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  • Author: J. G. Watson x
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R. L. Matteri, J. G. Watson and G. P. Moberg

Summary. This study examined the effects of varying treatment durations and doses of adrenocorticotrophin (ACTH) as well as restraint stress on the LH response to exogenous LHRH. Injection of 80 i.u. of a concentrated ACTH preparation at 11, 6, 3 or 1·5 h before LHRH administration was effective in suppressing the LH response. Injection of 40, but not 20 or 10, i.u. ACTH 3 h before an LHRH challenge inhibited the magnitude of the LH response, while cortisol values did not vary between ACTH doses. Injection of 200 μg of synthetic ACTH1–24 also resulted in a reduced LH response when given 3 h before LHRH. Restraint stress caused elevated corticosteroid levels and reduced LHRH responsiveness. The results of this study suggest that stress may cause an inhibition of pituitary gland ability to respond to LHRH by way of an hormonal component of the adrenocortical axis. A glucocorticoid-independent mechanism may be involved.

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T. E. Adams, B. M. Adams and J. G. Watson

Summary. Blood samples were collected every 15 min for 6 h during the follicular (1 day before oestrus), and early (Days + 1 to + 3), mid- (Days + 4 to + 8), and full (Days + 9 to +14) luteal phases of the oestrous cycle. Serum concentrations of immunoactive LH were measured by radioimmunoassay. The biological activity of serum LH was determined by an in-vitro bioassay that uses LH-induced testosterone production from mouse interstitial cells as an endpoint. Only ovine and bovine LH and hCG had appreciable activity in this bioassay. The temporal pattern of secretion of bioactive LH paralleled the secretory pattern of immunoactive LH at all stages of the ovine oestrous cycle. However, the secretory pattern itself varied regularly through the oestrous cycle. The frequency of secretory excursions of LH was highest during the follicular phase (6·2 ± 0·9 pulses/6 h) and was progressively reduced through the luteal phase (1·1 ± 0·1 pulses/6 h during full luteal phase). Conversely, amplitude of secretory excursions of immunoactive LH was low during the follicular phase (0·79 ± 0·08 ng/ml) and significantly (P < 0·05) increased during the mid- and full luteal phases (1·49 ± 0·10 and 2·37 ± 0·20 ng/ml, respectively). The biopotency of LH (bioactive LH/immunoactive LH) at the peak of secretory excursions was 1·00 ± 0·03 during the follicular phase, 0·66 ± 0·02 during the mid-luteal phase, and 1·18 ± 0·19 during full luteal activity. The biopotency of LH was markedly reduced during the preovulatory surge of gonadotrophin. During the full luteal phase each pulse of LH secretion was associated with an abrupt increase in secretion of progesterone. These results indicate that both the quantitative and qualitative character of serum LH varies through the oestrous cycle of the sheep.

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T. E. Adams, J. F. Quirke, J. P. Hanrahan, B. M. Adams and J. G. Watson

Summary. Rates of ovulation differed significantly (P < 0·01) among ewes of the different genetic lines. However, of the reproductive characteristics studied, only progesterone concentration at the height of luteal function, duration of oestrus, and interval from onset of oestrus to peak of the preovulatory gonadotrophin surge showed significant positive association with rate of ovulation. The pattern of secretion of LH during the periovulatory period did not differ in the Galway and Finnish Landrace breeds. The total amount of LH secreted during the preovulatory surge did not differ amongst lines. Similarly, no difference in the plasma concentration of LH at the height of the preovulatory surge was noted among Galway and reference Finnish Landrace lines. However, the concentration of LH at the height of the surge was significantly (P < 0·05) reduced in the selected Finnish Landrace line. Plasma concentrations of FSH during the preovulatory period were significantly (P < 0·05) elevated in the breed (Galway) with the lowest prolificacy. When contrasted with either of the Finnish Landrace lines, the magnitudes of the preovulatory surge of FSH and the secondary surge of FSH were significantly greater (P < 0·05) in Galway ewes. These results suggest that genetic difference in rate of ovulation among sheep breeds is not tightly coupled to quantitative differences in plasma concentration of gonadotrophic hormones during the periovulatory period.

Keywords: gonadotrophins; periovulatory period; ovulation rate; prolific sheep

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Paul J Booth, Peter G Humpherson, Terry J Watson and Henry J Leese

