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The aim of the present study in Booroola ewes, either homozygous (BB) or non-carriers (++) of the Fec^B gene, was to test the specificity of the pituitary responses to exogenous hypothalamic releasing hormones by examining the plasma concentrations of FSH, LH, thyroid-stimulating hormone (TSH) and growth hormone (GH) after injecting the animals with different doses of GnRH, thyroid-releasing hormone (TRH) or growth-hormone-releasing hormone, (GHRH) which were administered on separate occasions. The animals (n = 8 per dose) received 0, 3.1 or 12.5 μg of thyroid-releasing hormone and GnRH (i.v.), whereas they (n = 9–13 per dose) received 0, 6.0 or 16.0 μg GHRH (i.v.). For each experiment there were no differences between the genotypes in bodymass or age. Gene-specific differences in the mean pretreatment concentrations of plasma FSH (BB > ++; P < 0.05) but not of LH, TSH or GH were noted. After treatment with GnRH, TRH or GHRH, significant effects of dose were noted for all the hormones; however, a gene-specific effect was observed only for FSH in response to GnRH (BB > ++; P < 0.01) with no genotype × dose interaction (anova). For LH, the effects of genotype and the genotype × dose interaction almost reached significance at the 5% level (genotype, P = 0.055; genotype × dose, P = 0.067). For TSH and GH the respective genotype × dose interactions were not significant. These results support the hypothesis that the Fec^B gene in Booroola ewes influences the release of pituitary hormones in response to hypothalamic releasing hormones only in the case of GnRH, which results mainly in different plasma concentrations of FSH.

Blood samples were collected for 13 days before and 20 days after ovariectomy from carrier (BB) and non-carrier (+ +) ewes of the Booroola Fec^B gene (n = 12 per genotype), at known stages of the oestrous cycle, after which the pituitary glands from these ewes were recovered. Pituitary glands were also collected from cyclic ewes (about day 12; n = 5 per genotype) to compare the effects of ovariectomy on pituitary gonadotrophins. Plasma samples and pituitary extracts were assayed for bioactive (B) FSH, immunoreactive (I) FSH and I-LH. Overall, BB ewes had significantly (P < 0.05) higher plasma I-FSH concentrations than did + + ewes before ovariectomy; the mean value was higher on 16 of the 17 days of the oestrous cycle (P < 0.01). For B-FSH, there were no overall genotypic differences, although the mean for the BB ewes was significantly higher on 13 of the 17 days of the oestrous cycle (P < 0.05), and significantly (P < 0.05) higher between days 13 and 16. No genotypic differences were noted for the plasma bioactive:immunoreactive (B:I) ratio for FSH before ovariectomy. After ovariectomy, there were significant (P < 0.001) increases in plasma for B-FSH, I-FSH and I-LH and a significant (P < 0.05) decrease in the B:I ratio for FSH, irrespective of genotype. Furthermore, BB ewes had significantly (P < 0.05) higher overall concentrations of B-FSH and plasma B:I ratios after ovariectomy than did + + ewes; overall I-FSH concentrations were not significantly different between genotypes but the BB ewes had a higher mean value on 17 of the 20 days after ovariectomy (P < 0.001). With respect to pituitary FSH, there were no significant effects of genotype or ovariectomy on B-FSH or I-FSH contents or concentrations. No genotypic differences were noted in either plasma or pituitary I-LH, except for a higher pituitary I-LH content in BB ewes after ovariectomy. These data show that both ovariectomy and the Fec^B gene cause qualitative and quantitative changes in plasma FSH, but have little effect on pituitary FSH.

Summary. Castrated adult Fec^B Fec^B and Fec ⁺ Fec ⁺ Booroola rams were injected with charcoal-treated bovine follicular fluid (bFF) (a source of inhibin-like activity) or given testosterone implants to examine whether the fecundity gene (Fec^B ) influences sensitivity to negative feedback hormones in males. Mean concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) did not differ between genotypes before treatment. In Expt 1, injections of 5 ml bFF, but not of 1 ml (each given four times at intervals of 8 h), significantly (P < 0·05) depressed concentrations of LH and FSH, but there was no effect of genotype. After treatment, gonadotrophin concentrations returned to pretreatment values and for 2–2·5 days scaled (divided by pretreatment mean) LH values (235 ± 49 for Fec^B Fec^B and 96 ± 26% for Fec ⁺ Fec ⁺ rams; P < 0·05) and scaled FSH values (106 ± 5 for Fec^B Fec^B and 85 ± 5% for Fec ⁺ Fec ⁺ rams; P < 0·05) were significantly higher in Fec^B Fec^B than in Fec ⁺ Fec ⁺ rams in the group that received 5 ml bFF. Irrespective of genotype, treatment with 5 ml bFF did not reduce mean FSH to concentrations observed in testis-intact rams.

