin (Monash assay) concentration in Texel ewes resulted in a differential ratio of both inhibin measurements for the Texel in comparison with the other breeds. No significant breed differences for FSH were observed during the oestrous cycle. It is concluded that, although significant breed differences in inhibin concentration are observed, the FSH-inhibin interaction is not the only factor responsible for breed differences in ovulation rate.

Prenatal survival in relation to peri-ovulatory phenomena and the site of ovulation in sheep: A review

Abstract Differences in ovarian follicular dynamics between ewe breeds and between lines within breeds were shown to result from a different follicle recruitment and selection process. Synchrony and asynchrony of embryos were shown to depend largely on luteinizing hormone (LH), progesterone and oestrogen levels in ewes before, during and post-mating. GnRH therapy suggested that the endocrine environment prior to ovulation has a fundamental influence on luteal function and hence on prenatal survival (PS). The decreasing effect of multiple ovulation on uterine efficiency was higher in androstenedione-immune Border Leicester×Merino (BL×M) than in immunized BL×Booroola Merino (BM) ewes. Exogenous progesterone increased lambing rate in Polypay (P) but not in Targhee ewes. The 200% of maintenance feeding level reduced plasma progesterone concentrations on day 12 near the threshold critical for embryo survival in M ewes but not in BL×Scottish Blackface ewes. The latter maintained pregnancy rate (PR) and PS at the same levels as the controls. In unilaterally twin ovulating ewes, foetal mortality was significantly lower in ewes in which distributive embryo migration occurred. Within this ovarian class, survival was lower in the Cheviot, probably because of a lower migration frequency, than in the Blackface breed. More embryos migrated in unilaterally twin ovulating M ewes in autumn than in summer mating, with a higher incidence of loss of one embryo in the latter season. A higher incidence of successful migration was observed in unilaterally twin ovulating BL×M than in M ewes. The higher mortality of a migrating embryo, compared with the nonmigrating, was attributed to an asynchronous environment in the contralateral horn, since ovine trophoblastine (oTP-1) might have preferentially altered the uterine environment of the ipsilateral horn. Studies on oTP-1 and protein in uterine flushings and on conceptus development at day 13 in ewes that displayed short or long oestrous cycles, as well as further studies on unilaterally ovariectomized ewes with two or three conceptuses, suggest that the ovine embryo stimulates the migratory process locally, in interaction with the dam. This review raises the question whether and to what degree pre-, peri-, as well as, post-ovulatory phenomena and the site of ovulation can be interacting factors for determining PS, especially in multiple ovulating sheep as a function of breed and breed–environment interactions.

Developmental expression of activin/inhibin α and β A subunit genes in the gonads of male and female chick embryos

catecholamines in the various sizes of ovarian follicles were found prior to lay. During sexual maturation, catecholamine concentrations in white (1–8 mm) and small yellow (8–14 mm) follicles decreased significantly. Thus, the results of this study show that in the ovary of maturing pullets, the concentration of catecholamines changes as in the growing follicles of mature laying hens. It is interesting that other biogenic amines like serotonin (Paczoska-Eliasiewicz and Rz sa, 1988) and histamine (Paczoska-Eliasiewicz and Rz sa, 1997, 1998) exhibit a similar pattern of changes during follicular development. Based on the results of the present study and our earlier observations that in vitro NA affects steroid secretion by chicken ovarian follicles (Rz sa and Paczoska-Eliasiewicz, 1997) we suggest that catecholamines, particularly NA, can exert an influence on the destiny and growth of developing ovarian follicles of the domestic hen.