The effect of reported prostaglandin synthetase inhibitors on estradiol - stimulated uterine prostaglandin biosynthesis in the ovariectomized rat

Aspirin, indomethacin and naproxen have been shown to inhibit the release of prostaglandins E and F (PGE and PGF) from the estradiol-stimulated uterus of progesterone-pretreated ovariectomized rats. Under the present experimental conditions indomethacin (1 mg/rat) was found to be a potent inhibitor of PGF and E biosynthesis, but the duration of action was less than 24 hours, after which a rebound above control levels was observed. The compounds were without effect on estradiol-stimulated increases in uterine wet weight. Δ′THC did not inhibit estradiol-stimulated PG biosynthesis but produced a significant rise (P<0.01) in PGE levels in uterine venous blood. A hypothesis is suggested to explain some of the pharmacological effects of Δ′THC.     

Decreased in vivo protein and phospholipid methylation after in vivo elevation of brain S-adenosyl-homocysteine

The administration of adenosine together with homocysteine resulted in a dose-related elevation of cerebral S-adenosyl-L-homocysteine without concomitant perturbation of S-adenosyl-L-methionine levels. The adenosine + homocysteine treatment also decreased the incorporation of labile and stable methyl groups into brain proteins. Brain [³H]-phosphatidyl N,N-dimethylethanolamine and [³H]-phosphatidylcholine were also significantly decreased while [³H]-phosphatidyl-N-monomethylethanolamine remained unchanged. The data indicate that elevated brain S-adenosylhomocysteine can markedly and selectively inhibit the $\text{in vivo}$ methylation of brain proteins and phospholipids.     

Prostaglandin synthesis in rat embryo tissue: The effect of non-steroidal anti-inflammatory drug in vivo and ex vivo

Aspirin and salicylate are well-known but poorly understood teratogens in laboratory animals. Because aspirin inhibits PG synthesis, we systematically examined PG synthesis in rat embryo homogenates, the inhibition of PG synthesis $\text{in vivo}$ and $\text{ex vivo}$ by various non-steroidal anti-inflammatory drugs, and tested the hypothesis that the inhibition of PG synthesis is responsible for aspirin-induced limb defects in rats. We report that embryonic rat homogenates synthesis 6-keto-PGF_1α, PGE, and PGF in large amounts from endogenous substrate, that aspirin and other non-steroidal anti-inflammatory drugs inhibit PG synthesis $\text{in vitro}$ but not necessarily $\text{in vivo}$, and that contrary to our original hypothesis, the inhibition of PG synthesis is likely not responsible for aspirin-induced limb defects in rats.     

Effect of metoclopramide on rat prolactin secretion in vivo

Metoclopramide, a potent antagonist to apomorphine, was used to the rats $\text{in vivo}$ to determine its effect on the release of prolactin. A single i.p. injection of metoclopramide at 10 or 100 μg/100 g b.w. under urethane anesthesia increased serum prolactin levels by 1.6 or 7.2 fold, respectively, compared with basa levels. This prolactin increase was completely abolished by 2-bromo-α-ergocryptine (CB-154).These data suggest that metoclopramide stimulates prolactin secretion in rat and this secretion is abolished by dopaminergic stimulant.     

The in vivo inhibition of gaba-transaminase by gabaculine

The naturally occurring amino acid gabaculine ((?)-5-amino-1,3 cyclohexadiene carboxylic acid) is a potent irreversible inhibitor of mouse brain γ-aminobutyric acid (GABA)-α-ketoglutaric acid transaminase. When administered I.P. gabaculine, irreversibly inhibits the mouse brain enzyme in a time dependent fashion. Concomitant with this inhibition is a rise in endogenous brain GABA levels. Administration of gabaculine at a concentration of 100 mg/kg mouse leads to the complete inhibition of the enzyme after 4 hrs. Brain levels of GABA continually rise after the administration of the drug. After 20 hrs they are 15–20 times higher than levels in the untreated animals.     

Effect of lyso-phosphatidylserine on rat hypothalamic cAMP, in vivo

Lyso-Phosphatidylserine, like its precursor phosphatidylserine, increases the concentration of cAMP in the rat hypothalamus. The effect is dose-dependent and reaches its maximum 10–20 minutes from the injection. Antiadrenergic drugs, such as reserpine, α-methyl-p-tyrosine (α-MpT), haloperidol and chlorpromazine, but not phentolamine or propranolol, prevent the accumulation of hypothalamic cAMP induced by lysophosphati dylserine. Serotoninergic, histaminergic, cholinergic and GABAergic drugs do not modify the lyso-phosphatidylserine effect. The obtained results suggest a primary involvement of the dopaminergic system in the mediation of the pharmacological effect of lyso-phosphatidylserine.     