In Expt 2, Silastic envelopes were implanted subdermally to give physiological or supraphysiological circulating concentrations of testosterone. Both doses significantly reduced scaled LH values in a biphasic manner, such that there was an initial suppression followed by a short-lived increase. During the initial period of suppression in the lower dose group, mean scaled LH values were significantly higher in Fec^B Fec^B than in Fec ⁺ Fec ⁺ rams (48·3 ± 7·5 versus 23·1 ± 5·5%; P < 0·05). Low doses of testosterone decreased LH pulse frequency in both genotypes but decreased (P < 0·05) pulse amplitude and mean concentrations in the Fec ⁺ Fec ⁺ animals only. In nonimplanted control rams, mean LH concentrations (in samples taken every 10 min for 12 h) were significantly lower in Fec^B Fec^B than in Fec ⁺ Fec ⁺ rams (0·6 ± 0·2 versus 1·3 ± 0·1 ng ml⁻¹; P < 0·05). The mean FSH response to testosterone was not related to genotype.

These data suggest that expression of the Fec^B gene results in an altered sensitivity of the pituitary gland to changes in negative feedback from testicular hormones and that, irrespective of genotype, neither testosterone nor inhibin-like activity alone can fully control FSH secretion in castrated rams.

Keywords: Booroola; follicular fluid; testosterone; LH; FSH; ram

Summary. Before castration, the mean plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) did not differ between FF and ++ Booroola rams. After castration, mean LH and FSH concentrations increased after 8 h, and for the next 14 days the rate of increase in FSH, but not LH, secretion was significantly faster in FF than in ++ rams (P < 0·05). Mean FSH concentrations over this period were significantly higher in FF than in ++ rams (P < 0·05). In both genotypes, the ranked FSH values did not significantly change their order over time, i.e. a significant within-ram effect was noted (P < 0·05). Repeated-measures analysis of variance indicated a significant effect of genotype on mean FSH secretion (P < 0·05) and a significant effect of sire in the FF (P < 0·05), but not the ++ (P = 0·76), genotype. From Day 28 to Day 58 after castration, FSH and LH concentrations were variable and no overall increases in concentrations were observed. The mean concentrations of both hormones over this period were not related to genotype.

There were no gene-specific differences in pulsatile LH secretion 14 weeks after castration. However, the mean LH, but not FSH, response to a bolus injection of 25μg of gonadotrophin-releasing hormone (GnRH) was significantly higher in FF than in ++ rams (P < 0·05) and this was not significantly affected by sire.

These studies support the hypothesis that the F gene is expressed in adult rams, in terms of pituitary responsiveness to an injection of GnRH and to the removal of the testes, but it is not clear from this study whether the influence of sire is related to or independent of the apparent gene-specific differences.

Keywords: Booroola; rams; LH; FSH; castration; fecundity

Summary. No gene-specific differences were found with respect to LH or testosterone pulsatile secretion (over 12 h), or in 12 hourly mean FSH concentrations in adult Booroola FF and ++ rams. Also, no differences between genotypes in the LH response to an injection of testosterone propionate, the FSH response to an infusion of bovine follicular fluid, or the testosterone response to injections of PMSG were noted. However, during the phase of seasonal testicular development, mean testosterone pulse amplitude (over 12 h) and the FSH response to 25 μg GnRH were higher in FF than in ++ rams (P < 0·05); there were also significant effects of sire (P < 0·05 in FF genotype only) and litter size (P < 0·05) on testosterone pulse amplitude and GnRH-stimulated FSH release, respectively. During the breeding season, mean LH, but not FSH, concentrations were higher in FF than in ++ rams, after an injection of 0·5 μg GnRH; LH release was not affected by sire or litter size (P > 0·05).

Long-term studies revealed that the FF rams were born in significantly larger litters, they weighed significantly less than ++ rams (P < 0·05), and that bodyweight was significantly correlated (P < 0·05) with litter size. There were no differences in testis size, and testis size was not significantly correlated with bodyweight. There was a strong tendency (P = 0·056) for overall mean FSH concentrations, measured weekly for 9 months, to be highest more often in FF than in ++ rams.

