Biomedical subjects

S L Silavin

Publications and source records attributed to S L Silavin.

14 recordsLinked to original sources

PubMed1994

Intravenous administration of cocaine stimulates gravid baboon myometrium in the last third of gestation.

OBJECTIVE: The hypothesis for this investigation was that intravenous cocaine results in a dose-dependent increase in myometrial activity of the unanesthetized, chronically instrumented gravid nonhuman primate. STUDY DESIGN: Seven chronically instrumented gravid baboons were individually caged in an environment of 14 hours of light and 10 hours of darkness. Maternal femoral artery and vein catheters and three pairs of myometrial electromyographic wires were surgically placed at 90 to 121 days' gestation (term 180 days). At least 5 days after surgery, bolus intravenous cocaine hydrochloride doses of 0.05, 0.1, 0.3, 0.5, and 1.0 mg/kg maternal body weight were administered according to various schedules. Myometrial activity was analyzed by quantifying the myometrial electromyographic envelope data as the power spectral density window of contraction activity and as the total area under the rectified electromyographic voltage signal (i.e., total electromyographic activity) before and during the experimental period. RESULTS: Myometrial contraction activity increased after the 0.3 mg/kg dose (p < 0.01), the 0.5 mg/kg dose (p < 0.005), and the 1.0 mg/kg dose (p = 0.07) compared with baseline. The total myometrial electromyographic activity also increased as the cocaine dose increased. CONCLUSION: Intravenous cocaine results in increased myometrial contractions in the gravid baboon during the latter third of pregnancy.

Animals↗

PubMed1993

Effects of labetalol on uterine blood flow and cardiovascular hemodynamics in the hypertensive gravid baboon.

OBJECTIVE: The purpose of this study was to investigate the effects of labetalol on uterine blood flow and cardiovascular parameters in acutely instrumented, hypertensive gravid baboons. STUDY DESIGN: During the latter half of pregnancy six gravid baboons were acutely instrumented, with ultrasonic flow probes placed on ipsilateral, external iliac, and uterine arteries and a flow-directed pulmonary artery catheter in the pulmonary artery. After a stable arterial pressure baseline was obtained, norepinephrine was infused to increase mean arterial pressure by at least 20%. A 20-minute hypertensive steady state was obtained. Labetalol at 0.5 and 1.0 mg/kg was randomly infused, followed by a 2.0 mg/kg dose, each over 1 minute. A 20-minute recovery period followed every labetalol infusion, allowing the hypertensive steady state to reestablish. External iliac and uterine blood flow measurements were continuously recorded during the baseline and experimental trials. Mean arterial blood pressure, heart rate, pulmonary artery and capillary wedge pressure, central venous pressure, and cardiac output were obtained at 5, 10, and 15 minutes during each steady state and after each labetalol infusion. RESULTS: Labetalol at all dosages significantly reduced the mean arterial pressure and the systemic vascular resistance at 1.0 and 2.0 mg/kg. External iliac blood flow was not consistently significantly reduced; however, uterine blood flow was significantly reduced after the 1.0 and 2.0 mg/kg labetalol dosages (p < 0.05). Although uterine vascular resistance tended to increase after the 1.0 and 2.0 mg/kg doses, statistical significance was not achieved. CONCLUSION: Low-dose labetalol (0.5 mg/kg) significantly reduces the pharmacologic hypertensive gravid baboon's mean arterial blood pressure without adversely affecting uterine blood flow.

Animals↗

PubMed1992

Different patterns of myometrial activity and 24-h rhythms in myometrial contractility in the gravid baboon during the second half of pregnancy.

