The metabolic clearance rate and the production rate of estradiol in sexually immature and adult female rhesus monkeys

High feed intake increases liver blood flow and metabolism of progesterone and estradiol-17beta in dairy cattle

Increased liver blood flow (LBF) resulting from elevated feed intake in lactating dairy cows may increase steroid metabolism. Continuous infusion of bromosulphthalein (BSP; specifically metabolized in liver) was used to measure LBF. Similarly, progesterone (P4) and estradiol-17beta (E2) were administered by continuous infusion. Circulating concentrations at steady state were used to calculate the metabolic clearance rate (MCR) of BSP, P4, and E2. Experiment 1: Variation in LBF was determined in thee nonlactating and four lactating cows over 3 d at 3 to 5 h after feeding. Coefficients of variation ranged from 14 to 31% among cows within day and from 4 to 8% within cows across days. Experiment 2: Six nonlactating cows were used in a 3 x 3 Latin-square design with three feed regimens: no feed, 0.5 maintenance diet (M), and 1.5 M. Experiment 3: Eight lactating cows were used in a 4 x 4 Latin-square design with four feed regimens: no feed, 0.5 M, 1.5 M, and 2.2 M. In experiments 2 and 3, LBF and MCR of P4 increased immediately after feed consumption and increases persisted longer at higher intakes. The LBF reached a maximum at 2 h after feeding and MCR of P4 reached maximum at 3 h after feeding with a positive correlation (r = 0.92) between LBF and MCR for P4. Experiment 4: A crossover design was used to determine MCR of E2 in unfed or full-fed lactating dairy cows. The MCR of E2 increased immediately after feeding and stayed elevated throughout the 4.5-h infusion period. Thus, LBF and steroid metabolism were acutely elevated by feed consumption in lactating and nonlactating cows. Higher rates of LBF and steroid metabolism in lactating than in nonlactating cows may indicate chronic effects of higher feed intakes as well.

Direct effect of plasma sex hormone binding globulin (SHBG) on the metabolic clearance rate of 17 beta-estradiol in the primate

Sex hormone binding globulin (SHBG) has been shown to be a major determinant of testosterone clearance in the primate. It has also been suggested that SHBG would also be a determinant of estradiol clearance (MCR-E2). However, published studies have suggested that the MCR-E2 do not always vary with changes in the level of SHBG. Therefore, the present study was undertaken to address this issue. The baseline MCR-E2 was determined in adult male pigtail macaques (Macaca nemestrina). Following the baseline determination of MCR-E2 the animals were infused with either purified human (h) SHBG or antibody against hSHBG, which also has a high degree of cross-reactivity with primate SHBG. Following the infusions of either hSHBG or anti-SHBG, MCR-E2 was again determined. In addition, luteinizing hormone (LH) was measured using a mouse Leydig cell bioassay. Following the infusion of hSHBG, a marked increase in serum SHBG was noted and the MCR-E2 decreased. Associated with the increase in SHBG, the SHBG bound T levels decreased and LH increased. Following the infusion of antibody, serum SHBG decreased, and the MCR-E2 also decreased. With the decrease in SHBG following the antibody infusion, non-SHBG bound T increased and serum LH fell. This study demonstrates that an increase in the serum SHBG levels is associated with a decrease in MCR-E2, however, an acute decrease in serum SHBG also decreases the MCR-E2. This later result demonstrates that factors in addition to serum SHBG binding may be important in determining the MCR-E2.

Effect of dexamethasone treatment on sex steroid-binding protein, corticosteroid-binding globulin, and steroid hormones in cycling rhesus macaques

We tested the hypothesis that dexamethasone lowers sex steroid-binding protein levels and observed the effect of dexamethasone on corticosteroid-binding globulin and specific steroid hormones in plasma. Four cycling rhesus macaques were studied during three consecutive menstrual cycles (first and third cycles served as controls). In the second cycle, each animal received 0.5 mg of dexamethasone intramuscularly at 8:00 AM and 8:00 PM daily for 21 consecutive days. Blood samples were taken at 1- to 3-day intervals during each cycle. Concentrations of sex steroid-binding protein, corticosteroid-binding globulin, cortisol, testosterone, progesterone, and estradiol were measured in plasma. The percentage and plasma concentration of free testosterone were also determined. Within 2 days of treatment, dexamethasone suppressed cortisol to 5% of baseline values, which returned in the third cycle. All cycles were ovulatory. Dexamethasone significantly lowered plasma levels of all the compounds except progesterone: sex steroid-binding protein, -30%; corticosteroid-binding globulin, -14%; testosterone, -36%; and estradiol, -45%. The percentage of free testosterone was significantly elevated, but free testosterone concentrations were unchanged. Although our data conclusively show that dexamethasone suppresses plasma sex steroid-binding protein levels in the rhesus macaque, it remains to be established whether this suppressive effect leads to an increase in the metabolic clearance rate of testosterone.