- The endocrine mechanisms involved in the initiation of sperm release
from the vertebrate testis have not been elucidated. A seasonally
breeding anuran amphibian, Hyla regilla, was selected as a model for
testing the hypothesis that steroid action is involved in gonadotropin-stimulated
sperm release. Experiments were carried out in vivo and in
vitro utilizing three steroid inhibitors: 1) Flutamide, a nonsteroidal
androgen receptor inhibitor, 2) CI-628, an estrogen receptor inhibitor,
and 3) Cytadren, an arotnatase inhibitor. The rationale for using
these drugs was to test the effect of steroid inhibition on sperm
release from LH-stimulated testes.
In vivo, Flutamide significantly inhibited sperm release compared to
controls, by reducing the number of sperm released. CI-628 and Cytadren tended to increase the number of sperm released.
In in vitro experiments excised testes were incubated in a Kreb's
Ringers solution, prescreened for sperm, and then LH or LH and
inhibitors were added. After incubation with the drugs, the number of
sperm released into the medium were counted using a hemacytometer. The
results of several experiments indicated that Flutamide treatment
increased the incidence of total inhibition of sperm release.
Further insight into the effect of Flutamide was gained by comparing
sperm release of contralateral testes. Again, Flutamide significantly
inhibited sperm release primarily by total inhibition, but also by
reducing the number of sperm released by testes that responded.
Preliminary results from the in vitro experiments using CI-628 and
Cytadren tended to show a paradoxical response. In some cases these
drugs inhibit the release of sperm while in other cases they stimulate
In addition, experiments were carried out in vitro using
contralateral controls to test the effects of various steroids on sperm
release. In these experiments, E₂, estrone, estriol, progesterone, T,
DHT and corticosterone had no sperm-releasing effect. A low dose of DHT
when given in conjunction with LH tended to increase the number of sperm
released. A high dose of DHT plus LH, however, significantly inhibited
This study provides evidence for the hypothesis that steroids are
involved in gonadotropin-stimulated spermiation. In particular, it is
suggested that androgens may mediate the action of LH on the testis
during the release of sperm. Estrogens also may be involved in spermiation either directly or indirectly, by regulating androgen
biosynthesis. The particular roles of estrogen and androgens in the
regulation of testicular function need further study.