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G. A. Jahn, N. Alonso and R. P. Deis

Summary. Administration of progesterone (5 or 10 mg) to pregnant rats increased serum prolactin significantly on the afternoon of Days 4, 6, 7 and 8 of pregnancy, but had no effect on later days. On Day 10 progesterone administration increased serum prolactin only in rats treated with oestrogen the day before. A similar treatment with oestrogen and progesterone was unable to stimulate secretion on the afternoon of Day 13 of pregnancy. In rats from which the corpora lutea had been unilaterally removed and hence endogenous progesterone levels were 50% of the normal values, or in those that carried 4 conceptuses, progesterone treatment after oestradiol priming was partly effective in inducing prolactin release on Day 13. However, in rats ovariectomized, with bilateral excision of the corpora lutea, or with 2 conceptuses left, treatment with ovarian steroids markedly increased serum prolactin values. By Day 13 all the rats from the ovariectomized group or with bilateral excision of the corpora lutea had aborted. On Day 13, therefore, the high serum concentrations of feto-placental factors and of progesterone are responsible for the blockade of the spontaneous and ovarian steroid-induced prolactin release. On the other hand, on Day 16 of pregnancy the decrease of circulating progesterone by excision of the corpora lutea or by ovariectomy followed by oestradiol treatment significantly increased serum prolactin on Day 17. Removal of all the conceptuses did not modify the effects of these treatments.

The present results demonstrate different roles of progesterone upon the control of prolactin secretion. After a stimulatory action during the first days of pregnancy, there is a change to an inhibitory control at the end of pregnancy. At mid-pregnancy the association of maximal circulating concentrations of fetal-placental factors and progesterone prevents the spontaneous and ovarian steroid-induced release of prolactin.

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A highly purified and potent hyaluronidase preparation extracted from bull testis was employed to induce heterologous antibody by sensitizing adult rabbits. Specific anti-enzyme antibodies were demonstrated by Ouchterlony's method, and by passive cutaneous anaphylaxis (pca), and haemagglutination and complement fixation tests. In order to localize the cellular site of the accumulation of the enzyme, direct and indirect immunofluorescent techniques were applied to tissue sections and to isolated germ cells of adult bull testis. Specific fluorescence adequately checked by control reactions appeared in the perinuclear area of spermatids, in the acrosomes of spermatozoa and with less certainty in the cytoplasm of other cells tentatively identified as spermatocytes. Non-specific fluorescence could be seen in the basal cell line of the seminiferous tubules.

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C Hidalgo, C Díez, P Duque, J M Prendes, A Rodríguez, F Goyache, I Fernández, N Facal, S Ikeda, C Alonso-Montes and E Gómez

Retinoids have been shown to enhance developmental competence of the oocyte in cattle, sheep and pigs. In this study we investigated whether exogenous retinol stimulates the bovine oocyte during its intrafollicular growth and the time limits of exposure to exogenous retinol. In addition, we also determined the efficiency of ovum pick-up techniques in combination with retinol treatment and the viability of embryos after transfer to recipients. In Experiment 1, heifers were injected with retinol or vehicle, and concentrations of retinol in the blood were analysed on Day 0 (prior to injection), Day 1 and, together with follicular fluid, Day 4. Blood retinol increased by Day 1 and cleared on Day 4, but retinol remained higher within the follicle. In Experiment 2, oocyte donors were injected weekly with retinol or vehicle four times during a twice-per-week cycle of eight recovery sessions (starting 4 days before the first session), followed by a second eight-session cycle without treatment. Oocytes recovered were fertilized and cultured in vitro. Retinol treatment yielded higher numbers of low-quality oocytes throughout, although retinol measured during cycles did not change. Total oocytes, and morulae and blastocyst rates, increased during the first five sessions following treatment with retinol. As previously shown with oocytes from slaughterhouse ovaries, retinoic acid stimulated blastocyst development. Following transfer to recipients, blastocysts from oocytes exposed to retinol were unable to establish pregnancy. Our study confirms the existence of an effect of retinol on the intrafollicular oocyte in the cow and provides evidence regarding the teratogenic effect of retinol.