Crystallization and preliminary X-ray diffraction studies of human cytochrome P450 reductase

The two functional domains of a cloned human fibroblast NADPH-cytochrome P450 reductase have been expressed in Escherichia coli and purified on the milligram scale for crystallization studies. One domain contains the cofactor FMN-binding site and the other contains the binding sites for cofactor FAD and substrate NADPH. Crystals of both domains have been obtained by the microbatch method. The crystals of the FMN domain belong to the monoclinic space group P21, with unit cell dimensions of a = 39.3 A, b = 51.5 A, c = 47.8 A, and beta = 105.7 degrees and have one molecule in the asymmetric unit. Diffraction data up to 2.3 A were collected with a merging residual on intensity of 9.3%. The crystals of the FAD/NADPH domain belong to the ortho-rhombic space group P212121 with unit cell dimensions of a = 55.9 A, b = 58.6 A, c = 131.1 A and have one molecule in the asymmetric unit. Diffraction data up to 2.6 A were collected with a merging residual on intensity of 8.0%.

Alternatives to Aroclor 1254-induced S9 in in vitro genotoxicity assays

A working party was set up by the UK Environmental Mutagen Society to consider alternatives to Aroclor 1254 (Aroclor)-induced S9 in in vitro genotoxicity assays, with the aims of considering whether a replacement for Aroclor in its role in general screening assays could be readily identified. The working party concluded that there was sufficient support in the literature to justify the use of an appropriate phenobarbital/beta-naphthoflavone regime as an acceptable alternative to Aroclor.

Markers of atresia in ovarian follicular components from rhesus monkeys treated with estradiol-17 beta

A new model for the investigation of atresia in rhesus monkeys is presented. This model is based upon the reliable induction of an atresia-like process in the dominant preovulatory follicle (DF) by estradiol-17 beta administered subcutaneously via Silastic capsules for 24 h. Data obtained from follicular contents aspirated from treated animals demonstrated alterations in the putative markers of atresia similar to those described in other models of atresia. Although follicle size and appearance and volume of follicular fluid (FF) were unaltered in treated animals, FF was much more viscous than that aspirated from follicles in untreated animals; this was apparently due to a greater quantity of intercellular matrix that was sensitive to digestion by hyaluronidase. In treated animals, FF concentrations of estrogen (E) and progesterone (P) were depressed 3- and 6.6-fold, respectively. Viability of granulosa cells (GC) from these animals was reduced by 40%, as was their ability to release basal amounts of E and P in vitro. Accumulation of P by GC from treated animals approximated unstimulated control levels when human follicle-stimulating hormone (hFSH) was included in the culture. Therefore, FSH may have a limited capability to "rescue" GC from atresia induced by estradiol. The percentage of cells that bound 125I-hFSH maximally, as measured by autoradiography following 72 h in culture, was not altered by treatment. Oocytes from animals treated with estradiol showed signs of degeneration at aspiration, and deteriorated further in culture. This model is unique in that atresia can be induced in the single DF of a primate species, and thus avoids the disadvantages inherent to studying atresia of heterogeneous follicles in polytocous species.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal effects on ovarian folliculogenesis in rhesus monkeys

Reproductive performance is reportedly reduced in some rhesus monkeys during the summer months, even when environmental conditions are controlled. The mechanism(s) underlying this phenomenon remain unknown. We noted that the pattern of folliculogenesis appeared to be altered in rhesus monkeys that continued to exhibit ovulatory menstrual cycles during the "nonbreeding" season. This study was designed to investigate the effect of season on development of the dominant follicle (DF) and upon levels of serum gonadotropins and sex steroids in animals maintained in a controlled environment. Forty-four menstrual cycles were evaluated from October, 1982 to October, 1983. Animals were housed individually in controlled light (12L:12D) and temperature (22-25 degrees C). A DF was identified by laparoscopy on Day 6 of the cycle in only 45% of cycles during the months of May through September, compared with 87.5% the remainder of the year. No effect of season was detected on either the length of the menstrual cycle or luteal phase, mean follicular diameter, or the percentage of ovulatory cycles. During the follicular phase, amounts of follicle-stimulating hormone (FSH) in peripheral sera were depressed, whereas those of luteinizing hormone (LH) were consistently elevated. Amounts of circulating estradiol were similar between groups. However, serum concentrations of progesterone were markedly reduced in the summer. Development of the DF appeared to be delayed in the early follicular phase during the summer months in those rhesus monkeys that had ovulatory menstrual cycles. This delay was accompanied by an alteration in the FSH to LH ratio. Although most cycles were ovulatory, altered follicular development resulted in deficient luteal function.

