Search PubMed⌕ Search

Biomedical subjects

C G Smith

Publications and source records attributed to C G Smith.

At least 55 records · Page 3Linked to original sources
PubMed1987

Drug abuse and reproduction.

It is clear that a number of CNS agents, including drugs of abuse, can inhibit reproductive function. Figure 1 shows the chemical diversity of some of the drug groups that affect reproductive hormones. Their structural dissimilarity to the steroid hormones is also readily apparent in the figure. These chemically diverse drugs share an important pharmacologic property: they are highly potent neuroactive drugs, and they can disrupt hypothalamic-pituitary function. Although it is frequently difficult to distinguish between direct drug actions on the hypothalamic-pituitary axis and subsequent effects on gonadal hormones and sex accessory gland function, the distinction is an important one. Most neuroactive drugs produce only transient effects on the central nervous pathways necessary for normal gonadotropin secretion. The disruptive effects of these drugs are likely to be transient and completely reversible, and tolerance to the inhibitory drug effects may occur even with continued drug use. Under these circumstances, normal adults may experience only subtle changes in sexual function. However, individuals with compromised reproductive function may exhibit major problems. It is also likely that adolescents may be at substantial risk for reproductive damage from these neuroactive drugs since the endocrine events associated with puberty are dependent on the normal development of the hypothalamic-pituitary axis.

Adolescent↗
PubMed1987

Biochemical and ultrastructural processing of [125I]epidermal growth factor in rat epidermis and hair follicles: accumulation of nuclear label.

Although the intracellular ultrastructural processing of epidermal growth factor (EGF) and its receptor have been described in cell culture systems, very few studies have examined this phenomenon in intact tissues. We have examined the ultrastructural and biochemical handling of [125I]EGF in the epidermis and hair follicle bulb of intact, viable, 3- to 5-day-old rat skin the EGF receptor distribution of which has already been documented and in which EGF has been shown to be biologically active. After incubation of explants with 10 nM [125I]EGF for 2.5 h at 25 degrees or 37 degrees C, radiolabel was detected over the basal cells of the epidermis and hair follicle outer root sheath, confirming previous light microscope observations. More specifically, silver grains were observed near coated and uncoated plasma membrane and coated membrane invaginations, Golgi apparatus, lysosomal structures, and nuclei. Sodium azide inhibited internalization of label, whereas a series of lysosomal inhibitors (chloroquine, monensin, and iodoacetamide) caused a slight increase in silver grains associated with lysosomal vesicles and a decrease in nuclear label. Biochemical analysis indicated that greater than 35% of radioactivity following incubation at 37 degrees C was in the form of degraded [125I]EGF fragments and that inclusion of chloroquine, monensin, and iodoacetamide reduced this value to 20.8%, 8.6%, and 4.0%, respectively. In addition, chloramine T-prepared [125I]EGF was found to be covalently cross-linked with low efficiency to a protein having the molecular weight of the EGF receptor. These data are discussed in the light of the effects of EGF on epithelial cell proliferation in skin.

Animals↗
PubMed1986

Primary structure and cDNA cloning of human fibroblast collagenase inhibitor.

We report the primary structure and cDNA cloning of human fibroblast collagenase inhibitor, a glycoprotein that appears to play a central role in modulating the activity of a number of metalloendoproteases of connective tissue origin including collagenase, gelatinase, and proteoglycanase. Secreted human fibroblast collagenase inhibitor was purified and subjected to automated Edman degradation. The secreted protein consists of 184 amino acid residues; it contains two sites of N-linked oligosaccharide linkage and six disulfide bonds. Synthetic oligonucleotide probes based on selected amino acid sequences of the inhibitor were used to screen a lambda gt10 cDNA library from a human fibroblast line. Two overlapping cDNA clones were characterized to determine the complete coding and noncoding sequences of the specific mRNA. The amino acid sequence deduced from the nucleotide sequence agrees with that determined by protein sequencing. One clone appears to contain the complete 5' end and, in addition, the cDNA sequence predicts a 23-amino acid leader peptide. The other clone represents the 3' end of the mature message and includes a short poly(A)+ tract. This 3' sequence is remarkably similar to a reported cDNA encoding part of the protein derived from mouse fibroblast poly(A)+ RNA. However, this inhibitor has no substantial homology with previously sequenced protease inhibitors.

