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T. R. Hansen, R. D. Randel and T. H. Welsh Jr

Summary. Granulosa cell responsiveness at an early (1–2 h) or late (14–16 h) stage of differentiation following the onset of oestrus [and presumably the LH surge] was studied in 16 cows. Follicular fluid collected at the early stage (8 preovulatory follicles) had a higher concentration of testosterone (P < 0·05), oestradiol (P < 0·01) and oestrone (P < 0·01) than did follicular fluid collected at the late stage of oestrus (8 preovulatory follicles). No difference in follicular fluid progesterone was noted between follicles collected at the early and late stages of oestrus. Granulosa cells collected at the early stage of oestrus had a higher in-vitro response (progesterone production) to LH (P < 0·05), forskolin (P < 0·08) and diacylglycerol (P < 0·05) than did granulosa cells collected at the late stage of oestrus. However, later stage granulosa cells produced more (P < 0·01) progesterone after culture with prostaglandin E-2 than did earlier stage granulosa cells. These results show that follicular fluid oestrogen decreases, which suggests a loss of aromatase activity as oestrus progresses, and that granulosa cells become refractory (low progesterone production) to in-vitro LH, forskolin, and diacylglycerol challenge, yet acquire responsiveness to prostaglandin E-2 as oestrus progresses.

Keywords: cow; granulosa cells; LH; ovary; progesterone

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U. O. Andersen, T. C. Bøg-Hansen and S. Kirkeby

A histochemical avidin–biotin technique with three different α1-acid glycoprotein glycoforms showed pronounced alterations in the cellular localization of two α1-acid glycoprotein lectin-like receptors during cell differentiation in the developing rat testis. The binding of α1-acid glycoprotein glycoforms to their receptors is inhibited by steroids. Testosterone, oestradiol and progesterone inhibited the binding of α1-acid glycoprotein glycoform A to its receptor. Cortisone, aldosterone, oestradiol and progesterone inhibited the binding of α1-acid glycoprotein glycoforms B and C to their receptor. A difference in the cellular content of α1-acid glycoprotein glycoforms and α1-acid glycoprotein receptors separates the spermatocytes and the early spermatids from the late spermatids. The difference in receptor composition implies a difference in the effect of different steroid hormones. The Leydig cells contained α1-acid glycoprotein and lectin-like receptors for one of the glycoforms of α1-acid glycoprotein from birth. The interaction between α1-acid glycoprotein glycoforms and their receptors may modulate the actions of testosterone and other steroids in the testis.

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S. D. Helmer, T. S. Gross, G. R. Newton, P. J. Hansen and W. W. Thatcher

Summary. Evidence exists that conceptuses alter endometrial protein secretion and modulate prostaglandin (PG) synthesis and secretion in cattle. The present study was designed to test the effect of bovine conceptus secretory proteins (bCSP) in general and the bovine trophoblast protein-1 complex (bTP-1) in particular on endometrial function. Endometrial explants from cyclic cows (N = 4) at Day 17 after oestrus were incubated for 24 h with 0, 4·8, 24 or 120 μg BSA/ml, 1 μg bTP-1/ml or 12·7 μg bCSP/ml. Both bCSP and bTP-1 decreased (P < 0·005) release of radiolabelled macromolecules into medium and incorporation of radio-labelled precursors into tissue compared to BSA-treated tissues but not tissues treated with medium alone. Secretion of a protein of M r = 14 900 was enhanced by bCSP treatment as compared to treatment with bTP-1 (P < 0·025). Both bCSP and bTP-1 decreased PGF secretion of explants (P < 0·01) compared to BSA. Overall, PGE-2 secretion by bCSP- and bTP-1-treated tissues did not differ from that of BSA cultures, but PGE-2 secretion was greater (P < 0·025) for bTP-1 than bCSP-treated endometrium. Cotyledonary microsomes from parturient cattle were utilized as a PG-generating system for the detection of inhibitors of PG synthesis. PGF synthesis by the generating system was decreased (P < 0·05) by 9% by cytosol from BSA-treated explants, whereas cytosol from bCSP-and bTP-1-treated explants decreased (P < 0·01) PGF synthesis by 42% and 35%, respectively. In summary, both bCSP and bTP-1 inhibit PGF secretion, induce synthesis of an intracellular inhibitor of PGF synthesis, and decrease protein synthesis and secretion. The bTP-1 complex therefore alters PG dynamics by explants in a manner that would function to prevent luteolysis and support the establishment of pregnancy.

Keywords: endometrium; cattle; conceptus proteins; prostaglandins; prostaglandin synthesis inhibitor

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Rocío Melissa Rivera, Gabriella M Dahlgren, Luiz Augusto de Castro e Paula, Robert T Kennedy and Peter J Hansen

The mechanism by which heat shock disrupts development of the two-cell bovine embryo was examined. The reduction in the proportion of embryos that became blastocysts caused by heat shock was not exacerbated when embryos were cultured in air (20.95% O2) as compared with 5% O2. In addition, heat shock did not reduce embryonic content of glutathione, cause a significant alteration in oxygen consumption, or change embryonic ATP content. When embryos were heat-shocked at the two-cell stage and allowed to continue development until 72 h post insemination, heat-shocked embryos had fewer total nuclei and a higher percentage of them were condensed. Moreover, embryos became blocked in development at the eight-cell stage. The lack of effect of the oxygen environment on the survival of embryos exposed to heat shock, as well as the unchanged content of glutathione, suggest that free radical production is not a major cause for the inhibition in development caused by heat shock at the two-cell stage. In addition, heat shock appears to have no immediate effect on oxidative phosphorylation since no differences in ATP content were observed. Finally, the finding that heat shock causes a block to development at the eight-cell stage implies that previously reported mitochondrial damage caused by heat shock or other heat shock-induced alterations in cellular physiology render the embryo unable to proceed past the eight-cell stage.

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A. J. Smith, M. Mondain-Monval, K. Andersen Berg, P. Simon, M. Forsberg, O. P. F. Clausen, T. Hansen, O. M. Møller and R. Scholler

Summary. Melatonin administration to male blue foxes from August for 1 year resulted in profound changes in the testicular and furring cycles. The control animals underwent 5-fold seasonal changes in testicular volume, with maximal values in March and lowest volumes in August. In contrast, melatonin treatment allowed normal redevelopment of the testes and growth of the winter coat during the autumn but prevented testicular regression and the moult to a summer coat the following spring. At castration in August, 88% of the tubular sections in the testes of the controls contained spermatogonia as the only germinal cell type, whereas in the treated animals 56–79% of sections contained spermatids or even spermatozoa. Semen collection from a treated male in early August produced spermatozoa with normal density and motility.

Measurement of plasma prolactin concentrations revealed that the spring rise in plasma prolactin values (from basal levels of 1·6–5·4 ng/ml to peak values of 4·1–18·3 ng/ml) was prevented; values in the treated animals ranged during the year from 1·8 to 6·3 ng/ml. Individual variations in plasma LH concentrations masked any seasonal variations in LH release in response to LHRH stimulation, but the testosterone response to LH release after LHRH stimulation was significantly higher after the mating season in the treated animals, indicating that testicular testosterone production was maintained longer than in the controls.

The treated animals retained a winter coat, of varied quality and maturity, until the end of the study in August.