Collectively, these results suggest that the F gene is expressed at the level of the pituitary gland in adult males, although in intact animals gene-specific differences are suppressed by the negative effect of hormones from the testis.

Keywords: Booroola rams; GnRH; LH; FSH; fecundity

Summary. The cAMP outputs by granulosa cells from 3–4·5 mm diameter (medium) follicles of Booroola FF ewes were similar to those by cells from ≥5 mm diameter (large) follicles of ++ ewes with respect to time or dose of FSH, cholera toxin or forskolin. Likewise, the cAMP outputs by cells from 1–2·5 mm diameter (small) FF follicles were similar to those by cells from small and medium ++ follicles with respect to time or dose of FSH, cholera toxin or forskolin. At FSH, cholera toxin or forskolin doses of 1 μg/ml, 0·5 μg/ml and 10 ⁻⁴ m respectively, the granulosa cell cAMP outputs of medium FF or large ++ follicles were approximately 2-fold (P < 0·05) higher than in the respective small FF and medium ++ follicles. The effects of cholera toxin plus forskolin or FSH plus forskolin were additive irrespective of genotype or follicle size, with significant differences (P < 0·05) observed between follicle sizes but not genotype. No differences were noted between cholera toxin plus forskolin or FSH plus forskolin on granulosa cell cAMP output.

For the FSH and forskolin treatments, increased mean cAMP outputs were evident after 10 min, whereas after cholera toxin treatment they were not evident until after 20 min incubation. For all treatments the rate of cAMP production tended to slow down after 40–60 min.

Pre-incubation of granulosa cells with pertussis toxin subsequently resulted in a significantly greater (P < 0·05) FSH-induced output of cAMP relative to the untreated controls irrespective of follicle size. However, no gene-specific differences were noted when the cAMP outputs of cells from medium or small FF follicles were compared with cells from large or small–medium ++ follicles respectively.

These results indicate that the activity (or composition) of the regulatory and catalytic components of adenylate cyclase in the FF granulosa cells change in a manner similar to those observed in ++ cells with the only difference being that the increases in cyclase in FF ewes occurs as follicles enlarge from 1–2·5 to 3–4·5 mm in diameter, whereas in ++ ewes they occur as follicles enlarge from 3–4·5 to ≥ 5 mm in diameter. No evidence was found to link the F gene to the granulosa cell cAMP response independently of follicle size. It is suggested that the association between the F gene and the size-specific difference in follicle maturation may be unrelated to the FSH receptor/cAMP generating system.

Keywords: FSH; cholera toxin; pertussis toxin; forskolin; cAMP; granulosa cells; Booroola ewes; F gene

This study investigated the effects of short-term (20 days) ovariectomy, the effects of FSH assay (radioimmunoassay, receptor assay or in vitro bioassay) and of FecB^B genotype on the characteristics of pituitary FSH from Booroola ewes. Pituitary extracts were obtained from ovariectomized homozygous carriers (BB) and non-carriers (++, n = 8 per genotype) and ovary-intact controls (n = 4 per genotype). The extracts (n = 4 per genotype per treatment) were subjected to agarose suspension electrophoresis and the eluates were assayed by the three FSH methods. There were significant effects of ovariectomy (P < 0.01) and assay system (P < 0.05) but not of genotype on the median charge of FSH isoforms. The mean ± sem migration rates for FSH in intact and ovariectomized ewes were 0.469 ± 0.006 and 0.439 ± 0.006 albumin mobility units, respectively (P < 0.01), indicating a shift to more basic isoforms after short-term ovariectomy. When the pituitary extracts were subjected to anion-exchange HPLC, there was a significant (P < 0.01) shift to more basic isoforms in the ovariectomized ewes as shown using agarose electrophoresis, and no gene effects were noted. When the pituitary extracts (n = 4–8 per group) were injected into mature female mice, there were no significant effects of ovariectomy or genotype on the circulating half-lifes of the pituitary FSH isoforms. These results indicate that after short-term ovariectomy, the increase in plasma FSH concentrations is accompanied by a shift in the median charge of pituitary FSH isoforms without any observable change in their metabolic clearance rates. Moreover, the FecB^B gene has little effect on the median charge or half-life of pituitary FSH.

