Search PubMed⌕ Search

Biomedical subjects

D W Davidson

Publications and source records attributed to D W Davidson.

At least 19 recordsLinked to original sources
PubMed2005

6-alkylsalicylic acids and 6-alkylresorcylic acids from ants in the genus Crematogaster from Brunei.

The defensive chemistry of two species of ants from Brunei in the genus Crematogaster (Physocrema group) has been investigated. Ants in this group release a white secretion from hypertrophied metapleural glands on their thorax when they are disturbed. Previously, one species in this group has been shown to produce alkylphenols and alkylresorcinols. In the present investigation, similar compounds along with salicylic acids and resorcylic acids that are anacardic acid and olivetolic acid homologs, respectively, are described from two species. The structures of these compounds were suggested by their spectroscopic data and confirmed by direct comparison with synthetic samples. Some of these compounds occur in lichens and have well documented physiological activities.

Anacardic Acids↗
PubMed2004

The chemistry of exploding ants, Camponotus spp. (cylindricus complex).

A detailed comparative analysis of the exocrine chemistry of nine Bruneian Camponotus species in the cylindricus complex is reported. Workers of these species are known to have hypertrophied mandibular glands and release their glandular contents suicidally from the head by rupturing the intersegmental membrane of the gaster. All of the species produce mixtures of polyacetate-derived aromatics, including hydroxyacetophenones, which display pH-dependent color changes, and aliphatic hydrocarbons and alcohols. In addition, three species contained (6R)-2,6-dimethyl-(2E)-octen-1,8-dioic acid (9) or (3S)-8-hydroxycitro-nellic acid (10a), previously unreported from insects. These compounds were characterized from their spectral data, and confirmed by comparison with synthetic samples. The allomonal role of these compounds is based on numerous field observations, and their chemotaxonomic value is presented.

Acetates↗
PubMed1992

A 1988 survey of federal service optometrists.

A mailed questionnaire was used to survey federal service optometrists in the U.S. Air Force, U.S. Army, U.S. Navy, U.S. Public Health Service, and the Department of Veterans Affairs. The purpose of this survey was to determine the scope of practice and level of job satisfaction of these optometrists. The results of the study were compared with those of a similar survey conducted 5 years earlier.

Humans↗
PubMed1991

Oral contraceptives, androgens, and the sexuality of young women: I. A comparison of sexual experience, sexual attitudes, and gender role in oral contraceptive users and nonusers.

Female undergraduates (108) volunteered for a study of hormones and sexuality, 55 of whom were oral contraceptive (OC) users. In this paper, OC users and nonusers are compared on measures of sexual attitudes and behavior, use of erotic fantasy, and gender role. In the second paper, the effects of OC on androgen levels and the relationship between androgens and behavioral measures within each group are reported. OC users were more likely to have a current sexual partner and less likely to be virgins. The two groups did not differ in frequency of masturbation or use of erotic fantasies. OC users reported less restrictive sexual morality and more interest in erotic images. These differences persisted when women without current partners were excluded. Among those in active sexual relationships, OC users reported more frequent sexual intercourse, higher psychosexual motivation and enjoyment, and were more positive in their evaluation of their partners than OC nonusers.

Adult↗
PubMed1991

Oral contraceptives, androgens, and the sexuality of young women: II. The role of androgens.

The relationships between plasma free testosterone (FT) and measures of sexual attitude, sexual behavior, and gender role behavior were assessed in 55 oral contraceptive-using and 53 nonusing female undergraduates. Plasma FT and other measures of androgenicity were substantially lower in the oral contraceptive (OC) group. Correlations between FT and certain behavioral and attitudinal measures were found in the OC users but not the nonusers. In the OC users, FT was positively associated with frequency of sexual intercourse but not with frequency of masturbation. It was negatively associated with restrictive sexual morality. Correlations between FT and measures of gender role behavior were negligible, and FT was unrelated to proceptivity, homosexual interest, or the use of sexual fantasy. The occurrence of some predicted correlations among pill-using women but not the nonusers requires explanation, particularly in view of the substantially lower levels of FT in the pill-using group. It is suggested that androgen-behavior relationships in women are easily obscured by psychosocial influences and in this sample of young women such influences may have been more powerful among those not using OCs. Such psychosocial influences are likely to differ at different stages of women's life cycles. The importance of controlling for such influences in any study of hormone-sexual behavior relationships in women is emphasized, and the need for prospective studies of women before and after starting on steroidal contraception is recognized.

Adult↗
PubMed1990

Testosterone and sexual behavior in oral contraceptive users and nonusers: a prospective study.

The relationship between plasma testosterone (T) secretion and patterns of sexual behavior was examined in 18 women using oral contraceptives (OCs) and 13 nonusers matched for partner availability. Retrospective assessments of perimenstrual symptoms, sexual attitudes, and sexual experience were obtained and women completed daily ratings of the frequency of sexual activities and the level of well-being for 1 month. Plasma levels of sex hormone binding globulin (SHBG), progesterone, Total T, Free T, and non-SHBG bound T were determined by radioimmunoassay at four phases of the pill or menstrual cycle. Overall, women not using OCs had higher plasma levels of Total, Free, and non-SHBG bound T and lower plasma levels of SHBG than those of OC users. Further, only nonusers had perimenstrual decreases in plasma levels of Total and Free T. The two groups were comparable on most retrospective measures. However, OC users reported more satisfaction with their sexual partners than did nonusers and prospective monitoring revealed that they engaged in sexual interactions more frequently than did nonusers across the cycle. In contrast, both groups reported a similar frequency of autosexual activities across the cycle. There were no correlations between average levels of T and levels of sexual desire, sexual interactions, or autosexuality. Moreover, only nonusers reported a decrease in levels of sexual desire during the perimenstrual period that was associated with the changes in Free T over the menstrual cycle.