Amino Acid Sequence↗
PubMed1986

Rapid isolation in large numbers of intact, viable, individual hair follicles from skin: biochemical and ultrastructural characterization.

A rapid, novel method is described by which large numbers of intact, viable, individual hair follicles may be isolated from rat skin. Follicles are freed from the surrounding connective tissue by shearing, which is effected by repeated cutting with a loosely fitting pair of scissors, and collected individually under liquid using gentle aspiration. Ultrastructural analysis indicates that the follicles are sheared away from the surrounding dermis in the region of the connective tissue capsule which encircles the hair. The follicles appear viable by light and electron microscopy and, within 2 h of isolation, retain the capacity to incorporate [3H]thymidine into DNA and [35S]methionine into proteins as judged by autoradiography. A histologic comparison indicates that the structural integrity of follicles isolated by this new method is significantly superior to those plucked from the animal at the same time. The method affords the isolation of large numbers of hair follicles, without resort to enzyme treatments, suitable for biologic studies in the absence of other skin appendages and dermis.

Animals↗
PubMed1986

Effects of delta 9-THC, the principal psychoactive component of marijuana, during pregnancy in the rhesus monkey.

The effect of delta 9-tetrahydrocannabinol (THC), the principal psychoactive component in marijuana, was studied in pregnant and lactating rhesus monkeys. THC (2.5 mg/kg/d) or vehicle was administered during different periods of gestation, and effects on pregnancy outcome and hormone concentrations during pregnancy were studied. The most obvious effects were observed with administration early in pregnancy; three of five pregnancies aborted within days after the drug injections began, and one pregnancy resulted in a stillbirth at term. The three abortions were associated with a rapid decrease in chorionic gonadotropin and a subsequent fall in progesterone concentrations to nondetectable levels. In the two pregnancies that continued until term, estradiol concentrations were significantly higher than in vehicle control pregnancies. Daily THC administration during the middle or third portion of gestation resulted in lesser pregnancy loss (one premature birth and four live births at term with THC treatment during the middle portion; two premature births and three live births at term with THC treatment during the third portion). All the premature infants died within two weeks of birth. The weights of the infants at birth and weaning were not significantly different for the infants from vehicle control pregnancies and for full-term infants exposed to THC during gestation. Also, no effects on intrauterine growth and development were detected with ultrasound in the drug-treated pregnancies. With acute administration, THC readily crossed the placenta at term in rhesus monkeys and was transferred into the milk of nursing mothers. Significant blood levels of THC and depressant effects were observed in both mothers and neonates when the drug was administered to the mothers one hour before birth or during lactation.

Abortion, Spontaneous↗
PubMed1985

Disposition and bioavailability of various formulations of tetrahydrocannabinol in the rhesus monkey.

Oral delta 9-tetrahydrocannabinol (THC) in gelatin capsules is under evaluation as an antiemetic agent in cancer patients, but knowledge concerning its bioavailability is incomplete and, furthermore, alternative routes of administration may be desirable. In this study, the disposition of THC was determined in four rhesus monkeys given 2.5-mg/kg doses using the following routes of administration and formulations: intravenous (iv); orally (po) on a cookie and in gelatin capsules; intramuscularly (im) in Tween-80 and in Emulphor-EL620; rectally in various suppository bases. Serum THC concentrations were measured by RIA and analyzed by weighted nonlinear regression. Serum concentrations were best described by a sum of two exponentials with alpha and beta half-lives (mean +/- SD) of 0.74 +/- 0.59 and 14.9 +/- 12.5 h. Apparent bioavailability (%F +/- SD) of various formulations of THC were: gelatin capsules, 26 +/- 14; cookie, 89 +/- 16; intramuscularly in Tween-80 and in Emulphor, 39 +/- 13 and 102 +/- 15, respectively. Using the method of statistical moments, mean residence times in the body (h +/- SD) were: intravenous, 6.08 +/- 1.60; cookie, 21.92 +/- 3.11; gelatin capsule, 26.80 +/- 23.61; intramuscularly in Emulphor, 10.92 +/- 3.46 (in Tween-80, not calculated). THC was not bioavailable by the rectal route. We conclude from this study that THC formulated as a gelatin capsule exhibits a low and variable extent of bioavailability and that intramuscular THC may be a useful alternative route of administration since it is more completely bioavailable.