Two clearly distinct epochs of myometrial contractility were observed in 13 pregnant baboons when recorded either as intraamniotic pressure (IAP) or myometrial electromyogram (EMG). Contractures, epochs lasting longer than 3 min, were the characteristic form of myometrial activity throughout pregnancy. Contractures generated only small increases in IAP. Short-lived contractions, generating larger increases in IAP, were characteristic of labor and delivery. Power spectral analysis of IAP and myometrial EMG activity proved to be an effective means whereby periods when the myometrium was in the contractures or contractions mode could be easily distinguished. Concomitantly recorded maternal intraabdominal temperature showed significant 24-h variations. When myometrial activity switched from low-amplitude, long-lasting regular contractures of pregnancy to contractions, the switch always occurred around the onset of darkness. Five baboons went into spontaneous labor, 3 prematurely and 2 at term. In these animals the switch from contractures to contractions occurred for several nights before delivery. The recurrence and timing of the switch from contractures to contractions for several nights before delivery were similar to the pattern we and others have observed in the pregnant rhesus monkey. The presence of 24-h periodicity in the patterns of specific types of myometrial activity in another nonhuman primate lends support to the view that similar 24-h patterns of myometrial activity may occur in pregnant women.

Animals↗

PubMed1991

Effect of intravenous cocaine on uterine blood flow in the gravid baboon.

Cocaine abuse during pregnancy is associated with adverse perinatal outcome, believed to be a result of potent vasoconstrictive effects that cocaine has on the maternal cardiovascular system. The direct effect of cocaine on the pregnant, nonhuman primates' uterine vasculature in vivo has not been examined. We investigated the effects of intravenous cocaine on maternal arterial blood pressure, uterine blood flow, and uterine vascular resistance in four unanesthetized, chronically instrumented pregnant baboons. Baboons were instrumented during the latter half of pregnancy, placing an ultrasonic flow probe around one uterine artery and catheters in the maternal inferior vena cava and aorta. Bolus intravenous cocaine hydrochloride doses of 0.05 mg/kg, 0.1 mg/kg, and 0.3 mg/kg by maternal weight were infused 30 minutes apart at least 5 days after surgical instrumentation. The maternal blood pressure rose 7.3% and 12.0% after the 0.1 mg/kg and 0.3 mg/kg cocaine infusions, respectively, and the uterine blood flow fell in a dose-dependent fashion 13.1% and 22.7%. Plasma norepinephrine levels rose in response to the 0.3 mg/kg cocaine infusion. These studies show that low doses of cocaine significantly reduce uterine blood flow in the pregnant baboon in a dose-dependent manner by increasing uterine vascular resistance.

Animals↗

PubMed1989

Control of the steroidogenic machinery of the human trophoblast by cyclic AMP.

Human cytotrophoblasts express adenylate cyclase activity and possess membrane-bound regulatory proteins that bind guanine nucleotides (G proteins). Stimulation of the cyclase by forskolin or addition of 8-bromo-cAMP augments progesterone secretion by cultured cytotrophoblasts at least in part, by promoting accumulation of components of the cholesterol side-chain cleavage system. This is the consequence of increased synthesis of the proteins participating in steroidogenesis as a result of the 8-bromo-cAMP-provoked increase in their respective mRNAs. We propose that progesterone synthesis by cytotrophoblasts is up-regulated by cyclic AMP, which acts to increase expression of genes encoding the steroidogenic machinery. Paracrine or autocrine factors may initiate this cascade by stimulating the cytotrophoblast adenylate cyclase.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1989

Luteotrophic agents and steroid substrate utilization.

