A Study of the Source of Estradiol-17β in the Bull

Summary

A study was designed to determine if the bull testes secretes estradiol-17β, as has been reported for several other species. Two experiments were conducted. In the first experiment, five Angus-sired crossbred bulls were fitted with catheters in the spermatic and jugular veins and sampled every 15 min for six hours. One was bled from three cannula, the third being in the spermatic artery. In the second experiment, these same bulls were castrated and jugular vein blood was collected at timed intervals for two hours. Plasma samples were assayed for estradiol-17β (E₂) and testosterone (T) using highly specific radioimmunoassays.

This experiments gave evidence that:

a. Concentrations of E₂ were significantly lower (P < .05)in the jugular vein than the spermatic vein in each of the five bulls, although the mean concentration for all bulls was not great for either vein nor was the difference great between the two veins. In confirmation of past studies, T concentration in the jugular vein was much lower than in the spermatic vein in each bull as was overall mean.

b. Removal of the testes caused E₂ to decrease during the 25 min post-castration but the difference was not significant (P > .05), whereas T decreased 4-fold (P < .01). During the next 95 min., the concentrations of both hormones increased 3- and 6-fold, respectively, as did cortisol concentration. It is concluded that the bull testes secretes E₂, but the secretion is minor to that of T and that another source of both hormones can be the adrenal gland, such as during stress.

Key-Words

Estradiol - Testosterone - Source - Disappearance Rates - Bull