Monitoring the stereospecificity of morphine action in vivo and in vitro through brain membrane lipid fluidity

Differential scanning calorimetry of crude brain mitochondrial lipids obtained from control and morphine treated rats was carried out and the lipid phase transition measured. Morphine treatment resulted in a significant decrease in the temperature range and enthalpy of the phase transition. This effect was found to be dose dependent and reversible both $\text{in vivo}$ and $\text{in vitro}$ by naloxone. Studies with levorphanol and dextrorphan demonstrated stereospecificity. Furthermore, the ether precipitable fraction of total lipid extracts was shown to mediate the opiate response.     

Studies on closure of the ductus arteriosus. X. in vivo effect of prostaglandin

The effect of prostaglandins F_2∝, E₁ and of 7-oxa-13-prostynoic acid on the newborn rat and rabbit ductus can be studied using the whole-body freezing technique. PGF_2∝ and PGE₁ were able to re-open the closing ductus arteriosus in adequately oxygenated animals. PGF_2∝ administration was accompanied by a strong physical reaction in the rat but less in the rabbit. PGF₁ had sedative effects in both animals. A prostaglandin antagonist, 7-oxa-13-prostynoic acid had no effect on normal ductal closure nor did it counteract the effects of PGF_2∝ and PGE₁. The role of prostaglandins in homeostasis during the fetal and newborn period may be to modify ductal tone.     

Sites of in vivo extraction and interconversion of estrone and estradiol in the dog

The interconversion and extraction of estrone and estradiol-17β across and within different tissues or areas have been studied in the dog by the constant infusion technique. The results were calculated using the ³H/¹⁴C ratios and radioactive concentrations of estrone and estradiol obtained from afferent and efferent blood and tissues at equilibrium. From these results it is concluded that: (1) there is no significant difference between metabolic clearance rates of estrone and estradiol, (2) blood transfer constants indicate a higher conversion of estradiol to estrone than of estrone to estradiol, (3) the transtissue interconversion favors the formation of estrone while the intratissue interconversion favors the formation of estradiol, (4) no interconversion of the two estrogens is observed in adipose tissue, (5) the extraction of estradiol entering a tissue was lower than the extraction of estradiol formed in these tissues, (6) calculation of the tissue metabolic clearance rates show that 63% and 61% of the total metabolism of estrone and estradiol, respectively, occurs in the splanchnic bed, and (7) the contribution of each tissue to the total interconversion of estrone and estradiol show that more than 90% of this interconversion occurs extrahepatically.     

Characterization of specific in vivo binding of neuroleptic drugs in rat brain

$\text{In vivo}$ binding of ³H-spiperone is saturable in the striatum, the limbic system and the frontal cortex but not in the cerebellum. A specific binding is different in all the brain regions thus the amount of labelling in the cerebellum may not be considered as a blank value.³H-spiperone binding revealed a specific subcellular distribution only when a very low dose was injected into rats.$\text{Ex vivo}$ experiments allow the assessment of biochemical profiles of neuroleptic drugs according to their relative affinity for dopamine or serotonin receptors.     

Antigen-Induced leukotriene relaese from rat lung in vitro

Chopped lung from inbred hyperreactive rats was challenged with antigen following active on passive sensitization and supernatants were assayed for the presence of leukotrienes (LTs) by radioimmunoassay. Dose-related increases in the release of LTC₄- and LTB₄-immunoreactive material were obtained with significantly more material being released following passive sensitization. Chromatographic analysis indicated the presence of LTB₄, LTC₄ and LTE₄. When LT release inbredred rats was compared to Sprague-Dawley or Fischer rats, the amounts released were as follows: Inbred > Sprague-Dawley > Fischer. It was concluded that the release of LTs in the three strains correlated with the degree of non-specific bronchial hyperreactivity.     