The cells of the CL are derived from precursors in the ovarian follicle. For their existence and function, they are dependent on a combination of various substances, collectively described as luteotrophins. These luteal stimulatory agents, including luteinizing hormone and prolactin from the pituitary, chorionic gonadotrophin from the placenta, and insulin from the pancreas, are classified as endocrine luteotrophins because they are produced at a distance from their target organ, the CL. Paracrine and autocrine luteotrophins are substances produced by the ovary with specific stimulatory effects on the CL: oestrogens and insulin-like growth factors meet this criterion. The CL produces progesterone from cholesterol which can be synthesized de novo or be derived from cholesteryl esters stored in the CL or from free and esterified cholesterol from lipoproteins in circulation. Cholesterol appears to be transported within the luteal cell by means of the cytoskeleton, by a specific, labile intracellular protein and/or by a specific sterol carrier protein. In this review, we have presented evidence to indicate that the luteotrophins have effects on all forms of cholesterol available to the CL. A major mechanism of action of luteotrophins appears to be the management of cholesterol supplies. LH, acting through a cAMP second messenger system, initiates the process of progesterone synthesis by induction of the cleavage of the side-chain on free cholesterol to produce pregnenolone. LH also acts to hydrolyse cholesteryl esters to produce free cholesterol. HDL metabolism appears to be affected by LH, hCG and cAMP. There is good evidence to suggest that luteal cell binding of HDL is regulated, in part, by LH. All phases of the process of utilization of LDL-cholesterol, including the availability of the LDL receptors, internalization of the LDL receptors and ligands into the luteal cell and degradation of LDL, are regulated by LH and cAMP. These agents induce an increase in mRNA for the LDL receptor. These processes may be, in part, controlled by an intracellular negative feedback mechanism for which cholesterol is the effector. However, in experiments where intracellular cholesterol was elevated by hydroxylated cholesterol or by inhibition of the conversion of cholesterol to pregnenolone, it was demonstrated that LH can override the cholesterol negative feedback mechanism. PRL plays an active role in cholesterol homeostasis in the luteal cell. The available evidence suggests that it is not involved in cholesterol side-chain cleavage, and enhances rather than reverses the formation of cholesteryl esters.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Involvement of cyclic AMP in the functions of granulosa and luteal cells: regulation of steroidogenesis.

The findings reviewed above demonstrate that cAMP can act at several distinct loci to enhance steroidogenesis. Analogs of cAMP stimulate the accumulation of the mRNAs which encode components of the steroidogenic machinery, such as the receptor for LDL and the system for the cleavage of the cholesterol sidechain. This apparently coordinated accumulation of specific mRNAs results from increased transcription of the relevant genes. Transacting factors modulated by cyclic AMP may influence common enhancer sequences (e.g., TGACGTCA), and such interactions would account for the simultaneous increase in expression of specific genes on several different chromosomes. These actions of cyclic AMP enable ovarian cells to support long-term increases in steroid synthesis by increasing the quantities of proteins involved in steroidogenesis. Such changes would obviously be important during luteinization, when the potential of granulosa cells to secrete progesterone is greatly increased. Although we speak of these effects as "long-term", it is evident that they occur within a relatively short time (hours) after exposure of cells to the tropic agent. Cyclic AMP also acts to stimulate steroidogenesis post-transcriptionally. It may influence events at the translational level via interactions in the formation of "labile" proteins. In addition, the regulation of cholesteryl ester hydrolase, as well as of other enzymes involved the metabolism of cholesterol, seems to involve post-translational modifications (e.g., phosphorylation). The effects of cAMP on the cytoskeleton may be another manifestation of a post-translational response. These actions of cAMP promote acute increases in steroidogenesis (i.e., within minutes). They encompass the transport of cholesterol to the mitochondria and the regulation of access of sterol to the inner mitochondrial membranes. Future research should be directed at elucidating the exact mechanisms which permit cAMP to exert coordinate effects on the genome (Figure 8), as well as its post-transcriptional effects on various proteins and enzymes which play a role in the synthesis of steroid hormones.

Animals↗

PubMed1985

The role of cholesterol esterification in ovarian steroidogenesis: studies in cultured swine granulosa cells using a novel inhibitor of acyl coenzyme A: cholesterol acyltransferase.