Preimplantation embryos can consume and produce amino acids in a manner dependent upon the stage of development that may be predictive of subsequent viability. In order to examine these relationships in the pig, patterns of net depletion and appearance of amino acids by in vitro produced porcine preimplantation embryos were examined. Cumulus oocyte complexes derived from slaughterhouse pre-pubertal pig ovaries were matured for 40 h in defined TCM-199 medium (containing PVA) before being fertilised (Day 0) with frozen-thawed semen in Tris–based medium. After 6 h, presumptive zygotes were denuded and cultured in groups of 20, in NCSU-23 medium modified to contain 0.1 mM glutamine plus a mixture of 19 amino acids (aa) at low concentrations (0.02–0.11 mM) (NCSU-23aa). Groups of 2–20 embryos were removed (dependent on stage) on Day 0 (1 cell), Day 1 (two- and four-cells), Day 4 (compact morulae) and Day 6 (blastocysts) and placed in 4 μl NCSU-23aa for 24 h. After incubation, the embryos were removed and the spent media was analysed by HPLC. The net rate of amino acid depletion or appearance varied according to amino acid (P < 0.001) and, apart from serine and histidine, stage of development (P < 0.014). Glycine, isoleucine, valine, phenylalanine, tryptophan, methionine, asparagine, lysine, glutamate and aspartate consistently appeared, whereas threonine, glutamine and arginine were consistently depleted. Five types of stage-dependent trends could be observed: Type I: amino acids having high rates of net appearance on Day 0 that reached a nadir on Day 1 or 4 but subsequently increased by Day 6 (glycine, glutamate); Type II: those that exhibited lower rates of net appearance on Days 0 and 6 compared with the intermediate Days 1 and 4 (isoleucine, valine, phenylalanine, methionine, arginine); Type III: amino acids which showed a continuous fall in net appearance (asparagine, aspartate); Type IV: those that exhibited a steady fall in net depletion from Day 0 to Day 6 (glutamine, threonine); Type V: those following no discernable trend. Analysis of further embryo types indicated that presumptive polyspermic embryos on Day 0 had increased (P < 0.05) net rates of leucine, isoleucine, valine and glutamate appearance, and reduced (P < 0.05) net rates of threonine and glutamine depletion compared with normally inseminated oocytes. These data suggest that the net rates of depletion and uptake of amino acids by pig embryos vary between a) amino acids, b) the day of embryo development and, c) the type of embryos present at a given stage of development. The results also suggested that the net depletion and appearance rates of amino acids by early pig embryos might be more similar to those of the human than those of the mouse and cow.

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X. Zhang, G. M. Kidder, A. J. Watson, G. A. Schultz and D. T. Armstrong

The sensitive mRNA phenotyping technique of reverse transcription–polymerase chain reaction was used to demonstrate that insulin receptor mRNA is present in rat embryos during the preimplantation period. In addition, mRNA encoding insulin-like growth factor (IGF) type I and type II receptors have also been detected in rat preimplantation embryos. IGF-I mRNA was not detected in preimplantation embryos but was found in oviducts and uteri of prepubertal and early pregnant rats. IGF-II mRNA was present in both embryos and in oviducts and uteri during the preimplantation period. These findings suggest that insulin and IGF-I could influence early embryo development in endocrine or in paracrine fashions, whereas IGF-II may have an additional autocrine mode of action in affecting preimplantation embryos in rats.

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T. D. G. Watson, L. Burns, C. J. Packard and J. Shepherd

The incidence of hyperlipaemia in ponies is highest in mares in late gestation and then early in lactation. Plasma lipid and lipoprotein concentrations were measured to establish the metabolic basis for this and the lipoprotein composition of six healthy Shetland ponies was analysed before pregnancy, in the last six weeks of gestation and one month after foaling. In the pregnant ponies, the concentrations of cholesterol and triglyceride were significantly increased (both P < 0.05) because of increased concentrations of high density lipoproteins (HDL) and very low density lipoproteins (VLDL), respectively (both P < 0.05). The VLDL were significantly enriched in triglyceride and depleted of protein (P < 0.05 in each case), with the majority of cholesterol in the free rather than esterified form. These changes appeared to reflect increased hepatic triglyceride synthesis and VLDL secretion because the activities of lipoprotein lipase and hepatic lipase, the enzymes responsible for the catabolism of VLDL and their remnants, were unaltered. After foaling, the concentrations of triglyceride and VLDL decreased significantly (both P < 0.05) because of increased lipoprotein lipase activity consistent with the induction of the enzyme in mammary tissue to provide for milk fat synthesis. Plasma cholesterol and HDL concentrations remained high and non-esterified fatty acid concentrations were significantly increased (P < 0.05). The VLDL remained enriched in triglyceride but had normal cholesterol and protein compositions, although the mass of phospholipids was reduced. The changes in plasma VLDL concentration and composition found in the pregnant ponies mimicked those previously reported in ponies with hyperlipaemia and suggested a metabolic basis for the incidence of the disease in late gestation.

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S. A. A. Bander, S. C. Watson and J. G. M. Shire

Summary. The cumulus oophorus surrounding eggs from C57BL/6 mice was digested by bovine or leech hyaluronidase significantly more rapidly than that surrounding eggs from BALB/c mice. The zona pellucida of C57BL/6 eggs was also more rapidly attacked by pronase. Three other sublines of C57BL showed the same characteristics. Measurements of susceptibility to hyaluronidase and pronase on eggs from the CXB recombinant inbred strains indicated that variation at a minimum of 2 loci affected each character. The lack of correlation between susceptibilities to the 2 enzymes across the recombinant strains implied that these differences separately affect the substrates of the enzymes, rather than reflecting a common difference in the process of oocyte maturation. The variation in susceptibility was unrelated to differences, controlled by the Ped and Qa-2 loci, in the rate of later embryonic cleavage. However, pronase susceptibility was significantly correlated with the early onset of the first cleavage.

Keywords: cumulus; zona pellucida; inbred strains; fertilization; cleavage; mouse