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C. S. T. Pow and L. Martin

The ovarian–uterine vasculature was examined in three Australian species of flying fox (Pteropus scapulatus, P. poliocephalus and P. alecto). Vascular casts and histological sections were used to determine the relationship between the blood supply and the localized endometrial reaction, which occurs ipsilateral to the ovulating ovary. The ovarian artery coils extensively just cranial to the ovary, gives off a branch to the ovary and continues caudally as the major vessel supplying the cranial tip of the uterus, where it anastomoses with the smaller uterine artery. The coil of the ovarian artery is completely enclosed by a venous sinus that drains the cranial pole of the ovary. The ovary is heavily encapsulated, with primordial follicles restricted to the caudal pole; thus, the corpus luteum is completely internal and placed cranially, close to the coil of the ovarian artery. This arrangement would allow countercurrent or crosscurrent transfer of ovarian steroids from ovarian vein to ovarian artery and on to the cranial tip of the ipsilateral uterine horn. The steroids could thus reach high concentrations locally and generate localized endometrial growth. Cranial to the coil, the ovarian artery is enclosed in a venous sinus that derives from uterine as well as ovarian veins. This would allow countercurrent transfer of bioactive substances from uterus to ovary.

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R. G. WALES, L. MARTIN and T. O'SHEA

Summary.

Adult does were inseminated with a constant number of spermatozoa in different volumes of diluent or with varying numbers of spermatozoa in a constant volume. The number of spermatozoa required for maximum fertility was 1 × 106; 50% of does littered when inseminated with 1 to 2 × 105 cells and inseminations with 2 to 4 × 104 cells were sterile. Even when the number of spermatozoa approached the minimum for fertility, increased dilution rates did not decrease the numbers of does kindling. Some litters were obtained with semen diluted 1 in 10,000 with calcium-free Krebs'-Ringer phosphate.

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J. E. Norman, L. M. Ward, W. Martin, A. D. Cameron, J. C. McGrath, I. A. Greer and I. T. Cameron

The purpose of this study was to determine the relaxant effects in vitro of two nitric oxide donors, glyceryl trinitrate and sodium nitroprusside, which are currently available for use in vivo, on contractions of non-labouring myometrium from pregnant women. Since nitric oxide also mediates relaxation by increasing the concentration of cGMP, sensitivity to 8-bromo-cGMP (a cGMP analogue) was also determined. The effects of the K+-channel opener lemakalim and of the Ca2+-channel blocker nifedipine were studied for comparison. After the addition of glyceryl trinitrate (0.1–100 μmol l−1), sodium nitroprusside (0.1–100 μmol l−1) or 8-bromo-cGMP (0.001–3 mmol l−1), the spontaneous rhythmic contractility of myometrial strips was inhibited in a concentrationdependent manner: the maximum inhibition produced by the highest tested concentration of each drug was 40 ± 7%, 53 ± 8% and 39 ± 8% of the original degree of contraction, respectively. Myometrial contractions were completely abolished by lemakalim and by nifedipine and verapamil at concentrations of ≥ 10−5 mol l−1. The nitric oxide donors, glyceryl trinitrate and sodium nitroprusside, attenuate myometrial contractions and are therefore useful as tocolytic agents. However, at equimolar concentrations in vitro, the ability of glyceryl trinitrate and sodium nitroprusside to attenuate myometrial contractions is less than that of lemakalin, nifedipine and verapamil. Controlled trials are required to determine the side-effects and clinical efficacy of each of these agents in vivo.