Administration, Oral↗
PubMed1985

Naloxone reversal of stress-induced reproductive effects in the male rhesus monkey.

Adolescent male rhesus monkeys, stressed by placement in tethering systems, were administered naloxone to discern the involvement of endogenous opioids in the stress-induced reproductive dysfunction. Stressed monkeys exhibited decreased plasma levels of luteinizing hormone (LH), testosterone, and increased levels of prolactin. Administration of naloxone temporarily returned hormone levels to non-stressed values. Stress depressed sexual activity was increased following naloxone treatment. GnRH administration stimulated plasma LH and testosterone levels. These results indicate that stress-induced changes in reproductive function may be mediated by opioids at levels above the pituitary.

Animals↗
PubMed1985

Past, current, and future safety and efficacy trends in the drug industry.

In view of the enormity of the subject on which I have been asked to speak, I consider it advisable, prudent, and pragmatic to attempt to focus the scope of my discussion on the area of my immediate expertise. In my lecture, I shall attempt to survey "the past" via a very brief discussion of some of the methods used for the determination of both safety and efficacy as well as the results achieved. With respect to "current practices," I intend to present an overview of the scope of safety and efficacy evaluation with new drugs, emphasizing both the pros and cons as perceived from the vantage point of a pharmaceutical scientist dedicated to the discovery and development of new therapeutic agents that will ameliorate disease states and human suffering while, at the same time, returning profit to the industry that has generated such drugs, so as to permit continued expansion of our therapeutic armamentarium by continued research efforts.

Animals↗
PubMed1985

Opioid effects on plasma concentrations of luteinizing hormone and prolactin in the adult male rhesus monkey.

The role of endogenous opioid peptides (EOP) in the neuroendocrine control of primate gonadotropin and PRL secretion was studied in nonrestrained adult male rhesus monkeys. Morphine (0.5-1.0 mg/kg) was used as the prototype opiate, beta-endorphin (beta-END; 10-20 micrograms/kg) and [D-Ala2,D-Leu5] enkephalin (DADLE; 5-20 micrograms/kg) were used as representatives of EOP, and naloxone (0.5-2.0 mg/kg) was used as an opiate receptor blocker. Drugs were administered and blood was collected (at 20-min intervals for 4 h) through an indwelling jugular catheter. LH and PRL levels were measured in plasma by RIA. Intravenous administration of morphine (1.0 mg/kg) and DADLE (10 micrograms/kg) produced decreases in LH levels of 64% and 40%, respectively. These decreases occurred within 1 h after drug injections and lasted for approximately 3 h. beta-END had no effect on LH levels. Naloxone, at all doses studied, significantly increased LH levels (5- to 8-fold). The LH rises occurred within 20 min and lasted for up to 2 h. Both morphine and beta-END produced immediate increases in PRL, which remained elevated for 3 h. DADLE did not alter PRL levels. Naloxone (1.0 and 2.0 mg/kg) decreased PRL concentrations (45% and 60%, respectively). Pretreatment with morphine or DADLE did not alter the LH response to GnRH (100 micrograms) stimulation, indicating a hypothalamic site of action for the opioid inhibition of LH release. Naloxone administration reversed the inhibitory effects of morphine and DADLE on LH. The stimulatory effect of morphine on PRL levels was also reversed by naloxone. These studies further define the postulated physiological role of EOP in primate reproductive neuroendocrinology. Based on receptor selectivities of these opioid agonists, the inhibition of LH may be mediated by delta-receptors, whereas PRL release appears to be mu-mediated.

Animals↗
PubMed1984

Relationship of heparan sulfate proteoglycans to the cytoskeleton and extracellular matrix of cultured fibroblasts.

