Prothrombin requires two sequential metal-dependent conformational transitions to bind phospholipid. Conformation-specific antibodies directed against the phospholipid-binding site on prothrombin.

Prothrombin is a gamma-carboxyglutamic acid-containing protein that binds to phospholipid vesicles in the presence of calcium ions after undergoing a metal ion-induced conformational transition. To integrate recent data into a scheme that is compatible with our knowledge of prothrombin-metal interaction, we have proposed a new model of prothrombin structure. In this model prothrombin undergoes two metal-dependent conformational transitions: PT----PT'----PT*. The first transition is not cation-specific, but the second transition is metal-selective for Ca(II), Sr(II), or Ba(II). Only the PT* conformer binds to phospholipid surfaces. To test this model, anti-prothrombin antibodies that only bind to prothrombin in the presence of Ca(II) but not Mg(II) (PT*-specific) were isolated, and termed anti-prothrombin X Ca(II)-specific. Half-maximal binding of antibody to prothrombin was observed at 0.1 mM CaCl2 or 1 mM SrCl2, but no binding was observed with Mg(II), Mn(II), or Ba(II). However, prothrombin in the presence of both Mg(II)/Ba(II) or Mn(II)/Ba(II) demonstrated significant interaction with the antibody. Prothrombin binding to phospholipid vesicles was inhibited by the anti-prothrombin X Ca(II)-specific antibody or its Fab fragment, but was not inhibited by anti-prothrombin X Mg(II) antibody or its Fab fragment directed at the PT' conformer. These results support this three-state model for prothrombin. The metal specificity characteristic of prothrombin-phospholipid interaction is a property required for the expression of the phospholipid-binding site in the binary prothrombin-metal complex.

Hormonal profile during termination of midtrimester pregnancy by extraovular instillation of saline: plasma levels of prostaglandins, progesterone and human chorionic gonadotropin.

Midtrimester abortion was initiated for psychosocial reasons in 5 patients, and premature delivery in 2 patients with intrauterine fetal death using a new method for termination of pregnancy--the instillation of normal saline through the cervical canal into the extraovular space. Blood levels of 15-keto-13,14 dihydro-prostaglandin F2 alpha (PGF2 alpha-M), progesterone (P) and Human Chorionic Gonadotropin (HCG) were determined from the start of the procedure up to the expulsion of the fetus at frequent intervals in the peripheral circulation of these patients, by highly sensitive and specific RIA procedures. Following saline instillation and initiation of contractions, the concentration of PGF2 alpha-M increased significantly, reaching peak values either shortly before or at the time of delivery. This rise was associated with a significant decrease of P levels. Levels of HCG were variable. The possible significance of these results is discussed.

Effect of antihypertensive drugs on plasma renin activity and urinary excretion of prostaglandin E2.

Urinary prostaglandin (PGE2) and plasma renin activity (PRA) were determined in 3 groups of hypertensive patients before and following 5 days of treatment with different antihypertensive drugs. In all 3 groups studied a substantial decrease of blood pressure was noted following treatment. However, whereas administration of chlorthalidone and hydralazine initiated a significant rise of PGE2 and PRA excretion, treatment with propranolol was associated with a decrease of these two parameters. In view of these findings it seems therefore as if renal production of PGE2 (at least with regard to propranolol, a beta-blocking agent), is not related to the hypotensive effect of the drug.

Effect of chronic and acute changes in sodium balance on the urinary excretion of prostaglandins E2 and F2 alpha in normal man.

1. The effects of changes in sodium balance on renal prostaglandins have been hitherto studied mainly in experimental animals and the results have been controversial. In this study the 24 h urinary excretion of prostaglandins E2 and F2 alpha was measured by radioimmunoassay in seven normal subjects under basal conditions and after 5 days of a diet containing less than 20 mmol of sodium/day. Subsequently a sodium chloride (150 mmol/l: saline) load (300 mmol of sodium over 4 h) was infused and prostaglandins were again measured in hourly urine collections. Plasma renin activity and aldosterone were also measured under basal conditions, after the low sodium diet and at 2 and 4 h of the saline infusion. 2. Dietary sodium restriction was associated with a marked increase in prostaglandin E2 excretion (from 769.7 +/- 201.6 SEM to 1761.3 +/- 304.9 ng/24 h, P less than 0.0005). Prostaglandin F2 alpha also increased from 1187.0 +/- 390.1 to 1435.6 +/- 344.6 ng/24 h, but this was not statistically significant. The prostaglandin E2/prostaglandin F2 alpha ratio increased from 0.83 +/- 0.2 to 1.52 +/- 0.34 (P less than 0.01). Plasma renin activity and aldosterone rose significantly (P less than 0.05 and less than 0.0025 respectively). 3. During the saline load prostaglandin E2 decreased after 2 h from 142.4 +/- 29.9 to 86.7 +/- 22.9 ng/h (P less than 0.05) and to 36.9 +/- 5.96 ng/h after 4 h. Prostaglandin F2 alpha decreased at a slower rate, from 98.4 +/- 18.7 to 37.5 +/- 8.8 ng/h at 4 h (P less than 0.02). At 4 h the prostaglandin E2/prostaglandin F2 alpha ratio returned to control values (0.90 +/- 0.17). Plasma renin activity and aldosterone decreased significantly after 2 h (P less than 0.02 and less than 0.0025 respectively) and reached control values after 4 h. 4. The present study demonstrates that chronic and acute changes in sodium balance induce changes in the excretion of prostaglandin E2 parallel to changes in plasma renin activity and aldosterone. The similar but quantitatively smaller changes in prostaglandin F2 alpha and the inversion of the ratio between the two prostaglandins during sodium deprivation suggest that at least two factors are involved: increased delivery of substrate for prostaglandin synthase and decreased activity of the prostaglandin E1 9-keto-reductase. Prostaglandins probably play an important role in the adaptation of the kidney to changes in sodium balance.

