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PubMed1982

In vivo and in vitro production of progestins by the corpus luteum of pregnancy of the hamster.

Synthesis by hamster corpora lutea (CL) in vitro and serum levels of progesterone (P4), 17 alpha-hydroxyprogesterone (17OHP) and 20 alpha-dihydroprogesterone (20DHP) were assessed for different days of pregnancy (Day 1=day of sperm; Day 16=day of delivery). Highest serum levels of the progestins were observed on Day 14 (P4=33 ng/ml; 17OHP=2 ng/ml; 20DHP=3 ng/ml), followed by precipitous declines on Day 16. The highest in vitro levels of luteal P4 and 17OHP were attained on Days 2-6 (production rates of P4=9-30 ng/mg CL/h; 17OHP=0.6-1.5 ng/mg CL/h), and dropped gradually thereafter. In contrast, the production rate of luteal 20DHP was extremely low on Days 2-8 but abruptly increased on Day 10 and was maintained through Day 14 (4-8 ng/mg CL/h). The in vitro production rates of all 3 progestins dropped abruptly on Day 16. Thus, in the pregnant hamster on the day of parturition (Day 16) there was good agreement between in vivo and in vitro levels of the progestins, contrary to the situation in the rat, where on Day 22 the CL in vitro produce large quantities of P4 and 20DHP while the serum levels are very low (Taya and Greenwald, 1981). Addition of 25 ng/ml of ovine LH to the incubation media containing hamster CL increased production rates of P4 (18-55 ng/mg CL/h) and 17OHP (1.5-2.4 ng/mg CL/h) on Days 2, 4 and 14 of pregnancy but the CL were refractory to this dose of LH from Days 6 to 12. The production rate of luteal 20DHP ws never stimulated by the addition of 25 ng LH. These results indicate that P4 is the principal progestin in the pregnant hamster with 17OHP and 20DHP as minor metabolites. The latter 2 progestins have been measured for the first time in the pregnant hamster and the levels are very low in comparison to the pregnant rat.

Algestone↗
PubMed1981

In situ subcellular distribution and metabolism of progesterone, estradiol and androstenedione in the vascularly separated and isolated hypothalamus of the female rhesus monkey.

A neurosurgical procedure has been developed for the vascular isolation of the hypothalamus-thalamus region of the rhesus monkey brain. The circulation to the left and right halves of the hypothalamus was also isolated and each half of the hypothalamus was perfused simultaneously, but separately, with a dextran-blood solution which contained radioactive gonadal steroids. The hypothalamus in situ efficiently converted [3H]androstenedione to [3H]estrone and this aromatization was inhibited by the presence of androsta-1,4,6-triene-3,17-dione (ATD) in the perfusate. [3H]Progesterone was metabolized predominantly to 5 alpha-pregnane-3,20-dione (5 alpha-DHP) and 20 alpha-hydroxypregn-4-ene-3-one (20 alpha-OHP). Subcellular fractionation of the hypothalamus after the in situ perfusion with [3H]-progestin or [3H]estradiol to the hypothalamus of estrogen-treated ovariectomized monkeys or oil-treated ovariectomized monkeys, respectively, indicated that the retention of [3H]estradiol in the nucleus was a saturable, limited-capacity phenomenon. No saturable subcellular distribution of [3H]progesterone or [3H]R 5020 was observed. This latter observation might be attributable to the presence of a progesterone receptor in too small a concentration to be detected by the methods used.

20-alpha-Dihydroprogesterone↗
PubMed1982

Progesterone metabolism by the hypothalamus, pituitary, and uterus of the aged rat.

Progesterone metabolism was examined in tissues of rats in three stages of reproductive senescence (constant estrus, repeated pseudopregnancies, and anestrus) and in young rats. Metabolites were quantitated by reverse isotopic dilution analysis after incubation of the hypothalamus, pituitary, and uterus with [3H]progesterone. The metabolism of progesterone to 5 alpha-dihydroprogesterone and to 20 alpha-hydroxy-5 alpha-pregnan-3-one and the formation of total 5 alpha-reduced products was significantly reduced (by half) in pituitaries of constant estrous rats compared to rats in all other stages. The formation of 3 alpha-hydroxy-5 alpha-pregnan-20-one and total 3 alpha-reduced products was about 2-fold higher in pituitaries and hypothalami of pseudopregnant and anestrous rats than in constant estrous and young rats, but these differences were statistically significant only in the pituitary samples. In the uterus, progesterone metabolism to 20 alpha-dihydroprogesterone was significantly increased in anestrous rats compared to that in constant estrous and pseudopregnant rats. The results indicate that progesterone metabolism by target tissues, particularly the pituitary, is altered during reproductive senescence. They suggest the possibility that changes in the tissue metabolism of progesterone may be one means by which the effectiveness of progesterone is decreased during aging.

Aging↗
PubMed1985

In vitro luteinizing hormone-releasing hormone release from superfused rat hypothalami: site of action of progesterone and effect of estrogen priming.