Summary. No gene-specific differences were found during either the luteal or follicular phases of the oestrous cycle in the venous secretion rates of ovaries or in concentrations of immunoreactive inhibin in peripheral plasma between Booroola ewes that were homozygous carriers (BB) or non-carriers (++) of the Fec ^B gene. In three experiments in which concentrations of plasma inhibin and follicle-stimulating hormone (FSH) were compared, gene-specific differences were noted for FSH (P < 0·05), but no significant correlations were noted between FSH and inhibin for either genotype. Granulosa cells and follicular fluid, but not theca interna, stroma or corpora lutea, were the major intra-ovarian sites of inhibin; no gene-specific differences were noted for inhibin concentrations in follicular fluid or in any of the intra-ovarian tissues. The mean concentrations of inhibin in follicular fluid remained constant irrespective of follicular diameter whereas the mean total contents of inhibin increased significantly with increasing diameter (P < 0·05). Inhibin secretion rates were four times higher in ovaries with oestrogen-enriched follicles (i.e. ≥ 50 ng oestradiol ml⁻¹) than in ovaries with no such follicles (P < 0·01). Moreover, inhibin concentrations were higher in follicular fluid of oestrogen-enriched follicles than in those with low oestrogen (i.e. < 50 ng ml⁻¹; P < 0·05). Ovariectomy resulted in a significant reduction in concentrations of immunoreactive inhibin from plasma (P < 0·01). The residual plasma inhibin in some Booroola ewes was not associated with genotype.

It is concluded that, although antral follicles are a major source of inhibin in Booroola ewes, immunoreactive inhibin is not associated with the Fec ^B gene and is not responsible for the gene-specific differences in concentrations of FSH in plasma.

Keywords: Booroola ewes; Fec ^B gene; inhibin; FSH; peripheral plasma; ovarian secretion rates

Summary. A significant increase in the plasma concentrations of FSH (P < 0·05) and LH (P < 0·001) was observed during the luteal (Days 9–11) phase but not during the subsequent cloprostenol-induced follicular phase in androstenedione-immunized ewes compared to those in control ewes. Over the same time period the geometric mean (and 95% confidence limits) androstenedione antibody titres in the immunized ewes was 1/305 (1/158, 1/590) whereas they were not detectable in the controls. In the subsequent cycle, the ovulation rates were 1·6 ± 0·2 for the immunized ewes and 1·1 ± 0·1 for the control ewes (P < 0·05) and the luteal progesterone concentrations were significantly higher in the immunized ewes compared to the controls (P < 0·01). Collectively, these results suggest that active immunization against androstenedione leads to an increase in the plasma concentrations of both FSH and LH. The results are consistent with the hypothesis that FSH plays a central role in determining the ovulation rate in sheep.

Keywords: FSH; androstenedione immunization; sheep; ovulation rate

The aim of this study in sheep ovaries was to determine the total number of granulosa cells in primordial follicles and at subsequent stages of growth to early antrum formation. The second aim was to examine the interrelationships among the total number of granulosa cells in the follicles, the number of granulosa cells in the section through the oocyte nucleolus, and the diameter of the oocyte. A third aim was to examine whether proliferating cell nuclear antigen labelling occurred in flattened granulosa cells in primordial follicles or was confined to follicles containing cuboidal granulosa cells. The follicles were classified using the section through the oocyte nucleolus by the configuration of granulosa cells around the oocyte as type 1 (primordial), type la (transitory), type 2 (primary), type 3 (small preantral), type 4 (large preantral), and type 5 (small antral). In type 1 follicles, the number of granulosa cells and oocyte diameter were highly variable in both fetal and adult ovaries. Each type of follicle was significantly different from the others (all P < 0.05) with respect to oocyte diameter, number of granulosa cells in the section through the oocyte nucleolus and total number of granulosa cells. Follicles classified as type 2, 3, 4 or 5 each corresponded to two doublings of the total granulosa cell population. The relationships between oocyte diameter and the number of granulosa cells (that is, in the section through the oocyte nucleolus or total population per follicle) could all be described by the regression equation log_e X = a + b log_e Y with the correlation coefficients R always > 0.93. For each pair of variables the slopes (b) for each type of follicle were not different from the overall slope for all types of follicle pooled. Immunostaining for proliferating cell nuclear antigen was observed in granulosa cells in type 1 follicles, as well as in the other types of follicle. These findings indicate that 'flattened' granulosa cells in type 1 follicles express an essential nuclear protein involved in cell proliferation before assuming the cuboidal shape. Thus, when considering factors that regulate specific phases of early follicular growth, it is important to consider: (i) the follicle classification system used; (ii) the animal model studied; (iii) whether type 1 follicles are all quiescent; and (iv) the likelihood that each follicle type represents more than one doubling of the population of granulosa cells.