Urinary prostaglandin-E2 in chronic renal disease.

Renal excretion of prostaglandin-E2 was measured by radioimmunoassay in patients with chronic renal diseases. Significantly elevated urinary prostaglandin-E2 amounts were found in patients with moderate renal insufficiency (creatinine clearances 20-59 ml/min). In mild and severe renal insufficiency, the urinary excretion of PGE2 was within the normal range. In the non-terminal stages of kidney failure, a definite correlation was found between the degree of renal impairment and the daily amounts of PGE2 in the urine. It is therefore concluded that in these stages of the disease the kidney produces elevated levels of PGE2 in an attempt to improve the decreased renal blood flow caused by the disease.

Effect of furosemide on renal prostaglandins E2 and F2 alpha in normal subjects and in patients with essential hypertension.

The urinary excretion of prostaglandins (PG) E2 and F2 alpha, which reflects the renal synthesis of these substances, was evaluated by radioimmunoassay before and after an i.v. injection of furosemide in 10 normal subjects and in 10 patients with essential hypertension. In most normal subjects, urinary PGE2 increased after furosemide injection, whereas PGF2 alpha decreased to undetectable levels. In the hypertensive subjects, PGE2 increased to a lesser degree or decreased, but PGF2 alpha excretion was unchanged or augmented. These results suggest that furosemide may increase PGE2 synthesis not only by increasing the availability of the substrate arachidonic acid or by inhibiting the action of the catabolizing enzyme 15-hydroxyl-PG-dehydrogenase, as has been proposed, but also by depressing the activity of the enzyme PGE2-9-ketoreductase, which catalyzes the conversion of PGE2 to PGF2 alpha. In essential hypertension, an increased activity of PGE2-9-ketoreductase could explain the decreased levels of PGE2 that have recently been described in these patients. Whether these abnormalities in PG interconversion play a role in the pathogenesis of the hypertensive state or are secondary to it remains a question for further investigation.

Significance of prostaglandins in the regulation of cyclic events in the ovary and uterus.

We examined the role of prostaglandins in three pivotal events of the female reproductive cycle: ovulation, luteolysis, and menstruation. Four general approaches were adopted, using in vivo and in vitro models: use of inhibitors of cyclooxygenase and of PG action; immunoneutralization of individual prostaglandins; administration of exogenous prostaglandins; and attempts to correlate PG levels in tissues and body fluids to physiologic events. It can be concluded that prostaglandins or related metabolites of arachidonic acid are essential in laboratory rodents for follicular rupture and the release of a fertilizable oocyte, but not for other LH actions on the follicle that are mimicked by PG or for the neuroendocrine triggering of ovulation. PGs control the cyclic regression of the corpus luteum and appear also to be implicated in the decidual reaction and in the menstrual shedding of the endometrium in primates. Some aspects of the control of follicular PG formation and of PG action were analyzed. Gonadotropins stimulate follicular PG synthesis by a steroid-independent cyclic nucleotide-mediated induction of cyclooxygenase. Both the thecal and granulosa cell compartments show this response. An effect of the phytolectin conconalavin A on ovarian PG synthesis is described. The response of follicular cells to prostaglandin E2 exhibits the phenomenon of desensitization and is influenced by agents modifying the structure and function of cytoskeletal elements. Evidence is put forward for the view that abrogation by PGF2 alpha of the stimulatory action of LH on luteal adenylate cyclase is the biochemical basis of the luteolytic action of this prostaglandin. While the precise mechanism of PG action on the endometrium remains to be defined, PG-synthetase inhibitors have already found useful applications in the management of menstrual disorders, such as functional dysmenorrhea and menorrhagia. The role in ovarian and uterine physiology of the more recently discovered labile arachidonate metabolites, such as the endoperoxides, prostacyclin, and thromboxanes, has not yet been adequately explored.