The distribution of heparan sulfate proteoglycans (HSPG) on cultured fibroblasts was monitored using an antiserum raised against cell surface HSPG from rat liver. After seeding, HSPG was detected by immunofluorescence first on cell surfaces and later in fibrillar deposits of an extracellular matrix. Cell surface HSPG aligned with microfilament bundles of rat embryo fibroblasts seen by phase-contrast microscopy but was diffuse on transformed rat dermal fibroblasts (16C cells) which lack obvious stress fibers. Focal adhesions isolated from either cell type and monitored by interference reflection microscopy showed a concentration of HSPG labeling with respect to the rest of the membrane. Increased labeling in these areas was also seen for fibronectin (FN) by using an antiserum that detects both plasma and cell-derived FN. Double immunofluorescent staining of fully adherent rat embryo fibroblast cells showed some co-distribution of HSPG and FN, and this was confirmed by immunoelectron microscopy, which detected HSPG at localized areas of dorsal and ventral cell membranes, overlapping cell margins, and in the extracellular matrix. During cell shape changes on rounding and spreading, HSPG and FN may not co-distribute. Double labeling for actin and either HSPG or FN showed a closer correlation of actin with HSPG than with FN. The studies are consistent with HSPG being closely involved in a transmembrane cytoskeletal-matrix interaction; the possibility that HSPG coordinates the deposition of FN and other matrix components with cytoskeletal organization is discussed.

Animals↗
PubMed1984

Acute, short-term, and chronic effects of marijuana on the female primate reproductive function.

Studies with laboratory animals clearly show that the crude drug marijuana and delta-9-THC, the principal psychoactive ingredient, inhibit secretion of the pituitary hormones LH and FSH as well as prolactin. These changes in pituitary hormone levels produce decreases in sex steroid hormones and cause disruption of ovulation and spermatogenesis. With chronic drug use, disruption of sex accessory organs has also been observed. A principal site of THC action is the hypothalamus, because THC effects on pituitary hormone production can be reversed with hypothalamic releasing factors. It is now known that drug effects in sexually mature animals are reversible when drug treatment stops. In adults, tolerance develops to hormone changes brought on by the use of marijuana. Clinical studies on human subjects generally agree with the animal findings, although conflicting results have been reported as well. It is likely that the differences in results obtained in experiments with laboratory animals and with humans are caused, at least in part, by differences in experimental design. Further, it is not known how much disruption of reproductive hormone levels is necessary for changes in human fertility and sexual function to occur. The use of marijuana by pregnant women or by women who are attempting to become pregnant is cause for special concern. Studies with laboratory animals and retrospective studies on women who have used marijuana during pregnancy show that the risks of pregnancy loss and other adverse effects on the fetus are increased by marijuana use. THC crosses the placental barrier and while the potent teratogenic and mutagenic effects suggested for marijuana some years ago have not been confirmed, significant changes consistent with retardation of fetal growth and development have been observed. Effects of THC on the proper functioning of the placenta may be responsible for these effects on pregnancy. Pregnancy that occurs after the development of tolerance with chronic marijuana use may involve an ovum that has been damaged by exposure to the drug during critical developmental stages. More studies need to be done before the mechanisms of toxic effects on pregnancy and fetal development can be described. While there have been no clinical studies relating marijuana use to adolescent development, studies in laboratory animals show that the developing reproductive system during adolescence is particularly vulnerable.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Tolerance develops to the disruptive effects of delta 9-tetrahydrocannabinol on primate menstrual cycle.

Long-term exposure of sexually mature female rhesus monkeys (Macaca mulata) to thrice weekly injections of delta 9-tetrahydrocannabinol resulted in a disruption of menstrual cycles that lasted for several months. This period was marked by an absence of ovulation and decreased basal concentrations of gonadotropin and sex steroids in the plasma. After this period, normal cycles and hormone concentrations were reestablished. These studies demonstrate that in rhesus monkeys subjected to long-term treatment with delta 9-tetrahydrocannabinol tolerance develops to the disruptive effects of the drug on the menstrual cycle.

Animals↗
PubMed1983

Fibronectin in cultured rat keratinocytes: distribution, synthesis, and relationship to cytoskeletal proteins.