Angiotensin stimulates cortisol biosynthesis in human adrenal cells in vitro

Adrenal glands obtained from patients undergoing therapeutic adrenalectomy were used to study the effects of angiotensin on human adrenal steroidogenesis. It was observed that angiotensin stimulated cortisol biosynthesis. Although this has been demonstrated to occur in canine and bovine adrenals, angiotensin-induced cortisol biosynthesis has not been established in man. The possibility that angiotensin merely stimulated glomerulosa cells to secrete precursor steroids which accumulated in the medium and then diffused into fasciculata cells to provide substrate for cortisol biosynthesis was excluded by demonstrating that 3β-hydroxy-5-pregnen-20-one (pregnenolone) and progesterone (the only pertinent precursors) did not accumulate in angiotensinstimulated cell suspensions. In addition, angiotensin stimulated cortisol biosynthesis in a fasciculata cell suspension in which angiotensin did not stimulate aldosterone production. Therefore, in human adrenal cell suspensions angiotensin appeared to act directly to stimulate cortisol synthesis by fasciculata cells. In normal subjects pre-treated with dexamethasone, angiotensin infusions failed to stimulate an increase in plasma cortisol. The physiological importance of angiotensin as a regulator of cortisol secretion remains, therefore, to be established.     

Inactivation of aromatase in vitro by 4-hydroxy-4-androstene-3,17-dione and 4-acetoxy-4-androstene-3,17-dione and sustained effects in vivo

4-Hydroxy-4-androstene-3,17-dione (4-OHA) and 4-acetoxy-4-androstene-3,17-dione (4-AcA), in addition to being competitive inhibitors of aromatase, cause time-dependent, irreversible, loss of enzyme activity in both human placental and rat ovarian microsomes. $\text{In vivo}$, treatment of rats with 4-OHA also causes loss of ovarian aromatase activity. To test whether this loss of activity could have $\text{in vivo}$ significance, rats with hormone-dependent, mammary tumors were treated with 4-OHA on alternate weeks. Tumor regression continued to occur during the weeks without treatment. These findings suggest that inactivation of aromatase is important in the mechanism of action of the compounds $\text{in vivo}$.     

The lack of an effect of furosemide on uterine prostaglandin metabolism in vivo

We determined the effect of 2 mg/kg intravenous furosemide on the production and metabolism of prostaglandin E₂ in the utero-placental unit of pregnant dogs. Uterine venous prostaglandins E₂ and 15-keto-13,14-dihydro E₂ were measured by gas chromatography-mass spectrometry. Even though the dose of furosemide was adequate to effect a good diuresis, neither the production nor the metabolism of prostaglandin E₂ by the uterus was altered by that dose of the drug. Using radioactive microspheres to measure hemodynamic parameters, we observed no change in uterine vascular resistance while renal vascular resistance decreased. Although the renal concentration of furosemide may be higher than the uteroplacental concentration, there is so far no evidence $\text{in vivo}$ that usual doses of furosemide enhance the production or inhibit the metabolism of prostaglandin E₂.     

The effect of the cholesterol content of small unilamellar liposomes on the fate of their lipid components in vivo

We have investigated the effect of the cholesterol content of small unilamellar liposomes composed of egg phosphatidylcholine (PC) and containing 6-carboxyfluorescein (6-CF) on the in-vivo fate of their radiolabelled PC (³H-PC) and tracer [1-¹⁴C]-cholesteryl oleate (¹⁴C-cholesteryl oleate) components. Chromatography of the blood plasma of mice at various times after injection with liposomes composed of equimolar amounts of PC and cholesterol (PCCHOL liposomes) showed a main peak (peak A) containing most ³H-PC, ¹⁴C-cholesteryl oleate and 6-CF and representing intact liposomes. With cholesterol- free liposomes (PC liposomes) on the other hand, there was increasing transfer of the two radiolabelled lipids from peak A to the subsequently eluted high density lipoproteins (HDL) (peak B) paralleled by increasing loss of liposomal stability as evidenced by 6-CF release. Studies on the rate of clearance of PCCHOL liposomes showed half-lives of 110 min (³H-PC) and 120 min (¹⁴C-cholesteryl oleate marker). Similar studies with PC liposomes revealed complex patterns of clearance evaluation of which was hampered by a number of observed or anticipated concurrent events: removal of liposomes by tissues, transfer of PC and cholesteryl oleate to HDL, clearance of HDL and donation of the two lipids by HDL to, or their exchange with lipids of, tissues.     

Bronchoconstrictor effects of leukotriene B4 in the guinea pig in vivo

Administration of leukotriene B₄ (LTB₄) to anesthetized spontaneously breathing guinea pigs either by the intravenous or aerosol route produced pronounced changes in pulmonary resistance and dynamic compliance. The effects were short lived and were completely abolished by pretreatment of animals with the cyclooxygenase inhibitor indomethacin. Histological examination of lungs following aerosol administration of LTB₄ showed a pronounced neutrophil infiltration. These results confirm previous $\text{in vitro}$ studies in which LTB₄ was shown to produce contractions on guinea pig parenchymal strips indirectly by releasing thromboxane A₂.