Differences in prostaglandin formation between thymocyte subpopulations.

The concentration of prostaglandin E and the activity of prostaglandin synthetase were determined in mature and immature mouse thymocytes. Hydrocortisone resistant thymocytes, or thymocytes separated from the immature cell population after agglutination of the latter by peanut agglutinin served as a source of mature thymocytes. It was found that mature thymocytes contain a much higher concentration of prostaglandin E and have an increased activity of prostaglandin synthetase than immature cells.

Changes in immunological activity of rat lymphoid organs during pregnancy.

Immune reactivity in lymhoid organs of rats during the last week of syngeneic (Lewis: L x L) or allogeneic (females Lewis x males Wistar: L x W) pregnancy was compared with that found in non-pregnant animals. The thymus weight was slightly reduced and the response of thymic lymphocytes to phytohaemagglutinin and concanavalin A was slightly, but not significantly, elevated in pregnant rats. By contrast, the response of lymphoid cells from spleen and mesenteric lymph nodes to the mitogens was reduced in rats during advanced pregnancy. The immune response of lymphocytes from pregnant L x W rats to allogenic (Brown-Norway: BN) or semiallogeneic (W) irradiated cells was tested by the mixed lymphocyte culture (MLC) assay. The MLC response of para-aortic lymph nodes towards the unrelated BN cells was elevated over that of non-pregnant rats on day 15 of pregnancy. No significant enhancement was observed at the same time in the MLC response of mesenteric lymph nodes. On day 20 of pregnancy, a reduced MLC response towards BN cells was found in the mesenteric and para-aortic lymph nodes. On day 15 of pregnancy, the MLC response of mesenteric and, more markedly, that of para-aortic lymph nodes to paternal (W) cells was enhanced, as compared to that of non-pregnant rats. On day 20 of pregnancy, the response of mesenteric lymph nodes was suppressed, while the response of para-aortic lymph nodes was similar to that found in non-pregnant rats. Since the latter lymph nodes are the most directly exposed to antigenic stimulation from the uterus, it seems unlikely that the suppression in response to T-cell mitogens observed in the spleen and mesenteric lymph nodes during pregnancy accounts for the survival of the foetus. It seems more plausible that local factors in the vicinity of the uterus protect the foetus from being rejected.

Preovulatory changes in ovarian cyclic AMP and prostaglandins in immature rats injected with PMSG.

In 28-day-old rats injected with PMSG, ovarian cyclic AMP and PGE and PGF increased 2 and 3-4 h respectively after the LH peak.

Changes in steroid concentration in the ovaries of immature rats treated with pregnant mare serum gonadotrophin and human chorionic gonadotrophin.

The concentrations of testosterone, progesterone and 20alpha-hydroxypregn-4-en-3-one (20alpha-OHP) were measured in the ovaries of immature rats in which ovulation was induced by treatment with pregnant mare serum gonadotrophin (PMSG) and, 48 h later, with human chorionic gonadotrophin (HCG). The concentration of testosterone in the tissue increased significantly 48 h after treatment with PMSG, reached a peak 4 h after the administration of HCG and declined to the basal level 4 h later. Increases in the levels of progesterone and 20alpha-OHP were observed 4 h after the administration of HCG. Whereas the level of 20alpha-OHP continued to rise during the subsequent 30 h, progesterone levels declined near the presumed time of ovulation (12 h after administration of HCG). It is concluded that 20alpha-hydroxysteroid dehydrogenase activity is present in the immature rat ovary before ovulation and that an increase in the production of testosterone in the ovaries of rats treated with PMSG and HCG precedes increased production of progesterone and 20alpha-OHP in these ovaries.

Endocrine and reproductive repercussions of immunization against progesterone and oestradiol in female rats.

Mature female rats were immunized with BSA-conjugates of oestradiol-17beta-6-carboxymethyloxime or progesterone-11-hymisuccinate. Sera tested two months later at 1/2000 dilution bound 63.3% +/- 3.1 SEM and 21.2% +/- 2.3 of the homologous tritiated hormone (10 pg),--oestradiol-17beta(Oe2) and progesterone (P), respectively. Rats immunized against Oe2 had a significantly longer oestrous cycle (8.2 days vs. 4.5 days in BSA-immunized rats), with a prolonged leukocytic phase. The cycle of rats immunized against P was also prolonged (10.5 days), but in this group the cornified smear phase was abnormally extended. The luteinizing hormone (LH) normally observed on the afternoon of pro-oestrus failed to occur in the rats immunized against Oe2 and in 70% of rats immunized against P. The latter animals, however, showed sporadic LH discharges during periods of persistent cornification. Immunization against P resulted in elevated total (free plus bound) plasma P levels; immunization against Oe2 prevented the pro-oestrous rise in plasma P. Mating of rats immunized against Oe2 resulated in normal pregnanices, while none of the rats immunized against P delivered.

