Summary. Metabolic adaptations of goat mammary tissue during pregnancy and lactation were monitored in serial biopsies of the tissue. Changes in the synthetic capacity of secretory cells were studied by combining measurements of enzyme activities with short-term culture of mammary explants to measure lactose, casein and total protein synthesis. By these criteria, the main phase of mammary differentiation began in late pregnancy and was essentially complete by Week 5 of lactation, coinciding with the achievement of peak milk yield. While milk yield declined after Week 5, the activities of key enzymes expressed per mg DNA and the rates of lactose and casein synthesis in mammary explants were maintained over a considerable period. The results suggest that changes in the synthetic capacity of epithelial cells may account for much of the rise in milk yield in early lactation, but are not responsible for the declining phase of milk production characteristic of lactation in ruminants.
C. J. Wilde, A. J. Henderson and C. H. Knight
C. J. Henderson, M. J. Hulme and R. J. Aitken
Summary. The notion of a contraceptive vaccine based on gamete-specific surface antigens was first proposed over a decade ago, as the result of in-vitro and in-vivo studies, and in recent years has been the subject of intensive research. In particular, the zona pellucida has attracted much attention as a potential target for immunological intervention in the fertilization process. Such is the rapidly-expanding nature of research into the biochemical and biological characterization of this structure, that a review of the implications for the development of a contraceptive vaccine seems timely.
Keywords: zona pellucida; contraceptive vaccine; antibodies
R. J. Aitken, M. J. Hulme, C. J. Henderson, T. B. Hargreave and A. Ross
Summary. Washed ejaculated human spermatozoa were surface labelled with 125I, using solid phase (iodogen) or enzymic (lactoperoxidase) methods, while membrane components possessing terminal galactose or galactosamine residues were labelled with the galactose oxidase–sodium [3H]borohydride technique. All three procedures revealed the presence of 2 major labelled surface components. The first comprised a broad band of radioactivity migrating just behind the ion front on SDS-PAGE, which could be extracted with chloroform and methanol, suggesting a lipid-like composition. The second fraction exhibited properties consistent with a major glycoprotein component of the human sperm plasma membrane, giving a peak of radioactivity with M r = 20 000, within which a discrete doublet of bands (M r = 17 000 and 19 000) could be resolved by autoradiography. A more detailed analysis of the labelled protein fraction after TCA precipitation revealed a number of other surface components, the major ones of which exhibited M r values of 30 000, 45 000, 66 000, 115 000 000 and 160 000.
Western blot analysis was then used to determine whether any of the surface components described above interacted with the γ-globulin fraction of antisera obtained from patients exhibiting idiopathic autoimmunity against sperm antigens. Using a purified membrane preparation as the target, antibodies were detected against numerous high molecular weight bands with M r values similar to the major components of the human sperm surface (35 000, 45 000, 66 000, 90 000 and 150 000). The nature of the antigens targeted by these antisera did not correlate with the ability of the latter to stimulate or suppress sperm–oocyte fusion.
J. C. Currie, P. A. Houston, A. Henderson and A. P. Payne
Summary. Newborn female Albino Swiss rats received testosterone propionate, dihydrotestosterone benzoate or oestradiol benzoate for 4 days after birth. The neonatal administration of all three hormones maintained neurones of the spinal nucleus of bulbocavernosus (SNB) complex in adulthood at levels intermediate between those found in normal females (∼40 neurones) and those found in normal males (∼220 neurones). Dihydrotestosterone benzoate was the most effective treatment. Oestradiol benzoate, while as potent as testosterone propionate in maintaining SNB neurone numbers, could not maintain the perineal muscles which are their normal target. Dihydrotestosterone benzoate and testosterone propionate maintained both neurones and muscles.
Newborn male Albino Swiss rats received either the aromatase inhibitor 4-OH-androstenedione, or the 5α-reductase inhibitor aza-steroid 17β-N,N-diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one (4-MA). Only neonatal treatment with 4-MA led to reduced SNB neurone numbers in adulthood, but the reduction was modest (−16%). The results of the two experiments suggest that several hormones can maintain SNB neurone numbers in Albino Swiss rats, but that 5α-reduced metabolites of testosterone may be particularly effective.
Keywords: neonate; motor neurones; hormones; perineal muscles; rat
J M Young, S Henderson, C Souza, H Ludlow, N Groome and A S McNeilly
Little is known about the role of activin B during folliculogenesis. This study investigated the expression levels of activin/inhibin subunits (βA, βB, and α), steroid enzyme, and gonadotrophin receptors in theca (TC) and granulosa cells (GC) by QPCR and activin A and B and inhibin A protein levels in follicular fluid (FF) of developing sheep follicles during estrus and anestrus. The effect of activin B on androgen production from primary TC cultures in vitro was also assessed. During folliculogenesis, in anestrus and estrus, FF activin B concentrations and thecal and GC activin βB mRNA levels decreased as follicle diameter increased from 1–3 to >6 mm regardless of estrogenic status. Estrogenic preovulatory follicles had reduced concentrations of FF activins B and A, and TC and GCs expressed higher levels of activin βA mRNA at 3–4 mm, and TCs more inhibin α mRNA at >4 mm stages of development compared with nonestrogenic follicles. Activin B decreased androstenedione production from primary TCs in vitro, an effect blocked by inhibin A. Thus, sheep follicles 1–3 mm in diameter contained high FF levels of activin B, which decreased as the follicle size increased, and, like activin A, suppressed thecal androgen production in vitro, an effect blocked by inhibin. Furthermore, the theca of large estrogenic follicles expressed high levels of inhibin α and activin βA mRNA suggesting local thecal derived inhibin A production. This would inhibit the negative effects of thecal activins B and A ensuring maximum androgen production for enhanced estradiol production by the preovulatory follicle(s).
K. P. McNatty, N. L. Hudson, K. M. Henderson, S. Lun, D. A. Heath, M. Gibb, K. Ball, J. M. McDiarmid and D. C. Thurley
Summary. Overall, significantly more antral follicles ≥ 1 mm diameter were present in Romney ewes during anoestrus than in the breeding season (anoestrus, 35 ± 3 (mean ± s.e.m.) follicles per ewe, 23 sheep; Day 9–10 of oestrous cycle, 24±1 follicles per ewe, 22 sheep; P < 0·01), although the mean numbers of preovulatory-sized follicles (≥5 mm diam.) were similar (anoestrus, 1·3 ± 0·2 per ewe; oestrous cycle, 1·0 ± 0·1 per ewe). The ability of ovarian follicles to synthesize oestradiol did not differ between anoestrus and the breeding season as assessed from the levels of extant aromatase enzyme activity in granulosa cells and steroid concentrations in follicular fluid. Although the mean plasma concentration of LH did not differ between anoestrus and the luteal phase of the breeding season, the pattern of LH secretion differed markedly; on Day 9–10 of the oestrous cycle there were significantly more (P < 0·001) high-amplitude LH peaks (i.e. ≥ 1 ng/ml) in plasma and significantly fewer (P < 0·001) low amplitude peaks (<1 ng/ml) than in anoestrous ewes. Moreover, the mean concentrations of FSH and prolactin were significantly lower during the luteal phase of the cycle than during anoestrus (FSH, P < 0·05, prolactin, P < 0·001).
It is concluded that, in Romney ewes, the levels of antral follicular activity change throughout the year in synchrony with the circannual patterns of prolactin and day-length. Also, these data support the notion that anovulation during seasonal anoestrus is due to a reduced frequency of high-amplitude LH discharges from the pituitary gland.