Androgens are secreted by the interstitial cells of the vertebrate testis, and have
also been identified in the ovary, adrenal cortex and the mammalian placenta. In
the male animal they are necessary for the normal growth, differentiation and
maintenance of the reproductive organs and other sexual characters. Small amounts
of androgens are necessary for the optimal function of the female reproductive sys -
tem, just as oestrogens are necessary in the male. Testosterone is the principal and
most potent naturally occurring androgen, but others such as androstenedione have
a wide distribution.
The secretions of the gonadal steroid hormones are regulated by the gonadotrophic hormones of the adenohypophysis (FSH and LH or ICSH), and the respective
circulating levels of these two groups of hormones are controlled by the negative
feed-back system described previously.
a) Osmoregulatory Significance of the Gonadal Steroids
The actions of the hormones of the ovary and testis on water and salt metabolism
are indirect and somewhat conjectural. Osmoregulation in gonadectomized animals
appears to be adequate. The added needs for water and salt during reproduction
and care of the young are obvious. These requirements appear to be adequately
met by the usual osmoregulatory mechanisms, though some added adjustments
may be necessary.
Many species migrate to certain areas to breed, and in many fishes this may
involve movement from the sea into rivers or in the opposite.direction. It is doubtful that the gonadal hormones playa direct role in initiating such migrations, as
sexually immature animals may also make the journey and gonadal development
usually does not accelerate till arrival at or near the breeding ground (BARRINGTON,
1963). Oestrogens and androgens, respectively, facilitate and inhibit the development of the adrenocortical tissue, an action that is due to changes in the release of
the corticotrophic hormone (see VAN OORDT, 1963). Potentially they could thus
influence osmoregulation through the adrenal cortex. Such effects may account for
the hypertrophy of the adrenocortical tissue during sexual maturation of the migrating salmon (ROBERTSON and WEXLER, 1959). It should be remembered however, that the role of the adrenocortical tissue in osmoregulation of these fish is
uncertain.
The similarities in the chemical structures of the gonadal steroids, with those
secreted by the adrenal cortex, suggest that some interactions of their effects may
occur. Progesterone, thus, can facilitate sodium excretion in man (LANDAU et al.,
1955), an effect that may be due to its antagonism to aldosterone in the kidney
tubules. CRABBE (1963) has shown such an antagonism in vitro; high concentrations
of progesterone reduce the increases in sodium transport produced by aldosterone
in the toad bladder. Oestrogens and androgens have also been shown to produce
salt retention by mammals (see KRUHOFFER, 1960), but their sites of action are not
clear. It is unknown whether such effects of gonadal steroids occur normally, or
even in abnormal circumstances. It has been suggested that fluid retention in
women prior to menstruation may be due to altered sex steroid levels. The increased
levels of circulating aldosterone seen during pregnancy, could be the result of its
67
also been identified in the ovary, adrenal cortex and the mammalian placenta. In
the male animal they are necessary for the normal growth, differentiation and
maintenance of the reproductive organs and other sexual characters. Small amounts
of androgens are necessary for the optimal function of the female reproductive sys -
tem, just as oestrogens are necessary in the male. Testosterone is the principal and
most potent naturally occurring androgen, but others such as androstenedione have
a wide distribution.
The secretions of the gonadal steroid hormones are regulated by the gonadotrophic hormones of the adenohypophysis (FSH and LH or ICSH), and the respective
circulating levels of these two groups of hormones are controlled by the negative
feed-back system described previously.
a) Osmoregulatory Significance of the Gonadal Steroids
The actions of the hormones of the ovary and testis on water and salt metabolism
are indirect and somewhat conjectural. Osmoregulation in gonadectomized animals
appears to be adequate. The added needs for water and salt during reproduction
and care of the young are obvious. These requirements appear to be adequately
met by the usual osmoregulatory mechanisms, though some added adjustments
may be necessary.
Many species migrate to certain areas to breed, and in many fishes this may
involve movement from the sea into rivers or in the opposite.direction. It is doubtful that the gonadal hormones playa direct role in initiating such migrations, as
sexually immature animals may also make the journey and gonadal development
usually does not accelerate till arrival at or near the breeding ground (BARRINGTON,
1963). Oestrogens and androgens, respectively, facilitate and inhibit the development of the adrenocortical tissue, an action that is due to changes in the release of
the corticotrophic hormone (see VAN OORDT, 1963). Potentially they could thus
influence osmoregulation through the adrenal cortex. Such effects may account for
the hypertrophy of the adrenocortical tissue during sexual maturation of the migrating salmon (ROBERTSON and WEXLER, 1959). It should be remembered however, that the role of the adrenocortical tissue in osmoregulation of these fish is
uncertain.
The similarities in the chemical structures of the gonadal steroids, with those
secreted by the adrenal cortex, suggest that some interactions of their effects may
occur. Progesterone, thus, can facilitate sodium excretion in man (LANDAU et al.,
1955), an effect that may be due to its antagonism to aldosterone in the kidney
tubules. CRABBE (1963) has shown such an antagonism in vitro; high concentrations
of progesterone reduce the increases in sodium transport produced by aldosterone
in the toad bladder. Oestrogens and androgens have also been shown to produce
salt retention by mammals (see KRUHOFFER, 1960), but their sites of action are not
clear. It is unknown whether such effects of gonadal steroids occur normally, or
even in abnormal circumstances. It has been suggested that fluid retention in
women prior to menstruation may be due to altered sex steroid levels. The increased
levels of circulating aldosterone seen during pregnancy, could be the result of its
67