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Biomedical subjects

C G Smith

Publications and source records attributed to C G Smith.

At least 91 records · Page 5Linked to original sources
PubMed1979

Effects of danazol on gonadotropin levels in castrated rhesus monkeys.

Danazol is widely used in the management of endometriosis and mammary dysplasia. However, its mechanism of action is still obscure because of the few studies done and the controversial results obtained. Antigonadotropic activity has been postulated by some investigators, whereas others have observed no effect on the gonads. In the present study, three castrated female rhesus monkeys received 400 mg of danazol daily, by gavage for 19 days, while 2 controls received 400 mg of lactose daily. Blood samples were drawn every other day from 2 weeks prior to 3 weeks after the administration of the drug. Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) decreased rapidly and then were maintained until danazol was discontinued. Prompt return to pretreatment levels occurred 1-2 days after the discontinuation of therapy. Prolactin levels were normal during therapy. Luteinizing hormone releasing factor (LH-RF), 100 microgram, administered intravenously during danazol therapy, caused a normal, prompt release of gonadotropins, demonstrating an intact pituitary response. The authors conclude that 1) danazol is a potent antigonadotropic agent, 2) its effect is abolished promptly after discontinuation, and 3) its probable biological action is at the hypothalamic level.

Animals↗
PubMed1979

Precoital single doses of delta9-tetrahydrocannabinol block ovulation in the rabbit.

delta9-Tetrahydrocannabinol (delta9-THC) inhibits pituitary gonadotropin secretion in castrated rhesus monkeys. Also, delta9-THC blocks the ovulatory reflux in rabbits. We report now the dose-response relationship of precoital single doses of delta9-THC on luteinizing hormone (LH) release and ovulation in the rabbit. Forty-five female rabbits in estrous were divided into nine groups of five animals. Groups 1 to 5 received a single intramuscular dose of delta9-THC (5,2.5, 1.25, 0.612, and 0.306 mg/kg, respectively) 2 hours before mating; animals of group 6 received vehicle only. In animals of groups 7 and 8 ovulation was induced with 100 IU of human chorionic gonadotropic (hCG), given intravenously 2 hours after the administration of delta9-THC (5 mg/kg) or vehicle. Rabbit luteinizing hormone (rLH) was measured in plasma 90 to 120 minutes after coitus or hCG administration. After the injection of 5 mg of delta9-THC, luteinizing hormone-releasing factor (LH-RF) (20 microgram intravenously) was administered to the animals of group 9. All animals of groups 6, 7, and 8 ovulated. A dose-response curve was observed in the animals treated with delta9-THC and natural mating. Whereas none of the animals treated with 5 or 2.5 mg/kg ovulated, one of the group treated with 1.25 mg/kg, two of the group treated with 0.612 mg/kg, and all treated with 0.312 mg/kg ovulated. Ovulations correlated with postcoital levels of rLH. All animals of group 9 ovulated, indicating that the site of action of delta9-THC is suprapituitary, probably hypothalamic.

Animals↗
PubMed1978

Experimental dysraphism in the rat.

An experimental treatment that results in dysraphic lesions in rat embryos was studied to gain insight into the origin of such lesions. Pregnant rats given 100,000 units of vitamin A by gavage tube on gestational Days 8, 9, and 10 produced abnormal litters, and 50% of the embryos had exencephaly and/or spina bifida. Study of these embryonic lesions revealed hyperplesia of neural tube tissue that extended laterally to the edge of an epidermal defect. The epidermal defect consisted of the absence of fetal epidermis over the hyperplastic neural tissue. At no stage in development was embryonic hydrocephalus noted. In fact, the central canals of the embryos with malformations were poorly developed and smaller than those of control embryos. Results with this model indicate that the malformations arise through a process of overgrowth and hyperplasia and not from embryonic hydrocephalus. Continued work with this and other models is required to delineate new mechanisms and to offer alternative postulates for the origin of dysraphic lesions.

Animals↗
PubMed1977

The effect of marihuana (delta-9-tetrahydrocannabinol) on the secretion of luteinizing hormone in the ovariectomized rhesus monkey.

Despite the widespread use of marihuana by large numbers of young adults in the reproductive years, little is known about the effects of this drug on reproductive function. information on the effect of the drug on the woman is particularly meager. The rhesus monkey provides an excellent animal model from which to generalize to man. While the primary purpose of the project is to determine the effect of long-term administration on the cycling female monkey, the initial studies were carried out in the ovariectomized monkey with resulting elevated gonadotropin levels under conditions of short-term administration of the drug. Marihuana causes a reversible depression in luteinizing hormone levels in the ovariectomized female rhesus monkey.

Animals↗
PubMed1976

Mechanisms of cell adhesion: early-forming junctions between aggregating fibroblasts.

When cultured fibroblasts (16C) are mildly dissociated with EGTA or trypsin/EDTA, they aggregate rapidly. The formation of aggregates has been found to involve junctions of the gap and adhaerens types which are seen by electron microscopy within minutes of allowing cells to come together. The process of adhesion between freshly dissociated, transformed 16C fibroblasts is therefore organized and establishes its usefulness as a model for studying cellular interactions in relation to supracellular organization.

Cell Adhesion↗
PubMed1976

Evidence for the secretory transport mechanism of intestinal immunoglobulin. The ultrastructural distribution of IgM.

The intracellular localization of IgM in porcine intestinal tissue has been studied by immunoelectron microscopy and immunofluorescence. IgM was demonstrated in vesicles in the cytoplasm of crypt epithelial cells particularly in the supranuclear region. It was also shown in the ergastoplasmic cisternae of plasma cells in the intercryptal lamina propria. The findings are compared with those of a previous similar study on secretory IgA and their implications for possible mechanisms of selective transport are discussed.

Animals↗
PubMed1976

Tympanometric detection of middle ear effusion in infants and young children.

Tympanometry, a test of middle ear status new to clinical pediatrics, was carried out on 280 subjects, 10 days through 5 years of age. The tympanograms obtained were compared with otoscopic findings and, in 107 of the subjects, with findings at myringotomy. Seven distinct tympanometric curve types were identified and defined, based on their degree of correlation with the presence or absence of middle ear effusion. In subjects 7 months of age and older, curves suggesting normal (high) tympanic membrane compliance in combination with atmospheric or near-atmospheric middle ear air pressure were rarely associated with effusion. Conversely, curves suggesting low tympanic membrane compliance were highly correlated with the presence of effusion. Curves suggesting intermediate compliance or reduced middle ear air pressure were also correlated with effusion, but the degree of correlation was dependent on the shape of the curve. In infants less than 7 months of age, many of the ears with effusion had "normal" tympanograms, presumably because external auditory canal walls in such infants tend to be highly distensible. Tympanometry is a simple, rapid, atraumatic, valid, and objective test, easily administered by paraprofessional personnel. Its use can result in improved detection of middle ear effusion and other middle ear abnormalities, and also appears to promote improvement in diagnostic acumen.

Child, Preschool↗