ON TESTIS AND EPlDlDYMlS OF RATS - Pondicherry University ...

1.1.1.3 Tcsticular steroidogcnesiv
Testis secretes a variety of steroids which are synthesized from cholesterol
which itself can be synthesized from acetatc. Thc principal sccrctory stcn)id product
in male is testosterone of which 95% is synthesized in the Leydig cells and the
remainder being produced by the adrenal glands. Cholesterol is derived from two
sources, consisting of an uptake mechanism by which circulating low-density
lipoprotein bind to specific receptors on Leydig cells or by internalization. that
provide n ready source ol'cholcstclol. It1 rat I.cydig cells. receptors lir I~igli-ilc~lsily
lipoprotein have also been reported (Chen el al., 1980). Cholesterol has been shown
to get converted into pregnenolone in the testicular tissues by successive oxidations
under the influence of C20-C22 desmolase complex (Cytochrome P-450) in
mitochondria in the presence ofNADPH and oxygen (Burstein and Gut, 1971).
Tcsticular homogenates of rat has been shown to convert pregnenolone more
to progesterone than that of 17-hydroxypregnenolone. Incubation of labeled 17-
hydroxypregnenolone has been shown to produce dehydroepiandrosterone instead of
17-hydroxyprogesterone (for review, see Hall, 1988). Existence of an alternative
pathway of conversion of 17-hydroxypregnenolone to androstenediol
withor~t
involving dehydroepiandrosterone or androstenedione has also been reported
(Slaunwhite and Burgen, 1965). Formation of A~') ketosteroids such as progesterone.
17-hydroxyprogesterone, androstenedione and testosterone from A'" P-
hydroxysteroids in the presence of 3P-hydroxysteroid dehydrogenasel A~~ isomerase
has been reported (Hall, 1970; Eik-Nes, 1975). Progesterone has been shown to get
convened into 17-hydroxyprogesterone, androstenedione and testosterone by 17-
hydroxylase, 17-20 lyase and 17P-hydroxysteroid dehydrogenase respectively (Hall.
1970, Eik-Nes, 1975). Progesterone has also been shown to get converted into
17-hydroxyprogesterone, androstenedione and testosterone in the incubation of slices
or homogenates of testis of hypophysectomized or immature rats treated with human
chorionic gonadotrophin (hCG) to increase the volume of the interstitial cells
(Slaunwhite and Samuels, 1956). Testis has the capacity to produce 17p-estradiol,