Steroid-protein interactions in bovine plasma

Tissue culture media supplemented with 10% fetal calf serum contains a castrate level of testosterone

BACKGROUND

Human prostate cancer cells are routinely maintained in media supplemented with 10% Fetal Calf Serum (FCS) to provide androgen. In the present study, total and free testosterone levels in 10%FCS supplemented tissue culture media were determined and compared to levels in intact and castrated human males. Dextran-coated charcoal stripped FCS (i.e., DC-FCS) is often used instead of FCS to minimize the level of androgen provided in 10% serum supplemented media. Therefore, total and free testosterone levels in 10%DC-FCS containing media were likewise determined.

METHODS

Total testosterone, free testosterone, and total dihydrotestosterone (DHT) were determined on RPMI-1640 media supplemented with either 10%FCS or 10%DC-FCS by ELISA assays before and after exposure to LNCaP human prostate cancer cells in culture. The growth and PSA secretion by these cells was also determined.

RESULTS

Ten percentage FCS supplemented media contains a castrate level of testosterone. However, even with this castrate starting level of testosterone, LNCaP cells concentrate and metabolize the testosterone to produce a physiologic (i.e., 10 nM) level of intracellular DHT which optimally stimulates the growth of these cells in vitro.

CONCLUSIONS

The present studies document that prostate cancer cells auto-regulate their androgen metabolism so that an optimal level of DHT for growth is maintained during both up and down fluctuations in the supply of testosterone. These results have significant implications for whether exogenous androgen should be added to the 10%FCS supplemented media to grow prostate cancer cells from intact versus castrated patients.

Effect of passive immunization against testosterone on reproductive hormone secretion and ovarian function in dairy cows and pubertal beef heifers

Multiparous dairy cows were divided in 3 groups from Day 5 up to Day 56 post partum: high energy level (Group H, n=10), low energy level (Group L, n=10) and low energy level plus anti-testosterone bovine immunoglobulins (Group LI, n= 10). Undernutrition decreased body weight, body condition score, milk yield and energy balance in Groups L and LI compared to Group H (P<0.05), but had no effect on secretory pattern of LH. Passive immunization against testosterone increased LH secretion in Group LI (P<0.05). Follicular score and the presence of follicles >/= 10mm on the ovary were not affected by underfeeding but were higher in Group LI than in Group L after immunization (P<0.01). The duration of the first luteal phase was shorter in Group H than in Groups L and LI and maximum progesterone levels reached were higher in Group LI than in Group H (P<0.01). Reproductive performance was not depressed by underfeeding and immunization. In the pubertal beef heifers maintained in anestrus by undernutrition had very low LH secretion. After passive immunization against testosterone, the increase of LH pulses number became almost significant (P=0.07). Following injection of exogenous LH, the number of follicles >/= 9mm was higher in immunized (Group I, n=8) than in control heifers (Group C, n=7). Group I developed a dominant follicle sooner and of greater size than Group C. Passive immunization against testosterone increased LH secretion and follicular development.

The plasma sex steroid binding protein (SBP or SHBG). A critical review of recent developments on the structure, molecular biology and function

Significant developments have taken place within the past five years on the characterization, molecular biology and function of the plasma sex steroid-binding protein, SBP (or sex hormone binding globulin, SHBG). During the span of that time, amino acid sequences of two SBPs have been established, amino acid residues in the steroid-binding site have been identified, the structure of the human SBP gene has been deduced and evidence for the possible existence of a SBP membrane receptor has been presented. This review covers the salient aspects of these and other developments including a critical analysis of the various proposed models and interpretations with regards to the structure, evolution, molecular biology and function of SBP.

Concentration decrease of corticosteroid binding globulin (CBG) in plasma of the mare throughout pregnancy

A significant decrease of CBG binding capacity in plasma of the mare throughout pregnancy was demonstrated using equilibrium dialysis and gel equilibration methods. As indicated with immunoelectrophoresis experiments, the pregnancy related fall of CBG binding capacity was linked to an actual decrease in blood CBG concentration. This result contrasts sharply with data on most other mammalian species, with the exception of the gestating rhesus monkey.

Plasma sex-steroid binding protein in a seasonally breeding reptile, Alligator mississippiensis

The properties of a sex-steroid binding protein (SSBP) in the plasma of the American alligator, Alligator mississippiensis, were partially characterized. Alligator SSBP has a sedimentation coefficient of 4S in a 5-20% sucrose gradient. It binds to estradiol-17 beta (E2) and testosterone (T) with limited capacities and moderate affinities (association constant for [3H]E2 is 4.70 +/- 0.09 X 10(8) M-1 and for [3H]T is 1.05 +/- 0.07 X 10(8) M-1, mean +/- SEM of six determinations). Plasma SSBP level, as measured by plasma [3H]E2 binding capacity, varies from 30 to 140 nmol per liter plasma (nM) and was found to be dependent on the gender, sexual maturity, and reproductive state of the animal. Distinct annual fluctuations in plasma SSBP level were observed in female alligators. In adult females, plasma SSBP levels were high (122 +/- 6 nM) in the fall during the nonbreeding season and low (30-60 nM) in spring and early summer during the breeding season. A minimum (33 +/- 6 nM) was reached in mid-June coinciding with the time of oviposition and rapid decline in circulating estrogen levels. This decline in adult female plasma SSBP levels during the breeding season was not observed in immature females. On the contrary, plasma SSBP levels in immature females increased from 81 +/- 14 nM in April to 134 +/- 9 nM in June. Plasma SSBP levels in male alligators showed little changes throughout the entire breeding season; they remained within the range of 80-100 nM from March to June. We believe that seasonal fluctuations in plasma SSBP levels constitute part of the mechanism involved in the regulation of free steroid delivered to target organs in female alligators and that such a mechanism does not exist in male animals.