Adolescent↗
PubMed1987

Increasing circulating androgens with oral testosterone undecanoate in eugonadal men.

The effects of oral testosterone undecanoate (TU 80 mg; Organon) on plasma testosterone was assessed in 9 men (average age 55 yrs) complaining of loss of sexual interest. Absorption tests were carried out following the first dose of TU and again after 3 or 4 weeks of chronic administration. Absorption was variable in timing, peaks occurring from 30 min to 5 1/2 h after the oral dose. Increases in plasma testosterone of at least 50% of baseline levels occurred in 14 of the 18 tests. Apart from a slightly faster metabolic clearance on the second test, associated with a significant reduction in SHBG, there were no other significant differences between the first and second absorption tests. Variability of absorption may be related to dietary factors. If this can be reduced by dietary control, TU offers distinct advantages over injectable esters and implants in the short-term administration of testosterone to eugonadal men.

Absorption↗
PubMed1985

Introduction to computer communications.

Telecommunications is the process of transmitting and receiving information, over the phone lines, by computer. This article will describe the hardware and software required to permit an office computer to participate in telecommunications. The article also describes various benefits to the practicing optometrist available through this new technology.

Computers↗
PubMed1982

The behavioural effects of testosterone undecanoate in adult men with Klinefelter's syndrome: a controlled study.

The behavioural effects of exogenous testosterone in men with marginally low circulating androgen levels were investigated. Four adult men with Klinefelter's syndrome, low normal testosterone levels and normal sexual activity and interest were given testosterone undecanoate (TU 160 mg daily by mouth; Organon International) and placebo using a double blind cross-over design. A modest increase in sexual interest was observed during TU administration compared to placebo, though there were no effects on self-reported mood or energy, or on erectile responsiveness in the laboratory. Increase in circulating hormone levels during TU administration was more marked for DHT than for testosterone. The possible implications of this are discussed.

Adult↗
PubMed1982

Structure and gametogenic potential of seminiferous tubules in ageing mice.

The gametogenic potential of young male CBA/Ca mice aged 4-5 months was compared with that of animals 20-23 months of age which had recently ceased to sire offspring. The older mice had substantially lower circulating levels of testosterone and smaller testes. Testicular and epididymal spermatozoa were reduced in number, had more abnormal forms and fewer were progressively motile. Ageing seminiferous tubules varied in the degree of functional atrophy from complete depletion of germ cells to maintenance of sperm production. They were enclosed by a thickened basal lamina and more collagenous connective tissue and occasionally allowed the penetration of lanthanum between Sertoli cells into the ad-luminal compartment. There was no evidence of autosensitization to sperm antigens.

Aging↗
PubMed1981

Androgen replacement with oral testosterone undecanoate in hypogonadal men: a double blind controlled study.

The effects of androgen withdrawal and replacement were investigated in six hypergonadotrophic and six hypogonadotrophic men with hypogonadism. A double blind cross-over design was used comparing testosterone undecanoate (T.U., Organon International), 160 mg daily by mouth, with placebo. There was a significant effect of T.U. on all measures of sexual interest and behaviour. Sexual interest increased within the first week of T.U. administration, ejaculation usually returning within the second week. Behavioural responses were similar in the hyper- and hypogonadotrophic groups. The rise in plasma testosterone during T.U. administration was modest, not reaching the normal range in several cases. 5 alpha dihydrotestosterone rose more substantially. There was a significant fall in sex hormone binding globulin, a rise in oestradiol and no significant change in gonadotrophin concentrations during T.U. administration.

Adult↗
PubMed1980

Androgens and sexual behaviour in women using oral contraceptives.

Twenty women using oral contraceptives and complaining of impaired sexual function were compared with twenty women without sexual problems, matched for age and oral contraceptive. Whilst the sexual behaviour differed in the two groups, the plasma testosterone, androstenedione, oestradiol and SHBG concentrations were very similar. The total androgen levels were low in both groups. Plasma testosterone and oestradiol concentrations were correlated with measures of sexual interest in the no-problem group, but not in the problem group. Administration of exogenous androstenedione to women in the problem group, using a double blind cross-over comparison with a placebo, failed to improve their sexual function except in one case. The majority of women showed a rise in androgen and oestradiol between day 24 of one pill cycle and day 4 of the next. The possible behavioural indications of this pattern are discussed.

Adult↗
PubMed1979

The influence of clinical judgment on the rate of referral from a school vision screening program.

It has been observed that black preschool children low income families have a higher than average rate of referral from a school vision screening program. One potential contributing factor results from the fact that examiners often modified the referral criteria based on their clinical judgment. This study was designed to investigate the influence of the application of clinical judgment on the proportion of referrals as a function of ethnicity and socioeconomic income level. The results suggest that modifying the referral criteria based on clinical judgment does not significantly influence the proportion of referrals based on ethnicity or socioeconomic income level.

Black or African American↗