Stochastic methods for aerosol chemistry: a compact molecular description of functionalization and fragmentation in the heterogeneous oxidation of squalane aerosol by OH radicals.

The heterogeneous oxidation of organic aerosol by hydroxyl radicals (OH) can proceed through two general pathways: functionalization, in which oxygen functional groups are added to the carbon skeleton, and fragmentation, in which carbon-carbon bonds are broken, producing higher volatility, lower molecular weight products. An ongoing challenge is to develop a quantitative molecular description of these pathways that connects the oxidative evolution of the average aerosol properties (e.g. size and hygroscopicity) to the transformation of free radical intermediates. In order to investigate the underlying molecular mechanism of aerosol oxidation, a relatively compact kinetics model is developed for the heterogeneous oxidation of squalane particles by OH using free radical intermediates that convert reactive hydrogen sites into oxygen functional groups. Stochastic simulation techniques are used to compare calculated system properties over ten oxidation lifetimes with the same properties measured in experiment. The time-dependent average squalane aerosol mass, volume, density, carbon number distribution of scission products, and the average elemental composition are predicted using known rate coefficients. For functionalization, the calculations reveal that the distribution of alcohol and carbonyl groups is controlled primarily by the initial OH abstraction rate and to lesser extent by the branching ratio between secondary peroxy radical product channels. For fragmentation, the calculations reveal that the formation of activated alkoxy radicals with neighboring functional groups controls the molecular decomposition, particularly at high O/C ratios. This kinetic scheme provides a framework for understanding the oxidation chemistry of a model organic aerosol and informs parameterizations of more complex systems.

Apolipoprotein A-I-containing lipoproteins in human umbilical cord blood. Relation to proapolipoprotein A-I and lecithin:cholesterol acyltransferase.

Lipids, apolipoproteins, lipoproteins, as well as lipoproteins containing both apo A-I and apo A-II (Lp A-I:A-II) or apo A-I but no apo A-II (Lp A-I), proapolipoprotein (proapo) A-I and the activity of lecithin:cholesterol acyltransferase (LCAT), were investigated in umbilical cord sera of 67 term human neonates (30 females and 37 males). Lp A-I and Lp A-I:A-II were present in umbilical cord sera with levels of 0.26 +/- 0.1 and 0.33 +/- 0.15 g/l, respectively. Furthermore, the absolute amount of proapo A-I was lower in cord blood than in adult plasma, but in view of the lower apo A-I levels in umbilical cord sera it comprised 10.48 +/- 3.86% of total apo A-I and was thus significantly higher than in adult plasma (7.1 +/- 0.9%). Proapo A-I was highly correlated with HDL cholesterol and apo A-I. Total serum LCAT activity was about 50% of adult plasma and was highly correlated with Lp A-I, but not with Lp A-I:A-II. We conclude that human umbilical cord serum contains both Lp A-I and Lp A-I:A-II particles and that the LCAT activity is predominantly related with the Lp A-I subfraction. The higher percentage in umbilical cord sera of proapo A-I may indicate a higher turnover of apo A-I or a lower activity of the proapo A-I cleaving enzyme which is still not identified.

Twin vessels in von Hippel-Lindau disease.

We examined ten patients from three families with von Hippel-Lindau disease and 26 of their at-risk relatives for the presence of twin vessels, defined as a paired retinal arteriole and venule that are separated by less than the diameter of one venule and extend for a distance of more than one disk diameter. They were compared with 36 age- and sex-matched controls. Of the 36 subjects in the study group, 23 had twin vessels compared with two controls (P less than 10(-6). Of the ten patients, nine (14 eyes) had twin vessels; no twin vessels were found in their controls (P = 5.9 x 10(-5)). Fourteen at-risk relatives and two of their controls had twin vessels (P = 9.4 x 10(-4)).

Androgens in the feedback regulation of gonadotropin secretion in men: effects of administration of dihydrotestosterone to eugonadal and agonadal subjects and of spironolactone to eugonadal subjects.

To study the role of androgens in the feedback regulation of gonadotropin secretion, we measured the effects of administration of dihydrotestosterone undecanoate (DHTU) and of spironolactone. Basal and LRH stimulated LH/FSH levels were determined in: Six eugonadal men, before and after six weeks' DHTU 120 mg/day. Six agonadal subjects after 12 weeks' DHTU 120 mg/day. The results of B were compared to those of Six agonadal subjects without sex steroid treatment. Six eugonadal subjects were studied before and after six weeks' administration of spironolactone. In the two groups of eugonadal subjects, administration of either dihydrotestosterone or spironolactone had no effect on basal and LRH-stimulated gonadotropin levels. A clear but modest suppression was observed in agonadal subjects. Possibly DHT exerts some suppressive effect on gonadotropin secretion in the absence of other testicular products (estradiol, testosterone, inhibin), known to play a role in the negative feedback regulation. From these data it seems unlikely that in the eugonadal male circulating DHT has an important role in the feedback regulation of gonadotropin secretion.

Prolactin secretion in the human male is increased by endogenous oestrogens and decreased by exogenous/endogenous androgens.

There is evidence that prolactin may be involved in testicular steroidogenesis, and we have therefore investigated whether there is feedback regulation of androgens/oestrogens on prolactin secretion in the human male. To assess this we have measured basal and TRH-stimulated prolactin levels in: Six eugonadal men before and after 2 weeks' administration of the aromatase inhibitor delta'-testolactone, which led to a fall in oestradiol levels with unchanged levels of testosterone. In these patients, prolactin levels decreased. Six eugonadal subjects before and after 6 weeks' administration of dihydrotestosterone undecanoate. In these subjects, prolactin levels decreased. Six agonadal subjects, tested after 12 weeks' treatment with dihydrotestosterone undecanoate and compared to: Six agonadal subjects who received no sex steroid treatment. Again, it was found that dihydrotestosterone treatment decreased prolactin levels in patients from Group C. Six eugonadal subjects were also studied before and after 6 weeks' administration of the androgen receptor antagonist, spironolactone, and this treatment increased Prl secretion. It is concluded that in the human male, endogenous oestrogens increase prolactin secretion whilst exogenous/endogenous androgens decrease prolactin secretion.