We have used a novel competitive inhibitor of acyl coenzyme A:cholesterol acyltransferase (ACAT), Sandoz compound 58-035 [3-(decyldimethyl-silyl)N-[2-(4-methyl-phenyl)1-phenylethyl propanamide], to assess the importance of the cholesterol esterification reaction in ovarian steroidogenesis. Compound 58-035 markedly (greater than or equal to 96%) inhibited ACAT activity of swine ovarian microsomes in a dose-dependent (0.1-3.5 micrograms/ml) fashion. In addition, treatment of cultured granulosa cells with this fatty acylamide effectively (greater than or equal to 98%) suppressed hormonally stimulated cholesterol esterification, as assessed by the incorporation of [3H]oleic acid into cholesteryl ester. Accordingly, we used this inhibitor to test the role of cholesterol esterification in ovarian cells. In cultures with limited or no serum supplementation, long term (2- to 6-day) treatment of granulosa cells with compound 58-035 significantly increased basal progesterone production and amplified by 2- to 10-fold the stimulatory actions of trophic hormones, such as estradiol, FSH, estradiol combined with FSH, or insulin. The amplifying effect of ACAT inhibition on hormone-stimulated progesterone production could be mimicked by providing exogenous cholesterol substrate in the form of low density lipoprotein (LDL). Cotreatment with compound 58-035 and LDL resulted in no further augmentation of steroidogenesis. In contrast to the facilitative effects of compound 58-035 in longer term cultures, this ACAT inhibitor did not alter progesterone biosynthesis acutely (2-20 h) in swine or hamster ovarian cells. These observations suggest that there is an obligatory partitioning of some sterol into the ester pool in granulosa cells. In times of diminished availability of cholesterol, inhibition of the esterification pathway can make additional cholesterol available for use in steroid hormone biosynthesis. Thus, in the intact Graafian follicle, where LDL cholesterol delivery to granulosa cells and intracellular cholesteryl ester stores are limited, regulation of the ACAT reaction may significantly modulate rates of progesterone biosynthesis. The present results indicate that the use of a selective inhibitor of cholesterol esterification can permit one to probe the functional significance of the esterification reaction in steroidogenic cells.

Amides↗

PubMed1984

Reevaluation of the effects of cytochalasins on steroidogenesis: studies on hamster granulosa cells.

Cytochalasin B (CB), a drug that inhibits microfilament polymerization, as well as having other actions, such as inhibition of hexose transport, is reported to block tropic hormone-stimulated steroidogenesis. Cytochalasin D (CD) is a more effective inhibitor of microfilament polymerization than CB, but has no effect on hexose transport. We reevaluated the effects of these inhibitors of microfilament function on steroid formation by freshly isolated granulosa cells from PMSG-primed hamsters. These cells have been shown to produce increased progesterone in response to tropic stimuli using endogenous steroidogenic precursors during short term incubation. In addition, they use exogenous substrate in the form of hydroxysterols for steroid production. Thus, we could examine effects of CB and CD on the metabolism of exogenous and endogenous sterol substrates. To determine the specificity of actions of cytochalasins, the metabolism of other steroid intermediates was examined: the conversion of pregnenolone to progesterone and the conversion of androstenedione to estradiol. Also, the oxidation of [14C]octanoate to 14CO2, a process that occurs in the mitochondria, was examined. Both CB and CD (1-10 micrograms/ml) inhibited LH- and 8-bromo-cAMP-stimulated progesterone production. Neither cytochalasin inhibited the production of progesterone in response to pregnenolone, nor were endogenous pregnenolone levels increased in the presence of CB or CD. Treatment with CB, but not CD, resulted in decreased progesterone production in response to hydroxycholesterol and decreased the side-chain cleavage of [3H]25-hydroxycholesterol. CB completely blocked the conversion of androstenedione to estradiol, whereas the aromatase reaction was unaffected by CD. CB, but not CD, significantly reduced the oxidation of [14C]octanoate to 14CO2 by hamster granulosa cells. Our findings demonstrate significant differences in the effects of CB and CD on granulosa cells. CB, in contrast to CD, has wide-spread effects on granulosa cell function, interfering with the metabolism of hydroxycholesterols, the oxidation of fatty acids, and aromatization. The failure of CD to interfere with these same functions suggests a more specific action of CD on the steroidogenic machinery. We conclude that microfilaments play an important role in the process of steroid formation from endogenous substrate. CD appears to affect a post-cAMP step between the conversion of cholesterol to pregnenolone, presumably the delivery of endogenous cholesterol to the mitochondria.