Induced follicular atresia in rhesus monkeys: strength-duration relationships of the estrogen stimulus

We have demonstrated that 17 beta-estradiol (E2) administered to monkeys for 24 or 48 h from day 6 of the menstrual cycle results consistently in degeneration of the preovulatory follicle. The present experiments were conducted to determine the strength-duration characteristics of this effect and to evaluate the occurrence of partial atresia together with subsequent effects on luteal function. Square wave increments in circulating amounts of estrogen were achieved by varying the number and size of Silastic capsules containing E2. Treatments included 0.5, 1, 2, 4, or 10 capsules placed sc for 6, 12, or 24 h. Forty-six menstrual cycles were studied in 33 animals. Increments in serum concentrations of estrogen approximating 300-400 pg/ml and sustained for 24 h or those greater than 600 pg/ml for only 6 h were maximally effective, while 300-400 pg/ml for 12 h or 100 pg/ml for 24 h were almost as effective. Increments less than about 60 pg/ml were essentially ineffective in inducing atresia. After induced atresia, follicular phases were extended by about 8 days, permitting a substitute follicle to develop. Partial atresia, represented by delayed ovulation of the original follicle, was noted in only three cycles. However, another apparent effect of estrogen on follicular development was evident in the form of luteal phase defects which occurred with high incidence in all groups, whether the corpus luteum resulted from the original or substitute follicle. Thus, full atresia induced by estrogen is largely an all or none phenomenon, but lesser effects may be manifested as deficient luteal function. This atretogenic effect of estrogen may be exerted at the ovarian level or may be mediated by the transient suppression of FSH. On the other hand, increases in FSH after treatment may stimulate development of a substitute follicle or maintain follicles not undergoing full atresia.

In vivo uptake and metabolism of low density lipoprotein in the guinea pig adrenal

Adrenal uptake and metabolism of circulating low density lipoprotein (LDL) was examined in female guinea pigs. [H3]LDL was prepared by exchange labeling with [H3]cholesteryl linoleate. After its injection plasma [H3]sterol ester concentration declined rapidly. This decline was slower in those animals pretreated with dexamethasone than in untreated controls. At 120 min after [H3]LDL administration [H3]-cholesteryl esters and [H3]cholesterol were detected in the adrenal gland. The levels of both radioactive and radioinert esters were lower in animals given dexamethasone. In contrast no difference in radioactive or radioinert cholesterol concentration was evident. In a second experiment [H3]LDL was prepared by reconstitution of the LDL-core with [H3]cholesteryl linoleate. After administration its disappearance from the circulation was similar to that observed in the first experiment. Other organs also took up [H3]LDL including the liver and kidney. Free and esterified [H3]cholesterol concentrations were greater in the liver than in the adrenal gland at 120 min after injection. The results from these two experiments were interpreted to mean that th adrenal cortex is capable of taking up LDL and metabolizing its cholesteryl esters. Uptake may be stimulated by ACTH.

Serum progesterone and corpus luteum function in pregnant pigtailed monkeys (Macaca nemestrina)

Corpus luteum (CL) function and control during pregnancy and early lactation in the pigtailed macaque was investigated. Peripheral concentrations of progesterone (P) on day 10 of pregnancy were 12.98 +/- 2.21 ng/ml and decreased progressively to 7.96 +/- 1.27 ng/ml by day 21 of pregnancy. The concentration of P increased around day 27 of gestation and reached peak levels of 18.48 +/- 2.45 ng/ml on day 37, thereafter gradually decreasing to a nadir at about midgestation. Ten days before parturition P concentrations increased again (P < 0.05). Concentrations of P decreased from 6.62 +/- 1.48 ng/ml on the day of delivery to 2.16 +/- 0.43 ng/ml on day 2 of lactation and remained low thereafter. Ovariectomy on day 35 did not affect the normal course of gestation or the patterns of P secretion during pregnancy. However, in these ovariectomized animals, in spite of suckling, P was not detectable after parturition. In intact monkeys, serum concentrations of P in the utero-ovarian vein at days 80 and 159 of pregnancy were higher relative to the uterine vein. Incubation studies utilizing 3H-cholesterol as a substrate revealed that the CL were capable of synthesizing P on days 35 and 159 of gestation. Histologically, the CL contained active luteal cells at late pregnancy. Low serum concentrations of chorionic gonadotropin were detected on day 10 of gestation; concentrations of this hormone reached high levels between days 18 and 24 and the titers were nondetectable after day 40 of pregnancy. Luteinizing hormone was present in constant amounts in the circulation during pregnancy and lactation. These data suggest that the CL of pregnancy in the pigtailed monkey is functional or capable of functioning during various stages of pregnancy. However, the fetoplacental unit is the primary source of P during the latter 4.5 months of gestation. As in other primates, a functional CL is not required for maintenance of pregnancy after implantation nor for lactation. Thus, the physiological significance of CL function during pregnancy is unclear.

Progestin metabolism in the rhesus monkey corpus luteum

For the purpose of describing the pathway by which estrones are synthesized in the rhesus monkey (Macaca mulatta) corpus luteum (CL), CL were obtained during the midluteal phase of the menstrual cycle and fragments incubated with equimolar amounts of [7-3H]pregnenolone plus [4-14C]progesterone. Metabolites including 3H-progesterone, 3H,14C-20 alpha-dihydroprogesterone, 3H,14C-17-hydroxyprogesterone, 3H-estrone and 3H-estradiol-17 beta appeared in the medium during the first 20 minutes of incubation. 3H,14C-Androstenedione was not consistently noted until after 60 minutes. Despite the fact that the 14C/3H-17-hydroxyprogesterone ratio quickly approached a constant value in the medium, 14C-estrogens were not detected in the medium or tissue fragments suggesting that progesterone was not a principal precursor for estrogen synthesis. As evidenced by the observation that the 14C/3H-progesterone ratio was significantly higher in luteal fragments than the 17-hydroxyprogesterone ratio, 17-hydroxyprogesterone appeared to be synthesized from pregnenolone both by way of progesterone and by another route which did not include progesterone. C21- and C18-Steroids were more concentrated in tissue fragments after 120 minutes of incubation than in the medium indicating that these steroids were sequestered by luteal tissue.