Role of protein synthesis in rabbit follicular testosterone production

Effects of cycloheximide on in vitro testosterone secretion from RANA catesbeiana ovaries

A 1 hr exposure to 20 micrograms/ml of the protein synthesis inhibitor, cycloheximide (CHX), essentially abolished secretion of testosterone (T) by bullfrog ovarian fragments during simultaneous administration of homologous pituitary extract and CHX. Removal of CHX from the medium after 4 hr of treatment reversed the inhibition of T secretion, allowing it to attain control levels. Pre-exposure of ovarian fragments to CHX was not required to obtain an inhibition of T secretion. These data supported the hypothesis that protein synthesis is required for acute and chronic gonadotropic stimulation of steroidogenesis by the bullfrog ovary.

Lutropin stimulates de novo synthesis of short-lived proteins required for lutropin-dependent steroid production in tumour Leydig cells

Continuous protein synthesis is required for the hormonal regulation of cholesterol side chain cleavage activity. A protein with a short half-life (t1/2 = 2-13 min) is believed to play an important role, but the regulation of the synthesis of this putative rapidly-turning-over protein is largely unknown. The steroid production rate in tumour Leydig cells can be increased more than 4-fold after addition of lutropin. However, steroid production by cells preincubated for 60 min with medium containing cycloheximide (89 microM) could not be stimulated when lutropin was added to the medium. Thus, the putative protein with the short half-life is apparently not derived from a stable precursor protein. Moreover, in tumour Leydig cells incubated with low concentrations of cycloheximide (0.2-0.8 microM), inhibition of steroid production was significantly greater in lutropin-stimulated cells than in control cells. These results support the hypothesis that lutropin regulates the de novo synthesis of rapidly-turning-over proteins by increasing the rate of initiation of the translation step of protein synthesis.

Acute effects of LH on incorporation of [35S]-methionine into proteins by isolated rabbit ovarian follicles

The incorporation of [35S]-methionine into follicular protein was investigated during 5 min intervals up to 20 min, and correlated with testosterone production. At 5 and 20 min after stimulation with luteinizing hormone (LH) there was no difference in the [35S]-labelled proteins from the controls. At 10 and 15 min, LH seemed to decrease the intensity of a protein band with a molecular weight of approximately 25,000 daltons. There was no significant difference in the amount of TCA precipitable radioactivity between control and LH treated follicles. Testosterone production increased within 10 min of stimulation with LH. Under the conditions employed these data suggest that repression of a an inhibitor protein may be required for testosterone production by isolated rabbit ovarian follicles.