3-Hydroxysteroid Dehydrogenases↗

PubMed1984

Stimulation of progesterone synthesis in luteinized human granulosa cells by human chorionic gonadotropin and 8-bromo-adenosine 3',5'-monophosphate: the effect of low density lipoprotein.

Primary cultures of luteinized human granulosa cells reduced progestin secretion when taken from serum- and gonadotropin-containing medium into serum- and hormone-free medium. When added individually hCG, 8-bromo-cAMP and low density lipoprotein (LDL) stimulated progestin secretion by the cells after they spent 48 h in serum- and hormone-free medium. However, combinations of hCG or 8-bromo-cAMP and LDL were most effective in increasing steroidogenesis. The effects of hCG in enhancing steroidogenesis in the presence of LDL were first detectable after 3 h, but were most marked after 20 h of culture. hCG and 8-bromo-cAMP increased the conversion of [3H]cholesteryl linoleate, which had been incorporated into the core of LDL, into [3H]progesterone. hCG also stimulated cellular accumulation of LDL cholesterol, as assessed by incorporation of [1-14C]oleic acid into sterol esters or by measurement of total cellular cholesterol in the presence of amino-glutethimide to block steroidogenesis. In contrast to progesterone secretion, estradiol secretion was not affected by the addition of LDL in the absence or presence of 8-bromo-cAMP. We conclude that LDL cholesterol is required for maximal rates of progestin synthesis by human luteinized granulosa cells. When granulosa cells are stimulated by hCG, uptake of LDL cholesterol is promoted, and there is increased utilization of LDL cholesterol for steroid synthesis.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1984

Steroid production by isolated theca and granulosa cells after initiation of atresia in the hamster.

Hypophysectomized PMSG-primed hamsters were injected with PMSG antiserum and the theca and granulosa cells of the resulting atretic follicles were incubated in vitro. In the absence of added hormone, 17 alpha-hydroxyprogesterone and oestradiol production was not detectable in granulosa cells collected and incubated at 0, 12 and 24 h after antiserum. Progesterone production was not detected in control incubations at 0 h but was measurable with cells collected at 12 h after PMSG antiserum. When incubated with androstenedione or pregnenolone (10 ng/ml for each) 17 alpha-hydroxyprogesterone and progesterone production by granulosa cells were significantly increased at 0, 12 and 24 h after antiserum. Granulosa cells were capable of aromatizing androstenedione to oestradiol at all times examined. At 0 and 12 h after antiserum to PMSG, isolated thecal shells produced androstenedione. LH stimulation caused increased androstenedione production in all thecae at 0 h, in 50% of the thecae at 12 h and in none at 24 h after antiserum. Thecal shells produced 17 alpha-hydroxyprogesterone in response to LH at 0, 12 and 24 h after antiserum, and produced progesterone at all times examined. Thecae also responded to LH with increased progesterone production up to 72 h after antiserum. These experiments demonstrate that one important steroidogenic event in atresia may be the loss of activity of C 17,20 lyase in the theca leading to loss of substrate (androstenedione) for granulosa cell aromatization, although aromatase activity is present until at least 24 h after the induction of atresia.

17-alpha-Hydroxyprogesterone↗

PubMed1983

Progesterone production by hamster granulosa and luteal cells during short-term incubation. Effects of lipoproteins, compactin and 25-hydroxycholesterol.