The aim of this study was to investigate whether epidermal cells can synthesise fibronectin and whether the distribution of this glycoprotein is related to the adhesion and cytoskeletal organisation of these cells. The production of fibronectin by newborn rat epidermal cells was shown by indirect immunofluorescence staining of cultures grown in the absence of a feeder layer using an antiserum which had been cross-adsorbed with foetal calf serum proteins to remove antibodies which recognised serum fibronectin. The distribution of fibronectin in areas of cell-cell and cell-substratum contact, characteristically in the form of short radial stitches, was examined in more detail using immunoelectron microscopy with colloidal gold as marker. This showed the close proximity of fibronectin to the cell membrane, with the ventral surface and fine cellular processes showing the heaviest labelling, and also revealed evidence of a relationship between external fibronectin and internal structure in epidermal cells. Immunofluorescence showed that tonofilaments (keratin) and microtubules were present as fibrillar arrays but were not related to fibronectin distribution. Vimentin and desmin were absent. Actin was distributed as a circumferential bundle of filaments, with finer stands running radially to the edge. The latter were reminiscent of the radial fibronectin stitches and a spatial correspondence between fibronectin and actin was confirmed by double-label immunofluorescence which revealed many instances of overlap and colinearity of actin and fibronectin filaments. The ability of keratinocytes to produce fibronectin suggests that these cells can contribute to the formation of the basement membrane in skin. The localisation of fibronectin and its close association with actin also suggests that it is involved in keratinocyte adhesion and is related to the internal organisation of these cells.

Actins↗
PubMed1983

Stages in specialization of fibroblast adhesion and deposition of extracellular matrix.

Fibroblast cells seeded on a serum glycoprotein shown previously to mediate a spread shape without focal adhesions or microfilament bundles (Stage 1 spread) are now shown to have substratum contacts in which coated pits are abundant and associated with small globular deposits of glycocalyx bridging to substratum and staining for fibronectin and acidic glycoconjugates. After stimulation with serum or fibronectin to form focal adhesions and microfilament bundles (Stage 2 spread), clathrin-based structures remain at the cell underside but no longer in conspicuously higher concentration than on the dorsal surface; extracellular material at adhesions is now as regular strands which stain for acidic glycoconjugates but (as reported earlier by Chen and Singer) not always for fibronectin. During these stages of adhesion, striking changes are seen in the cellular display of fibronectin monitored by immunofluorescence. In rounded cells this is granular and cytoplasmic, concentrated around the submembranous cortex; on spreading to Stage 1, it remains granular and intracellular but is now oriented strongly towards the lower cell surface; only in Stage 2 does externalisation proceed to deposit fibrillar fibronectin on the substratum. While cytoplasmic orientation of matrix precursors can be determined by cell contact, organised externalisation is therefore coupled to fully developed adhesion status.

Animals↗
PubMed1983

The effects of marijuana extract and delta 9-tetrahydrocannabinol on luteal function in the rhesus monkey.

The effects of marijuana extract (ME) and delta 9-tetrahydrocannabinol (THC) on corpus luteum function were studied in the rhesus monkey by the use of in vivo and in vitro techniques. THC (2.5 mg/kg) or vehicle (3% Tween 80 in saline) was administered by an intramuscular injection to rhesus monkeys on day 20, 21, or 22 of the menstrual cycle. Progesterone (P) levels were measured at 6-hour intervals for the first 24 hours after treatment. THC caused a significant decrease in P levels during this 24-hour period. This decrease was reversed by the administration of human chorionic gonadotropin (hCG) at 6 hours after THC administration. When THC was administered 2 hours after hCG, it failed to inhibit the expected rise in serum P levels caused by hCG. Direct effects of the drugs on P production were studied with the use of dispersed luteal cells obtained from monkeys on day 21 or 22 of the menstrual cycle. Neither ME nor THC had any effect on basal P production in these in vitro studies. These data suggest that the inhibitory effect of THC on P levels during the luteal phase are not mediated by a direct effect of the drug on ovarian steroid production.

Animals↗
PubMed1983

Reproductive toxicity: hypothalamic-pituitary mechanisms.

The hypothalamic-pituitary axis serves as the primary control center for reproductive hormones. Several agents can inhibit this control center and thereby disrupt reproductive function. Of major interest among these agents are the neuropharmacologic drugs that alter the central nervous system input to the hypothalamus. Such drug classes as the barbiturates, narcotics, certain tranquilizers, and marijuana can inhibit gonadotropin secretion by this mechanism. Changes in gonadotropin and prolactin levels can result in disruptive effects on the reproductive system including infertility, changes in libido, and problems with sexual function.

Animals↗