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G. A. Langford and G. J. Marcus

Summary. Progestagen-impregnated vaginal sponges + PMSG were used to synchronize oestrus in crossbred adult ewes which were inseminated 56 h after sponge removal with 0·5 ml diluted semen containing 400, 200, 100, 50 or 25 × 106 spermatozoa per insemination. The diluent was skim milk-citrate or pooled seminal plasma.

There was no difference in reproductive performance due to the insemination medium. Fertility (no. of ewes lambing) after insemination of 400 or 200 × 106 spermatozoa was 68% and was similar to that observed after natural service at progestagen-induced oestrus. When ≤ 100 × 106 spermatozoa were inseminated, fertility fell markedly and the number of lambs per ewe inseminated decreased. A decrease in litter size also occurred. The data indicate that insemination of 200 × 106 spermatozoa, i.e. less than 10% of the number in a single ram ejaculate, allows normal conception rates in progestagen-treated ewes.

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Recently, in a brief communication, Coppola, Ball & Brown (1966) reported an incidence of 17% spontaneous deciduomata in pseudopregnant rats. One to three discrete zones of decidualization per uterus were observed. One of us, (M.C.S.), who has been concerned with the problem of decidualization for many years, has never observed as high an incidence of spontaneous decidualization. Because of the importance of the decidual response and decidual induction as a model system in the study of nidation (Shelesnyak, 1957) and of mammalian tissue growth and differentiation (Shelesnyak, 1962), it is essential to have a reliable index of the efficiency, or lack thereof, in induction of the decidual response under experimental conditions. Any degree of spontaneous decidualization would decrease the reliability of the experimental system by making unreliable such usual criteria as the weight of

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A single intraperitoneal injection of pyrathiazine induces extensive decidualization of the progravid uterus of the rat. This action was considered to be mediated by the release of histamine. The present study was undertaken to show that pyrathiazine, an antihistaminic drug, causes histamine release.

Injection of pyrathiazine in rats produced a characteristic histaminerelease syndrome, and caused a twofold increase in the urinary excretion of histamine. Pretreatment with pyrathiazine protected rats from the lethal effects of challenge doses of histamine-liberator Compound 48/80 but not of histamine.

These actions of pyrathiazine demonstrate that it releases histamine in the rat, and that its effectiveness as a decidual inducer is consistent with the postulated role of histamine in decidual induction.

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Pregnant and pseudopregnant rats were depleted of histamine by treatment with histamine liberator Compound 48/80 or pyrathiazine. The response to decidual induction by systemic histamine release was compared with the response to direct stimulation of the endometrium. The decidual reaction in response to endometrial trauma and to the presence of ova was markedly reduced, whereas systemic induction with pyrathiazine could be prevented completely. These observations support the hypothesis that induction of decidualization by systemic pyrathiazine is mediated by the release of histamine systemically, whereas induction by local stimuli is mediated by release of uterine histamine only.

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B. K. Tsang, L. Ainsworth, B. R. Downey and G. J. Marcus

Summary. Dispersed granulosa and theca interna cells were recovered from follicles of prepubertal gilts at 36, 72 and 108 h after treatment with 750 i.u. PMSG, followed 72 h later with 500 i.u. hCG to stimulate follicular growth and ovulation. In the absence of aromatizable substrate, theca interna cells produced substantially more oestrogen than did granulosa cells. Oestrogen production was increased markedly in the presence of androstenedione and testosterone in granulosa cells but only to a limited extent in theca interna cells. The ability of both cellular compartments to produce oestrogen increased up to 72 h with androstenedione being the preferred substrate. Oestrogen production by the two cell types incubated together was greater than the sum produced when incubated alone. Theca interna cells were the principal source of androgen, predominantly androstenedione. Thecal androgen production increased with follicular development and was enhanced by addition of pregnenolone or by LH 36 and 72 h after PMSG treatment. The ability of granulosa and thecal cells to produce progesterone increased with follicular development and addition of pregnenolone. After exposure of developing follicles to hCG in vivo, both cell types lost their ability to produce oestrogen. Thecal cells continued to produce androgen and progesterone but no longer responded to LH in vitro. These studies indicate that several functional changes in the steroidogenic abilities of the granulosa and theca interna compartments occur during follicular maturation.