Virgin females of two inbred strains of rats, a Sheffield–Wistar albino (originally derived from Boots Ltd, Nottingham) and a PVG hooded (from the colony of the Department of Zoology, Hull, established from stock of the M.R.C. Laboratories, Carshalton) were used. The strains had been bred in the same premises in Cardiff for 3 years before the experiment and environmental conditions were standardized for all the animals. Diet pellets (Modified Breeding Diet: Pilsbury) and water were freely available. Room temperature was 23–25°C and the artificial lighting schedule was 12 hr light (07.00–19.00 hours)/24 hr. The animals were housed at opposite ends of the room (5·4 × 8·1 × 2·7 m) in mesh-bottomed cages. Females were kept with litter mates until paired; each female remained with the male until a vaginal plug was found or she was obviously pregnant and she was then returned to her litter mates for 14 days before being isolated in a maternity cage. Numbers of young were counted on the day after birth but litters were not handled unless several dead or dying young were seen. The animals were mated at the ages of 8, 12, 16 and 20 weeks during each month of the year. There were 4–8 animals in each group and the time of appearance of vaginal plugs, size of litters and rearing success to weaning at 14 days were recorded.
P. N. Humphreys, D. Bellamy, A. Stevenson and Diana E. Lewis
D. J. Tortonese, P. E. Lewis, H. Papkoff and E. K. Inskeep
Summary. Prepubertal crossbred beef heifers were injected (i.v.) with 50 μg bovine LH every 2 h for 48 h (first injection at 0 h). At 28 h, number and diameter of ovarian follicles were determined by ultrasonic scanning, and unilateral removal of either the ovary bearing the largest follicle (Group UL, N = 5) or the opposite ovary (Group UO, N = 4) was performed; control animals remained intact (Group I, N = 5). Blood samples were taken every 2 h (starting at 0 h) for a 60-h period to assess concentrations of gonadotrophins and oestradiol. Preovulatory-like surges of LH occurred in 0/5, 4/4 and 5/5 heifers for Groups UL, UO and I respectively; the time of the LH surge did not differ between animals in Groups I and UO (mean = 40 h). FSH in Group UL heifers rose to a plateau immediately after unilateral ovariectomy; this pattern was not observed in the other two groups (P < 0·01). The area under the curve for FSH was significantly different (P < 0·05) among groups after 28 h. Preovulatory-like surges of FSH occurred coincidently with those of LH, except for one Group I heifer. An increase in the concentrations of oestradiol between 0 and 28 h was detected in all animals. Profiles of oestradiol during this period did not differ between heifers that had an LH surge (Groups UO and I) and those that did not (Group UL). After 28 h, concentrations of oestradiol declined to basal levels in Group UL heifers, but in the other two groups it was not possible to characterize, by linear, quadratic or cubic regression, any particular pattern of oestradiol before the LH surge. Ovulation, as determined by rectal palpation and concentrations of progesterone, occurred in 0/5, 4/4 and 4/5 animals for Groups UL, UO and I, respectively. All induced luteal phases were of short duration (<9 days). It is concluded that: (1) repeated injections of LH in the prepubertal heifer are able to induce surges of gonadotrophins and formation of a corpus luteum, (2) the ovary containing the largest follicle is required to mediate the stimulatory effect leading to the LH and FSH surges, and (3) the opposite ovary plays no important role in this mechanism.
Keywords: LH; FSH; oestradiol; dominant follicle; prepubertal heifers
K. F. Breuel, P. E. Lewis, E. K. Inskeep and R. L. Butcher
This study investigated whether treatment with progestagen, which improves fertility after early weaning in postpartum cows, altered concentrations of gonadotrophins or development and function of follicles. Patterns of luteinizing hormone (LH), oestradiol and follicle-stimulating hormone (FSH) and of follicular growth before first postpartum ovulation were compared in two experiments. At 17 to 25 days post partum, suckled anoestrous beef cows received an ear-implant containing 6 mg progestagen (norgestomet) for 9 days or served as untreated controls. Calves were weaned from all cows 7 days after initiation of treatment. Cows were observed for oestrous behaviour twice a day until 10 days after weaning. As expected, the proportion of anoestrous cows that formed a corpus luteum with a normal lifespan was greater (P < 0.01) in cows treated with norgestomet (Expt 1, 17 of 24; Expt 2, 18 of 22) than in control cows (Expt 1, 2 of 16; Expt 2, 3 of 18). In general, patterns of secretion of LH and oestradiol and of final growth of the preovulatory follicle did not differ between control and norgestomet-treated cows. However, there was a transient rise in FSH in association with weaning in control cows that did not occur in norgestomet-treated cows. In addition, mean LH increased more rapidly and mean oestradiol was higher during the 3 days immediately before the preovulatory surge of LH in the norgestomet-treated cows (P < 0.01). These alterations in LH, FSH and follicular function, in the absence of any difference in rate of final growth of the preovulatory follicle, may mean that there was a lack of synchrony between follicular maturation and the LH surge in control cows which resulted in ovulation of a follicle that was not at an optimal stage of maturation. In comparison, treatment with norgestomet may partially synchronize follicular maturation and the LH surge.
P. Hooper, E. Smythe, R. C. Richards, C. V. Howard, R. V. Lynch and D. I. Lewis-Jones
The aim of this study was to make unbiased quantitative estimates of the number of T8 cytotoxic cells and T4 helper cells and macrophages in the head and tail of rat epididymides, using newly developed design-based stereological methods in fertile control animals, and to compare these with results from vasectomized animals. The location of these cells within the intra- and interepithelial compartments of the epididymis was also studied. In control animals, both the T4 helper cells and macrophages and T8 cytotoxic cells were found in significantly higher numbers (P < 0.01) in the head interepithelial location than in the intraepithelial site. In addition, there were significantly more (P < 0.01) T8 cytotoxic cells in the tail interepithelial region. Within the head region of vasectomized rats, there was a significant increase in T8 cytotoxic cells in the intraepithelial location (P <0.01), and a decrease in T4 helper cells and macrophages in the interepithelial region (P < 0.05). Serum samples from vasectomized animals, when compared with those from control animals, showed a significant increase in cytotoxic antisperm antibody. This suggests that, in response to the increased spermatozoal antigenic absorption that takes place in the epididymis after vasectomy, the immune system redistributes its T cell subsets to modify the immune tolerance that may occur.