Decidual extracts suppress antibody response in vitro.

Extracts of decidual tissue produced in pseudopregnant rats were found to suppress in vitro antibody response to alpha-2,4-dinitrophenyl-polylysine. The peak levels of both the total antibody response and the 2-mercaptoethanol-resistant fraction were reduced. Extracts prepared in a similar manner from uteri of normal untreated or pseudopregnant rats did not exert such an effect.

Acute effect of delta1-tetrahydrocannabinol on the hypothalamo-pituitary-ovarian axis in the rat.

Administration of delta1-tetrahydrocannabinol (delta1-THC), the principal psychoactive ingredient of cannabis, to proestrous rats (2 mg/rat, i.p., between 12.00 and 16.00 h) suppressed the proestrous rise in the plasma levels of LH, FSH and prolactin (Prl) and caused a 24 h delay in ovulation. Furthermore, the increased accumulation of prostaglandins of the E-type (PGE) in the ovaries, normally seen on the evening of proestrus, was prevented. Earlier (08.00-10.30 h) or later (18.00 h) administration of the drug on the day of proestrus was only partially effective in inhibiting ovulation. The suppressive effects of delta1-THC on ovulation and gonadotropin secretion were prevented by administration of gonadetropin releasing hormone (GnRH, 0.2 microgram/rat) 1 h after the drug, indicating that the central action of delta1-THC was exerted on the hypothalamus and not on the pituitary gland. Administration of ovine luteinizing hormore (oLH, 2.5 microgram/rat at 16.30 h on the day of proestrus restored ovulation and ovarian PGE accumulation in Nembutal-treated rats, but not in delta1-THC-treated rats; higher doses of oLH (5-10 microgram/rat) reversed the action of delta1-THC on these two parameters.

Effect of luteinizing hormone on the pattern of steroid production by preovulatory follicles of pregnant mare's serum gonadotropin-injected immature rats.

Preovulatory follicles were explanted on the day before ovulation from immature rats given a single injection of Pregnant Mare's Serum gonadotropin (PMS) 2 days earlier. The follicles were incubated for 4 h in modified Krebs bicarbonate buffer containing glucose and albumin in absence or presence of ovine luteinizing hormone (NIH-LH-S18; 0.1-10 mug/ml). The accumulation of progresterone, androstenedione and 17beta-estradiol in the medium was determined by radioimmunoassay. As in indicator of LH exposure the meiotic stage of the follicle-enclosed oocyte was determined at recovery by interference contrast microscopy. The first group of follicles were explanted in the morning, before the endogenous gonadotrophin surge. In hormone-free medium the oocytes remained in the dictyate stage, whereas addition of LH induced oocyte maturation. These follicles, when incubated in hormone-free medium, secreted predominantly androstenedione and estradiol and only low amounts of progesterone. In the presence of LH the secretion of all steroids was enhanced. The second group of follicles were explanted in the evening, 2-4 h after the endogenous gonadotrophin surge. After incubation in hormone-free medium the follicle-enclosed oocytes had matured. The steroid secretion by the follicles was different from that of the first group. In hormone-free medium they secreted predominantly progesterone and low amounts of androstenedione and estradiol. Addition of LH to the medium caused further enhancement of progesterone secretion, but had no effect on androstenedione and estradiol secretion. The third group of follicles were explanted in the evening from rats in which the preovulatory gonadotrophin surge had been prevented by Nembutal treatment. Oocyte maturation and steroid secretion did not differ from that found for the first group of follicles explanted in the morning. The results are compatible with the hypothesis that LH, after a transitory stimulation, inhibits androgen and estrogen secretion and stimulates progesterone secretion by the preovulatory ovarian follicle.

Oocytic meiosis in cultured rat follicles during inhibition of steroidogenesis.

Steroid release by cultured Graafian follicles explanted from rat ovaries on the morning of pro-oestrus was measured by radioimmunoaso the medium reduced the basal level of steroid secretion (progesterone, androstenedione and oestradiol-17beta) and abolished the steroidogenic effect of luteinizing hormone (LH; 5mug/ml) and prostaglandin E2 (PGE2; 10 mug/ml). However, the induction of oocyte maturation by either LH or PGE2 was not impaired by total suppression of the steroidogenic response of the follicles to these hormones by cyanoketone or aminoglutethimide. It is concluded that the meiosis-inducing action of LH on the mammalian egg is not mediated by the effect of the hormone on the rate and pattern of follicular steroidogenesis.