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Peripheral plasma testosterone levels in the male rat were increased above control levels 5 min after the first intromission with an oestrous female, or 8–10 min after first contact with the female. The levels remained raised for at least 30 min if copulation was allowed to continue. Intravenous injection of human chorionic gonadotrophin resulted in an increased peripheral concentration of plasma testosterone after 10–15 min and an increase of testosterone content of the testis 5–10 min after injection, indicating that the rat testis has a potential to respond rapidly to gonadotrophin. The results suggested that if the testosterone surge during copulation was gonadotrophin-dependent, it was initiated before the first intromission. Indeed, plasma testosterone levels were raised in male rats 5 min after being placed in the proximity of oestrous females but not allowed physical contact.

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The levels of pregnenolone, dehydroepiandrosterone (DHA), androstenedione, testosterone, dihydrotestosterone (DHT), oestrone, oestradiol, cortisol and luteinizing hormone (LH) were measured in the peripheral plasma of a group of young, apparently healthy males before and after masturbation. The same steroids were also determined in a control study, in which the psychological anticipation of masturbation was encouraged, but the physical act was not carried out. The plasma levels of all steroids were significantly increased after masturbation, whereas steroid levels remained unchanged in the control study. The most marked changes after masturbation were observed in pregnenolone and DHA levels. No alterations were observed in the plasma levels of LH.

Both before and after masturbation plasma levels of testosterone were significantly correlated to those of DHT and oestradiol, but not to those of the other steroids studied. On the other hand, cortisol levels were significantly correlated to those of pregnenolone, DHA, androstenedione and oestrone.

In the same subjects, the levels of pregnenolone, DHA, androstenedione, testosterone and DHT in seminal plasma were also estimated; they were all significantly correlated to the levels of the corresponding steroid in the systemic blood withdrawn both before and after masturbation.

As a practical consequence, the results indicate that whenever both blood and semen are analysed, blood sampling must precede semen collection.

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H. Rui, B. S. Welinder, K. Purvis, and Ø. Dolva


Immunoassayable TRH in human ejaculate was eluted from a gel column in a form with a molecular weight larger than that of the native peptide. With reverse-phase high-performance liquid chromatography (HPLC) the same activity co-eluted with standard TRH. Incubation of ejaculates at room temperature for 8 h was associated with a time-related increase in the total immunoassayable TRH. Analysis by HPLC of ejaculates after 12 h of incubation at room temperature indicated that, whereas the levels of the peptide co-eluting with native TRH declined with time, there was a concomitant increase in the concentration of a molecular species which also cross-reacted with the TRH antiserum, but which was more hydrophobic. The latter species is presumably identical to the tetrapeptide recently described by others and which may arise from the proteolytic degradation of secretory macromolecules. Although immunological activity was present in all six fractions of split ejaculates, the bulk of the peptide was associated with the later portions, implying a major vesicular contribution. However, secretions isolated from surgical preparations of the seminal vesicles contained undetectable levels of peptide, suggesting that the ejaculation process may represent a stimulus for its appearance in the semen. This study is further support for a local involvement of TRH in male reproductive function.

J. Endocr. (1987) 114, 329–334

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Testosterone levels in plasma obtained from the jugular vein of rams were measured using a radioimmunoassay. The assay antiserum had a specificity for testosterone such that chromatography was not used during determinations. Blood was taken every ½-1 h under conditions approximating to the natural environment at the particular time of year. Measurements during a 48 h period in January demonstrated that marked episodic bursts of testosterone occurred. Two rams showed eight peaks of testosterone in 24 h with levels reaching 12–14 ng/ml. Two other animals showed four peaks in 24 h, the levels reaching 8 ng/ml. The pattern for all animals was similar in the second 24 h period. In one animal, a testosterone profile obtained over 24 h in the previous November corresponded to that obtained in January although the animal had been serving ewes in the interim period and suggests tentatively that a particular pattern may be inherent in an individual animal.

The rams were maintained in the absence of females until early March and sampled again for 7 h during which time they were allowed contact with an ovariectomized ewe induced into oestrus. The libido of the rams appeared normal. Testosterone levels were low throughout, exceeding 5 ng/ml on one occasion only, and were not affected by copulation. A testosterone profile obtained for two of the rams over a 24 h period in late March demonstrated that the levels were still low. A further testosterone profile was obtained for one of these rams in June. Levels were high and the pattern had reverted to that found the previous November and January.

To obtain evidence that the low levels of testosterone found in March were a result of season rather than lack of regular copulation at this time, blood was obtained from four rams maintained at the Meat and Livestock Commission A.I. Centre, Selby. Two of these animals had not been used for semen collection since January and two were in regular use with a teaser female and semen was collected twice weekly. Maximum testosterone levels of 5 ng/ml were obtained over 12 h in both groups.

During this work, in periods when the testosterone levels were high, there were disruptions in apparently periodic fluctuations in testosterone levels which could be correlated with the proximity of other animals.