The study examined the effect of estrogen priming on progesterone (P4)-induced LHRH release, the tissue site of action of P4, and the effect of 5 alpha-dihydroxyprogesterone (5 alpha-DHP) on LHRH release from hypothalamic fragments superfused in vitro. Immature female rats were ovariectomized (OVX) and, at 28 days of age, Silastic capsules containing estradiol (E2) were implanted. Two days later, animals were killed and hypothalamic fragments were removed and transferred to superfusion chambers. The hypothalamic units received P4 or 5 alpha-DHP delivered in an intermittent mode (10-min on, 20-min off). LHRH was determined in perfusates by RIA. After the input characteristics of different infusion modes (single pulses, intermittent, and continuous) of P4 infused into superfusion chambers were assessed, an intermittent infusion mode (10-min on, 20-min off) was selected for further examinations. In the mediobasal hypothalamic-anterior hypothalamic-preoptic area (MBH-AHA-POA) tissue preparations, we observed: 1) an infusion of 5 alpha-DHP was ineffective in stimulating LHRH release; 2) the release pattern of LHRH in response to three different P4 doses (10, 20, and 50 ng/ml) was similar in terms of percent changes (202% to 219% over control values); and 3) E2 priming was absolutely required for P4-stimulated LHRH release, and this requirement appeared to be dose dependent. Upon an examination of three hypothalamic tissue boundaries [the MBH, the POA-suprachiasmatic nuclei (POA-SCN), and the median eminence (ME)] to better delineate the in vitro site of action of P4 on LHRH release, it was demonstrated that the MBH responded upon P4 infusion, whereas the POA-SCN was unable to do so. The ME also responded upon P4 infusion, and LHRH release followed closely the pulsatile administration of P4 since upon each challenge of the steroid at the concentration of 10 or 20 ng/ml, a significant rise in LHRH release occurred. However, the temporal patterns of LHRH release from the ME appears to be different from those obtained from the MBH as well as the MBH-AHA-POA. These observations demonstrate that an intermittent infusion of P4, but not 5 alpha-DHP, is effective in activating the neural LHRH apparatus. Estrogen is an obligatory requirement for this P4-stimulated LHRH release, and the neural site of action of P4 resides within the MBH. However, this steroid also can act directly upon the ME nerve terminals to release LHRH.

Algestone↗
PubMed1977

Oestrogen formation from C19 precursors in human choriocarcinoma in culture.

A cloned cell line of human choriocarcinoma was evaluated as a model of human placental oestrogen production. Oestrone formation from dehydroepiandrosterone (D), D-sulphate (DS) or 4-androstenedione (A) was less than or equal to 5% of oestradiol-17beta (Oe2) formation. Oe2 formation from D and A was similar (100-150 pmole/h/10(7) cells); that from DS was 10 times less. Omitting serum from the medium increased Oe2 yield from DS 4-fold; addition of albumin restored these yields to control values (P greater than 0.05, t-test), presumably by binding DS. N6,O2'-dibutyryl-adenosine 3',5'-cyclic monophosphoric acid and theophylline treatment for 72 h stimulated (P less than 0.01) Oe2 formation from D (36%), DS (66%) and A (183%). In intact cells, sulphatase activity, Oe2 formation from D and Oe2 formation from DS equalled those in homogenates (P greater than 0.05) but Oe2 formation from D was greater than that from DS in both systems (P less than 0.001), indicating a deficiency of sulphatase relative to subsequent enzymes of oestrogen synthesis. Steroids, at concentrations previously shown to inhibit placental sulphatase or 3beta-hydroxysteroid dehydrogenase, did not inhibit choriocarcinoma enzymes. Except for its relative sulphatase deficiency and insusceptibility of oestrogen synthesizing enzymes to steroid inhibitors, choriocarcinoma appears to be a useful model of placental oestrogen synthesis.

Algestone↗
PubMed1981

Luteal blood flow and plasma steroids in rats with corpora lutea of different ages.

Ovarian and luteal blood flow rates were measured at different stages of luteal development in anaesthetized rats using 15 +/- 5 micron radioactive microspheres. Ovulations were induced by injection of 8 IU of PMSG at 28 days of age. Steroid concentrations in peripheral plasma were determined using radioimmunoassays. The highest luteal blood flow was found in the youngest corpora lutea and decreased gradually with luteal age. Luteal flow on days 13 and 14 was significantly lower than that of days 2, 4, and 6. Ovarian stromal blood flow remained unchanged throughout the lifespan of the lupus luteum. Peripheral progesterone concentrations rose significantly on days 4, 6, and 8 with a maximum on day 8, as compared to day 2, and fell significantly after day 8. The levels of 20 alpha-OH-progesterone increased sharply on day 10, indicating that functional luteolysis. The progesterone levels fell significantly between day 8 and 10 without a concomitant significant decline in luteal blood flow. Since a fall in progesterone production seem sto precede a drop in luteal blood flow, the initiation of luteolysis does not appear to be caused by a vascular mechanism.

Algestone↗