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C Viñoles, B L Paganoni, K P McNatty, D A Heath, A N Thompson, K M M Glover, J T B Milton and G B Martin

In adult ewes, we tested whether ovarian function, including the response to short-term supplementation, was affected by the nutrition of their mothers during the pre-/post-natal period. A 2×2 factorial design was used with nutrition in early life (low or high) and a 6-day supplement (with or without) as factors. All ewes received three prostaglandin (PG) injections 7 days apart, and the supplement (lupin grain) was fed for 6 days from 2 days after the second until the third PG injection. We measured reproductive and metabolic hormones, studied follicle dynamics (ultrasonography), and evaluated granulosa cell numbers, aromatase activity and oestradiol (E2) concentrations in follicular fluid in healthy follicles at days 3 and 7 of supplementation. Ovulation rate was increased by 25% by exposure to high pre-/post-natal nutrition (1.5 vs 1.2; P<0.05), in association with a small decrease in FSH concentrations (P=0.06) and a small increase in insulin concentrations (P=0.07). The number of healthy antral follicles was not affected. Acute supplementation increased the number of granulosa cells (3.7±0.2 vs 3.0±0.2 million; P<0.05) in the largest follicle, and the circulating concentrations of E2 (4.6±0.3 vs 3.9±0.3 pmol/l; P<0.05) and glucose (3.4±0.03 vs 3.3±0.03 mmol/l; P<0.01). Both early life nutrition and acute supplementation appear to affect ovulation rate through changes in glucose–insulin homoeostasis that alter follicular responsiveness to FSH and therefore E2–FSH balance.

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A. R. Scanlon, S. J. Sunderland, T. L. Martin, D. Goulding, D. O'Callaghan, D. H. Williams, D. R. Headon, M. P. Boland, J. J. Ireland and J. F. Roche

Two experiments were conducted in cyclic beef heifers to determine whether active immunization against bovine inhibin α 1–26 Gly-Tyr (bINH) affected follicular dynamics, hormone concentration or ovulation rate. In Expt 1, heifers (n = 9) were actively immunized against bINH conjugated to human α globulins (HAG) using bisdiazotized benzidine in non-ulcerative Freund's adjuvant (NUFA; primary on day 0; booster injections on days 53, 84 and 116 using conjugated bINH and on days 176 and 366 using unconjugated bINH; ten heifers were used as controls). Ovaries were examined daily using ultrasound scanning (days 70–155 and 384–391) and corresponding blood samples were collected for bINH antibody titre, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestradiol determinations. Four treated and four control heifers were injected with 10 μg gonadotrophin-releasing hormone (GnRH) on day 386 (day 2 of the oestrous cycle). Although bINH-immunized heifers had variable antibody titres ranging from 4 to 50% I125-labelled bINH bound to serum diluted 1:2000, ovulation rate was unaffected. In oestrous cycles with three dominant follicles, the ovulatory follicles grew faster (2.5 ± 0.2 versus 1.6 ± 0.3 mm day−1; mean ± sem), had shorter durations of growth (5.7 ± 0.8 versus 9.6 ± 1.6 days) and duration of detection (7.5 ± 0.8 versus 12.0 ± 2.4 days) in immunized heifers. Mean concentrations of FSH, LH and oestradiol were unaltered in most cases during oestrous cycles in bINH-immunized compared with control heifers. There was no significant difference in the percentage increase in FSH or LH, after GnRH injection, between control and immunized heifers. As ovulation rate was unaltered in the first experiment, a second similar study was designed using a different immunization protocol. In Expt 2, heifers were immunized with bINH conjugated to human serum albumin using glutaraldehyde with the following doses: 0.0 (control; n = 7), 0.33 (n = 7), 1.0 (n = 8) and 3.0 (n = 7) mg. Three booster immunizations were given 33, 66 and 209 days after primary immunization. Immunization increased the number of oestrous cycles with multiple ovulations (42 of 132 (32%) oestrous cycles examined) compared with controls (1 of 30 (3.3%) oestrous cycles examined). Neither titre nor ovulation rate was affected by dose of bINH used. In summary, following bINH immunization, ovulation rate was not increased despite changes in follicular dynamics in Expt 1, but was increased in 32% of oestrous cycles in Expt 2. We conclude that immunization protocols can affect responsiveness of heifers to bINH immunization, and that immunization against inhibin can increase ovulation rate.