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P. Sourdaine and D. H. Garnier

Seminiferous lobules of dogfish (Scyliorhinus canicula) testis comprise cysts formed by steroidproducing Sertoli cells associated with germ cells at an identical stage of spermatogenesis. These lobules were isolated in four populations corresponding to lobules with spermatogonia (A), spermatocytes (B), early spermatids (C) and late spermatids (D). They were used for steroid radioimmunoassay or incubated with 22a-hydroxycholesterol or with dibutyryl cyclic AMP (dibutyryl cAMP) to measure steroid production. Our results indicate that progesterone was the major steroid in seminiferous lobules at all stages of spermatogenesis except in lobules A. Furthermore, marked changes in the distribution of steroids were observed according to the stage of spermatogenesis; progesterone, 4-androstenedione, testosterone and 17α-hydroxy,20β-dihydroprogesterone concentrations were highest in lobules D, whereas dihydrotestosterone concentrations decreased during spermatogenesis. No significant stage-related change was observed for 3α-diol and 3β-diol. Incubation experiments revealed that the isolated seminiferous lobules at all stages can synthesize steroids from hydroxycholesterol and that lobules D have the highest basal contents of androstenedione and testosterone. Furthermore, when dibutyryl cAMP and 10 μmol hydroxycholesterol l−1 were added together to the cultures, an enhancement of the steroid secretion was observed rather than a change in synthesis. Our results also indicated that the responsiveness of the lobules to dibutyryl cAMP varies according to the stage of spermatogenesis and to the steroid assayed. Overall, this study indicated that germ cells probably markedly influence Sertoli cell steroidogenesis in the adult dogfish testis.

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D. H. Garnier, M. Terqui and J. Pelletier

Summary. After injection of castrated rams with 600 mg testosterone or testosterone propionate, plasma LH levels were biphasic, with significant decreases at 6–10 and 96 h after treatment. These results support the suggestion that testosterone acts at the hypothalamo-pituitary level by two different mechanisms.

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J. Pelletier, D. H. Garnier, M. M. de Reviers, M. Terqui and R. Ortavant

Summary. Blood was collected hourly for 24 h in December, February, April, June and September from Préalpes du Sud and Ile-de-France rams. Coincidence of the LH and testosterone peaks was found for 96·4% of a total of 670 LH peaks and 647 testosterone peaks. The number of LH and testosterone peaks increased by 66% in Ile-de-France rams and 200% in Préalpes du Sud rams between December and June (P < 0·01). Values in June and September were similar in Préalpes du Sud rams. There were no differences between breeds in December, but in June, Préalpes du Sud had significantly more peaks than did Ile-de-France rams (P < 0·025). The numbers of LH and testosterone peaks increased significantly (P < 0·05) in Préalpes du Sud rams between December and February or April. These results indicate that, although numbers of peaks of LH and testosterone increase when the animals pass from the non-breeding to the breeding season, the genotype influences the pattern of release through the year.

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R. Ortavant, A. Daveau, D. H. Garnier, J. Pelletier, M. M. de Reviers and M. Terqui

Summary. The time of appearance of plasma LH and testosterone peaks through the day was determined in 75 Préalpes du Sud and 41 Ile-de-France rams in December and in 44 Préalpes du Sud and 11 Ile-de-France rams in June. The distribution of peaks throughout the day was non-random for the two hormones in the two breeds and for both times of the year (P < 0·01 at least on each occasion; P< 0·001 on pooled data from the two breeds). The most striking features were the occurrence of (1) a minimum of LH and testosterone peaks immediately after 'dawn' (lights on) in both months; (2) a maximum of peaks 3 h after 'dawn' in June and 4 h after 'dawn' in December.

For several hours after the increase in frequency of peaks the probability of measuring peaks of LH and testosterone remains high. This and the correlation between the LH values in December and June when adjusted for the time of 'dawn' suggest that dawn could act as a synchronizer of gonadotroph activity.

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B. Jégou, J. L. Dacheux, D. H. Garnier, M. Terqui, G. Colas and M. Courot

Summary. The electrophoretic mobility, effect of pronase, temperature stability, affinity constant and specificity of androgen-binding protein (ABP) were compared in rete testis fluid (RTF), cauda epididymal plasma (CEP) and seminal plasma (SP) of the ram in which the levels of ABP, dihydrotestosterone (DHT), total protein and the number of spermatozoa were also measured. The characteristics of the ABP appeared to be almost identical in all 3 fluids. ABP was highly concentrated in the cauda epididymidis although 50–75% of it was utilized or destroyed during transit through the epididymis. The levels of ABP were higher in the breeding season and positively correlated with DHT in RTF and SP. It is concluded that ABP might be responsible for the increase in DHT in the reproductive tract of the ram during the breeding season and that ABP in the SP might serve as a useful marker of Sertoli cell function in the ram.