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The dna content of individual ejaculated spermatozoa and of spermatozoa recovered from the epididymis and ampulla of fifteen rabbits was measured by means of two microspectrophotometric methods: (i) direct determination of ultra-violet (uv) light absorbed at 260 mμ by unstained spermatozoa, and (ii) determination of visible light absorbed at 560 mμ by Feulgen-stained spermatozoa. The dna determinations in uv light for ejaculated spermatozoa and for those recovered from the male ducts revealed no difference, as contrasted with the results obtained by measuring the Feulgen-stainability. The differences in Feulgen-stainability, i.e. in the quantitative response of spermatozoa to the Feulgen reagent, are attributed to an ageing process in the sperm cells: ampullary spermatozoa yielded significantly lower Feulgen-dna values than those obtained from the epididymis; ligation of the vas deferens resulted in a decrease of the Feulgen-dna content of epididymal spermatozoa; the variable Feulgen-dna content of individual ejaculated spermatozoa is attributed to varying percentages of older sperm cells in the ejaculates.

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The gonadotrophic control of spermatogenesis varies with age. Thus, ovine fsh stimulates spermatogenesis in the hypophysectomized prepubertal rat more effectively than ovine lh whereas the opposite is found in the adult (Ortavant, Courot & de Reviers, 1969; Courot, Ortavant & de Reviers, 1971). Gonadotrophic hormones reduce the proportion of germinal cells which undergo degeneration. It was thought probable that this effect was the result of actions of these hormones on the metabolism of germinal cells. We have started to investigate this problem by studying the effects of fsh and lh on the synthesis of DNA by spermatogonia and primary spermatocytes in the rat. It has previously been shown that hypophysectomy reduces the intensity of [3H]thymidine-labelling of the DNA in these cells (R. Ortavant, unpublished data).

Six prepubertal and six adult Wistar rats were hypophysectomized

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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.