Granulosa and luteal cells from immature, hormone-primed hamsters increased progesterone production in response to luteinizing hormone (LH) in a dose-dependent manner. Both cell types responded to 8-bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP) with increased progesterone production. Lipoproteins (hamster or human) did not enhance progesterone production by either cell type in the presence of LH during short-term incubation; human high-density lipoprotein (HDL) inhibited progestin production. Compactin, an inhibitor of cholesterol biosynthesis, had no significant effect on progesterone production by either cell type. Granulosa and luteal cells increased progesterone production in response to 25-OH-cholesterol. The response to 25-OH-cholesterol was more rapid than that to LH. Increased progestin levels were apparent within 15 min of incubation whereas a response to LH was not seen until 30 min. LH in combination with 25-OH-cholesterol did not increase progesterone production above that seen with either agent alone. Cycloheximide blocked LH-stimulated steroidogenesis but not 25-OH-cholesterol-stimulated progestin production in both cell types. We conclude that 1) hamster granulosa and luteal cells rely upon endogenous, preformed cholesterol for the acute steroidogenic response to LH and 2) LH-stimulated steroidogenesis, but not 25-OH-cholesterol-stimulated steroidogenesis, is a cycloheximide-sensitive process which presumably involves an increase in the access of cellular cholesterol to the side-chain cleavage system.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1982

In-vitro progesterone production by ovarian interstitial cells from hypophysectomized hamsters.

Collagenase-dispersed interstitial cells from 5-day hypophysectomized hamsters produced progesterone (81 +/- 7 pg/10 000 viable cells/2 h incubation) and responded to ovine LH stimulation in vitro with a dose-dependent increase in progesterone. FSH and prolactin had no effect. The interstitial cells did not produce detectable levels of oestradiol, oestrone, androstenedione, 17 alpha-hydroxyprogesterone or 20 alpha-dihydroprogesterone although 17 alpha-hydroxyprogesterone production rose to 26 +/- 5 pg/10 000 cells/2 h in response to 25 ng LH/ml. Isoproterenol (500 ng/ml) and epinephrine (500 ng/ml) stimulated progesterone production and this response was blocked by concurrent administration of 6 x 10(-6) M-propanolol which had no effect on LH-stimulated progesterone production. Simultaneous LH and catecholamine stimulation did not produce an additive effect. Incubation in medium containing 10% serum from hypophysectomized animals did not affect progesterone production. The addition of 10(-6) M-D-ala6-LHRH to interstitial cells resulted in a significant reduction of baseline steroidogenesis. These results suggest long-term retention of functional LH receptors and integrity of the steroidogenic pathway through progesterone despite chronic gonadotrophin deprivation and may indicate a role for the interstitium in priming follicular growth following periods of anoestrus.

Animals↗

PubMed1980

Regulation of steroidogenesis in the ovine corpus luteum.

To examine the factor affecting LH-induced progesterone production in vitro in ovine luteal slices, an experimental procedure was employed wherein each slice served as its own control. The role of microfilaments in steroidogenesis was studied in luteal slices treated with cytochalasin B (an inhibitor of microfilament function). Cytochalasin B treatment resulted in significant reduction of progesterone production by luteal slices in response to LH and the addition of serum to the medium did not alter this effect. The ability of luteal slices to respond to LH with increased progesterone secretion was restored when cytochalasin B was removed from the medium. Further studies indicated that inhibition of LH-induced progesterone production by treatment with cytochalasin B was not a result of a change in: 1) cyclic adenosine 3',5'-monophosphate production in response to LH; 2) mitochondrial membrane permeability to cholesterol; or 3) activity of 3 beta-hydroxysteroid dehydrogenase, delta 5, delta 4-isomerase enzyme complex. The possibility existed that microfilaments were necessary for cholesterol transport to mitochondria in response to LH stimulation. However, mitochondrial cholesterol content was unchanged in response to LH in the presence or absence of aminoglutethimide (an inhibitor of cholesterol side-chain cleavage enzyme activity) as determined by uptake of 3H-cholesterol or total content determined by gas-liquid chromatography. Further, treatment with cytochalasin B had no effect on mitochondrial cholesterol content. These results suggest a role for microfilaments in LH-induced progesterone production at a point prior to the conversion of cholesterol to pregnenolone.

Aminoglutethimide↗